283 rebuild

Gentlemen,
I have a 60 Corvette with a 283 stock engine. The oil pressure was a little low and I always wanted a completely balanced engine. I pulled the engine and completely replaced all moving parts and had it bored .060 over. I had all the moving parts balanced by a reputable shop. The heads were completely rebuilt. The reassembly went smoothly. I am running a Edlebrock 500 cfm carb, performer intake manifold and a matching mild camshaft. Also a complete new MSD ignition system.
Problem: Number 7 plug is wet with both gas and a slight amount of oil. Compression test all even at 135 lbs. Leak down test is the same on all cylinders. I thought the cam and ignition timing was not correct so I installed a new cam. Same problem, wet #7 and the rest of the plugs are not the color they should be. The carb, intake and cam were running great before the rebuild. I am contimplating pulling the engine out and disassembling to see if anything went wrong. At this point I am affraid I will have a bench lined with all new parts and not have a clue as to what to look for. Any suggestions would be appreciated
Thanks, Tom


Register now (free) or login to remove ads

I'd be lookin' for misalignment of the intake gasket on the crankcase side of the intake ports. That one cylinder could be sucking oil vapors from inside the motor. Pop the intake off and closely inspect the gaskets for the proper "pinch" all the way around all the ports.

Something I've thought about doing but just have never gotten around to it is to make a plate to cover the carb mount on the intake and drill it for a tubeless tire air valve. Then when I get the intake mounted, back off all the rockers so that all the valves are closed and pump a little air pressure into the intake manifold. Even if a guy didn't have shop air, he could pressurize the system at home with a bicycle pump. You could even mount a low pressure gauge like an old fuel pressure gauge (10-15 psi) to see if the manifold would hold pressure. Then again, maybe it's a silly idea, but it's just the way my mind works.

I would also suspect the intake considering all you have done and checked has not turned up anything. Sounds like a sweet ride.

Vince

1960 doesn't have PCV, but this should still work. If it does have PCV, pull the valve out, and block the hole. Then remove the oil cap and start the engine. While it is idling, put a hose on your propane torch and insert it into the oil filler and turn it on. After a few moments, if the idle increases and smooths out, it's a good possibility that you have an internal intake vacuum leak. It's a quick and dirty way to check w/o pulling the intake.

Great idea. Thanks for the tip.

How many miles on the rebuild? May want to check routing of ignition wires. Does the engine run rough at all? Number 7 may be misfiring. Also do you notice any smoke in the exhaust? if so what color?Blue is oil-Black is fuel-White can be coolant. I suppose that its possible there may be a problem in the cyl. itself but you can tell this by pulling the cyl. head and looking at the piston top. Hope this helps. Goodluck

It could be a valve guide. My brother had a similar situation. Only there was more than 1 plug fouling...PC valve guide seals fixed it....JMHO.....GlennK