Bending the same pushrod?

9 LIVES

9 LIVES

Demolition Expert
Joined
Oct 29, 2006
Messages
4,051
#4 cylinder keeps bending the exhaust pushrod on my 98 12V

This time it broke the top cup off.... Last time it bent the cup where the ball sits direcly over.

I kinda knew something wasn't right when it shot a 2ft. flame out of the stack when I brought the rpm's up.

What would be something that could cause this? I was letting it idling for 20 minutes outside the shop then hopped in the truck and chopped the throttle a couple times before putting it in gear and it started making the funky noise...like a miss. Kept chopping the throttle to replicate the noise and track it down until we found it was a pushrod on #4 exhaust side for the second time.

Im thinking either a screwed up lobe on the cam or maybe the exhaust tappet is damaged?
 
Normally when I see a push tube bent it either from the cam follower sticking in the block or a bent valve hanging open and causing piston to valve contact.

Bent push tube won't cause flames , just poor performance.

But a bent valve will give you flames.
 
Ahh nice! everybody has to look forward to a bent valve here and there right? lol

There is no way to check the valve without pulling the head is there?
 
Yes: a compression test, but better yet a leakdown test.
TOMMY
 
Correct a leak down test will tell you everything.

The test must be done on a warm motor.
 
Heres what i was thinkin:
Back off both #4 rockers pull #4 injector appily compressed air to injector bore (with a big rubber tipped air blower) it dosen't matter wher the piston is, if there is a leak in one of the valves it should be easy to hear it in the intake or exhaust. this is how we used to do it on our motorcycles without actually having a leakdown tester (COONASS LEAKDOWN).
Hope this makes it easier than pullin the head.
From what ive seen (I'am old) most bent push rods are from valve spring coil bind , severe valve float or the valve sticking in the guide.
Do let us know what you find.
Always learning, TOMMY
 
check to see if the valve is stuck as well.. this same thing happened to a friends '97 recentlly. his valve was stuck in the guide. It was stuck so bad that the spring wouldnt pull it back up!!! i spent some QT with some 2+2 and some PB Blaster and a cordless drill and vioula!!!! it runs fine now
 
I haven't checked for a broken valve spring..good idea.
I thought at first it was defect in the pushrod seing that it broke it into two pieces...but being the same as last time I doubt that would be it.
 
You must log in or register to reply here.
Back
Top