Britbike forum
Posted By: perfect.tommy Head Gasket Impression in Head - 12/11/18 9:42 am
Every time I have removed my head, there is an impression left from the head gasket just in front of the centre bolt. It is usually about .0015" deep and that is the only place on the head where the gasket has left an imprint. Also suspect, is the 5/16 centre hole is not completely round anymore, wallowed ever so slightly laterally.

My head gaskets are annealed "dead soft" gaskets from MAP. Correct torque setting of 15ft/pounds is used on the centre bolt. Bike is a 1970TR6.

What would cause this issue?

Posted By: perfect.tommy Re: Head Gasket Impression in Head - 12/11/18 6:18 pm
My immediate thoughts are that the head bolt does not stretch enough to accommodate the thermal expansion of the aluminum head in this area: one of the hottest areas of the motor.

However, it may be an error in my workshop practices. I know John and RF must have seen this in their years, and hoping they can correct my oversights. The head is not warped, just a slight impression from the head gasket, and only in front of that centre bolt.
Posted By: Hillbilly bike Re: Head Gasket Impression in Head - 12/11/18 7:26 pm
How often do you remove the head and for what reason?
Posted By: tridentt150v Re: Head Gasket Impression in Head - 12/12/18 3:31 am
Can you vouch for the deck of the barrels? Have you measured them with a straight edge...just to rule it out?
Posted By: perfect.tommy Re: Head Gasket Impression in Head - 12/12/18 3:45 am
Barrel deck has been surfaced. They originally had a low spot brand new "out of the box".
Posted By: tridentt150v Re: Head Gasket Impression in Head - 12/12/18 4:34 am
OK, its not sitting hard on the PRT and when you tighten it you are pulling the head metal down/distorting it are you?
Posted By: perfect.tommy Re: Head Gasket Impression in Head - 12/12/18 4:56 am
As I said earlier the head is not warped, there is an indent from the head gasket. But since you are curious, crush height on the pushrod tubes is set between .025"-.030".
Posted By: tridentt150v Re: Head Gasket Impression in Head - 12/12/18 8:18 am
yeah and I should have thought about it, its an impression, not a raised bit.
Posted By: JubeePrince Re: Head Gasket Impression in Head - 12/12/18 5:01 pm
I know you said they're MAP gaskets. Sort of rules out a bad pattern on the gasket. Have you triple-double-checked the head surface for signs of warping?

Is there a performance issue from this .0015" indent (exhaust gases/oil blow-by, compression loss/leak)? If not, perhaps this is a common problem on 9-bolt heads and no one else has noticed it? Or at the very least, a "problem" you can live with?

Perhaps converting to 10-bolt head would solve the problem. But what, exactly, is the problem? Just grasping at straws here.....

Cheers,

Steve

Posted By: perfect.tommy Re: Head Gasket Impression in Head - 12/12/18 6:31 pm
I meticulously check the head with a Starrett straight edge whenever the head is off. The impression is significant enough to have me resurface the head. .002" variance is definitely enough to cause a leak, so i don't take chances.

In previous years i made the mistake of taking the head to the machine shop to have this done. First time they walked it over to an industrial belt sander. I didn't like that. The second time i requested they do it on the Bridgeport with .005" off max. It came back with .020" off and an invoice for $100. I now do all re-surfacing myself at my own shop with some sandpaper on a surface plate. This allows more control and as little metal removal as possible. Just the high spots.
Posted By: btour Re: Head Gasket Impression in Head - 12/12/18 8:56 pm
It is not a good idea to do that. It changes too many things. If the head is warped, it can be straightened.
Posted By: perfect.tommy Re: Head Gasket Impression in Head - 12/12/18 9:02 pm
Hey gang,

Please read my post before you chime in... the head is NOT warped.
Posted By: koan58 Re: Head Gasket Impression in Head - 12/12/18 11:01 pm
Possibly the barbarian with the belt sander did the initial damage in that area, and a 20 thou skim was the minimum to retrieve a gasket surface around the cylinders?
Just use it, setting pushrod tube crush accordingly is all I'd suggest.
Alternatively, you could keep skimming the head until it is just a gasket itself!
Posted By: perfect.tommy Re: Head Gasket Impression in Head - 12/12/18 11:27 pm
I don't think you are understanding the problem. And the industrial belt sander incident happened with another head anyway.
Posted By: Triless Re: Head Gasket Impression in Head - 12/12/18 11:55 pm
Well, trying to understand this, my thoughts are that the purpose of a gasket is to accomodate very minor imperfections. This is why copper gaskets are annealed to soften them. Wether a copper gasket is "pre annealed " or not, I always anneal them myself, anyway !
If it is only an impression being evident, with no sign of leakage or blowby, I think you may be worrying un necessarily !
Posted By: JubeePrince Re: Head Gasket Impression in Head - 12/13/18 1:44 am
Originally Posted by Triless
If it is only an impression being evident, with no sign of leakage or blowby, I think you may be worrying un necessarily !


