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Inter rocker oil seals

Submitted by david_cooper on Sat, 06/08/2022
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Inter rocker seals...

I must improve the oil leak situation.  I am trying to think of some possible improvements to the seals, and wonder if others have done something similar?

First, the sides. I think I read somewhere that the seals altered once or twice. Mine seem to have cork discs set into the cambox recesses, followed by steel washers against the rockers. The cork gives some spring to keep the steel surfaces in contact.  Has anyone tried PTFE (Teflon) instead of steel? Or might it move against the cork instead of against the steel?

Next, top and bottom.  The seals here seem to be solid rubber (nitryl now perhaps). But rubber is nearly incompressible (like water).  So since it is jammed in and compresed on all sides, it will lose the compression as soon as it wears even by a small amount.  If it had a 3/16" hole drilled along its length, that would squeeze in and give it more resilience. Or ot might just break up?

I know we have some experts around, but I'd like the satisfaction of improving it myself and getting it off and back on the road before summer is over! 

As a stop gap, I'm thinking of drilling 1/16" holes along the top and bottom rubbers, and pushing 1/8" brass rod into them to give them another lease of life.  But it's not been taken apart yet and I don't know what I shall find.

 

Submitted by john_holmes on Sat, 06/08/2022

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Have a read of on engineering design book for O rings and work from that. As you say the O ring is considered uncompressible if compressed on all 4 sides so the O ring groove always has more space than the O ring. But in one dimension the groove will be smaller than the O ring and the compression in that axis provides the seal and the O ring expands on the other axis with no restriction.

Submitted by david_cooper on Sat, 06/08/2022

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That's pretty much my thinking, John. I think I'm going to try seals that do not fully occupy the available space in the top and bottom grooves. 

Submitted by john_holmes on Sat, 06/08/2022

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You have lots of options with O rings, you can use metric or imperial with numerous X section sizes and also you can drop the ID used to below the ID of the groove if a particular X section is just that bit too large. As you stretch the smaller ID O ring to fit then the X section reduces, the more its pulled away from its natural length. X rings increase the number of sealing points of contact from 2 to 4 but range of sizes is smaller.

Submitted by david_cooper on Sat, 06/08/2022

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Possibly overthinking at present. The picture shows why (probably) it's been so messy.  The bottom seals have a steel half circle section backing bar. This has an adjusting screw to increase pressure. Not a brilliant design...how can one know how tight to make it?

At the top (inlet) is the result of overdoing it. No wonder it leaked!  The bent bar put much too much pressure in the middle, so it's worn the middle of the rubber.

At the bottom (exhaust), the bar has survived but the rubber has been squeezed out.

I've no idea when this happened, but new seals and at least one new backing bar are obviously needed.

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Submitted by paul_standeven on Sun, 07/08/2022

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are not just because the 'seals' are dodgy.  The oil feed squirts lots of oil into it, and somehow pressure has to be relieved.  It escapes past those rather feeble 'seals'.

A few years ago, an interesting solution was offered. There's a chamber at the top front of the crank case.  A vent here, with a one-way valve leading to a pipe will greatly reduce crank case pressure.  That will help draw the oil and cam box pressure downwards. ( It will be necessary to block the drive side crankshaft vent).  The poster stated that this reduced cam box oil leaks.

He then tried another stage, and fitted a garter oil seal between crank case and lower bevel chamber, garter towards the chamber.  Then, he made a small external pipe linking crank case and bevel chamber, also with a one-way valve.  This way, the crank case operates at below atmospheric pressure, draws pressure from the lower bevel chamber, and this draws down the oil and air from the cam box.  Much less leakage of oil.

Submitted by david_cooper on Sun, 07/08/2022

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Thanks Paul! Sounds a bit of a challenge.  The factory seemed to take delight in making changes to the breathing details of the cammy Nortons...almost as enthusiastically as changing silencers.  Probably best if the engine is already in bits.  The cam box comes off quite quickly, but I don't want to attack the bottom bevel area yet.

And thanks Barry...I'll follow your link.

 


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