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What is this Piston telling me? (replacing first post) #233486
01/19/09 8:11 am
01/19/09 8:11 am
Joined: Dec 2008
Posts: 25
Midlands, UK
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Quantumrevs Offline OP
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Hi all

...sorry about the first post, problems with the photos. Hope this comes out better.. so:

Hi

Still checking through my parts as I get everything together for the rebuild of my 1971 Tiger engine. I checked the for/aft diameter of the skirt on my +20 pistons and I think that they are just about OK to re-use -

LH piston - 2.8103 (skirt bottom), 2.8072 (just under rings)

RH Piston - 2.8089 (skirt bottom), 2.8073 (just under rings)

Both Barrels measure 2.815 top, 2.814 bottom (measured fore/aft)

Drawing on peoples experience and knowledge - do you concur?

I do now have another question. I was expecting to find carbon on the piston tops when I broke down the engine (infact I found probably a good 1mm of carbon all over - pistons, head, ports, etc..) However, not experienced in this field, I was not expecting to find anything below the level of the rings or inside the piston. Is this normal or are the pistons telling me something? Any comment would be most appreciated.







Best regards

Jon

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Re: What is this Piston telling me? (replacing first post) [Re: Quantumrevs] #233491
01/19/09 9:17 am
01/19/09 9:17 am
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Ger B Offline
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What I think I see in the bottom picture is that the scraper ring is worn so far that the upper and the lower carrying surface is flush with the dam between them.
I also think I see a large gap (clearence) between the top of the lower ring and the groove of the ring.

What you see is black deposits on the non carrying surface of the piston, most probably caused by blow by of combustion gasses, gasses wich passed the piston rings.

I think you need to have your cylinder bored and you need to install new pistons and new rings.


Ger B

Re: What is this Piston telling me? (replacing first post) [Re: Ger B] #233499
01/19/09 10:57 am
01/19/09 10:57 am
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Kent UK
Blapper Offline
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Further to Gers points, the coloured ring on the gudgeon pin indicates high temperature due to detonation and that detonation was probably caused by all that oil burning in with the petrol and reducing the octane rating. The carbon is burnt oil.

Man that oil is some black s**t!

Mine was less bad than that and I did the bore job.

Blapper redwine

Re: What is this Piston telling me? (replacing first post) [Re: Quantumrevs] #233505
01/19/09 1:28 pm
01/19/09 1:28 pm
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Emsworth, sunny south of Engla...
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dave jones Offline
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Hello Quantumrevs- I just looked in the manual and a plus 20 bore would be 2.8148 to 2.8153 when used with diecast pistons. If your measurements are correct then your barrels are practically new although you should compare the side to side figure to check for out of roundness. Have you got a lip at the top of the barrels where the top rings reach the limit of their travel?


You measure the top of the bore and if you have more than .005 wear when either comparing the top and bottom or out of roundness then you need a rebore. Therefore, your bores would have to measure 2.8203 at the top to require reboring. If they are ok you can hone them for new rings using, according to the manual a
grade 300 but according to this site some other grade.

As to the pistons I think it makes a difference if they are diecast or forged when checking the clearance between the these parts and the bores. With new bores and diecast pistons it would be .0106/ .0085 at the top of the skirt and .0061/ .0046 at the bottom.

The brown on the outside is blow by but your rings have been making good contact so you should check them. Place it at the bottom of the bore where there is no wear and measure the gap. It should be .010 to .014 but a worn one can be up to. 017

I would say that you should get the stuff measured again to make sure, check if you have diecast or forged pistons and go from there


dave

Last edited by dave jones; 01/19/09 3:09 pm.
Re: What is this Piston telling me? (replacing first post) [Re: dave jones] #233552
01/19/09 8:29 pm
01/19/09 8:29 pm
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Midlands, UK
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Quantumrevs Offline OP
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Hi Dave (All)

I measured the bores before I left the USA (I borrowed a bore gauge from one of the guys at Metro Triumph Riders in Detroit), so if I'm going to measure again I'll have to borrow one here in the UK. However, I double checked the readings that the gauge was giving me at the time with 2 different digital calipers that I have (I have 2 cheapies, so I thought that I had better use both to be sure) and was getting practically the same reading - so I'm pretty confident of the measurements. If I remember they were also pretty round (maybe a thou, 2 thou max).

I just checked the top of the barrels and there isn't a lip, just a change in surface texture - almost like a change in material. I have taken a few shots of the barrel so that you can look at the condition - but to me (granted, a novice) they look really smooth and in good nick and little wear (will get them honed though - or do it myself, trying to keep the costs down - down - down).

