wrxand280z Posted January 19, 2009 Share Posted January 19, 2009 I have a 78 350 with cast iron heads. The motor was rebuilt and then sat for several years. I threw it in to the z and it fired right up. The problem I'm having is that it looses power after a couple of trips. I changed the spark plugs and found that the #3 and #6 plugs have lots of oil and build up on them while the rest are white. I did a compression test with the motor cold and found I had 175-180 psi in both. This leads me to believe that it is the valve seals. What do you guys think? Is there an easy way to fix this? Joe Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted January 19, 2009 Share Posted January 19, 2009 Its reasonable to think the valve seals are defective on those two cylinders , possiably they were installed incorrectly or damaged, durring storage. Id sure try inspecting and replacing them as its a fairly easy job, and yes, allowing the engine to sit a few years may have easily damaged the valve seals as they could, have had rust on the valve or some other factor damage them. BTW having good compression numbers does not totally rule out rings as a source of the oil, Id also look into adjusting the valves and check clearances carefully, lots of guys install high lift cams without verifying coil bind or retainer to valve seal clearance with the result the valve seals get damaged, this might help http://forum.grumpysperformance.com/viewtopic.php?f=52&t=1053 Quote Link to comment Share on other sites More sharing options...
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