Pushrods

[al's yj]

Did a 4.0 head swap onto a 4.2 engine. Installed a new 4.0 head gasket. I also installed an aftermarket comp cam with a higher lift and duration. Do not have any compression now. Two questions.

1. Are the pushrods on a 4.0 and 4.2 different lengths? Do they need to be replaced?
2. Are the rocker arms different? Or do they need to be shimmed?

Any advice will be appreciated.

 

[PoliceMonkey161]

Hey Al,

Typically, you'd re-use the 258 push rods and rockers. But I've heard of guys using the 4.0 rods and arms as well.

Have you tried to start it? Did it run at all? You can check the length of the rods you have and do some troubleshooting but it will make a difference if the new lifters have run (pumped up) or not. If it did not fire up and the lifters are new, my gut feeling is you have timing issues if you have zero compression.

 

[jps4jeep]

Did you change teh valve springs? If not, with more lift, you can bottom the stock spring out and bend a push rod.

 

[carnuck]

or break off a valve top and punch the piston