+1

Steve
Posted By: perfect.tommy Re: Head Gasket Impression in Head - 12/13/18 8:10 am
Some of us are interested in a higher level of workmanship than yourself. I don't think you should be so quick to impose your lower standards on others. But thanks for your opinion all the same.

The head has leaked between cylinders during some previous assemblies. So this is a valid point of enquiry. I don't think that developing a dent in the jointing surface is part of a normal engine's service.
Posted By: Triless Re: Head Gasket Impression in Head - 12/13/18 8:18 am
Because Nick has a laid back attitude to life, that does not reflect on his high standards of mechanical work and his immense knowledge of such. He is a bloke I really pay attention to what he says. Don't confuse his humour with real ability .
Posted By: Hillbilly bike Re: Head Gasket Impression in Head - 12/13/18 12:52 pm
Exactly as Nick says, old turds.Many here would drop a turd if they saw how I work on these things using impact wrenches and "that's good enough" LOL...If the head surface is flat and smooth, the cylinder deck the same...and combustion blows past the head gasket, you have a problem..Otherwise there is no problem..If you took off the head multiple times? because of a combustion or oil leaks and found the indent despite have flat surfaces, you have to look closely around the center bolt area...Metal is moving when the bolt is tightened..And the center bolt torque is not extreme so there may be a :thin" spot on the head that distorts when tightened down..
Posted By: Triless Re: Head Gasket Impression in Head - 12/13/18 12:53 pm
Yes, dab hand with a knockchrometer ! Silly bugger !
Posted By: btour Re: Head Gasket Impression in Head - 12/13/18 2:22 pm
I am having a hard time following just what was done to this head and this barrel. This head was done in a bridgeport with 20 thou off? And then you have taken sandpaper to it? These barrels were resurfaced? How do you know where you are at now?

Has a stud been put in wrong way round and pulled some metal up round it?

Do a search here on John Healy and head straightening. It is much better than resurfacing. I can understand why you feel attacked. I have found that when I do something that I think is best, and it turns out to be wrong, I feel terrible and defensive.
Posted By: perfect.tommy Re: Head Gasket Impression in Head - 12/13/18 7:19 pm
I appreciate the recommendation to John's posts. I have read most of John's posts on this forum, and have printed every piece of literature he has posted on Vintage Bike and have them in a binder in my shop next to my workshop manual. I was hoping he would chime in here on the subject, or RF Whatley.

I am familiar with straightening warped heads, as this is common practice on heads with overhead cams (I have read John's posts on the subject as well). It would be relevant here if the head had been bowed to due to excessive pushrod crush, or uneven bolt torque. But what we are talking about here is an indent the size of a nickel in an area where these heads are susceptible to leaking. Especially when you move up to a 750cc barrel. There is not a lot of gasket material around that 5/16 bolt!

Just to set things straight, I feel neither terrible nor defensive. I am totally open to the possibility that I have done something wrong, which is why I have posted on the forum to begin with. Unfortunately, no one here has been able to provide an explanation. Instead the recommendations have been to ignore the problem, because these engines can't be rebuilt with some amount of perfection as the end goal. And I simply do not subscribe to that mentality. It is precisely that mentality (and workshop practices) that have given these bikes such a bad reputation to begin with.

As John Healy has pointed out time and time again, these bikes work quite well when they are maintained properly. Most of the problems he has encountered have been due to poor repairs by other mechanics. And John, I hope I am not speaking out of turn here by loosely quoting you.
Posted By: koan58 Re: Head Gasket Impression in Head - 12/13/18 9:25 pm
I suppose what would be most helpful to us would be a picture showing what we are trying to visualise from a few words.

Also a bit of a goose-chase from your irrelevant info about other heads, not making it clear that it wasn't this head being described.

I would still doubt that a 1.5 thou recessed small area as I imagine from your description would be a problem for an annealed gasket to accommodate.

However, if you are determined to eliminate it, I can only see 2 ways of doing it. Assuming the rest of the surface is flat:
Build with weld and re-surface, or a fine skim biased toward the front.

As to how it happened in the first place:

Can you remember the first time this impression was present? Had you had the head off on a previous occasion when the impression wasn't present? ie. do you know that it has appeared during your ownership?

It could be a defective casting that just barely made the grade originally when surfaced.

There could be a region of porosity in that area of the casting rendering it more impressionable.(you mentioned the bolt boss was deformed).

Unlikely, clutching straws, a hard,unsoftened patch of the gasket at some time ago? which acted as an incompressible mold.

A small long term seep of combustion gas eroding the alloy.

