Leakdown and Compression results

[billrigsby]

Seems after the siezed pulley/shreaded timing belt fiasco, I do have a bad cylinder.

I started the vehicle for a few seconds prior to putting the radiator/belts in just to see if it would start OK.

 

After completly putting it all together I have a cylinder with 0 psi compression and 63% leakage compared to 130 psi and 15-20% in the other 3.

 

Seems I was not so lucky after all.

 

 

Bill

[The Dude]

Some people might say that having only one cyclinder go bad is pretty good luck. It could have been much wose.

[OB99W]

Unfortunately, you have one particularly bad cylinder. Hopefully, it's ''just'' due to interference-caused valve damage, and some head work can resolve that.

 

However, the question is whether the remaining three cylinders are okay. The leak-down numbers aren't revealing enough (good engines can show surprisingly high leak-down), but compression of 130 PSI is low if the measurement was made properly. As long as the procedure was correct (clean oil, engine warmed, plugs removed, throttle fully open, battery sufficiently charged so that cranking speed was adequate), closer to 175 PSI would be expected.

 

If the 130 PSI compression readings were due to not doing the test properly, then you should redo it. If the numbers are still low, do a ''wet'' test to see if they improve. It's also possible for a slight mistiming to cause lowered compression. Once you know more precisely what's going on, you can determine whether one or both heads need to come off, etc.

[billrigsby]

compression of 130 PSI is low if the measurement was made properly. As long as the procedure was correct (clean oil, engine warmed, plugs removed, throttle fully open, battery sufficiently charged so that cranking speed was adequate), closer to 175 PSI would be expected.

 

All of the above was done except warm engine, did not want to run it too much having a problem.

 

If the numbers are still low, do a ''wet'' test to see if they improve.

 

What is the "wet" test you mention?

 

It's also possible for a slight mistiming to cause lowered compression.

 

Timing (acording to my scan tool) is at 10 deg.

 

Bill

[OB99W]

What is the ''wet'' test you mention?

 

Timing (acording to my scan tool) is at 10 deg.

For a ''wet'' test, a tablespoon or so of oil is added to the cylinder via the spark plug hole, the engine is cranked a couple of revolutions to help spread the oil, and compression retested. If rings weren't sealing well, the added oil will help and compression pressure increases somewhat (although with horizontal cylinders, the test is less than ideal). If there's no or very minimal improvement, the low compression is due to valve leakage (assuming the valve timing is correct).

[billrigsby]

Thanks, I'll try that and I can re-check the valve timing before I remove the timing belt.

 

With 194,600 miles, I am probably due for a vlave job any way?

 

 

 

Bill