LT1 has no compression
LT1 has no compression So we installed a new LT1 short block over the weekend in my friends 93 Z28.
The block came with a cam that was not stock, but we couldn't figure out what it was, it didn't have too much more (if any) lift than the stock cam, maybe more exhaust duration?
Anyway, when all the rockers are off, the motor makes some compression, soon as we put the exhaust or intake rocker on we get no compression at all.
We are using hotcam kit GM adjustable rocker arms, stock pushrods.
Ideas I have are
1 the basecircle of the cam is different so the stock length pushrods are not correct.
2 the valve is open even though its on the basecircle because we are torquing the rocker arms down too hard, they may not have enough oil to be pumped up yet
It would be nice if someone else could give us some insite as to whats wrong with our setup though.
The block came with a cam that was not stock, but we couldn't figure out what it was, it didn't have too much more (if any) lift than the stock cam, maybe more exhaust duration?
Anyway, when all the rockers are off, the motor makes some compression, soon as we put the exhaust or intake rocker on we get no compression at all.
We are using hotcam kit GM adjustable rocker arms, stock pushrods.
Ideas I have are
1 the basecircle of the cam is different so the stock length pushrods are not correct.
2 the valve is open even though its on the basecircle because we are torquing the rocker arms down too hard, they may not have enough oil to be pumped up yet
It would be nice if someone else could give us some insite as to whats wrong with our setup though.
how do you know there is no compression wen the rockers are installed??
why are you torquing the rocker arms?? you have to adjust them by finding zero lash and then turn the lock nut 1/4-1/2 turn.
why are you torquing the rocker arms?? you have to adjust them by finding zero lash and then turn the lock nut 1/4-1/2 turn.
We know because we have a compression gauge hooked up in the sparkplug hole and turn the motor over, it also spins free like all the sparkplugs are out (makes no compression sound)
We adjust the rocker arms by turning the nut on the top until there is no up and down play with the pushrod, then go 3/4'ths of a turn.
We adjust the rocker arms by turning the nut on the top until there is no up and down play with the pushrod, then go 3/4'ths of a turn.
TECH Resident
Joined: Jun 2002
Posts: 943
Likes: 2
From: Houston
all of your valves are in and the rockers adjusted correcty? If so, then you have faulty valve guides or bad piston rings. I doubt that though. If you have them tightened down too much, the valve wont close fully and you wont have compression. You didnt go back through and re-tighten after you adjusted them the first time did you? If you retightend them, the oil would have been bleed out of the resevoirs and it would seem that they were not adjusted right the first time when in fact they were. If you did, then again you would have adjusted them too tight and the valves would be slightly open letting the compression escape. I would take the lifters out, soak them in oil for a day and put them back in tomorrow with a 1/4 turn instead of 3/4 of a turn which isnt neccesary. Set the lash just once and then check for compression.
Ok, I will do that.
By the way, everything ran great before the shortblock swap so I really doubt I have any valve damage of any kind, and the pistons are great, remember when the valves are closed it does get compression.
I'll post a update tomorrow!
By the way, everything ran great before the shortblock swap so I really doubt I have any valve damage of any kind, and the pistons are great, remember when the valves are closed it does get compression.
I'll post a update tomorrow!
Alright, we have been overtorquing these adjustable rockers the whole time, it just didn't effect it on the old motor/lifters.
We did 1/2 a turn and got great compression
We did 1/2 a turn and got great compression
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