Overheating combined with porosity might do it?

Just free ideas
Posted By: Triless Re: Head Gasket Impression in Head - 12/13/18 9:53 pm
I have seen pictures of this head on another forum ( which for some reason unknown to me I can no longer post on ), and it seems that the offending portion is still just touching, no signs of blowby or anything from when it was all tensioned down. Personally, I think Tommy is looking for total perfection, and there is nothing wrong with that ! But I believe he is worrying un necessarily. The only thing I can think of, having seen the pics, is that the top surface of the cylinder block may be slightly out of parallel to the bottom gasket face . In other words, a very slight taper towards the front so miniscule that it could be difficult to discern with straight edges. In other words, bugger all , but only the blueing picks it up !
Posted By: HawaiianTiger Re: Head Gasket Impression in Head - 12/13/18 9:55 pm
Here's a story the might shed some light on the subject. Once in the early 70's a friend's 750 Atlas developed cracks right above the cylinder flange. We took it to a very capable specialist. He put a strobe light on the motor while it was running and I was flat stunned by what I saw. I had been operating on the assumption that these motors were a rigid assembly, but boy, was I wrong. We could see the entire head and cylinder grow and shrink, once slowed down by the strobe under the influences of those barely contained explosions going on inside the motor. It basically looked like Jello wobbling around....

Adding to that, I once had a customer who complained that his head bolts wouldn't stay tight. I assumed correctly that he was tightening them too tight and had stretched the bolts beyond their elasticity.
New bolts and much less torque solved his problem.

What helps to understand this is that there is a difference in the expansion rates and amounts of steel, vs. aluminum. Aluminum heats up quicker and expands more than steel or iron. Once everything has achieved proper running temperature, the motor settles down. Before that, things are moving around quite a bit. There is much more movement between parts in this type of motor than you might expect.

And fret marks like you describe here would be a result of that movement.

It's basic physics. Scratching your head and musing on the design can help with understanding of what is actually happening inside that motor.

Cheers,
Bill

Posted By: Hillbilly bike Re: Head Gasket Impression in Head - 12/13/18 10:23 pm
Perfect Tommy, go back and read post # #759161, the last sentence...
Posted By: tridentt150v Re: Head Gasket Impression in Head - 12/14/18 12:14 am
I always reckon that if your bike isn't leaving an oil stain on the concrete its one of two things:

1. Time to check your oil level, or

2. You have a damn good bike.

I strive for the latter, and just ride them. If I was doing something like speed trials or some such I guess I would question small imperfections or anomalies - in the pursuit of speed or a win - but mine are just road bikes so as long as its going, not dripping oil everywhere, and tuned right I'm happy.

Tommy one other thing that would be worth asking is was the gasket checked for uniformity [thickness] prior to installation? Something we all rarely do. And if the gasket was pre annealed - and you didn't anneal it yourself - is it possible that the centre hole was used to hang it and so wasn't annealed to the same consistency as the rest of the gasket [ie was harder] and this caused the issue? I realise that copper in any form is likely softer than alloy, but even so alloy would yield under a torque wrench, as the copper itself would have, but just not as much as the rest of the gasket. Long shots, but for strange outcomes.
Posted By: TR7RVMan Re: Head Gasket Impression in Head - 12/14/18 2:28 am
Hi Tommy, Find your observations most interesting.

I just measured used '69 Bonnie head gasket. Known history, genuine Triumph copper gasket. The thickness varies between .0452 to .0463" The thinner is along outside edges. The center bolt area is quite even from front to back with no dips at all. I measured with a micrometer at several places. With a straight edge the gasket is on perfectly flat. It has a slight twist & bow. About .005". Of course this could skew micrometer reading slightly as well.

My straight edge is rated at .0002" per foot. On my lathe ways it rocks with a .0005 blade under it so it seems quite flat.

Block showed flat within .0005. Straight edge pinched .0005" feeler blade. Head .0005 blade was a snug slip fit. .001" blade was pinched full tight. I'll call the warp .0005" on head. It was low on the outer edges. I found no dips or humps. The .0005 was a slight bow.

Point is on this motor I see no dip or humps in old gasket. I used Mercedes sealant on head gasket during assembly of this motor. The gasket area has remained bone dry for about 3 k miles so far.


My TR7Rv head & block both tested within .0005". Pinching feeler tight. Also used Mercedes sealant. Has remained dry for 6k miles so far.

I have measured pinch or should I say how much gaskets squeeze down on a handful of copper gaskets now. Overall I find they squish by only about .0012". Some times thinner near edges.