I'm just off on a business trip, so when I get back at the weekend I'll measure the pistons again - do the trick with the ring gap (I have new rings that I can use for this) - and measure the play of the rings to the ring channel wall. I think that the pistons are cast - but if anyone can tell from the pictures above, please advise.

Just a novices question - Are the pistons supposed to be round? Mine aren't quite. The figures I gave above are for/aft - the side to side measurement at the same bottom of the skirt point are about 8 thou narrower. Any comment?

Here are the barrel photos:










Re: What is this Piston telling me? (replacing first post) [Re: Quantumrevs] #233571
01/19/09 10:07 pm
01/19/09 10:07 pm
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Boston, Massachusetts
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John Healy Offline

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"What is this Piston telling me?"

We had a lot of fun together, but I am tired, and would love to finish my days as an Hepolite ash tray.


Re: What is this Piston telling me? (replacing first post) [Re: Quantumrevs] #233586
01/19/09 11:40 pm
01/19/09 11:40 pm
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Emsworth, sunny south of Engla...
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dave jones Offline
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John Healy is saying that your pistons are Hepolite which means they are forged. If he says they are no good then you had better chuck them away!

By the way, the pistons skirts are oval shaped rather than round and they must be a different size at top and bottom of the skirt because of the different clearance.

You are in a difficult postion because normally by the time the pistons look like yours the barrels have had it too but your barrels look ok! Your barrels look very much like mine with that discolouration at the top rather than a lip but my pistons did look a lot better with no blow by like yours have suffered. The matt area on the skirt is wear rather than partial seizure which you often see. This is a smearing of the metal. In your case, because the bores look ok, it seems a shame to machine away a load of metal for +40 pistons but this is the way you may have to go. You don't have to buy Hepolite as the cheaper ones like LFC, etc would do fine. I have Japanese pistons in mine which date from a time, I believe, when racing old bikes was a craze in Japan and they are very good quality. I have heard very good things on this site about JRC pistons too.

If I was unsure I would ship the lot off to SRM and get them to measure it all and to decide what should be done. A good shop won't just tell you to spend a load of money for nothing if there is another way. Len Craig also seems to know his stuff . Give them a ring.

Last edited by dave jones; 01/19/09 11:55 pm.
Re: What is this Piston telling me? (replacing first post) [Re: dave jones] #233596
01/20/09 12:51 am
01/20/09 12:51 am
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Boston, Massachusetts
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John Healy Offline

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"forged"

Hepolite's are cast - Look, you can see the 17844 Hepolite 650 part number inside the casting.

"By the way, the pistons skirts are oval shaped rather than round and they must be a different size at top and bottom of the skirt because of the different clearance."


Both true, but because they have changed the way they make this piston (The taper looks to be only .001 to .0015" - but on a shadow graph you can see that in the last approx. 1/4", just under the oil ring, that it does taper a lot more) it does not look like your father's Hepolite. On those the taper was linear, rather than non-linear.

Agree on SRM!!

Its JCC pistons, not JRC.

LFH not LFC

The point made above about the ring groove should be of concern. The ring should only have a .001 to .002" clearance in the groove. From the picture it looks like you are beyond that (but you have the pistons so I am only guessing). Loose rings in piston ring grooves have a tendency to take the top of the piston off as the ring slams back and forth as the pistons changes direction. They make much smaller and more interesting ash trays, but the story that comes with them is much more dramatic, and expensive.

Barrels look good, but you will know more when you put a real hone and it take a few turns in them.


Re: What is this Piston telling me? (replacing first post) [Re: John Healy] #233616
01/20/09 3:09 am
01/20/09 3:09 am
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georgia
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georgia
Note that a "real" hone is made by Sunnen or similar machine and costs vastly more than a "ball hone" from a local parts house. Maintaining (or correcting a SMALL ovality to) a round bore requires a tool guided and sized by more than simple flat spring or centrifugal force pressure. If your bore measures within tolerance for a hone spend the money to have a real machine shop hone the bore so it comes out as round as possible. You may yet find a bore required so do this before you acquire your new set of pistons. Either way you will have a serviceable bore and not spend any money twice which will keep your budget as small as possible. Please do not ask how I learned this lesson!


1974 TR5T
Re: What is this Piston telling me? (replacing first post) [Re: trumpetloon] #233631
01/20/09 7:24 am
01/20/09 7:24 am
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Out There!
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Nick Offline
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Out There!
Hate to sound like a spoil-sport, but your pistons look like a pair of fairly high mileage pistons from a good running bike. That is, they look pretty good. Yes, there's a little blow-by past the rings, but that's to be expected. If it were mine, and if the piston-to-cylinder clearance was within tolerance, I'd just hone the cylinder and put in a new set of rings, being careful to gap the rings correctly. And as long as the piston pins have no surface irregularities, just put 'em back in. As long as the cylinder is off, you might want to have someone with a knowledgeable set of hands check your rods.


