jriebe

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

91muddog

did you grind the valve seats?
adjust the cam and valves properly?

how ae the piston rings in the new block?

1styota4X4

going with non domed topped pistons will lower the compression but not make it zero. your sure the valves are seated and cam is degreed correctly?

91muddog

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.

jriebe

That is what I thought but the valves and valves seats were matched up at the machine shop. The valves are ENGBLDR's over sized and the shop cut the seats to fit them...

any other ideas? I am not discounting that possibility but I am hoping that there might be something else.

Thanks for the input...

Jon

jriebe

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?

91muddog

not necessarily, it could be misadjusted for the new valves, check all your adjustments.

also, how ar ethe ol valve seals lookin?

Willcipher

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.

jriebe

It looked like the valves were starting to burn out...I am thinking that maybe the old rocker arm assembly was adjusted too tight and helped the old valves go out, then to top it off, I put the damn thing on the new head which needed more slack due to the valve job so my valves are just permanently stuck open. I am going to use a feeler gauge and adjust the valve lash to make sure it is within specs...we'll see if this works out.

thanks for the ideas,

Jon

jriebe

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