I had a small stock pile of genuine copper head gaskets from 70s. I find they measure flat within about .0002", Measuring copper gaskets from Rabers they measure the same variation. So quite close to flat. I find the thickness overall has some variation from about .041" to .055". These are considered standard thickness. Oversize are available in .070 & .120" for 650. I've only seen .070" for 750 twin. I've used oversized to the exact same results as normal thickness. The compression of oversize seems very similar. Just over .001 so the extra thickness doesn't seem to change that. The oversize do not seem to migrate out or loose torque any different than normal.

My experience has been bow doesn't seem to make gasket leak, but dips between bolts has been at least prone to leaking what looks like oil from combustion area. There is no oil around the area so it has to be from combustion gasses. I find dips more than .0015 tended to result in actual blown gasket. This has been across cylinders, not to outside.

I have always skimmed heads I felt were not flat enough. I didn't know about straightening until 5 years ago. All the heads that I've worked on that blew gasket had low spot between cyl. I do not believe this could be straightened to flat enough tolerance.

Most of these heads had to have .007-.015" or so removed to get flat surface. Morgan Machine & Marine Walnut Creek, CA did work. Specifically Tim Morgan did it personally. The machine had a very large cutter head with multiple tool bits so entire gasket surface could be cut in one pass. Usually took 2-3 passes to clean up. Tim was most careful to mount head to keep from tilting rocker box surface & remove least metal as possible. All these had 100% success. Back in the 70s & 80s I used K&W copper coat on gasket. To be clear, every head that was marginal even with K&W seeped oil from head gasket. All the surfaced ones did not leak. The ones that needed surfacing, but didn't get it blew head gasket again within 3k miles or sooner.

I find in most interesting that many have good results with heads that measure much worse than mine.

Tommy, exactly how are you measuring thickness of head gasket?

Seems odd you gasket would measure this way with both sealing surfaces flat.

Don
Posted By: BigBars Re: Head Gasket Impression in Head - 12/14/18 6:26 am
Interesting diecussion, would also love to see a picture of the depression.
Posted By: Hillbilly bike Re: Head Gasket Impression in Head - 12/14/18 12:02 pm
Without a photo this conversation is a bit useless.....Aftermarket manufacturers of copper gaskets for performance engines say copper gaskets will conform to small imperfections but will not compress...I have have the head off my Triumph 650 race bike about 5 times.The same gasket is used, annealed each time..The gasket still measure .041" like it did the first time...
Posted By: kommando Re: Head Gasket Impression in Head - 12/14/18 12:40 pm
A bit of silk soaked positioned around potential leak points near the depression would be a good fix. Works on Commando heads to protect the push rod tunnels.

[Linked Image]

Posted By: Tigernuts Re: Head Gasket Impression in Head - 12/14/18 2:18 pm
Is that just ordinary silk thread? Soaked in water?
Posted By: kommando Re: Head Gasket Impression in Head - 12/14/18 4:31 pm
Ordinary silk thread, you can put some coppercoat or some sealant on it. It goes on both sides of the gasket.
Posted By: Hillbilly bike Re: Head Gasket Impression in Head - 12/14/18 4:50 pm
I'm envious that Nortons have flat top pistons...
Posted By: Tigernuts Re: Head Gasket Impression in Head - 12/14/18 7:15 pm
Great tip - I'm sure it will come in useful on non-Norton applications. I have pondered whether something like this might work but never known what material would be suitable. Long ago, boatbuilders would use single horse-tail hairs to seal between planks. Similar kind of principle.

Can I check about the "soaked" bit? Did you mean the silk thread should be soaked in something prior to this? or was that a typo? Thanks.
Posted By: koan58 Re: Head Gasket Impression in Head - 12/14/18 8:54 pm
Kom - intriguing! What's the principle at play here? Is silk critical, or can cotton do? Is it still there when you next take the head off, or just charcoal? I wonder if fine wire may do it?
Posted By: perfect.tommy Re: Head Gasket Impression in Head - 12/14/18 9:25 pm
Bill, this information is great and I think this is getting to the heart of the issue.

If we go back a few years, I had real problems getting the head gasket to seal. There were a platitude of reasons for this at the time; pushrod tube crush height and non-anealed gaskets being some of them. The one that alluded me for some time dealt with torque settings. An early mentor of mine had ingrained in me that fasteners were never to be used without lubricant. The problem here is that torque values in the Triumph workshop manual are only given dry. So I was using a conversion factor to estimate the reduction in torque when using moly. What became clear, especially after I had a conversation with ARP about their fastener lubricant, is that my calculations were at best, a guess.

On those early assemblies with blown gaskets we saw impressions in the head and gasket material running the length between cylinders. It seems more clear now that my guesstimated torque values were far over, not under, and the fasteners were tightened beyond their ability to continue to stretch.

If we look at modern head bolts, they have a "waistline" to allow for this kind of stretch during thermal expansion. Keith and Harold at Johnson Cam's modify their stock head bolts by turning down the mid-section on a lathe. Jim Schmidt in the Norton world provides tapered head bolts as well. These bolts, when not overtightened, have some elasticity.

