We just picked up a motor last week. 89 Renix out of a 93. So all of the renix stuff was already swapped to run with HO. We bought the motor with the understanding that it had a bad head. The guy we bought it from said it ran but over heated. Swapped head of the 92 HO that it is replacing. Installed motor and there is only 25psi of compression in every cylinder. Is there anything that could be causing this, or is this motor shot too.
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Need help bad. 25 PSI of compression
- Thread starter go1lum
- Start date
88 Wagonman
NAXJA Forum User
- Location
- Boise, ID
Try the compression tester on a different vehicle to test it's accuracy. Did you hold the throttle open when testing? Battery fully charged? How many times did you let the engine crank on each cylinder when testing?
If there is nothing wrong with the test and it truly is 25 lbs on each cylinder that is very odd. I don't know if it's possible, but if the pushrods are too long (different head?) maybe it would hold the valves open slightly? The best way to tell for sure is to do a leakdown test to see where the compression loss is. Be sure to post your results, I am very curious.
If there is nothing wrong with the test and it truly is 25 lbs on each cylinder that is very odd. I don't know if it's possible, but if the pushrods are too long (different head?) maybe it would hold the valves open slightly? The best way to tell for sure is to do a leakdown test to see where the compression loss is. Be sure to post your results, I am very curious.
joe_peters
NAXJA Forum User
- Location
- Grants Pass, OryGun
I would not expect to see an even 25 psi across all cylinders.
x2 test the gauge on a known good engine.
Even if the 92 head you are using is warped, I wouldn't expect it to be even across all cylinders.
x2 test the gauge on a known good engine.
Even if the 92 head you are using is warped, I wouldn't expect it to be even across all cylinders.
ceb0217
NAXJA Forum User
- Location
- oregon,corvallis
rings could be stuck how long did it set??? try putting a table spoon or so of oil in each hole and crank it over for like 45 sec. then retest
8Mud
NAXJA Forum User
- Location
- Central Germany
My first guess would also be a bad or leaky compression gage. Most have a check valve built in that can hang or screw up.
After you've tried the easy stuff and if it doesn't work out. Take off the valve cover and turn the motor over by hand until the number one piston is all the way up and you can wiggle both of the number one rockers, (both exhaust and intake) the valves should be fully seated and with a little play in the rockers. Check the timing marks, they should be close to Zero.
Remember you have four strokes and both the valves (on number one) should be fully closed on the compression stroke, with the piston at the top and the timing marks should align. You may be a couple of teeth off on the timing chain. It isn't common for the I-6 to jump timing, it may be impossible. But the chain can be installed wrong and there are two different tooth counts available (maybe more), one change in the tooth count was right around 93 or so. Look and see if there is any fresh looking silicon squeezed out on the timing chain cover gasket.
You can get the top of the number one compression stroke almost exact, by using a piece of welding (or coat hanger) rod with a slight bend in the middle to feel when the piston is all the way up and starts back down again. It may take a few tries, with the last movement of the engine while you are turning it by hand to the right, after backing up a quarter of a revolution. The object is to back up far enough to turn to the right again (as you are looking at the front fo the motor) and take up the slack in the timing chain. You have less chance of backing out the harmonic balancer bolt, if you take all the plugs out.
Timing chain jump is fairly common in the old Dodge LA motors, it would show very low compression on all cylinders when this happened. I'd be careful, on some motors it's possible for the valves to contact the top of the piston if the timing chain is very far off. It may or may not be a factor with the I-6 motor.
After you've tried the easy stuff and if it doesn't work out. Take off the valve cover and turn the motor over by hand until the number one piston is all the way up and you can wiggle both of the number one rockers, (both exhaust and intake) the valves should be fully seated and with a little play in the rockers. Check the timing marks, they should be close to Zero.
Remember you have four strokes and both the valves (on number one) should be fully closed on the compression stroke, with the piston at the top and the timing marks should align. You may be a couple of teeth off on the timing chain. It isn't common for the I-6 to jump timing, it may be impossible. But the chain can be installed wrong and there are two different tooth counts available (maybe more), one change in the tooth count was right around 93 or so. Look and see if there is any fresh looking silicon squeezed out on the timing chain cover gasket.
You can get the top of the number one compression stroke almost exact, by using a piece of welding (or coat hanger) rod with a slight bend in the middle to feel when the piston is all the way up and starts back down again. It may take a few tries, with the last movement of the engine while you are turning it by hand to the right, after backing up a quarter of a revolution. The object is to back up far enough to turn to the right again (as you are looking at the front fo the motor) and take up the slack in the timing chain. You have less chance of backing out the harmonic balancer bolt, if you take all the plugs out.
Timing chain jump is fairly common in the old Dodge LA motors, it would show very low compression on all cylinders when this happened. I'd be careful, on some motors it's possible for the valves to contact the top of the piston if the timing chain is very far off. It may or may not be a factor with the I-6 motor.
Last edited:
joe_peters
NAXJA Forum User
- Location
- Grants Pass, OryGun
So, what was the problem, and what was the cure?
this post you made was the waste of time.
what was the problem and how was it fixed. how about a little more of the story????
joe_peters
NAXJA Forum User
- Location
- Grants Pass, OryGun
