| j.grif | -- 06-10-2012 @ 9:50 PM |
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21 stud engine with compression of 70 psi pretty even on all eight cylinders. Will increase about 10-15 lbs after using squirting oil into spark plug hole. Would guess this is rings. About 20-30 miles and maybe a hour of engine running since reassembled with .060 oversize pistons and rings. Three ring pistons. No improvement as time goes on. 17 steady vacuum. Would four ring pistons have been used? Welcome any suggestions. Believe correct head and domed pistons used. Thanks
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| ford38v8 | -- 06-10-2012 @ 11:41 PM |
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Grif, compression will improve once the rings are fully seated. You need your 500 mile oil change before worrying about compression, and then check at full operating temperature, with all spark plugs removed. Break in with dinosour oil, then decide if you want to use synthetic. Alan
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| TomO | -- 06-11-2012 @ 7:57 AM |
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There should be very little difference in compression with 3 or 4 ring pistons. Some pistons designs require the 4th ring for better oil control. Alan gave you the straight scoop on the ring not seated as a cause of your low compression. Depending on the rings and the condition of the bore, the rings can take more than 1,500 miles to fully seat. Drive the car at varying speeds for the first 2,000 miles to get the best seal. Change the oil at 500 miles and at 1,000 miles and 2,000 miles. Do not use synthetic oil until the rings have seated, and even then, I would not spend the extra money. The oil changes on these seldom used cars are based more on time than mileage. Synthetic oils will extend the change interval on modern cars with full flow filters and fuel injection to keep the oil clean. Tom
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| supereal | -- 06-11-2012 @ 9:30 AM |
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I agree with Alan and Tom that it is likely that the rings have not seated. The success of the seating, and the time/mileage required, is directly influenced by the skill of the person who honed the cylinders during rebuilding. If the glaze wasn't broken, the rings may never fully seat. The aim of good honing is to produce an obvious "diamond" pattern on the cylinder walls. These minute ridges allow the new rings to produce a surface on the cylinder walls that accomodates the new rings.
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