While the last few assemblies have stayed sealed (since assembling dry with stock recommended torque values) I think it may be worth installing a brand new centre head bolt. And even though my torque wrench is made by Snap-On and came with a certificate of calibration it might be worth while getting it tested for accuracy.

I think it is lack of bolt stretch in this very hot area of the motor. Bill, I really appreciate you sharing this.

Posted By: perfect.tommy Re: Head Gasket Impression in Head - 12/14/18 9:27 pm
I think thin copper wire .005" thick is more common in the Norton world. Check Jim Schmidt's website for details.
Posted By: perfect.tommy Re: Head Gasket Impression in Head - 12/14/18 9:29 pm
[quote=NickL]The easiest way is to change your name to 'imperfect Tommy' /quote]


I like it.
Posted By: HawaiianTiger Re: Head Gasket Impression in Head - 12/14/18 10:25 pm
With regard to the silk thread method, it is routinely specified by aircraft engine manufacturers as an aid in sealing surfaces without gaskets. A thin film of sealant and the correct material thread is specified.

I would think that it would be something problematic that might drive you to try this technique. After all we have anaerobic sealants, Covseal gaskets and a few other proven techniques for our old bikes.

The weeping push rod tunnels on Commandos just might quality. I rode mine around for years with a weeping head gasket and just washed my bike weekly. Eventually I found and bought another head that solved my problem.

Cheers,
Bill

Posted By: perfect.tommy Re: Head Gasket Impression in Head - 12/14/18 10:31 pm
Don, great post. And finally, someone who measures in tenths!

Believe it or not, I have never measured my head gaskets for uniformity, though I seem to measure everything else. MAP's gaskets have definitely been the softest I have used, and anyone who has purchased parts from Marino can attest to their level of quality and precision. Tim Joyce's (5 year?) run as champion on an Triumph built with MAP components is certainly a testament to that as well. But now you have me curious...

Yes, my blown head gaskets have always been between cylinders too.

I think Bill from Hawaii is on to my issue. Wrong torque or unyielding bolt in an area that sees a lot of thermal expansion. While my last assemblies have stayed air tight, it would be nice to see an un-uindented gasket surface after disassembly. I think we are close now.
Posted By: gavin eisler Re: Head Gasket Impression in Head - 12/15/18 1:02 am
Originally Posted by TR7RVMan
Hi Tommy, Find your observations most interesting.

I just measured used '69 Bonnie head gasket. Known history, genuine Triumph copper gasket. The thickness varies between .0452 to .0463" The thinner is along outside edges. The center bolt area is quite even from front to back with no dips at all. I measured with a micrometer at several places. With a straight edge the gasket is on perfectly flat. It has a slight twist & bow. About .005". Of course this could skew micrometer reading slightly as well.

My straight edge is rated at .0002" per foot. On my lathe ways it rocks with a .0005 blade under it so it seems quite flat.

Block showed flat within .0005. Straight edge pinched .0005" feeler blade. Head .0005 blade was a snug slip fit. .001" blade was pinched full tight. I'll call the warp .0005" on head. It was low on the outer edges. I found no dips or humps. The .0005 was a slight bow.

Point is on this motor I see no dip or humps in old gasket. I used Mercedes sealant on head gasket during assembly of this motor. The gasket area has remained bone dry for about 3 k miles so far.


My TR7Rv head & block both tested within .0005". Pinching feeler tight. Also used Mercedes sealant. Has remained dry for 6k miles so far.

I have measured pinch or should I say how much gaskets squeeze down on a handful of copper gaskets now. Overall I find they squish by only about .0012". Some times thinner near edges.

I had a small stock pile of genuine copper head gaskets from 70s. I find they measure flat within about .0002", Measuring copper gaskets from Rabers they measure the same variation. So quite close to flat. I find the thickness overall has some variation from about .041" to .055". These are considered standard thickness. Oversize are available in .070 & .120" for 650. I've only seen .070" for 750 twin. I've used oversized to the exact same results as normal thickness. The compression of oversize seems very similar. Just over .001 so the extra thickness doesn't seem to change that. The oversize do not seem to migrate out or loose torque any different than normal.

My experience has been bow doesn't seem to make gasket leak, but dips between bolts has been at least prone to leaking what looks like oil from combustion area. There is no oil around the area so it has to be from combustion gasses. I find dips more than .0015 tended to result in actual blown gasket. This has been across cylinders, not to outside.




I have always skimmed heads I felt were not flat enough. I didn't know about straightening until 5 years ago. All the heads that I've worked on that blew gasket had low spot between cyl. I do not believe this could be straightened to flat enough tolerance.

