hjb981 Posted December 23, 2012 Report Share Posted December 23, 2012 As some of you know, I probably have a valve that leaks oil. The spark plug of cylinder 5 fouls with ash deposits, and the deposits are always on one side of the plug, not spread out evenly (indicating that they come through a valve). There is also a quickly disappearing tapping noise on cold-start, at camshaft frequency (half of crankshaft frequency). It is always only one tap per camshaft revolution, so it cannot be coming from more than one cylinder. The car also uses some oil without leaking (and also without any smoke from the exhaust, except during WOT after not doing it for a while, when some dust seems to come out). Up till now, I thought that the heads of a Northstar could not be serviced, but I just happened to come across page 6-76 and 6-77 in the 1997 FSM, where there are procedures for Valve Lifter Replacement and Valve Stem Oil Seal and Valve Spring Replacement. Can it be done? Why did I think that it could not be done (there must be something, maybe the valve seats)? How hard/easy is it to do? Is it problematic to do on the rear head of a '97 DeVille (the effected cylinder is #5). Link to comment Share on other sites More sharing options...
KHE Posted December 23, 2012 Report Share Posted December 23, 2012 The OEM seals are Viton and will usually last several engine lifetimes. That's why there is not much information on replacing them when engines are timeserted. I wouldn't want to tear into an engine just for that issue. The rear head is cramped and doing the valve seals with the engine in the car would be difficult if not impossible due to the lack of clearance. You might be able to lower the front of the subframe to gain clearance but that is an unknown. The only other option is to pull the engine to do the work. Depending on the miles, you might then want to Timesert the engine which is a considerable additional expense. If the engine does not misfire, I would be tempted to just leave it alone vs. going through all the work and expense. If you do repair it, be sure to use the OEM Viton seals. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
hjb981 Posted December 24, 2012 Author Report Share Posted December 24, 2012 If the engine does not misfire, I would be tempted to just leave it alone vs. going through all the work and expense. If you do repair it, be sure to use the OEM Viton seals. I reason in the same way on that one, and will continue to do if the work requires lowering the subframe or removing the engine. It is just that if it would have been a fairly easy repair, it could have been worth it to not have to replace that spark plug once per year or so, and also to reduce the amount of oil-filling between changes. Link to comment Share on other sites More sharing options...
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