Yvan Poulin

I'm looking at a 1984 Carrera and there was a compression test on it less then a year ago.

A- Should I do another, or trust that less then a year old is acceptable?
B- The results were (by cylinder)
1 - 185
2 - 180
3 - 165
4 - 170
5 - 180
6 - 185

Are these results ok? How much should I expect for a car that old with the original engine?

Thanks,

Yvan

BER

My experience with compression tests is the relative difference between cylinders, not the absolute values.

A leak-down test is one where you focus on cylinder leakage amounts.

The above numbers look OK. If it was my car, I would rotate the engine a couple of times and do it again to see if #3 doesn't come up a bit.

Bruce

Greg D.

The numbers don't look bad... What's important is that they are close to each other, rather than the compression number per se... But from memory that sounds about right...

If it drives right and your mechanic thinks it's a good car, why not...

Steve Weiner-Rennsport Systems

Yvan:

Thos numbers look OK but I'd sure follow up with a leakdown test and see whats up with #3. If the leakdown shows some valve leakage, I'd dump a large bottle of Techron in the tank and go drive the poop out of it,....

You'd be surprised what a difference that makes for engines with "leaky" valves,....

1FastRedSC

With a difference of 20psi between the lowest and highest results i'd also opt for a leak down. Mainly because it might not be the cylinder to piston ring leak but the valve to valve seat leaking, meaning a head job.

Steve Weiner-Rennsport Systems

1FastRedSC:

One does not always need a valve job if the valve are leaking,.....

Carbon buildup are a severe problem in this country due to the unleaded gasolines formulation and our driving style. Regular use of a good fuel additive such as Techron or LubroMoly prevents the majority of problems in this regard. The quantity of these detergents present in the fuel is really not enough to prevent this from occurring.

If I had a quarter for every unneccessary valve job done in this country for this reason, I'd be able to take everyone on the 911 Forum to dinner,... Its an immense profit center for dealers & shops when cars fail smog tests due to high HC and leaky valves are found to be the culprit. Many shops sell a valve job (not that its not needed in some cases) to the unwary without trying something that is FAR less expensive that in many many cases restores lost compression and lowers HC enough to pass smog tests.

Now then, if a treatment of Techron or LubroMoly doesn't change the results of compression & leakdown tests, then its prudent to do a valve job and take care of the problem.

1FastRedSC

I stand corrected, plus i am a cynical person who thinks worst case scenerio, sorry. I do know that carbon can unseat valves when it builds, i thought though that if that's the case (at least the exhaust valve anyway) that you'd need a head job any how because you'd get a burnt valve?

1FastRedSC

Also if that's the case, can't you use the water de-carboning method as descirbed several times on the pelican board? Involving the rev of the engine to be held high while you pour a modest amount of water into the intake to totally remove carbon from the motor.