Most of these heads had to have .007-.015" or so removed to get flat surface. Morgan Machine & Marine Walnut Creek, CA did work. Specifically Tim Morgan did it personally. The machine had a very large cutter head with multiple tool bits so entire gasket surface could be cut in one pass. Usually took 2-3 passes to clean up. Tim was most careful to mount head to keep from tilting rocker box surface & remove least metal as possible. All these had 100% success. Back in the 70s & 80s I used K&W copper coat on gasket. To be clear, every head that was marginal even with K&W seeped oil from head gasket. All the surfaced ones did not leak. The ones that needed surfacing, but didn't get it blew head gasket again within 3k miles or sooner.

I find in most interesting that many have good results with heads that measure much worse than mine.

Tommy, exactly how are you measuring thickness of head gasket?

Seems odd you gasket would measure this way with both sealing surfaces flat.

Don


Top work, well measured and written.
Posted By: btour Re: Head Gasket Impression in Head - 12/15/18 12:53 pm
Originally Posted by Hillbilly bike
I'm envious that Nortons have flat top pistons...


+1
Posted By: Hillbilly bike Re: Head Gasket Impression in Head - 12/15/18 2:34 pm
Lots of talk of precision measuring on engines that when running under heavy load are anything but true and straight grin In my opinion, many problems on Triumphs including funny head gasket business is caused by detonation. Many of you think if you hear the slightest ping the pistons will seize or fall into the sump..While that can happen if the rider just keeps it up...., what also can happen is the piston doesn't always fail and repeated mild detonation at high power levels can beat up on engine parts.It can cause barrels and heads to fret on the joints causing oil leaks . Like what Bill Hawaiian Tiger said. Detonation can crack cranks and ruin bearings..It's not easy to hear detonation at higher speeds , the rider may or may not feel it...
Posted By: perfect.tommy Re: Head Gasket Impression in Head - 12/15/18 7:36 pm
I think you are confused about what is going on here. There has been no evidence provided to support a case, or cause, for detonation in this thread.

And if you are suggestion that precision measuring when building engines is a waste of time... you might want to think again.
Posted By: Hillbilly bike Re: Head Gasket Impression in Head - 12/15/18 8:11 pm
Originally Posted by perfect.tommy
I think you are confused about what is going on here. There has been no evidence provided to support a case, or cause, for detonation in this thread.

And if you are suggestion that precision measuring when building engines is a waste of time... you might want to think again.


I'm just talking in general, not necessarily about your engine, ....... Do you use a torque plate when boring/honing the cylinders? Do you make sure the cylinders are bored at 90 degrees to the crankshaft? Do you make sure the crank main bearing bores are exactly the same? Do you check the cam timing with a degree wheel? Do you have valve jobs done on a single axis machine? What valve/guide clearances do you use? Do you assembly the rods with bearings and have a crank turned to the actual measurement rather than what's printed in the manual? Are the crank throws checked for clocking?.. Does your bike have an oil pressure gauge or you trust a precision engine to a indicator light?
A head can be checked with a straight edge or it can be placed rocker side down on ground flat table and checked with a dial indicators so you'll know if both surfaces are parallel...
Posted By: TR7RVMan Re: Head Gasket Impression in Head - 12/15/18 8:30 pm
Detonation.... In California, holed & destroyed pistons are extremely common. A very serious issue. I don't know all the related damage done to motors, but I've seen several heads where it looks like an object bounced around in combustion chamber leaving pock marks on head & piston.


However no know objects got into motor. The motor appears to have been working fine all along. Ping could be heard during heavy loading in each case. Remember ping is happening before you can hear it. I really can't tell difference between detonation & ping when I hear it.

I've ridden several machines where owners say they never hear any ping. I hear ping when I road test under load. 2 of these owners have holed pistons. One more than once. This is a serious matter that results in very costly repairs.

I've been building motors for over 40 years. Precision machining & build quality are everything. Poor tolerances & assembly assure a short motor life. See this all the time on the club rides. The well assembled motors do fine. The poor assembly often ends up in chase truck. Just the laws of physics. Sadly the factory tended to error on the side of just ok was good enough.

Interesting subject.
Don
Posted By: TR7RVMan Re: Head Gasket Impression in Head - 12/15/18 8:31 pm
Hi Tommy, So what is your gasket measuring with the micrometer? You didn't answer that.
Don
Posted By: Hillbilly bike Re: Head Gasket Impression in Head - 12/16/18 12:13 pm
Originally Posted by TR7RVMan
Detonation.... In California, holed & destroyed pistons are extremely common. A very serious issue. I don't know all the related damage done to motors, but I've seen several heads where it looks like an object bounced around in combustion chamber leaving pock marks on head & piston.