When people who should have known better cautioned me about the dangers of motorcycle racing, I always told them that a fear of death is nothing more than a fear of life in disguise.
Re: What is this Piston telling me? (replacing first post) [Re: Nick] #233632
01/20/09 9:18 am
01/20/09 9:18 am
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Emsworth, sunny south of Engla...
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dave jones Offline
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Sorry about the errors in my post. I thought that the old Triumph factory pistons were cast but the Hepolites forged but I was wrong. LFH pistons are available at Wileman's Motors in Derby.

As Nick says- Definitely worth cleaning your pistons up and checking them out thoroughly. I wanted to say what Nick said but I wouldn't like to take responsibility if something went wrong. However, on my bike I would be very tempted! I never even changed the rings or honed the barrels last time mine was apart 10,000 miles back and, as it still makes no smoke now, I still wouldn't if I stripped it. I don't like fixing things that aren't broken because I can't afford it! You have to make your own choice by reading the manual specifications.

When I was a teen I ran my 3TA until there was a massive lip on the barrels and one small end eventually gave out and cracked a piston making a smoke screen. I still got home and was satisfied to have got the most miles possible out of those barrels and pistons! I then had it rebored and fitted a new small end.

Good luck

Re: What is this Piston telling me? (replacing first post) [Re: Nick] #233675
01/20/09 6:14 pm
01/20/09 6:14 pm
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North Georgia, USA
RF Whatley Offline
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Originally Posted By: Nick
Hate to sound like a spoil-sport, but your pistons look like a pair of fairly high mileage pistons from a good running bike. That is, they look pretty good.


I'm with Nick and what John insinuated. Everything looks like normal wear and tear, no different from 1000 other engines I've taken down. The second photo does seem to show too much ring gland width on the second compression ring. This is showing up in the photo as light above the ring. However, this could be the ring worn thin too, so measurements would be required for a full determination.

I take exception to your measuring methods...
1) This is NOT a job for a caliper at all. You need micrometers and a dial bore gauge. The cylinder in not measured with a single measurement. Instead it is properly made with 9 to 12 measurements in which the bore is "mapped". This since normal bores wear patterns are oval and with a taper.

2) No measurements can be made because you haven't honed the cylinder. It should self explanatory why measurements are only made AFTER the final honing is complete.

Ultimately, one of the big determining factors in the decision to bore a cylinder is the difference between the cylinder and piston (the "running clearance"). In the old days there was only Hepolite. These days you may get your choice of 5 or more brands when you visit your local authorized Triumph service depot. That being the case, often you can fit 5 different piston brands and get 5 different clearances. If the bore is near to size, possibly one of those piston sets will dial in the correct clearance without boring.

The reasons to avoid boring at all costs is not so evident. On the face of it your cylinder can endure 6 bore jobs; one for each .010" increment. That is to say, like a cat, it has multiple lives. You will hardly ever have a bore clean up at +.010", because the boring machine will not be set up the same way it was at the factory. Therefore you are automatically at +.020". Then the low-life shop has no +.020" pistons in stock, so they gladly bore it to +.030" "at no extra charge". The point is: Half your cylinder life is gone, and the engine hasn't even hit a lick. So you want to avoid boring at all costs simply because it's a game at the average Brit bike shop.... and you are going to loose.


The thing you want to keep in mind is this. The Triumph engine was designed in 1938, therefore it is not the equivalent of a 2009 Formula 1 race engine in any way shape or form. These engines run very nicely with clearances that would make your average Jap bike puke oil out the exhaust pipes!! That is, not every measurement needs to be spot-on to the nearest .00001" to run correctly. Unfortunately, a great deal of the Brit bike fraternity (having been raised on Jap bikes) has come to this wildly fantastic and totally unsupported conclusion. So although it's important to know the exact clearances you're working with, it is not important to have every dimension you might find listed in your workshop manual. There is a difference.

Although not exactly the same, you'd do well to ask yourself, "If the same condition existed on my Briggs & Stratton lawn mower engine, would I do this repair? Will it really make that much difference?"

Hope this helps! bigt


Don't hide 'em, Ride 'em !!

