1959 thru 1962 390 rocker arms too tight causing compression loss?

[midwestisbest]

This is semi-related to my '62 390 'no-start' thread here:
'62 390 'No Start' thread

Someone just informed me that if the rocker arms were TOO tight, that this could result in compression loss. True?

I torqued mine to 75 ft pounds, per the manual. However, the heads DID have a valve job completed.

So, If I were going to try to loosen these, what would be the best practice?

1. Loosen all to 'finger tight', then re-torque to a lower value torque and check compression?

Or

2. Break them free (from the center > out) then re-torque to lower value. Recheck compression.

[J. Gomez]

Bill,

Someone just informed me that if the rocker arms were TOO tight, that this could result in compression loss. True?
 

not sure how that could be possible if everything is installed correctly and with the proper parts.

I torqued mine to 75 ft pounds, per the manual. However, the heads DID have a valve job completed.

If the torque is per the manual again see above

Now I'm not sure if this may apply in your case and/or for the late 390 heads, but have you installed the rocker arm shaft in the correct position?

I know on the 365 these would need to be installed correctly one way they are taller (correct way) while reversing them they are smaller compressing the valves open.

Maybe is worth checking just in case, good luck..!

[midwestisbest]

There was a lot of care that went into putting the rocker arms back together the correct way.

I know on the 390 the order definitely matters how you put the rockers back together. I wasn't aware they also had a height difference. I wonder how I'd know...

[TJ Hopland]

They probably took a little thickness off the heads when they were redone.  Another area I hear a lot about these days that wasn't an issue back in the day is the wrong thickness head gaskets.  If the new one is thinner that could be enough to not let the valves close.  Seems like more and more parts these days they just don't care to get it right, one size is close enough and fits none seems to be the motto. 

Try your leakdown test with the rockers off.  No rockers the valves can't be held open. 

[midwestisbest]

They probably took a little thickness off the heads when they were redone.  Another area I hear a lot about these days that wasn't an issue back in the day is the wrong thickness head gaskets.  If the new one is thinner that could be enough to not let the valves close.  Seems like more and more parts these days they just don't care to get it right, one size is close enough and fits none seems to be the motto. 

Try your leakdown test with the rockers off.  No rockers the valves can't be held open. 

The heads weren't taken to anyone. A friend and myself did the valve job and re-assembly.

The old head gasket was metal and way thinner than the new Felpro gasket.

Taking the rockers off/loose is the next test.

[midwestisbest]

I did not loosen the rockers today.

But I did a leak down test on cylinder 8 and did the following:

1. I made sure the exhaust valve was open and listened to it.

2. I repeated the test, but this time opening the intake and listened to it.

Two things:

1. I know what an exhaust valve leak sounds like. Its very clearly coming out the exhaust.
2. I know what an intake valve leak sounds like. You can hear it at the top of the carb.

Now, when I test the same cylinder with both valves closed, I hear a leak but its NOT a valve leak.

I still think its either bad rings or ... the head gasket?

[J. Gomez]

I still think its either bad rings or ... the head gasket?

Have you done the same test for the other cylinders?

Best is to loosen the rockers so all the valves are confirmed closed and repeat the test; if one failed one your test above it is possible others may have the same issue.

You can open the oil cap out and try to see/heard the "leak" if the rings are the culprit as you state.

I do recalled you had issues with oil burning or foul plugs when you got the engine running, but your previous compression test results seem way too low.
https://forums.cadillaclasalleclub.org/index.php?topic=172317.msg541674#msg541674

"If" you had the engine rebuilt it is possible the rings were not properly clocked "or" the rings gap are out of specs or wrong ones installed.

I had this issue on my side after a very long and tedious troubleshooting, the machine shop had install the wrong ones and not correctly place, the gap was way off and facing close to each other.   

Good luck..!

[midwestisbest]

UPDATE:

I loosened one of the rockers today and re-did the compression test. Same results. Low.