However no know objects got into motor. The motor appears to have been working fine all along. Ping could be heard during heavy loading in each case. Remember ping is happening before you can hear it. I really can't tell difference between detonation & ping when I hear it.

I've ridden several machines where owners say they never hear any ping. I hear ping when I road test under load. 2 of these owners have holed pistons. One more than once. This is a serious matter that results in very costly repairs.

Interesting subject.
Don

Posted By: Hillbilly bike Re: Head Gasket Impression in Head - 12/16/18 12:36 pm
Originally Posted by TR7RVMan
Detonation.... In California, holed & destroyed pistons are extremely common. A very serious issue. I don't know all the related damage done to motors, but I've seen several heads where it looks like an object bounced around in combustion chamber leaving pock marks on head & piston.


However no know objects got into motor. The motor appears to have been working fine all along. Ping could be heard during heavy loading in each case. Remember ping is happening before you can hear it. I really can't tell difference between detonation & ping when I hear it.

I've ridden several machines where owners say they never hear any ping. I hear ping when I road test under load. 2 of these owners have holed pistons. One more than once. This is a serious matter that results in very costly repairs.

I've been building motors for over 40 years. Precision machining & build quality are everything. Poor tolerances & assembly assure a short motor life. See this all the time on the club rides. The well assembled motors do fine. The poor assembly often ends up in chase truck. Just the laws of physics. Sadly the factory tended to error on the side of just ok was good enough.

Interesting subject.
Don



By holed pistons if you mean a hole in the piston crown, that's pre ignition not detonation.To distinct events with different causes....Detonation beats up on the circumference of the piston, can errode the piston crown, cracks rings and can heat the piston to seizure..
I was a construction electrician not a trained engine mechanic..I learned to work on vehicles because I always drove junk that needed repairing at times..I built a few bike and truck engines and they ran nice and didn't blow up so I figured I did it ok..Then I built the race bike and did some things that some here may consider, well, hillbilly .But it keep going faster and setting new speed records..Might not be stuff you want to do on a street engine but it can be surprising how long an engine built from a pile of parts on the floor can last if you keep it clean and use common sense..and if rebuilding an engine you took apart then the various pieces will have wear marks that can be clues to potential issues.
The OP on this tread has an engine that appears to have been checked over very carefully but it leaves a odd mark on the head ...I have to ask again, is it causing a problem and why has the OP pulled off the head more than once?

Posted By: desco Re: Head Gasket Impression in Head - 12/16/18 3:31 pm
+ 1 Hillbilly
There is a lot of misery out there due to people seeking perfection in an imperfect world.
On being a mechanic, I just keep removing bolts till something falls off.
Posted By: HawaiianTiger Re: Head Gasket Impression in Head - 12/16/18 6:17 pm
Originally Posted by Hillbilly bike




..I learned to work on vehicles because I always drove junk that needed repairing at times.




+1
Posted By: perfect.tommy Re: Head Gasket Impression in Head - 12/16/18 7:51 pm
Desco,

I think you are missing the point. Being stranded on the wrong side of a mountain range because you had an engine failure... that's misery.

Having peace of mind knowing that your bike is not going to leave you stranded on a 3,000 mile trip is the end goal here.
Posted By: perfect.tommy Re: Head Gasket Impression in Head - 12/16/18 8:15 pm
Hillbilly,

The bike has been apart for a number of reasons, some of which I will list here. I sense you may think that I am just taking the bike apart looking for problems, but I can assure you I would rather be riding than wrenching.

The head came off the first time for a full engine rebuild.

2) The cases were split due to low oil pressure. The machine shop had ground the journals on a taper.

3) The cases were split again. The second machine shop ground the journals with excessive clearance. At this point I finally invested in some quality micrometers. I eventually found a good machinist locally, though this is really a dying trade... and dying quite literally. My crank balancer passed away a few years ago and he had been doing it his whole life. Many of the manual machinists who are left are quite old. There has been very little interest from younger generations to pick up this trade, especially with the advent of CNC and so much outsourcing of work to China, etc.

4) Head came off another time to instal a big bore kit. At this time I invested in a second head which was rebuilt by Rob Hall at Hall's Custom Vintage in North Carolina. Nice work.

5) As mentioned earlier, there were a number of times where the gasket did not seal and leaked between cylinders.

6) The head is off now not because it leaked, but because I am unhappy with the cam change I made on the last teardown. I'm re-installing my previous set of cams because they come on cam lower in the rpm range.

I hope this satisfies your curiosity.
Posted By: perfect.tommy Re: Head Gasket Impression in Head - 12/16/18 11:23 pm
Well hopefully now that you have regained your sense of superiority, we can get back to focussing on the topic at hand.

