Nylon/Plastic Washer

I've seen both kinds of washers being used on the Norton oil pressure relief valave and the main oil drain plug.
My question which one is more effective in preventing oil seeping.
Thank you.

I use copper washers on all the oil fittings. You can get then at Napa Auto.
Not knowing where you are from, which should be a requirement for all members, it is hard to direct you to a local source for what you need.
You could be from Zimbabwe for all anyone knows.

I use Dowty washers (metal outer washer with a neoprene seal in the bore) they are far more effective at sealing than copper as the seal is made by the neoprene not by being crushed as with copper which may cause damage to threads if over tightened in attempt to seal a leaking joint fibre washer can spill as result of same over enthusiasm. Nylon tends to soften as temperature of engine raises which can cause leaks or the loosening of fittings as gripping force is lost.

Dowty sealing washers can be found on Ebay or your local hydraulic supply firm (search Google) they are cheap and reliable and available in wide range of sizes.

I've put a skim coat of RTV on some of my copper gaskets that seem hard to seal, but the Dowty seals are nice.

Dowty are good if you can find them in the correct size. Otherwise a little liquid teflon sealant on the threads and a copper washer .

Tim_S

I like Dowty washers wherever they can be used. Pay particular attention to the application....Dowty washers are thicker than copper or fiber, and can upset a critical fit, such as under a carb needle seat.

Slick

Aluminum sealing washers are available at most auto parts stores and are a better choice than copper for the sump drain plug. Softer than the material the case ($$$!!!) is made of, is apt to seal better and do less deforming.