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#833561 12/17/20 12:20 am
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Hello;

I still do not see a consensus regarding this gasket. Some put only the gasket; some put silicone; some put the gasket and silicone; some put Loctite 518 or 515; some put Loctite 510; some put permatex or other brands (all Loctite equivalents)
So, some included manuals advocate for dry assembly and others for the use of these other gasket substitutes.

In one bike; a T140E but with a rotary pump, I have a slightly oil leaking between the cases and the cylinders. PO used silicone and a thick gasket (0.75) due to compression etc; then I tried dry but leaked then I tried again what he did.

I have new cylinders; gasket etc to assembly but I am not so sure what route to take.
Even the factory Manual do not clarify well and all the other manuals do not have a consensus too. Again, the rotary pump really pumps and sometimes seems that I have too much oil in the cases if not I do not know why I could have a leak there. At a time (I needed to dismantle it) the bleed was besides the hole that the crankcase (RH) have to the cylinders and solved putting plenty of silicone all over the gasket and rebuild again.

Thanks

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Different strokes for different folks

For me, I like to lap the base gasket surface on both cases (bolted together)

When I use a base gasket I like to use Yamabond on both sides, however, it depends on the gasket and the material..

Dan's gaskets for example (Franz & Grubb) do not require sealer, and seal very well

Some will remove the base gasket to limit the volume in the head (high compression)

I remove all cylinder base studs and seal them off to prevent oil from working its way up the stud and causing a base gasket leak

I have tried Loctitie 518, Three-bond, etc with decent results

For me, I have found Yamabond (Permatex Grey) to seal very well and is usually my "go to" here in my shop when using / not using a gasket

Just my 2cents

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I have been using Hylomar for well over 50 years with no problems.
HTH

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no wellseal there?


i'm old enough to remember when patriotism meant not trying to overthrow the government.
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Seems to me that volume doesn't cause leaks as much as pressure. With a good breather system the crankcase should not have much pressure. If that rotary pump sucks the sump dry faster than it pumps the only oil in the crankcase is what is being thrown off by the rotating parts. There are so many different cures for leaks because there are so many reasons for leaks. If a quality base gasket with a good sealer on both sides does not cure your leak, you have other problems.

PS silicon is the worst thing to use. What squeeze's out can break off and plug up your oil lines.

Last edited by desco; 12/17/20 3:44 am.

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My take is to use a dry gasket but with a smear of Wellseal over the crankcase joints. It's a favorite spot for oil leaks. Lapping and levelling the cylinder base is nice, but a lot of work and something I only do on very special engines. The two inner cylinder flange studs on the TS block half needs a thread sealant, as mentioned.
However, on any engine with pressure fed exhaust cam followers, the oil ring that seals off the guide block WILL eventually develop a leak. There are two ways to fix this, you can pull off the head and barrels, knock out the guide block and replace the O-ring, which would be the proper way I guess. Or you can bodge it, like I did on a nice T140 daily rider. I removed the timing cover and inserted a plug in the oilway behind and inboard of the OPRV. I made the plug nice and tight and put some Loctite on it. That did the trick and with the added bonus of NOT diverting any oil away from the crank. Not a big issue I guess, but nice.
The Triumph cams 1969 on didn't need the pressure feed anyway, and Triumph actually deleted the feature towards the end.

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I assume that the oil pressure relief modifications were done (extra holes) as per the Morgo instructions? If not, there will be too much pressure.
I agree, though with Stein Roger, I use late top ends on pre-unit bottoms (so no oil feed), and with 69 on nitrided cams there is no problem

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I agree---plug off the feed to the exhaust cam follower if using the later nitrided camshaft.
I made a small aluminum plug with an interference fit and gently tapped it in with a touch of Loctite around it to 100% seal it.
On sealing faces in general I use Wellseal for metal to metal joints (such as crankcase halves) and Hylomar if there is a gasket.
I would be the first to agree that it is not the only way to go--maybe not the best way to go but--it certainly works for me!
HTH

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I believe Coventry Gaskets (John Healy) has some triumph gaskets which are superior at sealing. Not sure if they are for the 750 or all triumph twins??? If they are anything like the base gasket I got off Ed V for my A65 it sealed so darn good the worst thing I did was put wellseal on, I could hardly get the barrel off the next time I needed to.

It could be worth slackening the engine mounting bolts which hold the two case half’s together before tightening the barrel. Then tighten those bolts again. It will true the cases up and ensure you get the best seal possible. Then retighten the case bolts. If your dealer is half decent is should allow some flex for you to do this.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
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I think keeping the barrel to case joint oil tight starts with initial assembly of the cases.

I’m with TM in using Hylomar, I’ve found it very effective for decades. There may be even better ones, but I’ve not had cause to experiment.
I’ve been happy with it on both non-gasket joints and gasket joints (on which I give a smear on both metal surfaces).