Perhaps you fell out of your mother's womb with a wrench in your hand, but some of us had to learn our workshop skills from the ground up. And a lot of those learnt skills came from making mistakes. Very few people own precision measuring tools when they are first learning the trade. That's what you rely on your machinist for. Unfortunately I chose inept machinists to do the work. That's part of the learning curve.

If you want to hangout on the britbike forum and shame people for not knowing as much as you, or for the mistakes they may have made in the past, I think you are here for the wrong reasons. We are here to learn and help each other.

If you are going to use quotation marks, I said "lower standards". I made no comments on your engineering skills.
Posted By: Tridentman Re: Head Gasket Impression in Head - 12/17/18 3:05 am
You are too modest, Nick---as everyone else on this board will tell you.
However---a word to both you and Tommy---perfect or imperfect-----
I spent my career in manufacturing engineered products.
There we had a saying:
"The guy who never made a mistake never made anything".
So lets concentrate on these intriguing and compelling old Brit bikes rather than gunning for each other.
HTH
Posted By: perfect.tommy Re: Head Gasket Impression in Head - 12/17/18 6:58 am
I hear that.

And apologies again Nick if I came off a little hot.

Let's keep making mistakes. And learning.
Posted By: Hermit Re: Head Gasket Impression in Head - 12/17/18 1:16 pm
NickL, perfect.tommy - Well done lads!

We all come here to learn. Not everything we learn is about motorbikes. Sometimes we learn about ourselves and others. All good.
Posted By: btour Re: Head Gasket Impression in Head - 12/17/18 4:03 pm
Originally Posted by Hermit
NickL, perfect.tommy - Well done lads!

We all come here to learn. Not everything we learn is about motorbikes. Sometimes we learn about ourselves and others. All good.


Well said.
Posted By: TR7RVMan Re: Head Gasket Impression in Head - 12/18/18 5:47 am
Hi Tommy, Was looking at MAP website head gaskets.

Dead soft or normal... What's the difference in softness? Meaning how much softer? Would be curious to know. If you heated a normal gasket bright red to anneal would it then be dead soft or not?

Or.... are they a different copper alloy?

Is it feasible the dead soft are too soft & allowing head to flex compressing gasket .0015"?


What does the gasket measure in many places? Is the head flexing down at the outside end bolts?


How much flex does it take to make a sealing difference in the valve seats?


New question. How thick is your head measured from top to head gasket surface using depth gage?


On the '69 Bonnie I did recently I measured. Uncut head original with known history. The '69 head is very similar to your '70.

OUTER: RF 2.781", RR 2.86", LF 2.780", LR 2.787"

INNER: RF 2.799", RR 2.793", LF 2.799", LR 2.790"

CENTER 2.318".

If you draw this out, clearly the head was machined at a slope with rear of head thinner. Yet the rocker box surface is flat so it must have been machined this way from new. Yet the outer bolts are opposite with the thicker in rear. In actual practice this head is working good with no leaks or seeps at box gaskets or head gaskets.

In prior discussions I have in my notes the nominal head thickness was 2.755" to box gasket surface. Another discussion put head thickness new at 2.785-2.795". Triumph gives no spec I could find. My TR7RV head was skimmed aprox. .009". I didn't measure it before, dumb I know, but was back in 70s. After it measures 2.775-2.785". Sloping about 45deg angle across head with thicker on front. Was this from the skim or factory?? I don't know. Again rocker box surface is flat. No leaks from this head either. Again old copper gaskets crushed only about .001" and are fairly flat in crush.


Lastly you said your crank balancer passed. Sorry to hear that. Indeed this is common these days. Did you balance the crank on this motor? What factor did you use? On the '69 with light flywheel used 68%. A huge improvement 60-70 mph. Prior it was awful at freeway speeds. I have much interest in balancing as well.

Interesting stuff.
Don




Posted By: Triless Re: Head Gasket Impression in Head - 12/18/18 7:46 am
How complex and critical things have become ! Admittedly, I was a late starter, only getting into motorcycles in 1970, aged 17, but the information then, passed on by the old timers, held true ! I got my first Triumph in 1976 ( bought new, and still in my possession !), and the then available knowledge , still held true !
I can remember quite a few Triumphs being rebuilt with the then available genuine parts, and which went on for reasonable mileages ! And , believe me, many of these rebuilds weren't "tool room " jobs !
Now, it seems that parts available today ( of which I have some that surpass anything available in the day ) must be the reason why Triumphs, for instance, must be rebuilt to standards of far higher than that of the original factory builds! To compensate for builder ineptitude ?
I'm not meaning to be disparaging of the gifted few who can build to the standards of factory racers, but the production bikes never were, and ( mostly) functioned satisfactorily .
Cleanliness and factory torque and adherance to clearances are the keys to successful rebuilds !
That's my take, so, in the words of Harry " the Breaker " Morant, to his firing squad, " Blast away, you bastards !"
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