I'm going a bit crazy...

I removed the intake to fix an oil leak at the back and oil fouling the fifth cylinder spark plug.

attention : new GMPP cylinder heads and just 200-300 miles after new heads...

I have found all the intake valves with a good deposit of oil on them. less one . the fifth cyl intake valve is clean like new with fluid oil ( but lot of oil goes into that cyl and fouls my plug quickly)

by a visual check of the intake gaskets removed, I don't see great issues. I'm going to make a dry fit of the intake later today to see if it matches correctly or not

more: the fifth cylinder bore is the only of 8 to have a "ridge" at top. suspecting an oil leak there I have used in the last 300 miles 20W50 oil , but no difference in respect to a lighter oil.
today I have made a pressure test with compressed air applied through spark plug and cyl 5 behaved like cyl 3 ( that has no oil leak)

any idea?

I forgot.
I don't see unusual crankcase pressure. no oil in the top of intake and in its runners. so I don't think it's oil getting into , through the PCV circuit.my valve covers have oil shields too.

the plug was oil fouled at cyl 5 also before heads replacement. on old iron heads I found a worn valve guide and I judged the problem was that. but still oil now...

why all these problems at the same cylinder while all the other not?

 

do a leak down test.....

 

Check out that #5 intake runner on the bottom side for cracks or holes. Its been awhile since I've seen the bottom of a stock bb manifold does it have the shield that was riveted on ? If so check the rivets and if they have been driled all the way through.

 

Been awhile since I have looked at the stock intake bolt pattern but if I remember right if the inside bolts are not installed with sealant the oil from the valley will wick up the bolt and get into the cylinder......... that would cause oil to get into # 5.

Doug

 

-leak down test done . it performed OK
-the intake is the Alu L72 type. I see no damage or crack. I have done a test right now making a test fit with some grease applied . the match between intake and heads is OK. but the problem could be the use of the rubber-cork front and back selas. they rise the intake a bit. I will use RTV only this time
-I have already used the sealant on intake bolts

what else?
I'm going to fit again the intake tomorrow using a better FelPro performance , blue , instead of a cheaper Fel pro type used before. the one I'm going to use is all rubber, the other was metal inside-rubber outside

 

a couple of dead valve seals will allow oil into the bad cylinder through the valve guides. thats where i would look. you have already done everything else......