If you have a flat surface on the cases, and you keep the barrel nuts tight, all other things being normal, the joint will be oil tight. I’m not talking of leaks caused by the feed to the exhaust tappets, another matter.

I hear many folk don’t feel repeated re-torquing necessary after a fresh build. I personally do. It is quite obvious that gaskets (both card and copper) do settle a little in the first 1000 miles after a new build. This affects both the torque of the barrel and head bolts, the sealing at those joints, and of course the valve clearances.

If re-torquing of the barrel joint is delayed such that oil is allowed to leak through it, subsequent tightening may not reseal that leak.

Another aspect relating to the barrel joint is the effectiveness and truth of the head steady with respect to the engine mounting points.
The crankcase attempts to move according to the imbalance of the crankshaft assembly (both vertically and forward/backward relative to the frame).
Imagine that front to back oscillation, with a rigid, fixed head mount, putting strain on the barrel flange, fore and back. No wonder leaks develop.

Perhaps this was why the Triumph head steadies were pretty feeble?

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I have not used a gasket on any Triumph twin....First used RTV 45 years ago and then Loctite 518. With clean surfaces, a very slight bead of sealer, nothing leaks ....But if you prefer a gasket there's no reason not to use it


79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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4+ decades of 515 on cylinder base if I'm not using a gasket but only because I have lifetime supply otherwise I'd possibly look at 518. Obviously there's a number of sealers that do work well as can be attested by others. I caution against silicone RTV. Key critical is to clean back to bare metal, de-burr and things like sealing studs mentioned earlier are great forms of prep.
Hope this helps.

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Hi All, 518 is not recommended for gaskets. It doesn't harden fully like the others. It can cause gasket to migrate/slip.

I really like the fully hardening Loctites for base gaskets. I personally like the thin paper gasket with 510 or 515 painted on both sides. It soaks into paper & I find it works well for many years. Like at least 25.

Saying that the surfaces must be fairly flat. Dips, humps, grooves are pretty hard to overcome long term no matter the sealant.

I find with the 510 or 515 on gasket you don't even get seeping from around the tappet feed hole at base gasket.

It is important to put sealant on the 4 inner studs that go to oil space. Again 510. 515 is a perfect choice. I've sealed thousands of studs like this that were leak free for over 25 years. Also holds studs similar to blue loctite, but is much better as no leaks. 518 will work but no as well.

For trans bolts that go to outside I use 518 with good results but they don't see the force the cly studs do, plus you may have to remove them sooner. 518 on the case halves & trans covers (no gaskets) is my sealant of choice.

Regarding tappet blocks, I replace the o-rings if they are about 5 or more years old on principle. Use only Viton rings here. Normal rubber ones leak much sooner. Same with push rod tube o-rings. Viton only.
I can say this without question, no amount of blow by will make the gasket leak is surface is flat enough & you use the above sealants. I've installed many oil filter flanges with 510, 515 which run 100+ PSI hot motor with not even a seep. If blow by is causing leak, the gasketing is compromised anyway.

On a side note. I've resealed many cyl base stud/nuts after the fact where the builder didn't use correct sealants or didn't seal the 4 stud threads that leaked.

I remove nut, washer if possible. Blow out loose oil. Clean well with parts cleaner (or gas) & compressed air. If you can't remove nut, work nut up/down using cleaner to remove all oil from threads. Dry all threads well. Paint thick coat 510, 515 on threads, both sides of washer if used, bottom of nut. Work sealer into threads of nut if nut can't be removed. Tighten the nuts as normal. Wipe squished out sealant off. Only do 1 stud at a time. After all studs are sealed, let cure 24 hrs. It will not leak!

My take on plugging off tappet oil is if it makes cam last a little longer it's worth having the oil feed. Correctly assembled, I've not seen leaks from the gasket or o-ring for many years. Seems even viton PRT seals will start to seep after 6-7 years. I don't think I can do better on those.
Don


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Yes Don, if you think about it, why should the barrel/case joint be prone to leaking?

This is not unique to 750’s, it happens with 650’s and pre-unit 500’s and 650’s as well.

If some deny that, it’s only because they don’t use them hard enough.

Push a B-range Triumph twin and it will sweat from the base gasket and other places too.

It’s not something to worry about though, sweating is after all quite normal. What I was saying about the head steady is a real thing, most steadies are pretty rubbish and don’t really hold the head solidly at all. They allow the head to vibrate backwards and forwards quite a bit, with respect to the crankcase. That angular oscillation of the head (tiny as it may seem) puts a varying load on the barrel joint. I’m sure you can imagine the rest.

My 2 pence…

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Originally Posted by koan58
Yes Don, if you think about it, why should the barrel/case joint be prone to leaking?

