I have a 96 ws6 I bought off this board that has a xe 233 cam LE2 heads long tubes obd 1 mail order madz and the motor was said to be rebuilt within a year of purchase about 2000 miles seems to use alittle oil, but is running rich (needs computer tune) being it's down for the winter I thought I would do a compression test on it to make sure the lower end was sealed up good and If I had any oil usage issues it would be oil seals or something that didn't require a engine removal. here is what I got please share your opinions. all plugs were black, not wet.

left bank right bank
#1 160/195 #1 170/195
#2 170/190 #2 170/200
#3 170/190 #3 140/175
#4 160/200 #4 170/195

the first # is one revolution the second is after 4 revolutions.

 

Looks like #6 (what you call right bank #3 - passenger side???) may have a problem, since its 10-15% below the average of the other seven cylinders. The manuals will tell you 20% variation is OK, but I wouldn't use that criterion for a rebuilt performance engine.

 

Hopefully that is just caused by a little carbon gumming up the rings since you said it is rich.

 

so I should be ok? just he the tuning right? is there anything I can do on a low mileage rebuild motor to help seat the rings or am I ok? kinda new to this stuff I just want to know in the middle of the summer I won't be saying should have done something while it was down for the winter? i appreciate the information guys. as for the numbering rather than looking up the cylinder numbers I just went from to back left and right.

 

ttt

 

I think you're ok, just run it and keep an eye on the oil level. If it runs fine that's really all that matters. The one that read 140/175 is a bit low, but I don't think it's anything to freak out about.

 

Leak down test time.

 

educate me on what you mean by a leak down test? what does it do and how do you do it?
thanks

 

A leakdown test is done with compressed air going through a gage block and put into the engine through a cylinder's spark plug hole. You must put the cylinder you are working with at TDC. This efectively seals off the cylinder with both valves closed. Now setting the dial to the correct point, the gages will tell you what percent of air going in the cylinder is leaking out of the cylinder.

This is the best test to do to find out where you are loosing compression. Usually it is from a valve. It is the best test for a bad head gasket if the gasket is leaking into the cylinder.

When you pressure up the cylinder, the problem point will show up by listening to where you hear the most air. To explain further, if say the intake valve of the cylinder under test is leaking. Then you would hear "more" air rushing from the intake. If the exhaust valve where the problem, then you would hear more air rushing from the exhaust pipe.

If rings were the problem, you would hear more air coming from the valve cover cap. I caution you that you will always hear some air from the valve covers. A normal engine will have a small amount of air coming from the crankcase. DO NOT misinterpret this small amount of air. It is wise to test a few cylinders to see what is "normal" before interpreting the "bad" cylinder.

Remember that certain leakdown failures will be accompanied by other symptoms. If you thought rings was the problem, you probably would see oil burning symptoms like smoke or oil fouled plugs. If the head gasket were blown you could be seeing oil burning or water burning symptoms. Sometimes if the head gasket is blown to the water jacket, your leak downtest will cause the water level to rise in the radiator and or bubbles to come out.

See the point of looking for other symptoms? Think about what you see or hear.