To Cylinder Base Gasket on Not?

Yes Windy that seems right. We found that most old base gaskets are around .010 or 1/4 of a MM or so.
If I use anything it would be a steel one with a very light coat of goo.

ludwig said:

Or maybe I should buy a cheap second hand oven for garage use and for the sake of peace ..

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I think that is the better idea! :wink:

Debby

Danno said:

Leaked with a gasket. Rebuilt without and used Locktite Plastic Gasket, no leak. I'll never use another base gasket.

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It's funny, I had the exact opposite experience. Built my 750 with no base gasket and used Threebond 1104 on the joint. It leaks. :?

I fitted a gasket on my 850 and used some Hylomar as gasket dressing. No leak.

Now I'm inclined to always fit a base gasket, but "they" say not to do that on a 750...

Debby

I really don't think it is a major contributor to leakage either way. The story as passed down to me is that 750's had a habit of loosening base studs allowing the barrel to start moving with the pistons. Once loose,the barrels would cock in the crankcase spigot and crack the cases. I have observed these cracked cases in a couple P11, N15 and early '70's Commandos myself and wondered why they cracked.

The story continues that during the Combat problem investigation, this problem was observed to be on the increase. Norton theorized that the gasket was disintegrating allowing the barrels to move on the studs and loosen the nuts (or vice versa). The service bulletin went out to eliminate the base gasket and use a sealer. The issue was finally addressed with the 850 through bolts and gaskets were again used.

If this story is accurate, I don't see why using a base gasket does any harm, as long as periodic checks of the base nut torque is performed. If you have oil leaks at the cylinder base on a newly rebuilt engine, something was not done right on assembly whether you use a gasket or not. I personally don't use a gasket, especially when building one for someone else, because I feel if the owner does not check the tightness of the base nuts regularly, a gasket could only make the situation worse.

That's my story and I'm sticking to it.

I've always used a base gasket on my 750 racer.

The base nuts need checking after each race meeting and I tried putting blobs of paint on the nuts to see if they were loosening or the gasket was compressing...it was the gasket. The nuts weren't undoing on the studs.

I have found though, that the charcoal grey gaskets compress much worse than the brown paper ones.

Maybe I'll try it without a gasket, but then I'd have to do a dummy build and check the squish clearance, so maybe I won't.

I never use a base gasket for race or road (500 - 850cc twins), never have to retighten the base nuts, no leaks! I always use a silicon based plastic gasket, make sure the mating surfaces are flat and clean(very important) then apply an even thin layer of gasket all over one surface (after tightening the cilindernuts I always check for gasketresidue inside the small oil return channel by sticking a rod to the very bottom).

When I assembled my 850 bottom end I stuck the barrels on temporarily before I tightened the crankcase mating bolts, just to make sure the barrel mating surface was flat.
I believe the 850s prior to the MkIII didn't have a base gasket - there isn't one listed in the parts book. As Les has intimated, perhaps it was re-introduced on the MkIII to aid the electric-assist?
My T140 runs without a base gasket after it progressively spat the original one out :shock:
I rebuilt it with just a coat of Wellseal and it's been no problem - even after all the base nuts worked loose and lifted the barrel...oil everywhere. As a Get-U-home I just retightened everything and it stopped leaking altogether. The nuts have been retorqued once since and it's been fine :!:

Highly recommended:

I've sworn off essentially all gaskets but head and TS cover.
I've also sworn off tarry Wellseal and thicker grey bonds
for anything but a moderately operated Commando.
There is enough variation in Commandos that what may
work for one may not for another.

Past gasket materials may have been corrupted by the
UK CEO convicted a few years ago for substituting
almost any trash bulk fibrous crap he could source,
horse stall droppings to feather scrapes. Really.

Wellseal an grey Honda-Yama-bond glue parts together.
Only sealing is desirable you'll find on next opening,
especially the crank cases.
The grey stuff can become like Playdough, hardens
and then fractures from both engine heat and vibes
and the strong clamp force Nortons must have or weep
and shift its parts like putty.

I remain a Blue Racer Hylomar guy for every goop need now.
This can seal as big or bigger seam gap as the thick gray stuff,
never hardens and won't mare case surfaces trying to break
the glue with knives and levers and hammers.

hobot