Hi there. I listen to you all the time. I have a 1991 Jeep Grand Wagoneer, 8 cylinder, automatic. It was running fine when I parked it after hauling a trailer with a load of firewood. The next day it was making a loud thunking noise. My old man took off the valve cover and one of the push rods was very bent. I bought the new push rod today but I’m wondering if I have a bigger problem that caused it. Thanks for your help. Trish in Homer Alaska
Before you install the new pushrod, check to make sure the valve is free to move for that pushrod.
Take something like the handle of a hammer and place it on the end of the valve stem, and push on the head of the hammer to see if the valve can be opened and closed. If not, reverse your grip on the hammer and give the valve stem a good rap. Now reverse your grip again on the hammer, and see if the valve opens and closes. If it doesn’t, return that new pushrod.
Sometimes a pushrod will lose strength with so many cycles of heating and cooling going on over the years. If that is the case, you may need an entire set of them. Other than that, a valve or lifter may have siezed. And a collapsed lifter would make it fall out and then get bent because it caught sideways in the guide. See if it has a guide that broke or just a hole that it passes through.
A collapsed valve lifter leading to the pushrod being thrown could have also caused it.
Note if there are any marks on the inside of the valve cover, any marks on the rocker arm, and it would be a good time to pull the valve lifter and take a look at that also.
In some rare cases the end of a cam lobe can snap off. This should be apparent with the lifter removed.