RF Whatley
Cornelia, GA
Re: What is this Piston telling me? (replacing first post) [Re: RF Whatley] #233720
01/20/09 10:16 pm
01/20/09 10:16 pm
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australia
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douglas Offline
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Hear! Hear! Mr Whatley. Or is it Here! Here! Anyway i agree. Try and get the most out of your barrell.I've never had a piston crumble in my life, and i'm a cheapskate who throws a set of rings in any old worn bore. As long as it doesn't smoke! Of course i wont be classic racing it tho'.If there isn't excessive ring side clearance use those pistons again! I built this up on the dole using secondhand everything!

Re: What is this Piston telling me? (replacing first post) [Re: douglas] #233761
01/21/09 3:12 am
01/21/09 3:12 am
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georgia
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RF... please an honest answer here. If those pistons which show considerable mileage, quite a bit of wear and some FOD came from your Tbird; coupled with the shown barrels which show minimal ridge but probable rust pits from sitting... would you REALLY see if honing and a new set of rings were adequate to the task at hand or would you do as I would and pop for a fresh top end? No prize for any answer... just want to know if these parts are suitable in your own machine. No flame here; just a question and thanks.


1974 TR5T
Re: What is this Piston telling me? (replacing first post) [Re: trumpetloon] #233789
01/21/09 9:25 am
01/21/09 9:25 am
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Emsworth, sunny south of Engla...
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dave jones Offline
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Trumpetloon- You normally only change parts when they are out of specs or obviously no good whatever machine it is unless you are blapper in which case you bolt on every possible mod grin.
Dave

Last edited by dave jones; 01/21/09 9:49 am.
Re: What is this Piston telling me? (replacing first post) [Re: trumpetloon] #233847
01/21/09 6:25 pm
01/21/09 6:25 pm
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North Georgia, USA
RF Whatley Offline
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Originally Posted By: trumpetloon
RF... please an honest answer here. If those pistons which show considerable mileage, quite a bit of wear and some FOD came from your Tbird; coupled with the shown barrels which show minimal ridge but probable rust pits from sitting... would you REALLY see if honing and a new set of rings were adequate to the task at hand or would you do as I would and pop for a fresh top end? No prize for any answer...


I would do (and did do) exactly as I advised. I would hone the cylinder, map the bores, scrutinize the pistons (including measuring the piston ring glands and piston-to-cyl clearance), and then make an informed decision.

If the bores measured out fairly good, and I could get a new set of pistons with soft iron rings to fill the gaps appropriately, then I certainly would use the existing bores without any hesitation. And feel very good about it.

Beyond the excessive cost of boring and high likelihood of loosing "cylinder lives", IMHO there is simply nothing to be gained. Not 1 single HP can be gained by doing this. And even if you did gain a whopping 3 HP, would it make a difference to the average street rider? No, not one bit.

Why do I say this? Well, for starters name a bike of similar displacement made in the last 10 years that doesn't have double the HP. So who exactly is it that you hope to overtake on the road on a 35yo motorcycle that is lucky to be making 35 HP at the rear wheel? Who is it exactly that 36 HP will pass that 35 HP won't? laughing

These bikes are classics. As such, they are mostly relegated to what Shaun Kent calls "bimbling". That is, tooling around in the countryside on nice days with your SO on the pillion, or maybe tooling about with the lads from the Club. It's all in good fun. No money is at stake, and crushed egos are easily cured by making the winner of any sprint buy the beer at the end of the day.

Now if you're racing that's another deal entirely. Or, if you just hit the lotto 15 meg-billion jack pot then your pockets are a bit deeper than the average rider's. So I'm not talking about those guys. But the average guy only brings me his cylinder because it looks like this, and he "just wants it to run right." Or, "He doesn't want to loose any sleep." Or, "He wants to know it's right."

IME it simply takes a lot less to "run right" than most people think. Most owners would be better served (especially when it comes to picking up women) by putting the same $700 in a paint job! laughing

Hope this helps! bigt

Last edited by RF Whatley; 01/21/09 6:35 pm.

Don't hide 'em, Ride 'em !!

RF Whatley
Cornelia, GA
Re: What is this Piston telling me? (replacing first post) [Re: RF Whatley] #233964
01/22/09 3:40 pm
01/22/09 3:40 pm
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Jethro Offline
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Originally Posted By: RF Whatley
[
Although not exactly the same, you'd do well to ask yourself, "If the same condition existed on my Briggs & Stratton lawn mower engine, would I do this repair? Will it really make that much difference?"

Hope this helps! bigt



LOL... that was both rich AND a classic.

