HELP!! Fresh rebuild 390 compression problems

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#16

08-23-2016, 10:52 AM

thesuperbad234

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Quote:

Originally Posted by Oldschool2888

I have a question. Why did you you put automatic transmission fluid in cylinders a high detergent oil can inhibit rings seating. I don't know if it your problem. But I always non detergent oil for break in + addictives. Also if you have done any head work push rod lengths may change. You have non adjustable rocker arms this is how valve adjustments are made cam change also will also effect valve adjustment. I just went through this with my FE 390 Jerry

I've always used ATF for wet compression tests, the oil I have in the crankcase is Standard 10W30 with zinc additive and my cam was lubed with comp cams product. Being as the numbers are so consistent I'm going to hope its something in the valvetrain

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#17

08-23-2016, 10:54 AM

raytasch

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IMO, your cam shaft is out of time. Be sure the valves are operating correctly relative to the pistons.

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#18

08-23-2016, 05:13 PM

MIKES 68 F100

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Quote:

Originally Posted by thesuperbad234

I'll give that a shot right now. I just found out that I have pushrods that are .030 longer than factory so I have some more on the way just in case

well that would do it

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#19

08-26-2016, 05:13 PM

Destroked 450

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Loosen the rocker stands up quite a bit and see if compression comes up, push rods too long can cause low compression also wrong lifters will give problems. Ordered a cam kit once and they sent a set of small block lifters instead of FE lifters, they'll fit but are nearly 1/4" taller.
If loosening rocker stands doesn't help compression recheck your cam timing

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