Leakdown test Results ?
07-16-2010, 10:16 PM
#31
Burning Brakes
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I've checked a number of 928s with my leakdown tester (Tavia - made in USA) and I have always gotten 5% or less on a warm motor (and even a cold one recently), including my car at 200K miles, except for one car that had a leaky head gaskets (inadequately torqued Cometic) and was found on disassembly to have stone-honed cylinder walls. That car had a bunch of cylinders at 12% (and 150 or so compression test) right after the so-called "rebuild" and over time a couple of them went to 28%.
Thanks Bill!
07-16-2010, 11:47 PM
#32
Rest in Peace
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Thanks guys for all the comments and suggestions
I will double check the timing in the high bank.
The compression tests were done with the throttle closed but each cylinder cranked for 7 secs.
Hopefully warped heads are not an issue as both heads were decked when I had them off to renew the head gaskets. I Also asked the machine shop to ensure they removed the same amount from each head to avoid any water bridge problems.
I'm away for a few days but will report back later with more results prior to pulling the engine. I'm going to pull the engine regardless because I'm not confident of getting a good job done on the cam carriers with the engine in the car.
Again thanks for your input and discussion.
I will double check the timing in the high bank.
The compression tests were done with the throttle closed but each cylinder cranked for 7 secs.
Hopefully warped heads are not an issue as both heads were decked when I had them off to renew the head gaskets. I Also asked the machine shop to ensure they removed the same amount from each head to avoid any water bridge problems.
I'm away for a few days but will report back later with more results prior to pulling the engine. I'm going to pull the engine regardless because I'm not confident of getting a good job done on the cam carriers with the engine in the car.
Again thanks for your input and discussion.
Using a fully charged battery, with a boost capable battery charger hooked up on boost AT the battery, and with the throttle held wide open.
That will change the readings from what you got by a large margin.
Think about it, with the throttle closed you will get lower readings because the throttle is closed and limiting the amount of air that can be compressed and measured by your compression gauge.
With the throttle closed I can see where you could get a higher reading on cylinders with a bad ring seal as it would suck in air from the crankcase from the vacuum inside they cylinder during the testing.
In other words the difference between a good cylinder and a bad would not be as much in your PSI readings.
I hope this helps, I am not trying to be a know it all, trust me, knowing all there is to know about engines, that is just one of the things that eludes me.
07-18-2010, 08:53 PM
#35
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Most folks use either 3 (that is what I use) compression strokes or five, not sure why that is, but five seems to be the standard from what I have found from dealing with as many pro wrenches as I have hired and fired over the years.
Using a fully charged battery, with a boost capable battery charger hooked up on boost AT the battery, and with the throttle held wide open.
That will change the readings from what you got by a large margin.
Think about it, with the throttle closed you will get lower readings because the throttle is closed and limiting the amount of air that can be compressed and measured by your compression gauge.
With the throttle closed I can see where you could get a higher reading on cylinders with a bad ring seal as it would suck in air from the crankcase from the vacuum inside they cylinder during the testing.
In other words the difference between a good cylinder and a bad would not be as much in your PSI readings.
I hope this helps, I am not trying to be a know it all, trust me, knowing all there is to know about engines, that is just one of the things that eludes me.
Using a fully charged battery, with a boost capable battery charger hooked up on boost AT the battery, and with the throttle held wide open.
That will change the readings from what you got by a large margin.
Think about it, with the throttle closed you will get lower readings because the throttle is closed and limiting the amount of air that can be compressed and measured by your compression gauge.
With the throttle closed I can see where you could get a higher reading on cylinders with a bad ring seal as it would suck in air from the crankcase from the vacuum inside they cylinder during the testing.
In other words the difference between a good cylinder and a bad would not be as much in your PSI readings.
I hope this helps, I am not trying to be a know it all, trust me, knowing all there is to know about engines, that is just one of the things that eludes me.
If you also redo the oil tests, use a syringe and shoot a measured quantity of oil in (I use 10ml)' just before doing each one. Different quantities can alter results slightly
