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Author Topic:   Cam lobe going flat???
posted May 02, 2004 06:13 PM
Okay this isnt on my race car, but on my daily driver truck. This all happened the other day out of the blue. It seems like one of my rocker arms backed off and was loose. Pulled the valve cover off today, ran the valves. Drove the truck around the corner and back and then the same rocker arm was loose. What would have caused the lobe to go flat all of a sudden. This motor was rebuilt about 20,000 miles ago. it is a hydraulic cam with poly locks so i know it wasnt the nuts backing off.

So my question is what would cause the lobe to go flat all of a sudden?

Or is it a posibility that the stud pulled out? they are press in studs. And how would i find out if it has pulled out?

posted May 02, 2004 06:21 PM
we though my race cam was goin flat but what it turned out to be was a bad pushrod. it was wearing funny. the only thing i can think of is maybe the cam wasnt broke in properly, valve lash too tight maybe. as far as the stud pulling out, just remove the rockers and measure how far out the stud is sticking. hope that helps


posted May 02, 2004 06:34 PM
may be a bad lifter seen that before on hydro cams

posted May 02, 2004 07:11 PM
an easy to check is lay a strightedge across the the studs and see if they are all the same hight if not then you are pulling the stud from the head also see if the nut isfurther down than the rest if so you probaly loosing either a lifter or the cam went south hope this helps

posted May 02, 2004 08:50 PM
Not that this should happen on the truck - but make sure that the rocker stud isn't pulling out of the head... Also - check lift at the rocker and compare that to the other rockers - if it's a cam lobe then the lift number will be significantly smaller. Also - cut the oil filter and if there is metal shavings in there you've got something going south...

posted May 02, 2004 09:19 PM
I'd definitely cut the oil filter open. Lifter probably broke a spring and collapsed. Do you think it adjusted up where it belongs when you ran the rack?

posted May 03, 2004 10:46 AM
Is there an easy way to tell if the lifter is going bad? Like looking to see if that rocker arm is not oiling maybe?

thanks for the help in advance

Ego Racing
posted May 04, 2004 11:05 AM
You are running poly locks.... Has the top of the stud been ground flat to hold the set screw? If not it might not be getting enough seat to hold the lock under pressure and allowing it to move. How old are the locks? I have seen old locks that will not keep tight as the threads have been streached and the set screws are now loose in the lock. What kind of rocker arms and balls are you using? I have seen one splitting open on the bottom and caused this problem. Pull out the pushrod and roll it across a peice of glass to see if it still straight and you can check the ends for damage.

posted May 04, 2004 03:43 PM
pulled the valve cover off today and you can take the push rod and push the lifter like you are pumping it. it moves a good 3/8 to half inch and the other lifters dont move at all, so i think i have a bad lifter.

Now if it is a lifter, do i replace all the lifters and run the cam in again, or just replace that one lifter?

And it is a crane cam, do you think it would hurt anything to put rhodes lifters on it, or just put some more crane lifters back in?

thanks grnhorn

posted May 04, 2004 04:01 PM
I had the same problem 2 weeks ago, well actuallt I broke a rocker arm and found I had a bad lifter and a bent pushrod.All I did was replace that one lifter,pushrod,and rocker arm and car ran fine.

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