Stuntguy13

Has anyone done a replacement on a Davis Diesel head "O" ring? Bob never gave out to much information and wanted customers to return the head to them for "O" ring replacement. Since DDD is gone, I was wondering if someone has a procedure and what tools are needed to do a successful replacement.

1QwkSport2.5r

Based on how it’s assembled, I have a real hard time imagining it’s all that difficult to do. All you should need is get a SHCS longer than the original to push the contrapiston out. Replace the o-rings on the contrapiston, and reinstall. Because of the tight fit of the contra (and subsequently the o-rings), I would generously oil the o-rings and gently press the contra back into the head. Have some extra o-rings just in case one gets shaved during install into the head. Theoringetore.com has a large selection of o-rings made of different materials, some of which may be better suited than the originals (which I’d expect to be Buna-N).

Stuntguy13

Looking online I found a site that indicated you should use the proper hardness "O" ring, 70 rating is medium and should work for us. Next drop the "O" ring in hot water for a few minutes to soften them a bit then using "O" ring lube slowly push it into the bore. I think we could use our regular fuel mix oil (castor, sysn, minieral) to lube the "O" ring and slip it in.

Best, DennisT

Motorboy

Use Viton O-ring as replacement if broken o-ring in contra piston. Viton O-ring withstands high temperatures and has very good chemical resistance against e.g. mineral and synthetic oils, HFD oils, alcohols, hydrocarbons and organic acids. This combination, in addition to excellent resistance to weather and ageing, makes FKM a very useful material. Also don't use standard O-ring from shop.