Ukraine Train

my pushrods were ticking so i was adjusting the rocker nuts, well as i was working on one of them i noticed that one of the valves had stopped moving, i killed the engine and saw that the pushrod had snapped in half. i pulled the intake to get it out of the lifter valley and noticed that about half of the other pushrods were bent. there was a total of 5/8 turn past zero lash on all of them when the one broke. before i adjusted them today they were set to 3/8 turn past zero lash and were ticking. before i adjusted them today the engine ran at 3/8 turn for a total of about 30 minutes since i put the cam in (LT4 HOT cam-.492 lift).

i had the guides milled .050" to accomodate. the springs are at about 350lbs at full compression which is about the max recommended (hyd. roller). i haven't pulled any valve springs yet to see if the guides were hitting the retainers. the only causes for this i can think of are that the stock pushrods are too weak to handle 350# or the guides werent milled enough and the retainers hit. any ideas?

i think it's gotta be the pushrods are too weak because if it was a clearance issue, all the rods should have been bent.

No4NJunk

Those pushrods are too weak. You need hardened pushrods. Spend some money and this shouldn't happen again.

RB83L69

What springs? Also, what rockers, and are you running guide plates, or are the push rod slots in the heads tight to the push rods?

.492" lift should not cause problems by itself, except with GM springs, especially if they've been shimmed up to get seat pressure.

If the push rods were too weak, the'd all have been bent. Are they stock? If they're anything but stock or stock replacement, then they're adequate for what you have, if your springs are also not stock.

Ukraine Train

the springs are aftermarket, good to .570 lift. pushrods are stock, with guide plates. rockers are stock. i havent checked for retainer/guide damage yet but if it's ok then i'm driving to summit tomorrow to get these: http://store.summitracing.com/partdetail.asp?part=6393

RB83L69

Rockers are stock for what? Specifically, are they "self-aligning"?

No4NJunk

Not a flame but your wrong. The blower vette we have just broke a pushrod and bent 3 others. We installed hardened pushrods and haven't had a prob. since. Ideally your theory is right but realistically it isn't because naturally some of the pushrods are going to receive different stresses. Look at it this way RD83.......stranger things have happened. How old were the rods. Did they look fatigued from too much heat or lack of lubrication. If not then I would think that they were too weak for the application. If so then you needs new ones anyway so go with what you posted in the link. It can't hurt you and will give some peace of mind down the road especially if your thinking of doing some serious mods.

Note that I am only giving a suggestion. I just didn't want you to rule out the original thought of the PRs being too weak. RB83 seemed way too sure about his statement which I know from experience to be wrong. Just a thought.

AJ_92RS

First problem I see is that you're using stock pushrods with guideplates. Only hardend pushrods should be used with guideplates.

The second problem that RB is getting to is that you aren't supposed to use BOTH self aligning rockers with guidplates. They can argue with each other about where the pushrod should be.

The third is that you may have the improper length pushrods. If you had the heads milled then you defintetly need shorter pushrods. Think about it. You've brought the rockers closer to the cam, so the stock pushrods are now to long. Which may also mean that there is excessive valve tip and valve guide wear happening also.

AJ

EDIT: Sorry. Just read it again and noticed that you said you had the guides milled, not the heads.

But the first two things are both problems that need to be corrected.

RB83L69

AJ is right about where I was going with the rocker question... there are 3 possible methods for aligning the rocker over the valve: (1) slots in the heads that fit tightly (.015" or so) to the push rods, and non-"self-aligning" rockers which can then go where the push rods want them to go; (2) large holes in the heads, guide plates, and the same rockers as above; or (3) large holes in the heads, no guide plates, and "self-aligning" rockers. Each system works OK within its limits. The best all-around is #2. If you have 2 or more of these possible systems installed on your motor, then you have 2 things fighting each other over where the rockers are going to be aligned, and the thing that's going to get destroyed is the push rods.

I don't know where this business about having to have hardened push rods with guide plates came from. Lots of motors use guide plates in conjunction with the same crap for push rods as motors that don't; all Chevy big blocks for example, and aluminum-head L98s.

Chances are that your cam has enough lift that the rocker geometry is far enough off to require longer then stock push rods, probably by .050". Since you'll be buying push rods anyway, you'll most likely want to get 7.450" ones. But, if you have stock-length non-roller push rods (7.800" more or less), then they're .400" too long. That might cause all sorts of strange things to happen. The smart thing to do would be to get an adjustable push rod and check for the optimum length, and see if yours are at least close to that.

Ukraine Train

ok guys, i think i may have really screwed myself on this one. I went to summit tonight and picked the new pushrods, stock length for my engine, 7.20". so i pull all the old rods out, here's the count: 5 bent, one broken and two unbent intake rods; 8 unbent exhaust rods. at this point i felt a brick in my pants. i think the intake valves, being bigger than exhaust, hit the pistons, bending the rods. on the two cylinders with unbent rods i think the valve might have gone through the piston. the only abnormal noise i ever heard from the engine was ticking which i attributed to the pushrods not being tight enough.

the engine is a '91 corvette L98 with guide plates, head gaskets are .039 thick iirc, i've heard stock is .050. i know the chamber is smaller than an iron L98 but is that due to the surface being milled down or a different chamber shape?

i'm gonna go pull one of the heads now i think and see what's up. man what a crappy day.

Ukraine Train

after some surfing of the board i decided the valves didnt hit the piston. my current theory is that the retainers hit the positive lock seals on the intake sides, there were impressions of the retainers on the tops of the seals. i thought that there would have been more damage to the seals if they got hit hard enough to bend rods though. the umbrella seals on the exhaust didnt show any signs of damage. what i'm gonna do is pull the springs on the two intake valves that didnt bend the rods and see if those have impressons on them.

89BlueTA

The machine shop I used cut the valve fuides to clear .850 lift, I think they messed up the first cut and cut a little more off. But I have not had any problems so far. .495/.503 lift.

good luck

nick