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iamchappy's Avatar
 
Join Date: Feb 2003
Location: Minnetonka, MN
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Bad leak down numbers after rebuild

79 Sc 3.0 engine twin plugged with 91 turbo pistons and cylinders using the Sc rods and offset bushing, 86 Euro intake and fuel distributor, Supertec Head studs. Using BP 30 break-in oil.

Engine sat a little over a year after rebuild in a climate controlled environment.

Before bringing my car into the engine builders shop to start it, I primed the fuel distributor and injectors slightly without pulling the injectors like i normally would(I was being lazy as there not as easy as the Sc injectors that just pull out as I noted slightly), this did allow some fuel to run into the cylinders and I quickly turned the engine over by hand a few times to clear any out into the exhaust.

On our first try to start it cranking with the Cold start injector we allowed more fuel to wash the cylinders. Upon not firing, we re-indexed the distributor 180% as we were setting the distributor and putting the engine at TDC we found the leak down number on #1 really bad, upon pulling the rest of the plugs we found that #3 was also poor. #1 70% #3 40%, the rest were acceptable. After squirting some oil in and rechecking, the numbers improved only a little.
We went ahead and started the engine up and the engine sounded great after it warmed up we shut it down. I did notice there was some oil leakage around the base of the cylinder and case on #1.
Tomorrow we are going to start it and warm it up again, then time it.

Should I then go ahead and drive it to break-in and when time to readjust the valves recheck leak down and if things haven't sealed go back and tear it down, or should I tear it down now before we go any further.

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Old 11-29-2007, 05:30 PM
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Where is the leakdown? In the breather I assume.

It takes a while for the rings to seat. If it's not the rings, could the valves have bent during the timing procedure?
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Old 11-29-2007, 05:44 PM
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Checking compression via spark plug hole. Engine has not been timed yet, just started and warmed up. I dont think the valves are the problem unless the raw fuel had loosened up some carbon and it was sitting in the valves seat. After we start it again tomorrow and time it and let it cool down should i re-test #1, or should i just go ahead and drive it until things are broken-in to re-test it.
I doubt the valves could of gotten bent during the cam timing if that is what your implying, the shop is very reputable they have been at it since the early 70's and most of there business evolves around setting up race cars.

http://www.johnsonautosport.com/
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Old 11-29-2007, 06:09 PM
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motor wasn't run after rebuild, it's cold, there's no oil on the rings, so you get high leakage. normal. get it running, hot, get a few miles on it and check it again.

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Old 11-29-2007, 06:16 PM
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