This is not unique to 750’s, it happens with 650’s and pre-unit 500’s and 650’s as well.

If some deny that, it’s only because they don’t use them hard enough.

Push a B-range Triumph twin and it will sweat from the base gasket and other places too.

It’s not something to worry about though, sweating is after all quite normal. What I was saying about the head steady is a real thing, most steadies are pretty rubbish and don’t really hold the head solidly at all. They allow the head to vibrate backwards and forwards quite a bit, with respect to the crankcase. That angular oscillation of the head (tiny as it may seem) puts a varying load on the barrel joint. I’m sure you can imagine the rest.

My 2 pence…
Years ago there were stories of modified Japanese inline 4's pushing out cylinder base gaskets. The shredded gaskets lead to thinking that the crankcase and cylinder were fretting....The cause was detonation....Many here might think detonation leads to instant piston failure....But at high speeds it can't be heard and depending on the engine build may cause oil leaks, bearing wear and all sorts of problems..


79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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Something I've not seen mentioned is using the base gasket to help size the squish area. I've used different combinations of copper base and head gaskets in pursuit of this. BTW, I've not had any trouble with annealed copper base gaskets leaking or weeping on my race 650.

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Good point Mike, I have done the same on the modified T140 street bike and the race Triumphs. On a stock engine , in my experience, the .018 increase in piston height will help help with detonation control more than the slight compression increase will make it worse...It will require playing wihh push rod tube seals, some here hate that. lol.


79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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We've touched upon quite a number of different sealants by now...
Let me introduce one more, it's named "Reinzosil" and is made in Germany. I use it on copper R/B gaskets and gasket less joints, and on some engines with troublesome pushrod tubes, I use it on on the seal rings. I used to swear to use these seals dry, but have found that in some instances that they just won't seal without some kind of goo. Reinzosil was something I found by chance and I'm happy I did. It's what I use instead of a base gasket on my Trident, and what I used on the copper R/B gaskets on the Trident and others. I'll use CovSeal gaskets this time though, even better and no mess.

A comment on assembling the cases loosely and do up the cylinder base nuts before tightening the case bolts fully. It's what I do, but I still end up with a slight step sometimes. Besides, the edges can get ever so slightly rounded, leaving a microscopic canal for the oil to escape through. Using a light smear of your favorite compound is a sensible precaution to take. I HATE pulling the head and barrel on an otherwise good engine just to fix a leak there.

SR

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Hi; no Hylomar or Wellseal here.

Gasket is Inter face brand 0.020 Made in USA. I only specified the part number and they sent me this one. Never offered me a 750 cov seal cylinder base gasket. I bought cov seal rocker box gaskets.

I am asking due to as mentioned, last time I needed to dismantle again to fix the leak.
With the pre unit 500 I do not have a leak or sweat and I used a thin gasket and silicone. 500 leaks a lot from the rocker boxes and external oil pipes junctions.
I still think that the problem is a mix between the rotary pump and that have direct oil feed to the crank like the cars so very possible more oil at the same time there than most other 750s

Still do not know why the manuals do not specify dry or wet rebuilding. You do not know if you have a leak (rebuilding all by the "book") until you start the engine...

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If the PRV is doing it's thing, you shouldn't get any more pressure, it just dumps the excess oil back into the crankcase - thus my question about the recommended extra holes mod for the PRV!

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...those holes are needed in certain cases.
I have the pressure regulated at about 72psi all the time.

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Quote
Years ago there were stories of modified Japanese inline 4's pushing out cylinder base gaskets. The shredded gaskets lead to thinking that the crankcase and cylinder were fretting....

Kevin Cameron discusses this in the current issue of Vintage Bike magazine. Fretting is a common problem with engines. Where there has been evidence of fretting a common recommendation is to use a sealant that stays pliable. The old stand by ,Yamaha Bond No. 4 (aka Harley Bond, Kawasaki Bone, etc.)and made by Three Bond, stays pliabale and used on non-gasket surfaces helps reduce sealing failure from fretting. The gasket material we use doesn't require any sealant. It is made in the US by Interface. It is a cellulose base bound with Buna-N (rubber). It made for small engines, not bothered by gasoline, oil or the like and withstands fretting. To quote Inerface: "N - 8092 is composed of reinforced cellulose with a nitrile butadiene rubber binder. It exhibits excellent crush resistance at high flange pressures. Recommended for sealing oil, fuels and water in applications with intermittent operating temperatures."

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John, that sounds like the gasket set I bought from British Tools and Fasteners.
They recommended against using any gasket goo because of the Buna-N.


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What is the maximum temperature that the cases/ cylinder joint reaches?

Dave

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...yes; as mentioned is Interface brand N 8092 but without any metal sheet. The old one is the same and leaked a lot then, as mentioned too with silicone added solved 95% of the leaking.

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