e-mail about base gaskets

[JohnS_Rosamond]

Sorry to post this here, but someone sent me an e-mail with no text in it, just the title.  Title was asking about base gaskets.

So, here's some thoughts.

As you're removing the cylinders, before the piston comes out of the cylinder, push some rags into the case opening.  If any carbon falls out of the cylinder it wont (hopefully) get into the case.  Also, whgen you're cleaning the case mating surface, you'll be less likely to get anything down into the case.

If you don't have many miles bike since the last tear down, it's safe to just do one cylinder.  However, I usually suggest that if you're gonna do it yourself, it makes sense to do both.  It's not generally a good idea to pop the heads off without replacing the base gasket.  Now having said that, I have had a couple of people who use the metal base gasket say that if you don't otherwise disturb the cylinder (just removing the head), that it'll stay sealed one more time.  If it were my bike, I wouldn't wanna take the chance.  Try to get the sealing surface on the base of the cylinder and the case as clean and debris free as possible.  With the cylinder studs in the way, it's not easy.  However, I have found that when I use hylomar on the metal base gasket, when I go to replace the gasket, there is literally no gasket residue.  The whole thing peels right off in one piece, wipe mating surfaces with a rag (with a little cleaner on it) and it's ready to put back together again.  Genuine James or Cometic are both excellent choices on Brand name gaskets.  While you can use a single edged razor, a wire brush can work too, or one of the gasket removing compounds - making sure that you don't gouge the gasket surface (not always easy when your trying to scratch off an old gasket).  Generally I use a razor on the hard spot, wire brush on the rest.

While cleaning the combustion chamber on the head is not necessary, you might wanna check around the spark plug hole for cracks (from the exhaust valave to the spark plug hole).  Remember to clean the top of the cylinder (and bottom of the head) as clean as possible so that the gasket has the best sealing opportunity.

It's a good idea to check cylinder stud installed height.  Even if you don't have the measurement, make sure that they're all the same height from the deck.  If one is pulling out (or backing out) it may not be obvious.  Changing the studs is not madatory, though I do like the later model HD studs with the shoulder at the case rather than the earlier ones that had the shoulder up at the head interface.

Anyway, I hope that this might answer a few of the mystery callers questions.