No Compression!!!!????!!!
#1
No Compression!!!!????!!!
Hello, I am just a bit stumped.
I recently replaced the head on my 1986 pu. The head is off of a 1986 block with domed top pistons...My original motor did not have domed top pistons...
The new head I put on had brand new valves, keepers, springs etc...
I got everything put back together, double checked all my connections and torque specs and went to fire it up. It honestly sounded like the starter wasn't straining at all. The thing didn't fire up so I went through the usual checks, the thing is getting spark, and gas, so i checked the compression...0. That is zero on all 4 cylinders. At first I thought that maybe the cam wasn't spinning so I took the valve cover off and the thing is spinning just fine. My only guess is that the non-dome top pistons have a very negative effect or that my valves are being pushed and held open by the cam.
I am a little mystified and I hope maybe someone has a suggestion for me...
Thanks for any input,
Jon
I recently replaced the head on my 1986 pu. The head is off of a 1986 block with domed top pistons...My original motor did not have domed top pistons...
The new head I put on had brand new valves, keepers, springs etc...
I got everything put back together, double checked all my connections and torque specs and went to fire it up. It honestly sounded like the starter wasn't straining at all. The thing didn't fire up so I went through the usual checks, the thing is getting spark, and gas, so i checked the compression...0. That is zero on all 4 cylinders. At first I thought that maybe the cam wasn't spinning so I took the valve cover off and the thing is spinning just fine. My only guess is that the non-dome top pistons have a very negative effect or that my valves are being pushed and held open by the cam.
I am a little mystified and I hope maybe someone has a suggestion for me...
Thanks for any input,
Jon
#4
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the valves not seating properly can cause this alone, if yo did not grind the seats, there is no way the new valves can seat properly as the seats are worn for the old valves.
#5
any other ideas? I am not discounting that possibility but I am hoping that there might be something else.
Thanks for the input...
Jon
#6
You know, I just thought of something. I used the old rocker arm assembly on the new head...could that have done anything....? Maybe the old assembly is shorter than the new one?
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Check the valve adjustment (make sure they're not too tight) check valve train position in reference to piston position. Aside from valves not seated properly, the only things that can cause the compression loss are valves too tight and/or camshaft timing off by a mile. Pull the valve cover, line up the crank pulley at TDC and check to see that the valves are closed and you can wiggle the rocker arm slightly. If all that checks out ok, you prolly have valves not seating.
#9
thanks for the ideas,
Jon
#10
Alright...I figured it out. It was definitely the valve adjustment. I readjusted them and in some places I would swear they were at least 1/8" off of the correct adjustment. Now the thing starts right up and purrs instead of clanking and barely maintaining an idle...
Thanks for the suggestions...
Jon
Thanks for the suggestions...
Jon
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