1940 chief oil leak

[jn1972]

i recently finished restoring a 1940 chief , there is an oil leak that i can not locate the source of. when i ride the bike about 35 or 40 miles i have oil dripping off the rear top 3 or 4 fins of the rear cylinder .the tanks are new ,the oil lines are new and not leaking,the motor has all be rebuilt ,and as far as i know there should not be any oil above the cylinders. this has me stumped has anyone run into a similar problem ? thanks jerry

[PRG]

Howdy sir,

Is it viscous like oil or more like dark carbon laden tar? If the latter then likely a failed head gasket, they generally yield around the exhaust valve pocket as this is the area of greatest heat and dissimilar material (head/gasket/cylinder) expansion/contraction. Fiber gaskets based on the original design are more finicky and intolerant than copper. When replacing I'd verify both the head and cylinder deck surface are both perfectly flat. 70 plus years of the unnecessary 50 plus lb ft of head bolt torque causes the heads to warp or descend at each head bolt through hole.

[pisten-bully]

Jerry, I've never had that problem myself (other leaks... yes!) So when you say "top of the cylinders" then you're not talking about the heads, right? My first look would be at the valve spring covers, possibly if they leak then the oil is blown there, even the front ones could drip and have it blow onto the rear. Otherwise it depends exactly where on the cylinder you find the oil, valve side is most likely I guess. Just above the valve springs and valve guides? BTW, I did have a very slight oil line leak at one of the tank fittings one time, the oil would eventually run down the underside of the tank, unseen, and occasionally drip on the heads!

[jn1972]

1940 chief oil leak

the leak is motor oil ,i used the copper head gasgets on the heads,i will check for valve leakage but i did use the covers with o rings. if i let the bike run on the stand i could not find an oil leak ,but when you ride it for a while it shows up when you park the bike on the kickstand.is there any way one of the head bolts could leak oil ? the leak is on both sides of the rear cylinder but that could be how it sits on the kickstand thanks for your help jerry

[tomfiii]

Did you use oil on head bolts? Could be slight gasket leak to base of head bolt,oil gets hot and will spread like crazy past washer of head bolt.

[jn1972]

i am still chasing the oil leak ,i have some oil showing on the heads near the top motor mount bolts ,i torqued the bolts to 55 lbs when i put the heads on ,i also used copper gasgets,are the fiber gasgets more forgiveing ?is leakage there a common problem ? thanks

[RonH]

I used coppercoat on the copper head gaskets and they seem fine so far. Did you use that on the head gaskets? I still have a small seepage from the base gaskets in 2 areas. Nothing to worry about yet! Good luck on finding it

[jn1972]

Hi Ron ,no I did not use coppercoat on the gasgets , I took the heads off. Over the winter and reused the copper head gasgets I thought you could reuse them,maybe not .thanks for your help Jerry

[T. Cotten]

I always wondered, Folks,..

If you needed to seal copper gaskets, why not just use the sealer!

I have assembled a motor with cast iron heads and heatpaint, and it failed a bubble-test before it was even were fired.
Aluminum heads usually were associated with composite gaskets for reasons that should be obvious: You want the gasket to conform, not the head!

Jerry!

Squirt some soapy water around the gasket and kick it through vigorously. It there is a breach, it will show.
Are your plugs burning clean?

....Cotten

[RonH]

I had the heads and cylinders checked for being flat first, then I heated up the head gaskets to cherry red then dropped them in cold water to anneal them. Hit them with scotchbright then used the copper coat. This video helped me a lot.
https://www.youtube.com/watch?v=3ttu...ature=youtu.be