Bent push rods

I had horrible problems with my pushrods bending after a complete rebuild a few years ago.

Most of the issues were traced to improper head assembly-
valve springs not correct for my application
metal crud had not been cleaned up under the valve spring shims, which meant that the shims bent around this debris, changing installed height
My pushrod guides were not doing what they were supposed to do - they were sideloading the pushrods. They were cut apart and re-welded.

I frankly don't remember what the other issues were. There were a number of small factors that all added up to an engine that wouldn't live. To solve the problem, I had the heads completely disassembled and all parts replaced (despite the fact that they were new). I've had many miles of happy motoring ever since...

Hi Chalie

Thanks for sharing. The issue with guideplates sideloading the push rods is a bit tricky to messure. I have been looking at this and from what I can see and feel the look ok. If this would cause my problems, any ide why do this only happen att high rpm?

/Honken

Afraid I can't help you much more. I've read elsewhere that other people have had problems with certain combinations of guides and heads - Manley guides with Aussie 2v heads for example, and only sometimes. It is something to check, but if it doesn't appear to be a problem on your car, then it probably isn't.

IN any case, in my particular engine it was only one of several factors that all added up to a large collection of bent pushrods.

I'm afraid I can't tell you much more...

Honken, you must adjust the valvetrain geomery when parts are changed/upgraded. First, the rockerarms must touch the valve stems as close to the center of the stem ends as possible and this may require the pushrod guideplates to be cut apart, positioned correctly, then tack-welded back in position. Second, the rockers may need to be adjusted with slightly longer or shorter pushrods to center them on the valvestems. You blacken the end of the valvestems with a Magic Marker, then manually turn the engine over two full revolutions and examine the stem. If the mark is smeared too close to one edge or the other, the pushrod length(s) must be altered. There are checking-pushrods sold to find the proper length, and many shops make up longer/shorter custom pushrods. Adjustable pushrods don't work in high rpm engines- they are far too heavy and won't hold an adjustment anyway. Note that ALL 16 rockers should be checked and some engine combinations will require two different lengths of pushrod. Intake & exhaust valves have different length stems, anyway. Finally, if things check out OK, very stiff valvesprings and hgh revs may need larger diameter than stock pushrods which will be stiffer. Stock pushrods are 0.060"-wall x 5/16" OD while real race engines use 0.090-to-0.120-wall x 3/8 or even 7/16" OD pushrods for high revs w/stiff springs. And of course, the larger diameter pushrods will need larger clearance slots in the pushrod guide plates, and those slots are not straight up and down but are cut at a compound angle just like the valves. They're hardened, too so simple drilling won't work- they must be ground. Grinding the slots while mounted on the engine is a very bad idea- you'll NEVER get the hard grinding dust completely out of the engine without damage to the bearings.

I have a solution for guide plate problems ... throw them away.

If your head is already machined for guide plates install the Yella Terra #YT6321 rocker arms. The rockers mount solidly to the head on their pedestals and utilize a push rod cup adjuster for valve clearance or lifter pre-load adjustment.

For those of you whose heads are not machined for guide plates, don't bother with having them machined. Yella Terra #YT6015 rocker arms have pedestals designed to fit in the slotted rocker fulcrum mounts.

Not only does this eliminate all the possible problems caused by guide plates, it also allows you to utilize tapered push rods.

-G

Hi Bosswrench

Thanks for all the info there. I actually measured my geometry earlier this year and found to my surprise that I need shorter rods for my intake valves otherwise the rocker was placed to far "out" on the valve stem. So this is common?

The rods I use today are Cromolly SEA RP3226R (for exhaust) and SEA RP3225R (for intake). I'm still waiting for a valve spring tester I ordered. When I get the results I will know if I need stiffer springs or stronger rods. So, if the issue is weak rods, will this occur only at high revs?

If I buy thicker rods I will buy new plates as well and not fix the old ones

Or maybe I will get myself a couple of Yella Terra? Cowboy, if the mount is solid, how much can I adjust for push rod length?

Thanks to all of you! I'll post my results!

By the way, it's a 393 not a 383 as I wrote earlier

Cheers