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How do you get the primary cover oil tight?

PostPosted: Fri May 07, 2021 6:01 am
by Monti
I wonder if the gasket for the primary cover in the KH gasket kit is suitable (too many holes which are not required). I think that these holes for the later cover will lead to oil leaks, especially if you consider the thin walls of the crank case and that the cover is only fixed with 3 screws!
What do you do to get this cover oil tight?
Thanks a lot for your advice in advance.

Re: How do you get the primary cover oil tight?

PostPosted: Sat May 08, 2021 4:06 pm
by wz507
As you note, the three ¼-20 fasteners are surely not up to the task of altering the shape of the heavy gauge aluminum cover to force it to seal. Below are some solutions to consider.

Start by trying a Cometic foam gasket (aluminum frame with nitrile rubber foam on each side) which is 0.060” total thickness. Hopefully this will solve your problem. ... Swke9aTXNB

If the seam still leaks, I’d advise being more aggressive and sealing it together. My go-to procedure for this is the following. Clean both sides of seam with solvent and get it absolutely squeaky clean, i.e., free of any oil, debris, old gasket residue, old sealant, etc. Then carefully and quickly apply a uniform small bead (1/16” dia) of Permatex Ultra Grey silicone sealant to the cover (do full circumference of all holes), assemble immediately onto dowel pins and secure with the 3 fasteners. Wipe away any excess silicone that squeezes out of the seam with a small amount of mineral spirits on paper towels or Q-tip swabs. Allow 1 day to cure. If you’ve done this properly it will be dry for the rest of your life.

Many people dislike silicone sealants, and if that might be the case here, there are myriad other sealants to explore – Wellseal/Yamabond/Hondabond/Threebond, Loctite 515 & 518, etc, all of which may also work to seal the subject joint if you are averse to silicone.

Re: How do you get the primary cover oil tight?

PostPosted: Sun May 09, 2021 5:57 pm
by sportsterpaul
Thanks for the tip on that Cometic gasket, that is good to know. I am lucky in that the thin paper gasket seems to seal the tin cover on my 1962. The think there is that the cover is flat, and the engine case does not have any gouges in the gasket surface. One trick I see is to use adhesive-backed sandpaper on a surface plate. Rub the primary cover on that in a "figure-8" motion to get it it overall flat. You might get away with thick glass or even a countertop instead of the surface plate. If you could, it would be ideal to get the engine case up on that surface plate, but that can be impractical. Once the primary is flat, then you can hold it against the case to see if the case is also flat. Most times flatness is OK, it is that there are gouges and cuts across the gasket surface. For this I have tried just smoothing some JB-Weld in the gouge, it seemed better than sanding down the cover or the case a whole bunch. I think the deceptive thing is that it does not take a lot of screw force to seal the cover. I suspect a lot of folks over-torque the screws and deform the cover, making leaks. Remember that in theory, the primary is not under pressure. Do make sure the vent in the oil-fill cap is working, or oil is certain to weep out as the engine heats up. My motor builder welded up the transfer valve in my 1962, but I might reinstall it, thanks to the explanations from Dr. Dick and the FrenchOwl as to how and why it works. When that valve is working, it puts a little vacuum in the primary as the pistons rise.

Re: How do you get the primary cover oil tight?

PostPosted: Mon May 10, 2021 12:38 pm
by Monti
Thanks a lot for the tips.
This aluminium-nitrile gasket from Cometic would be great, but it also has the holes for the later cover.
Therefore, I made myself a new gasket and put some silicon sealants on both sides of the gasket as recommended.
I hope this will be solve this issue. I will let you know as soon as made put some miles on the KH.

Re: How do you get the primary cover oil tight?

PostPosted: Wed Jun 09, 2021 10:42 am
by Monti
Put some miles on the clock and it looks like the primary cover is oil tight.
Thanks again for all your help!