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tragiccomic1972
March 1st, 2012, 05:29
Ok... maybe I am going into some type of early senility here and I am missing something obvious.

1997 Cherokee 4.0-- Blown Head gasket... It was drivable, ran decent, just had low compression in # 1 and # 2 cylinders... I have seen this before... head gasket is allowing compression to escape into the adjacent cylinder... no problem... a trip to O'Reilly and 3 hours later.. viola!!! new head gasket installed... I've done no less that 10 of these on 4.0's... simple stuff...

...but I noticed as I was re-installing the rocker arms, that both valves were being compressed when tightening down the stock non-adjustable rockers... that's not supposed to happen... so I turned it over with the starter and sure enough it spun freely as if there was no compression...

I backed the rocker off a bit and it started up, but ran rough because the valves are not adjusted correctly... I checked all the pushrods to make sure they are sitting in the lifter seat...

I am baffled.... why would I have to adjust a non adjustable valve train??
Thoughts?

tragiccomic1972
March 1st, 2012, 06:56
anyone???

ct67_72
March 1st, 2012, 07:23
How far down were the valves being pushed when you tightened the rockets? Could have bad seats, allowing the valve stem to sit higher than its supposed to.

old_man
March 1st, 2012, 07:33
I have seen lifters get pumped up too much when you prime them as you build an engine and it lead to similar problems. Normally, if you crank it over a few times it goes away. After you got it started, you should now be able to tighten them back down.

The other thing is to make sure the pushrods are centered i the lifters.

tragiccomic1972
March 1st, 2012, 08:28
Lifters pumped up too much... maybe... I did try to adjust them while it was running... but when I began to tighten them down it killed it again... I did check to make sure the pushrods were seated in the lifter properly-- that was my first thought too...

the valves are being pushed pretty far down... more than a bad seat would allow for...

I wonder if I tap the top of the pushrod with a hammer it would force the oil out of the lifter and allow me to tighten the rockers down snug before I started it again?

tragiccomic1972
March 2nd, 2012, 07:17
ok- update... drained the oil... cranked it up and let it run for 20-30 seconds... enough to collapse the lifters... filled it with new oil, tightend the rockers down all the way and it fired right up...

old_man
March 2nd, 2012, 07:37
Bingo.