Valve adjustment wrong??????
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Senior User
Joined: Mar 2007
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From: arkadelphia, ar
Valve adjustment wrong??????
A little history. I did an in truck rebuild of sorts about 12k miles ago. Heads were rebuilt at that time. Now I have a miss that won't go away so checked the compression and on 3 and 4 have about 70 and 30lbs compression, compared to 130ish on 1 and 2. My mechanic freind says burned exhaust valves.
I talked to the machine shop and he said that it could be holding the valves open slightly, to loosen the bolt holding the lifter rail about a turn on each bolt and see if it helped. If it did to get some "shim stock" and put under the towers.
Has anyone heard of this and/or tried it?
By the way '73 360.
I talked to the machine shop and he said that it could be holding the valves open slightly, to loosen the bolt holding the lifter rail about a turn on each bolt and see if it helped. If it did to get some "shim stock" and put under the towers.
Has anyone heard of this and/or tried it?
By the way '73 360.
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
Now there is a good way to screw up your rocker arm. Do a compression test again and this time squirt oil into the cylinder. If the numbers come up more than 15 PSI, then it is rings. Otherwise it is valves. The only way the valves could be held open after 12K miles, is if the lifters had pumped up, so one way or another, the valve cover has to come off and probably the head. I would bet either the valves are bad or you have a piston issue.
FTE Leadership Emeritus
Joined: Jul 2002
Posts: 42,561
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From: Long Island USA
On top of what Bear said, if you want to see if the valves are staying open, pressurize the cylinder and see where the air is coming out - intake, open intake valve or bad valve/seat, exhaust is open exhaust valve or bad valve/seat. When you do this, back off on the rocker shaft bolts and see if it stops. If so, valves are slightly open. If not, valve/seat is bad.
Hotshot
Joined: Apr 2009
Posts: 14,333
Likes: 247
From: Stanley, VA
I am going to bet burned exhaust valves. Unless the machine shop installed hardened valve seats the exhaust valves are going to either sink into the head (Valve recession) or burn.
Even if the engine had the D2 heads with induction hardened seats from the factory, once you grind them a couple of times the hardness is gone.
Even if the engine had the D2 heads with induction hardened seats from the factory, once you grind them a couple of times the hardness is gone.
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