getting an oil tight seal at cylinder base - advice anyone?

Took my head off because of a bad valve guide oil seal causing a lot of smoke. Will put it back on in a few days.

While it's off though, I'd like to deal with my oil seepage (is that really different than a leak?), which seems to be coming from the base gasket, at the front. The previous owner had the cylinders off at 12,000 miles (mileage now at 14,800), and from old receipts, looks like a new gasket was put on.

However, every time I ride the bike, even 10 or 20 miles, I'm getting oil seeping out there.

Not sure whether to use:
1) a new gasket (in the mail as I type)
2) a new gasket plus some gasket goop
3) skip the gasket altogether and just use gasket goop

If someone has come up with a completely oil-tight solution, I'd love to hear it. If it involves gasket compound, which brand/type?

Waiting with bated breath and a catch bucket in Encinitas, CA
Keith [/img]

Keith, I recently had my cylinders off and it had been leaking slightly so after very thorough clean up of both surfaces of the base I re-assembled using a standard gasket with a faint smear of gasket cement called "gasket goo" (really!) on both surfaces. Quite a few miles later and no leaks, seems to have worked a treat.

A common problem and one I lived with for many years. If you don't have a one way valve on the breather fit one as there is a lot of pressure in the cases at normal engine speeds. It works on cam breather models, Combat and 850 style breathers. 850 is the best but earlier models can be made leakfree too. A good sealant and a gasket finishes it off. I use silicone but many hate it. It depends how much you use and just a smear either side of the gasket (keeping the drain hole clear with a piece of electrical cable poked down the barrels just in case) is all you need.
Also check the front stud. On some cases it does not have much engagement, is often stripped and this is an important clamping point.
Other than that of course the gasket surfaces have to be flat with no defects from earlier repair efforts and use of screwdrivers!

Keith,
Norton cylinder bases are notorious for weeping. I believe this is due mostly to the studs and/or nuts loosening and allowing the cylinder to slightly rise off the crankcase and hammer the gaskets to mush. This is evidenced in the extreme by the number of cases found with the bores cracked where the cylinders tilted.

Norton recognized this problem and issued a service bulletin in the '70's recommending that the base gasket be left out and the cylinders cemented to the crankcase with a product sold by Norton called "locktite plastic gasket". This was an anaerobic sealant much like Loctite's current 518 Gasket Eliminator flange sealant. Norton addressed the situation again with the through bolts used on the 850 at which time they reinstituted the base gasket.

I have used Loctite 518 (or 515) on case to barrell joints for many years and have never had it leak. In addition, disassembly is fairly easy. I am also one of those who swear at, (not by) silicone seal for this purpose. As I have said many times, silicone will squeeze out in little balls which harden and collect in sludge traps and bearing oiling holes. Anaerobics will not harden except where oxygen is eliminated. Excess will disperse in the oil and be removed with the next oil change.

It goes without saying that whatever you decide, go back several times to tighten the base nuts after heat/cool cycles.

oil tight seal at cylinder base

thanks for the suggestions. I forgot to mention - the bike is a '75 850 Mark 3. I think I will try light coatings of the Loctite 518 in combination with the standard gasket.

I have had good results using no base gasket and Yamabond...can't remember the number but its the grey non-hardening stuff. I have an 850 with the HELP brake booster valve in the case breather hose.

The Mk1 850 didn't have a base gasket while later models did. I think it was for two reasons one to ensure the oil drain hole never got blocked and to reduce the compression a little.
If you buy quality gaskets you shouldn't need a sealant. The gasket material manufacturer will have impregnated a sealant at great "expense".
I always fit gaskets dry and on an oil free surface, never failed me yet.

Cash

The Mk1 850 didn't have a base gasket while later models did. I think it was for two reasons one to ensure the oil drain hole never got blocked and to reduce the compression a little.

Click to expand...

Eliminating the base gasket raises compression. However it would probably be imperceptible.

By the way, there is no gasket shown in the parts book for the 750 (after 212278) or 850. However, my '73 MkV 750 came with a base gasket installed. I removed it when I did my first top end job.

Ron L said:

The Mk1 850 didn't have a base gasket while later models did. I think it was for two reasons one to ensure the oil drain hole never got blocked and to reduce the compression a little.

Click to expand...

Eliminating the base gasket raises compression. However it would probably be imperceptible.

Click to expand...

I think I read cash's comment as he meant it? = That the base gasket was reinstated to ensure the oil drain hole did not become blocked with sealant and to reduce compression?