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I'm about to have a machinist face the top portion of my cylinder head. I have considered doing the bottom copper gasket surface also but have read on this forum that taking too much off that surface will cause squish issues with the PR tube assembly parts. I'm wondering what the protocol is for facing the head, and what the alloy removal limits would be to keep it trouble free.

My present setup is pert near perfect, but it leaks. I would like to stop that leak. I've ordered Covseal rocker gaskets.

The head is too thin a design full stop, making it thinner will make it weaker still.

Is the head flat, if not the best cure is to bend it back to straight not to thin it, when you bend it you will get a flat head gasket side and the rocker covers side at the same time. Machine one or other and one side stays bent.

If its flat leaks are more likely to come from raised divots and bulging holes than holes and scratches (a good sealant gasket match works here) so concentrate on only the divots until they are flat and counter boring the stud holes to remove the bulge.

Yes I agree that the Triumph head is thin and weak and prone to warpage, but sometimes skimming the surfaces can't be avoided. The worst head I saw was a Harris Bonnie were the gasket was pressed into the alloy like an artful relief. It took 40 thou to clean it up. On that particular bike I used a standard head gasket and reveled in the increased compression. I used alloy PRTs as they are easily adjusted for height in the lathe.
This was 15 years ago and the bike's still on the road, so it does work. I've done similar things several times, sometimes with thicker head gaskets.

I've been toying with the idea of welding the rocker boxes to a head, and cut them down for access to the rockers and valves. Would have made for a very sturdy head.
Maybe I'll try it one day.

SR

I used this counter bore method when I assembled the cases. I don't believe I carried on when assembling the top end. It's coming apart anyway so I'll have a look at the surfaces. Question: how do you determine if the head is bent/warped? I'm thinking a straight edge won't cut it.

Hi Bola, So far as I can find, Triumph gives no specs to head surfacing. Or overall thickness either.

I always use a straight edge to check the head on the bottom side. I have .0005,.0001, .0015 & larger feeler blades. I clean sealing surface well. Then lay feeler gauge on surface, then place straight edge on top feel blade. I then pull blade. It should be trapped by the straight edge. Not slide freely. Straight edge & feeler blades is the tool of choice.

Use the straight edge in every direction. A flat head is flat no matter where you place straight edge or feeler blade.

.0005 is very fragile feeler blade. You cannot slide it under like a thicker one. So you must place straight edge on top of it.

Check top of cyl also.

Measure thickness of new head gasket all over to be sure it has no dips/high spots. Most are pretty close to dead flat, Deburr around bolt holes & cly bore holes as needed.

I personally don't reuse head gaskets. Just what I do. I would never reuse gasket with a skimmed head if you don't want leaks.

The head gasket only squishes a little more than .0005". So you want it pretty flat. The biggest killer for leaks is dips/low spots between head bolts.

I use Starret 18" straight edge. Some times Snap on also 30" but it's hard to manage so the 18" is better. These are actual straight edges for checking heads etc, not steel rulers or the like. A 12" combination square blade is long enough, but often not actually straight.

I find if the head is slightly bent, it doesn't seem to effect head gasket too much. However a dip or high spot in head will often result in at least seepage which will look much like an oil leak around head gasket, where there is no oil to the area. For example around or between 2 outside head bolts. Of course a leaky gasket will allow oil from rocker box area to leak actual oil also.

As was spoken of, any burrs around head bolt holes etc. must be removed.

If you have dips in head or high spots you have no choice but to skim. The head is not bent. An example of this is when alloy is eroded from head sealing surface from blown head gasket. Most common across center head bolt. Especially on 10 bolt head. The alloy can be eroded by .002 or more. The only cure is skimming in such case.

Extra thick head gaskets are available if needed. Sometimes they will be.

Regarding rocker box sealing, that can also be checked with straight edge on head using feeler gauges. The bolt holes often are raising thread around sealing surface. Most important to counter sink the top thread. Any threads that are even slightly compromised must be Helicoiled with the top of coil at least 1 full thread below surface. best to tap drill on drill press & start tap well with tap held in chuck of drill press. I recommend & will only use genuine Helicoil kit. Will use timesert type only if hole is so damaged there is not enough metal to Helicoil.

The studs on rocker boxes very often have raised alloy around them & the stud should be removed & hole chamfered. Keeping in mind not to remove too much sealing surface. If head top is flat you can put feeler blade to head & set rocker box on & test the fit of the mating surface. Very often the box will have a surprising amount of rocking as both head & box are no longer flat.

