Alloy Head single pushrod seal Mod

[pete.collings]

I have recently scanned details of a mod published in Cheval in the 80's, as an improvement in sealing the head/barrel pushrod joint. A copy of this shown with this post. The original fitment large rubber washers could swell and wear alloy pushrods, a later change was to fit an inner ring to the rubbers to reduce the chance of this happening.

The mod involves making an alloy holder for a rubber O ring (oil resistant Viton preferred) to sit in the head recess. When I did this mod, I checked the depth of the recess on the head, and the clearance between the head and barrel faces, and adjusted the dimensions to give 20 to 30 thou crush on the O ring when the head was tightened down fully. It is better to make the O ring holding lip a little too long, and then carefully file it down to give minimal clearance at the barrel face, to aid good location of the O ring. I held the carrier in the head with silicon sealant, allowing this to cure fully and trim off any excess, before fitting the head.

I've no idea if the firm mentioned as suppliers of Viton O rings are still in business, I had a batch made by a supplier in Cardiff, although these were a bit pricey as only 6 were ordered.

[john.nash]

awesome !!!
my pushrods are indeed slightly dished where the rubber seal sits ...

[keith.mettam]

Did a very similar mod to my NH a few months ago when the original style seals started weeping. When I took the head off it was clearly visible how they had expanded and were wearing the alloy push rods. Well worth doing next time you have to whip the head off.