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Leak Down Test On 964

Old 06-10-2004, 06:30 AM
Flat Top
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Default Leak Down Test On 964

My 964 with 71 000 miles on the clock has a very rough idle. Took the car the a reputable workshop who first -

1) Checked and set the tappets;
2) and then did a leakdown test to check for the possiblity of bent valves.

Leak down test showed the following.

Cylinder 1 - 10%
Cylinder 2 - 84% (Inlet- and exhaust valve leak)
Dylinder 3 - 90% (Exhaust valve leak)
Cylinder 4 - 22% (Valve Breather leak) ?
Cylinder 5 - 30% (Inlet valve leak)
Cylinder 6 - 20% l(Exhaust valve leak)

I do not have sufficient experience to analyse the test but it seems to be radically low. My question is that despite the test the car accelerates strongly without a feeling of disastrous loss of power why then the rough idling and the bad test?

Is a top end rebuild inevitable?
Does this invariably indicate bent valves?
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Old 06-10-2004, 09:32 AM
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I am amazed the car idles or runs at all - a real tribute to the DME system.

The first symptom of compression loss is rough idle. Acceleration does not suffer as much, because the cylinder compression is so fast that you don't lose much compression until the leak is really bad. You are probably dead missing at idle on cylinders 2 and 3, and running on the remaining 4.

What makes you think the valves are bent? Did you jump time and have an impact with the pistons? They are probably burned because somebody did not keep them adjusted.

Things will go down hill quickly - a burned valve cannot be salvaged, and it will continue to burn. I would not drive far or fast until this was fixed. The next problem you will have is a burned/overheating valve will break off its stem and punch a hole in the piston. It will destroy the cylinder head as well. Depending on the engine speed, this will also bend the connecting rod or crankshaft.

The top end overhaul will be cheap compared to what it will cost if you wait any longer.

How are things in Johannesburg? I grew up in Pretoria in the 1960s.
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Old 06-10-2004, 01:51 PM
Bill Gregory
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You want to get a second opinion on the leakdown, from another source. When I bought my 964, the first shop did the leakdown test, and showed leakdown of like 40%-50%, which didn't make sense with the smooth running engine. Had another shop do the test, and got results which did make sense. Given expensive decisions may be made based on the test results, it's worth the money to get a second opinion.
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