If head is bent attempt to straighten as possible. This can help both top & bottom. Then skim as needed. Generally you can burnish the rocker boxes to flat using 120 emery cloth on flat surface. Again Helicoil any compromised stud threads.

Overall, the rocker boxes & top of head seem to be able to bend and to mate each other fairly well as you tighten bolts. You can experiment with this on bench using no gasket & feeler blades.

I like & use only Coveseal type rocker box gaskets. You are supposed to install them dry. They do a surprisingly good job of not leaking & compensating for not flat surfaces. However I've gotten to 100% of time now using Mercedes Benz 001 989 98 20 10 sealant. Paint thin coat on both sides of gasket. This sealant is very good on copper head gaskets as well. Paint thin coat both sides. Loctite 510 & 574 is very similar & good results can be expected. I mean will be bone dry, not seeps at all. Also these are ideal for sealing washers rocker feed banjos & PRV. Most excellent for cyl base gaskets. Will not even seep.

PRT crush is only part of the equation. Rocker geometry is changed as well. So if you must skim anything that changes the rocker arm center from crank case flange rocker geometry is effected. So a thicker head gasket may be needed to help geometry as well.

PRT crush is not too big of problem. Even .015" is fine & won't cause leaks. Too much crush can bend head & squish out lower square seal. The key to PRT sealing is deburr bore in head well. Smooth the lead in edge on head. Deburr outside of tappet block well & smooth for O-ring to slide over. Make sure inside bottom & outside top of PRT is clean & smooth, no peeling chrome, which will cause leaks. I like a small smear of silicon sealant on O-rings. Assemble quickly. Not so much that silicon can get into inside of prt or tappet block. Use 4 NEW O-rings while trial fitting for crush. Then use 4 different new rings for final assembly. Micro scratches on rings gotten during trial assembly will leak later. Sometimes 2 years, but you should expect a good 5 years+ service on PRT seals. ONLY USE VITON O-RINGS THROUGHOUT MOTOR!

The square white seal use new during trial assembly. That same one can be used during final assembly if you don't see any damage to it after trial assembly.

If wedding band is loose on PRT you can take very sharp center punch & make some light punches around bottom of PRT to keep loose band from migrating up. Loose ones often migrate up & allow white square seal to deform & pop out.

Same thing with Tappet block o-ring area. Deburr/smooth cly bore & outside of block & o-ring groove. I grease Tappet block bore & O-rings so they can slide in easier. Often small tappet o-ring leak is mistaken for PRT seal leak. Factory did a very bad job on smoothing the sealing surfaces for all these o-ring areas & that is a root cause of so many leaks. The new seals are cut/scratched during assembly. Can be ok for some months, but then seep.

Be sure to Loctite 243 the 4 center cyl base studs as they go into crank case oil & oil can wick up threads. Leaking cyl base nuts can be sealed after the fact very successfully with Mercedes or the Loctite 210 or 274 sealants. 210 is a bit stronger plastic in the sealant. 274 is the Porsche equivalent to the Mercedes sealant.

I hate oil leaks/seeps. With flat surfaces & modern sealants, unit motors will not leak. They really won't.
Don

I totally agree with Don about using a sealant with the Coveseal rocker box gaskets. When I used them dry or with grease they invariably weeped or flat out leaked. When I began using a sealant (Hylomar in my case) that was the end of those problems - absolutely no leaks or weeps.

I've only used Covseal gaskets on one engine, a 66 Bonnie, no gasket goo, and it was dry as a bone as long as I ran it, a couple of thousand miles or so.
This is NOT meant to contradict you, simply an observation.
I'll possibly use some form of sealant next time. I've tested out a few compounds on the Trident copper R/B gaskets to cure the perennial sweating. A German silicon based goo named Reinzosil seems promising, dry as dust so far but early days. Here's a link for those interested. https://www.reinz-industrial.com/en/products/sealing-compounds/reinzosil.aspx
It would work even better with no gasket I think, but then I'd have to shorten the pushrods some more.

SR

Hi Stein, Interesting sealant. Thanks for the tip!

I've not seen it before. Sounds very similar to Mercedes 003 989 98 20 10. This is what most current production Mercedes use from factory & at dealerships& has been for many years. Very good stuff. I like it on PRT O-rings. It has a shelf life as does most silicon based sealants. When shelf life is exceeded it will never ever cure. Never.

