Compression test help - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

Kingtal0n · 01-15-2017, 05:13 PM

the test may indicate high mileage, or an atmosperic blow-off was used, which continually washes the rings with gasoline and gradually lowers compression on a stock sr20 (maf). 15 years of ring washing and/or 150,000 miles will bring the compression down to 120~ cold. The oil test is clearly showing a lack of ring sealing because it obviously jumped back to OEM target range with the oil in the cylinder, which wouldn't happen if the compression was leaking via valves. If it does not smoke and seems to run normal, the plugs come out clean, I wouldn't mess with it just keep driving it gently. Use an oil pressure gauge to ensure the bottom end doesn't become garbage so it can be re-furbished (hone + new rings + valve job) in the near future, this way you avoid the machine shop and get back a nearly fresh engine. (change the engine bearings using the stamps on the block, install a new oil pump, new timing equipment, buy a honing tool and new rings, don't let a machine shop touch the shortblock). Do it in a 'clean' room.

Option B is buy a next longblock, which would cost less but obviously will give you the same 20 year old parts so selection is thin and difficult. But entirely possible.

01-15-2017, 05:13 PM	#4
Kingtal0n Post Whore! Join Date: Jul 2005 Location: South Florida Age: 42 Posts: 4,829 Trader Rating: (17) Feedback Score: 17 reviews	the test may indicate high mileage, or an atmosperic blow-off was used, which continually washes the rings with gasoline and gradually lowers compression on a stock sr20 (maf). 15 years of ring washing and/or 150,000 miles will bring the compression down to 120~ cold. The oil test is clearly showing a lack of ring sealing because it obviously jumped back to OEM target range with the oil in the cylinder, which wouldn't happen if the compression was leaking via valves. If it does not smoke and seems to run normal, the plugs come out clean, I wouldn't mess with it just keep driving it gently. Use an oil pressure gauge to ensure the bottom end doesn't become garbage so it can be re-furbished (hone + new rings + valve job) in the near future, this way you avoid the machine shop and get back a nearly fresh engine. (change the engine bearings using the stamps on the block, install a new oil pump, new timing equipment, buy a honing tool and new rings, don't let a machine shop touch the shortblock). Do it in a 'clean' room. Option B is buy a next longblock, which would cost less but obviously will give you the same 20 year old parts so selection is thin and difficult. But entirely possible.