Old gasket turned to mush?

Very bad leak from the transmission cover. Just got it running -- oiled it up and it leaks, as in pours out from the transmission case in one day.

Three parts to the question:

1) Took off the kick start, etc., etc. And saw the gasket for the transmission case was turned to a goopy almost liquid state?! Now parts of it still had some form left (top parts), so it looked like it had been the traditional paper gasket, but for much of the rest it looked like the gasket was becoming liquid. Never saw that before on other engines. Could there have been a liquid sealer applied to the paper that did that?

2) Took out the paper gasket for the transmission that came with the small set of gaskets I found in a box of parts I got with the bike. I was overjoyed I could fix'er right up. But it was totally brittal. It was a little wavy and when I greased it and tried to stick it flat to one side of the case it broke in two like a cracker. Ok. Can I totaly dispense with a gasket and just use form a gasket or some such product? I ask only because some mating surfaces can be so bad they might need a filler of some sort even with the gasket in a tube stuff.

3) Never took apart then put back together a transmission case like this. Do I have to be careful with shift indexing somehow besides carefully noting shift lever and pointer positions upon disassembly (which I did)?

Removing gaskets will remove clearances internally as it brings the covers closer together, it will therefore reduce end floats etc. This is only really advisable if you know what you’re doing, and have measured the end floats carefully, and calculated it’s the right thing to do.

IMHO, stick to standard, buy yourself a proper gasket set from AN or an AN retailer and do the job right. At least then you’ll have less chance of having to do it twice...

As he says, buy or make new gaskets.

As for your other question, I have never seen a paper or compound gasket turn into anything like liquid.

I would make (cut) a new gasket, but not wanting to do this twice, what gasket material to use (thickness, compound type, etc.) readily available in the local auto supply shops? Otherwise, not riding this weekend, but ordering standard gasket from one of the AN supply houses. The brittal original looks like fairly thin, tough (used to be before it became brittal with age) paper.

not to go off topic, but speaking of gaskets -- kind of new (well, kind of born again new - ) to the bike thing, but years in automotive, so what's current, best method of sealing cases or case covers on these old brit bikes. it's been some 50 years, but I still remember my old, old triumph days - drip, drip, drip... - . I understand the fact about using factory style OE type gaskets (and proper fastener torque), BUT, best installed dry, with some sort of additional sealer or sealant? presently, one of my favorite products is Permatex gasket tack - a mild adhesive/sealant, and over the years I've had good luck with it. another product is hylomar blue - non-hardening and non-setting sealant. getting ready to install the gearbox outer cover (and maybe crankcase) - prefer on to do it twice. have an OE type gaskets from old brits. also, I have a new O-ring (from old brits) for the primary case - any additional sealer or sealant used with the O-ring? any other tips or tricks with installing case gaskets? TIA.

edit -

Joe Schlaberdowski said:

what gasket material to use (thickness, compound type, etc.)

Click to expand...

You’re putting more thought into it than the people who sell gaskets.

Loctite #518 on the gasket. Seals perfectly, peals off like a Post-It note when you want it to.

There is an excellent Gearbox rebuild video available from the UK based Norton Owners Club . Buy gearbox gasket set from Andover or US supplier. I generally receive my orders in about a week’s time. All should be aware that Andover is moving their operations to new premises mid October so service will be interrupted.

I second the suggestion to get the Mick Hemmings gear box re build video. It is very helpful.
There are also a few tech write ups with good pics on the process. Look in the Old Brits website tech section. I also found an old magazine article on line where Mick Hemmings went through a box with the writer.

Btw you didn't say what work you did while in the box. Most will insist the layshaft bearing is replaced with a more reliable option.

I did my box over last winter, renewing all bushes, bearings, seals and springs. Never did this before and the articles and video were very useful.

Watch some of the vegetable fiber materials out there if you roll your own because over time the results can be disheartening. They get all mushy and saturated......

Here is the magazine article I refered to earlier:
http://www.nortoncolorado.org/files/AMC gearbox overhaul.pdf

and the Old Britts Tech Article:

https://www.oldbritts.com/gearbox_d.html

Tornado said:

I second the suggestion to get the Mick Hemmings gear box re build video. It is very helpful.
There are also a few tech write ups with good pics on the process. Look in the Old Brits website tech section. I also found an old magazine article on line where Mick Hemmings went through a box with the writer.

Btw you didn't say what work you did while in the box. Most will insist the layshaft bearing is replaced with a more reliable option.

I did my box over last winter, renewing all bushes, bearings, seals and springs. Never did this before and the articles and video were very useful.

Click to expand...

Didn't replace any mechanical parts. Up in my original post I mentioned how, after I got it running, I put 90 wt in the gear box, determined to go for a ride around the block. And the oil came right back out. I tightened the screws a bit, but the result was the same. Took the cover off and was a little surprised to see a large portion of the gasket had actually turned to mush! Jbruney texted that vegetible fiber gaskets do that (mystery solved). So I tried to replace with an old but new gasket I got in a box with the bike. It was wavy (though not much) and when I tried to flatten it against the gearbox cover flange it just cracked. I may have work to do inside, but the cover comes off pretty easy. I'll wait to see how she runs first. Right now I've got a rubber-fiber gasket sheet 1/32. The one I had that cracked about 1/64. But the new one may be a touch squeezy ( down to 1/64?). Says it's good for oil water or gasoline.

Triton Thrasher said:

You’re putting more thought into it than the people who sell gaskets.

Click to expand...

Engineering paranoia. Or maybe engineering fun.

I haven't experienced a gear box gasket going to mush. It depends on which gasket failed. The inner cover to shell gasket affects end layshaft end float if using a roller layshaft bearing as well as the depth of the kickstart shaft bush. Shim accordingly. I used a paper gasket with Permatex sealer. For the Outer Cover to Inner Cover you can use a liquid gasket product as long as the faces meet nicely. If not paper gasket with sealer.