It dries with a death grip on metal to metal surfaces. If you put it on a timing cover, you could bend or break cover on removal. Properly used has a service life of 20+ years I've personally observed.

One caution about all silicon sealants is use it very thoughtfully. Don't over apply. Be very careful to not over apply & let it cure very fully. Any squish out that fractures off can get stuck in oilways. Starting motor before full cure (24hrs) almost assures you will have sealant squish fracturing off. Also if oil contaminates sealant, it retards/reduces curing & leads to leaks.

I see spec sheet suggests you can use it to seal leaking joints by applying along outside of joint surface. I have found the be very true & can be surprisingly durable. If leak is under oil pressure, the pressure will blow off the sealant applied to outside.

These industrial silicons are not the same as bath tub silicon. Much more durable in every way. Also much more costly, but worth every penny.
Don

You don't need to shorten the pushrods , it'll be fine... I generally don't use gaskets, just Loctite 518...However, I do have Covseal rocker gaskets on my T140 installed without sealer and they don't leak..Yet...

Has anyone noticed how leak proof the 10 bolt head bikes are? (or course, not ALL of them) I have. In fact, they're so dry that fasteners rust, alloy corrodes and stuff is super hard to get apart on these bikes. A little oil mist ain't such a bad thing.....
Cheers,
Bill

Hey TR7RMan,
Thanks for your comprehensive essay on the subject of cylinder head straightness and leak stoppage. Really appreciate you taking the time to share your knowledge. I'll look into the products you mentioned and thoughtfully assemble my top end with these things in mind.

I've used 518 as well but it costs a fortune and I'm cheap...
I don't worry much over the T140 boxes, they are lightly loaded compared to the older designs and dowelled to boot, so I use any old gaskets with good results. I'm sure the Covseal would be better though.
Next twin I do I'll try without gaskets and see how it works out. I did it on my first Triumph back in 75 but only because I didn't know better... As I recall it didn't leak...
My comment on shorter pushrods was for my Trident. I skimmed the head to clean up a damaged surface and left out the cylinder base gaskets, and then shortened the pushrods to suit the P&M valves and Elephant Foot adjusters from David Madigan. If I leave out the copper gaskets I may have to shorten them some more.
(Having mentioned the EF adjusters, I'm really pleased with them, and believe they do make a difference on valve gear wear and tear, and top end noise is reduced to a delightful rustle.)

SR

You can get ex MOD time expired 518 on eBay UK occasionally, the time expiration is extremely conservative making the cost benefit equation frugal.

How much of a gasket face do you have on the rocker-boxes where the head stud comes through?

I'll bet that the outside of the hole (the main 'footprint' of the rocker box) is about 5/32" (4mm) to 3/16" (4.76mm), but on the inside of the box there's a very thin seat where the stud hole is drilled through the boss on the rocker-box casting.
The head is fine in that respect - there's an even footprint for the rocker-boxes.

That's what mine looked like, and threre's barely any surface area there to seal any type of gasket, meaning that oil runs down the head studs etc (especially on the inlet side).

I had the thin part of the rocker-box built up with aluminium weld and flatted it back, and put a set of copper gaskets on.

Hi Komando, Using expired sealant is risky. If long expired it will not cure/seal. If more recent expired like 1 year it can seem to be fine, then some months later it starts to seep when fresh sealant would last for many years. I feel the money saved is not worth the risk. Been there done that. My recommendation is don't do it. Get fresh as possible.
Don

Tr7, these are MOD expiry dates not normal expiry dates, having worked for MOD suppliers the difference is significant I can assure you.

Loctite 518 50mm tube is about $18 to my door from places like Amazon..Or about $20 at the local auto parts store...One tube will do several complete engines and a few timing covers and rocker boxes....
A word of warning about anaerobic sealers like 518...I have seen even experienced guys glob this stuff on joints so a lot squeezes out when the joint is secured. ..They claim it only hardens in the absense of oil so excess will be washed away by the motor oil..Don't be so sure about that...I had a sudden and seemingly unexplained loss of oil pressure ion my T140 two year ago..I found nothing wrong but there was a small ball of hardened red sealer laying in the timing cover.The timing cover did have traces of a Loctite or Permatex red anaerobic sealer..I believe it was in the oil feed in the side cover...Only light smear is needed on properly fitting engine joints..If you have any doubts, mock up the cover or rocker box and check the fit using the thinnest feeler gauge...