940 Distributor Cap -- Needs a Gasket?

The cap shpould be replaced at regular intervals on any car, and that is more true with electronic, high-energy ignition systems. The atmosphere in the cap area is prone to condensation and eventually this causes carbon tracking- an arcing across the cap inside that leaves carbonized trails that conduct some of the energy to other spark plugs- one cause of mis-firing.

Most distributors are actually vented becasue the wide range of temperatures to which they are subjected precludes sealing them completely. They also need to be lubricated, so the bore in teh block is usually lubed with engine oil, and if the distributor is well worn oil can get into them. If the distributor has a mechanical advance mechanism this too needs to be lubricated, and if not done with a heavy oil this can spray about. If the distributor has points, the cam needs lubrication and this can splatter as well if the correct lube is not used. __ __ Randy & \ \/ /alerie's \__/olvo '93 960 Estate

The black powder is from the carbon center contact, normally the cap is replaced before it builds up to that extent. There isn't a gasket on the cap and if there's only a small amount of oil don't worry about it.

If your distributor is mounted on the rear of the head, oil can leak down the distributor shaft and past the internal seal. The seal is not available from Volvo (you buy a complete distributor for this problem) but is available from aftermarket sources.

Mike, my 940 Turbo has been bugging me for years with oil in the disti causing hesitation. Will a new back plate with the seal and shaft in it solve the problem completely? How much does it cost over there? Volvo where quoting me GBP100s.

It's just a standard type of oil seal, which can be had for a few bucks if you can find it. The whole distributor is over CDN$400 from the dealer, so GBP100 doesn't sound so bad.