heres the deal i have a 1989 trans am with a rebuilt engine and i have no compression i can only get about 30 psi. the heads are rebuilt and i had the machine shop test them to see if the valves leaked and they didnt. i tested the piston rings and poured oil into the cylinders and they didnt leak. i checked the timing of the camshaft many times and that is right. does any one have any ideas as to what my problem could be thanks for any help.

 

Do all cylinders read the same? Is your gauge working properly?

Are the valves set properly?

Too much pre-load, will cause the valve(s) to hang open.

 

Throttle blocked wide open during the test?

 

ive tried opening the throttle and loosening the rocker arms and even took them off and i still have nothing any more suggestions thanks

 

Obviously something is way wrong. Verify the cam timing by watching the rocker arms as you slowly turn the engine over by hand. On the #1 cylinder, the exhaust valve should just finish closing as the balancer mark passes TDC.
This means:
1. The valve should definately still be moving when the mark is 2" before the timing plate.
2. The valve should definately have stopped moving when the mark is 2" after the timing plate.
(info for stock cam and not 300° drag race cams)

 

Does this happen on all cylinders, or just one?

It could be a leak in the head gasket.

The valves need to be set properly in order for the compression test to
work.

If the rockers are too loose, the valves wont open and air wont get into
the cylinder.

If the rockers are too tight, the valves will hang open and there will be
no compression.

Try another cylinder on the opposite bank and report back with the results.

At this point, you can't even rule out the gauge. It might have a leak.

 

Does (did) the engine run, ever, AT ALL?

Why are we doing a compression test in th efirst place?

Some history would help us do better than just blind guessing at what you're doing wrong.

 

ive tried everything with the cam it all checks out
the head gaskets are new and torqued correctly i replaced them once already
the car ran once before it was hard to start and had a fuel problem the check valve in the tank wasnt working fixed that and it never would start again.

 

What are the readings on all of the other cylinders?

 

all the cylinders are very low no more than 30psi

 

I would take the pressure gauge out to my other car in the driveway and check it. Maybe the gauge is junk?

 

sounds to me .. like leaky valves.. or need to pull the timing cover and actualy check and see if the cam/crank are properly timed. check and see if the cam is turning when the crank is.. broken cam sprockets are a nightmare at times.. causes engines to do all kinds of wierd stuff . ive seen a 460 ford engine shoot fireballs out of the carb all day long cause of a broken cam. the key holding the cam/sprocket together broke and reaked havoc on every thing.

 

i thought it could be the gauge but checked on another car and it works
i just got done re checking the cam with the timing cover off and everything, checked for broken sprockets and stuff and put it back together and thats where im at now still wont start.

 

30 PSI on all cylinders, and you have verified the compression tester as being
good?

You also said the valves were set properly. Let's let that slide for a moment.

If all the valves are opening and seating as they should, and the tester is
fine you are left with the following:

a. Head gasket failure between all cylinders

b. too much clearance between the pistons and cylinder bores

c. incorrect piston ring gap, or ring orientation.

Did you have any work done to the pistons, block , or piston rings?

IE: Were the cylinders bored and pistons/rings replaced?

 

the bottom end is stock from another car with only around 70,000 miles
a friend told me to check the rings by poring oil into the cyclinder and seeing if it leeks down. they all checked out could their still be a problem with the rings? thanks for the help

 

Explain in as much detail as possible on how you set the valves.