Rocker arms

2000 BUICK LESABRE
160,000 MILES • 3.8L • V6
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STEVE WHITINGER
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I blew one of the head gaskets from overheating so I decided to take on the task of replacing them. I had no problems until I tried to start the car. When I tried to start it I had no compression in any of the cylinders. After a period of time of diagnosing it I found that it was the rocker arms that was the problem. When I tighten the rocker arm bolts to specs it causes the valves to be open making the loss of compression. I backed the bolts out on all cylinders until I got the car to run and it runs good but the problem is that the rocker arm bolts are just barley tight and this can't be right.

I check to make sure that the rocker arms, push rods and pivot retainer are installed correctly and they are. I am totally baffled! Any ideas would be greatly appreciated.
Dec 9, 2019 at 12:57 PM
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CARADIODOC
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Are you familiar with how to adjust the valves on older GM engines by centering the lifters in their range of adjustment? This engine is not adjusted the same way. According to GM, there is no adjustment for this valve train, so I suspect what is happening is the lifters got pumped up all the way, and they're not bleeding down by just sitting there. As long as the engine will run, gradually tighten just one bolt about a quarter turn at a time. You'll hear and feel the misfire when the valve is being held open, but the lifter should bleed down and the misfire should clear up within a few seconds. Once it does, tighten the bolt another quarter turn and wait for the misfire to clear up. Don't do that too quickly because the valve needs to close so heat can be transferred from its face to its seat to prevent overheating that valve.

Once you have that bolt tight, move on to the next valve and do the same thing. You can torque them all to specs later once they're all snugged down.
Dec 9, 2019 at 2:50 PM
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STEVE WHITINGER
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I agree with the probability of the lifters not bleeding down. I am wondering if I do the suggestion you made about running the engine and doing a 1/4 turn at a time, will the lifters still bleed down with the oil pressure created from the car running?
Dec 9, 2019 at 4:53 PM
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CARADIODOC
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Yup. That's exactly what they do in normal operation when the parts warm up and the push rods and valve stems expand. It shouldn't take more than 20 seconds for one to bleed down to self-adjust, but when tightening the bolt a quarter turn, you're asking it to bleed down a lot more and much faster than in normal operation.

Some lifters will not bleed down very well when steady pressure is held on them. That could be why they didn't do that when you first bolted everything together. They need the push and release of the cam lobe to let some oil out, and of course, that means you have to get the engine running first.
Dec 9, 2019 at 5:36 PM
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STEVE WHITINGER
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Okay, I understand and I will do this tomorrow and update when I am done. Thank you very much.
Dec 9, 2019 at 5:39 PM
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CARADIODOC
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Please do post the solution. That can help others who are researching the same problem.
Dec 9, 2019 at 5:48 PM