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Join Date: Dec 2006
Location: Norfolk, VA
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Leakdown and compression results on PPI- opinions?

Gent's I'm looking at a race car with a built up 3.0L SC engine (J&E pistons, 10.5:1 compression, Weber carbs, etc). 46 hours on the engine in the past two years running HSR events. I had a Porsche shop do the leak down and compression on the car.

cylinder: leak down # compression #
1 10% 180 psi
6 12% 178 psi
2 5% 185 psi
4 8% 175 psi
3 25% 165 psi
5 20% 170 psi

The mechanic said the leak is coming from the exhaust valves only. The car hasn't been run for 5 months. He said that leak down in 3 and 5 concerned him but then he did the compression test and thought that it didn't look as bad.

Could carbon buildup and moisture absorbed in then carbon be a culprit? Is it worth having the mechanic remove the valve covers and try to tap the engine to loosen the buildup after running the engine a bit with some cleaner and then trying another leak down?

If I am just doing track days (15 hours a year), can I wait a year or two before doing a valve grind or a top end?

Or is it too risky and I should just walk away?

The rest of the car is perfect. Brakes, suspension, transmission, clutch all great.

Looking forward to opinions...

James
1985 Carrera

Old 07-13-2010, 01:28 PM
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Originally Posted by thedude113 View Post
Could carbon buildup and moisture absorbed in then carbon be a culprit? Is it worth having the mechanic remove the valve covers and try to tap the engine to loosen the buildup after running the engine a bit with some cleaner and then trying another leak down?
That would be my first guess. Run it hard and try again.
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Old 07-13-2010, 02:44 PM
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James,

Whenever I see higher-than expected leakage from exhaust valves, the first thing I do is "stake" them to dislodge any loose carbon and redo the test. This involves removing the valve covers and striking the end of the rocker arm over the valve using a piece of wood and a small hammer.

I also use this opportunity to measure the sideplay in the valve spring assembly as a test for guide wear.
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Old 07-13-2010, 04:12 PM
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Thanks for the input. That's what I was looking for.

James

Old 07-14-2010, 02:08 PM
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