G80CS Short Stroke pushrod tunnel seals

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G80CS Short Stroke pushrod tunnel seals

Postby Matchymarty » Sun Aug 12, 2018 6:13 pm

Hi all,

I've done some forum searching but can't seem to find a definative answer on this one.

Finally got my '56 G80CS Short stroke running on the weekend after 2 years of trying to get it right. Starts first kick and runs like a brand new modern bike.! However, oil was pouring out of seals between the head and barrel.

I note that there is a couple of comments on this forum stating that this engine did not have a head gasket. The 'gasket set' I got, included a copper head gasket (that didn't fit over the 4 studs and I subsequently filed out the 4 holes to get it to fit) and, 2 rubber o'rings that fit loosely in the pushrod tunnel recess in the barrel, and, are only 2mm thick. They fit fine, but do not seal. I suspect the o'rings need to be 4mm at least to give enough squish to seal.

So 2 things.
1. I don't have and can't seem to find a parts list for my '56 G80CS which is the first of the short stroke engines and has enclosed push rod tunnels. My '56 manual does not show the short stroke engine. I have a 'supplement manual' covering the short stroke 350 and 500 but, is only a few written pages and does not include any parts information. Is there a parts list manual for the short stroke?

2. Does the short stroke really NOT have a head gasket? I note that Don Madden has made comment that he makes gaskets out of thin (2 or 3 thou from recollection) sheet copper from hobby store. My copper gasket is of a 'normal' head gasket thickness. Would that be causing my pushrod tunnels to not seal? Ie, does the lip of the cylinder that protrudes the barrel top, sit up in the head, and therefore, the thickness of my head gasket is separating the barrel and head too much?

Ok 3 things... hehehe.

3. I note that Don Madden had mentioned he uses 'X' rings for the pushrod tunnel seals. (top ones between barrel and head). Anyone got a source for these or, at least, good sized and quality o'rings?

I've ordered a few sets of o'rings from the club spares, but am not sure what thickness they are so only time will tell. If I can source some 'X' rings or other that would be great.

Cheers.
Marty

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Re: G80CS Short Stroke pushrod tunnel seals

Postby ajscomboman » Sun Aug 12, 2018 7:08 pm

There is no gasket on these motors as the head joint was lapped in. They are a complete bugger to do and take forever. I'm now going for a gasket that is supplied by AMC classic spares along with the required thicker o rings.

Check out Stevens website and you'll find all the bits you require for the CS motors. www.amcclassicspares.com

My CS didn't leak at all from the bottom O rings but did weep very slightly out the top after a 40 odd mile ride.

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Re: G80CS Short Stroke pushrod tunnel seals

Postby cbranni » Sun Aug 12, 2018 8:02 pm

I got the head gasket and seals from AMC Classics as Rob did, it worked for me.

Colin
only dead fish go with the flow

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Re: G80CS Short Stroke pushrod tunnel seals

Postby bjorn » Sun Aug 12, 2018 9:42 pm

Marty,

Parts lists, workshop manuals and more for Your 55CS and 56CS:

Google:

Archives.jampot.dk - /book/


Bjørn

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Re: G80CS Short Stroke pushrod tunnel seals

Postby Matchymarty » Mon Aug 13, 2018 1:03 am

Thanks fellas. I'll contact Steve from AMC Classic Spares and get some sent to me :) Cheers.
As it turns out, I spoke with a friend of a friend, and he had a 'Illustrated Workshop Instruction Manual' '57-'64, and it explicitly speaks of how to lap the head joint on the CS models.

If AMC spares have a suitable head gasket and seals, that'd be great. I'd rather do that. Although, I guess I can take the opportunity to pull the barrel again anyway, as I don't have a base gasket on the engine, as I ran out of them when I put the engine together. So, i can remedy this at the same time.

Cheers.

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Re: G80CS Short Stroke pushrod tunnel seals

Postby Matchymarty » Mon Aug 13, 2018 6:32 am

Thanks again for the help.
I dont' suppose you have a thickness on the top seals and gasket you got from AMC Classics?

Ok, So I've managed to obtain some very good fitting imperial o'rings. 21.82mm ID x 3.53mm thick. Apparently. I think the thickness is a little optimistic. I measure them at 3.47mm at best.

Now here's the fun part. Together with advice from here, the G80CS '56 is NOT supposed to have a head gasket. Problem is, I've now measured the cylinder sleeve protrusion from top of bore to be a median of 2.09mm. The recess in the head, varies wildly, but lets say an average of 2.38mm. (there's one spot where it's 2.47mm). So basically, there's no way I can 'LAP' the head to the barrel. The two do not meet! So, long and the short is I'm stuck using a head gasket.

So, I have a copper head gasket measuring 0.98mm. For interest's sake, and for the forum, the recess in the barrel for the pushrod tunnel top seal, is an average of 2.15mm deep, with, 21.3mm ID and 28.40 OD.

So with my new o'rings in place, i seem to have 1.2mm protrusion from the top of the barrel. Take out the thickness of the copper head gasket (0.98) , and I'm down to only 0.3mm of additional height of the o'ring to be squashed. Think I'd better look for a thinner head gasket or ... hope that the AMC Classic Spares gasket and o'ring combination has more available 'squish' from the o'rings. I don't think 0.3mm is going to give me a good enough seal.

The only other option I Have is this head gasket included in the gasket set I purchased. It seems to be, NOT paper, but some sort of vinyl feeling type material. It measures 0.80mm at best, so would help being a little thinner (0.15-0.19mm) than the copper one I have.

Anyone seen one of these gaskets or used one? Are they any good? I suspect they will squish a bit by the feel of it, so again, that will help ....


Thanks again for all your help.

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Re: G80CS Short Stroke pushrod tunnel seals

Postby bjorn » Mon Aug 13, 2018 9:01 pm

Marty,

"Now here's the fun part. Together with advice from here, the G80CS '56 is NOT supposed to have a head gasket. Problem is, I've now measured the cylinder sleeve protrusion from top of bore to be a median of 2.09mm. The recess in the head, varies wildly, but lets say an average of 2.38mm. (there's one spot where it's 2.47mm). So basically, there's no way I can 'LAP' the head to the barrel. The two do not meet! So, long and the short is I'm stuck using a head gasket."

Correct, a head gasket is not used on these engines. It is not the cylinder sleeve protrusion that is to be lapped, but the wide aluminium faces on the barrel and head that are lapped against each other. This is what I do and unless the head or cylinder mating surfaces are scratched or warped, it does not usually take much time or effort to lap them with fine grinding paste until you see a continuous grey surface on both head and cylinder.

(Must be thoroughly cleaned of grinding paste after the lapping)

Bjørn

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Re: G80CS Short Stroke pushrod tunnel seals

Postby Matchymarty » Mon Aug 13, 2018 10:31 pm

Thanks Bjorn. I was mistaken. I'd recently pulled a B31 apart, and it has a large wide area as an extension of the cylinder sleeve and matching recess in the head which, does not use a head gasket either. I figured the CS might have been similar. So, guessing that if I lap it in, I could maybe even use a bit of gasket goo to help?

Question is, how thick are the 'correct' o'rings? I don't want to use ones that are too thick which would inadvertently hold the head up off the barrel surface.

Cheers.

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