Board index Flathead Power-Technical Questions, Answers, and Suggestions Knuckles spring cup leak

spring cup leak

Moderators: Curt!, Pa

Post Mon Jun 05, 2000 4:29 am

Posts: 91
Location: Labadie, Mo.
I have a '47 that I just put springs,valves, and guides into. Everything is great, but I am getting oil misting out of the rear exhaust spring cup, and getting all over the seatpost down tube. The push rods are well sealed,(no leaks). I have checked the return line from the spring cup to the head, and it is clear of obstructions, and the line is sealed tighly to the nipple. There are no cracks in the flair at the nipple, and no leaks in the line. When putting it back together, I noticed that I have 2 different types of pushrods. The exhaust have like a bronze ring around the lower portion of the pushrod. The other ones(intakes) do not have this bronze ring. Could this affect the vacuum on the exhaust side?
It did not leak before I did this headwork. Any ideas as to what could be causing my leak?

Post Mon Jun 05, 2000 5:12 am

Posts: 325
Location: Viola, WI

Hi Paul,
If the pushrods are the same diameter they
should be O.K.
The exhaust tins are always under pressure
thru the guide. It´s important that they´re
very good sealed. Check that your tin is not a front intake with the little ventilation hole. Otherwise check everything that has to
do with the oilreturn from the heads.


Post Mon Jun 05, 2000 1:16 pm

Posts: 3061
Location: Central Illinois, USA
Worst possible scenario: hairline cracks often form on the flat base of the cup, perpendicular to the oil drain line entry into the cup. These can occur AFTER the guide and cup have been aligned and pressed into the head, as the handling of the oil line during rocker assembly can tweak it. Your leak would then be seeping as if it were from betwen the guide and the cup. I have quick-fixed a couple with a sealer from inside (after removing the spring and retainers) but properly it should be removed and silver-soldered, which messes up the valve job unless you index the guide accurately. Hope it's NOT this! Good luck!

[This message has been edited by Cotten (edited 05 June 2000).]

Post Wed Jun 07, 2000 3:49 am

Posts: 91
Location: Labadie, Mo.
Thanks for everyones input. I have checked for the hole in the rear cover, and do not see one. I am running the stock oil pump, and pull 20-30 lbs of pressure going down the road. The leak is coming from where the cover meets the spring cup. I tried tightening the cover screws, but that did not help. The last time I put it together, I sealed this area with sealer. This time I did not. Any other ideas before I pull the head to try to seal this? It would be great to find an easy fix!

Post Wed Jun 07, 2000 3:56 am

Posts: 3061
Location: Central Illinois, USA
Are you quite certain that the rocker arm is not hitting the cover? This is common when the seat is a bit sunk. It is possible to remove the cover and cut an extra thick gasket for it without removing the head. I've done it. (The point here is that there is not enough clearance.)

[This message has been edited by Cotten (edited 08 June 2000).]

Post Thu Jun 08, 2000 3:58 am

Posts: 801
Location: Planet Earth
I have sealed the covers on my Knuck using good old fashioned 3M weather strip adhesive (the good yellow Gorilla Snot) and a gasket. Put a bead of adhesive on the top cover and another on the bottom put the gasket in and screw it together. Wait at least 24 hours for it to dry before you start it up. Did that to mine over 8 years ago and they are still sealed.

Post Thu Jun 22, 2000 4:44 am

Posts: 91
Location: Labadie, Mo.
Thanks for everyone's input. I finally pulled the head, and found the leak was coming from under the spring cup. A crack was found in the spring cup, and was silver soldered up. I will be putting it all back together tomorrow.
Thamks again,

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