i just installed a new cam, comp cam 262h and crane ductile adjustable rockers. cranes instructions said to go to zero lash + 1/2 -1 turn. i went to zero lash plus 3/4 turn. started it up for cam break in and everything went fine. then i took it out to test drive it and every thing was great. drove about 15 miles then BAM! CLACK CLACK CLACK!!. got it towed home and pulled a valve cover and had a bent push rod. what went wrong? any help is much appreciated
mike

 

I had the same thing happen once. A valve stuck in it's guide. Turns out the valve to guide clearance is greater on FE's than other engines, and my machinist did not know this.

 

Sound like someone's going to get a bill for damaged parts, gaskets and correcting guide clearances. Your machinist work with FE's all the time?
You might of got lucky with only minimal damage.

 

but my heads are edelbrock heads. i ran them with the non adjustables for a while, then bought my adjustables after about 3000 miles. when i pulled it apart to change then i found a bent rod.... now with these new ones i got a bent rod on a different cylinder. i havent had anything done to the heads so they are as the come from edelbrock.... do you think it could have been lifter pump up or too much preload?

 

If it was lifter pump up intakes would go first and start popping thru the carb, if it was a sticking guide exhausts would hang open. You follow Edelbrock's lifter preload instructions? Fighting them on damage will be a losing
battle, good luck.

 

Sounds like you might also have a wiped cam lobe. Replace the bent pushrod, and crank the engine with the valve covers off and watch the one you replaced, loook to see that it's opening the valve the same as the rest. With your tightening of the rockers more than whats called for, you put the valvetrain in more stress, you want less stress on cam breakin.

 

" With your tightening of the rockers more than whats called for, you put the valvetrain in more stress, you want less stress on cam breakin."

How do you figure more stress if the preload is set between the minimum or maximum, oil pressure applied to the lifter is the same?
Bottomed out you would hold valves open and not run smoothly if run at all.
All valves set to maximum preload then the motor wound up until the lifters pumped up? This would result in many taged valves unless a small cam was installed.

 

Well the cam that i put in was a pretty small cam. the lift was something like .494. i followed cranes lifter adjustment instructions. it was running fine, great even, no poping or anything like that. does anyone know where i can buy pushrods in a set of 2 or individually.... or do any of you have extras you may be willing to sell? i have the crane chromoly rods

 

Summit PN CRN-34645-2. It's a pair of 'em. But they wont ship until the 17th of November...

I would recommend the Comp pushrods, but I dont know if they use the same cup diameter as the Crane rockers or not. According to Summit they do. The PN there is CCA-7533-1.

 

If the lifter does pump up and bottom out, you are applying a bit more force on the cam lobe when it's on the base circle. The more the spring is compressed, the more pressure it exerts. And that's something that's certainly not needed during the break in period.

 

If you have lifters pumping up during cam breakin you have problems.
The base circle has nothing to do with excess wear, wear is on the cam lift. Constant pressure on the cam is by the lifter trying to extend by the constant pressure from the oil pump unless the pump bypass isn't working, again problems.
The extension pressure of the lifter is the same be the lifter preloaded to almost bottoming out to almost against the lifter spring retainer during pump up unless the oil pump bypass is stuck closed as oil pressure is constant which results with a constant lifter extension pressure.
Only on idle will the oil pressure drop down as well the extension pressure by the lifter.
If you have a compressed spring on base circle your going to have valves held open, intake backfire, exhaust afterfire bad stumble missing, I would hope the person would detect this problem as not normal.

 

thanks kurt and beemer, right now im going to just get the new pushrod and re adjust them all to 1/2 to 1/4 past zero lash and go from there. if i taged the piston with a valve ill know it cause they wont seat properly and itll run really sh**ty right? or should i do a compression test to make sure everything seats as it should? once again thanks for all you help and advise

mike

 

I wouldn't install pushrods and turn the motor over as you may cause more damage or repeat again. Did you place a straight edge across the valve tips to see of any valves are hanging open or not fully seated because the valve head is bent? I would install a plug adapter and pressurize each cylinder while the pushrods are out then check the carb and tailpipe for hissing air, a sign of a bent valve not seating. Next I would hit each valve tip with a large plastic hammer to see if all the valves snap closed evenly, caution hit them in line of the stem and not bend the stem.Only if all the above comes out good then install pushrods, set preload at the minimum. Rotate motor easy in case you hit a valve, better to "feel it" than yank the breaker bar and bend a valve. Then run a compression check cold, checks good then fire up. You getting enough lube to the top end?
Those heads have valve seal or umbrellas?
I prefer umbrellas on the old iron heads, may use a little more lube but then the stems get more lubrication than seals. I tend to run motors 2 to 300K miles trouble free.

For some reason I can't post after 5 times this word, replaced by lube that starts with a o and ends with a l, same with plural of seal? The word oil gets removed every time.

 

ok thats what ill do check with strait edge, pressurize each cylinder and listen for leaks, hammer check, then ut the rods back in and rotate and make sure non of them tag, compression check, then finally start it again.... you guys have been a great help. oh and i just bought a whole other set of rods just in case moor are bent, i figure it cant hurt to have some extras

 

Roll all the used pushrods on a flat surface like a sheet of glass or table saw top with a light on the back side, any bowed or bent will be seen.