Re: What is this Piston telling me? (replacing first post) [Re: Quantumrevs] #233972
01/22/09 4:44 pm
01/22/09 4:44 pm
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EWebster Offline
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Quote:
I would do (and did do) exactly as I advised. I would hone the cylinder, map the bores, scrutinize the pistons (including measuring the piston ring glands and piston-to-cyl clearance), and then make an informed decision.


Ring glands indeed. I think you can see that kind of thing "down south". Engines! Man, Engines!

Re: What is this Piston telling me? (replacing first post) [Re: EWebster] #233974
01/22/09 4:52 pm
01/22/09 4:52 pm
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John Healy Offline

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Lands! Man, lands!

RF had his thoughts elsewhere:
"(especially when it comes to picking up women)"

john


Re: What is this Piston telling me? (replacing first post) [Re: John Healy] #233985
01/22/09 6:11 pm
01/22/09 6:11 pm
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RF Whatley Offline
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OK, you got me!


Don't hide 'em, Ride 'em !!

RF Whatley
Cornelia, GA
Re: What is this Piston telling me? (replacing first post) [Re: RF Whatley] #233991
01/22/09 6:51 pm
01/22/09 6:51 pm
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Originally Posted By: RF Whatley
snip
Why do I say this? Well, for starters name a bike of similar displacement made in the last 10 years that doesn't have double the HP. So who exactly is it that you hope to overtake on the road on a 35yo motorcycle that is lucky to be making 35 HP at the rear wheel? Who is it exactly that 36 HP will pass that 35 HP won't? laughing

snip


2006 BMW F650GS ...I believe about 50 hp. It's certainly not faster than my Triumph, and is about the same as my older BMW 650, an '81 R65. That doesn't mean it's not a nice bike. I want one.


Ed
1970 Bonneville
Re: What is this Piston telling me? (replacing first post) [Re: enigmaT120] #234003
01/22/09 8:22 pm
01/22/09 8:22 pm
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John Healy Offline

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"OK, you got me!"

Ring lands, not ring glands. Check the ring lands for excessive clearance (more than .002").

Ok?


Re: What is this Piston telling me? (replacing first post) [Re: John Healy] #234275
01/24/09 7:17 pm
01/24/09 7:17 pm
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Quantumrevs Offline OP
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Hi All

Just back from my trip and am impressed by all the responses - you guys are great.

Just to clear one point up (and it's my fault - the way I wrote it was not clear): When I said that I checked the readings with digital calipers, I was checking across the tips of the bore gauge that I was using, to double check what I was reading off the vernieer scale on the gauge.

I cleaned up the pistons a little, but especially in the ring channels. I put a new set of rings on and measured the clearance in the channel. I would say that with the new rings, the clearance of the Oil ring and the lower compression ring were in tolerance. However, I judged that the upper compression ring had 0.004+ (but not quite 0.005) clearance - so above the spec in the workshop manual (0.001 to 0.003).

Is this clearance just too much? Or with the good lower compression ring could it be acceptable?

Now here is a question! If the piston is by all accounts OK, except for the clearance of the top ring in it's channel - could I source a slightly thicker ring from somewhere? Two rings would seem to be cheaper than 2 new pistons! Has anyone done this before? The new rings I have measure 0.062 in thickness, so I would be looking for rings with the same diameter, width as a 650cc +0.020 ring but around 0.065 / 0.066 in thickness.


This bike is a sort of training project for me. As I have never done anything like this before, the idea was to completely strip the bike down, engine and all - then assess, rework, repair, replace and build it all back up again. Hopefully learning about bikes and the skills as it progressed. Having done the 'training', I plan to fully restore a 2nd bike that I have, a 1977 Bonneville.

So with the above objective in mind (and knowing that I'll need the dosh for the Boneville), I think that this is what I plan to do:

- Deglaze the barrels and see if I can borrow a gauge to double check / map the bores.

- Assuming that the bores are OK (and I think that they will be), I'll double check the pistons I took out in terms of clearance in the bores and try to get a thicker piston ring. Then fit the lot as is.

- If a thicker piston ring is something that does not exist and the current top ring clearance is too great (I await your opinions), then I guess it's a new set of pistons - but just another set of +20, so no rebore.

- After the engine is re-built and running, if it sounds unhealthy or clouds of oil smoke appear - I guess I'll just continue my learning experience by striping the top and barrels and getting the full job done!

Well, I would appreciate any last comments and thoughts - especially on the availability of a thicker ring. Oh! and Nick also wrote about getting the conrods checked - how is this done? I have already put then on a flat granite surface on each of their sides and they look flat / straight to me. Is there anything else that I should be looking out for?

Thanks again to everyone who has provided their thoughts and direction - it is greatly appreciated.

Jon


Moderated by  John Healy 


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