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Join Date: Dec 2013
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compression/leak down test on 86 930

I took this board's advice and got a compression/leak down test on a 1986 930 that I am interested in buying. There is a problem with the #3 cylinder exhaust valve. Does any body have an idea on how much that could run?

Compression test Cold (lbs)
1. 130
2. 130
3. 130
4. 135
5. 130
6. 130

Compression test HOT (lbs)
1. 130
2. 130
3. 130
4. 130
5. 130
6. 130

Leak Down test
1. 7 %
2. 7 %
3. 47 to 52% This test run multiple times
4. 4 %
5. 4 %
6. 2 %

Comments?

Thanks
James
Old 07-16-2014, 11:55 AM
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Location: wisconsin
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Not sure how you get the same compresion, consistently, and that leak down.

When I was adjusting the valves on my car, one of the leakdown numbers was slightly low. Turned out it was a small bit of carbon on the valves, and cleaning it off fixed the issue.

Where is the leak? valves? elsewhere?

Bo
Old 07-16-2014, 12:23 PM
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As I mentioned in email, that #3 cylinder is most likely carbon buildup ESP in the face of good compression #s. Also possible that the leak down part was consistently done incorrectly, not at tdc for ex. The compression test is relatively foolproof while the leak down has a lot more variables and potential error points.
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Last edited by Tt surgeon; 07-16-2014 at 12:33 PM..
Old 07-16-2014, 12:28 PM
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The technician said that the leak was coming from the #3 exhaust valve.
Old 07-16-2014, 02:46 PM
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How many miles on the motor? You can remove the exhaust valve cover and try rapping on the valve to dislodge any carbon. I had good compression readings but had leak down of 90% on one cylinder that turned into a complete top end rebuild. Proceed with caution.
Old 07-16-2014, 08:23 PM
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You can mist very slight trickle of water while the engine is running and up to operating temp. The steam generated from the combustion and water will clean all carbon deposits off. Like I said a mist not Niagara Falls.
Old 07-17-2014, 04:43 AM
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