Hi, I have a 1994 corvette. I had the engine rebuilt and since then I am having problems with my rocker arm studs snapping. I keep taking it back to them and they keep replacing them. It's snapped 5-6 rocker arm studs and I am getting frustrated. I took one of the push rods out and compared it to the push rods that were recommended to me by summit racing and the push rods they put in are about 1/16" shorter than the rods I got from summit. Could this be the problem.

I've read in other threads that many times studs snap because they are overtightened. I will make sure on Monday when I take it back in that they are not doing this, but I am curious about the push rods since there is that difference in length. Right now I have comp cam 1.6 roller rockers in there. Those seem to be snapping the studs more often. I had stock rockers in for a while and the car was fine for a about 200 miles. But ever since they put the 1.6 rollers back in I can't go more than 10-15 miles before I have a stud fail on me.

Do you guys have any idea? I have a 510 cam in there so maybe that is the culprit. I never had a problem with rocker arms snapping before the rebuild and it had that same cam in there. So It is something they did or are doing that is causing this. I heard that push rods being too long would snap the studs but would push rods being too short do the same thing?

Thanks for reading.

 

If you are running stock heads then .510 lift is too much and you are probably getting coil bind or otherwise bottoming the valve springs. I am coming from an L98 but I believe I read that the LT1 heads can't take more than .500 lift stock.

 

I heard something like that before, however, the corvette ran just fine, never having problems with rockers popping off before the rebuild. So something happened while they rebuilt the engine to cause this problem.

 

You can easily go over .500 lift on a stock LT1. Its the stock springs that can't take anything over .500 lift. There are a lot of variables involved here that probably go past my knowledge base but for a start I would look at these:
1. What cam are you running. You say a 510 cam - do you mean a Comp Cams 305 with .510 .510 lift? Or something along that line?
2. If that is your cam, what springs are you using? Comp recommends
these-
http://www.compperformancegroupstore..._Code=26915-16
and these -
http://www.compperformancegroupstore..._Code=26918-16
Check what springs they installed.
3. Which rockers are you using. Full rollers are usually too wide for the valve setup on the LT1 and rub. The Crane Cams rollers that were used by the factory for the LT4 were a narrow body and fit. I think also the Scorpions are narrow body and fit also.
4. If you are using the roller tip rockers from Comp I think there was a problem with the bottom slot being too small on some that were produced at one time.
5. On the stock engine from the factory the head gaskets extended into the lifter valley. They have holes that the pushrods go through and seem to act as a pushrod guide. Pull the valve covers and take a look.
6. Make sure your engine is using self-aligning rockers.
7. If you are using full roller rockers were the drip tabs trimmed on the valve covers? They have to be trimmed for proper operation of the rockers.
8. Have you checked the pushrods for straightness? Get a piece of plate glass and roll them one by one across it to make sure they are not bent.
9. I don't know if your pushrods are too short but if they are too short maybe you are bottoming the hydraulic lifters after adjustment - could it cause a "shock" to the valvetrain and break the studs? IDK but more knowledgeable members can probably tell you.

That's all I can come up with now.

 

If you are not comfortable doing all the good suggestions you got, then the first thing to do is find a different mechanic. This should not be happening and something is or should be apparent to a good mechanic. Valve to piston clearance is a major cause of broken studs along with coil bind but valve to piston clearance is the only thing not visible and other problems should be easy to spot. I would definitely not drive the car, you could end up breaking off a valve and that is major disaster.

 

Yes.

 

Are you using ARP studs? ARP should not break.

 

I think your problem is a few things.

First, you absolutely have to have the correct push rod length. Purchase a push rod length checker tool, remove a rocker arm, get a black magic mark and coat the tip of the valve stem with ink. Put the rocker on, adjust the valve, and crank it. You want to have a wear mark directly in the center of the valve stem tip. You'll be able to adjust the push rod length checker to find this out. Measure the length checker and order that size push rods.

Your valve springs are another thing. Someone else posted about those and that is also very important. If your coils are binding, it not only puts a strain on your valve springs but also a strain on the rocker arm stud.

As for your rocker arms, they had also mentioned rubbing, you don't want rubbing and you don't want it to hit the valve cover. If you are going to use NON - SELF ALIGNING rocker arms, you need to use push rod guide plates. To identify the difference, the self aligning should have a fin on each side of the roller tip, non self aligning will not have that.

 

Has your mechanic verified that the slots in the rockers are long enough that the ends of the slots are not touching the studs, either when the valve is closed or at maximum lift? Are the studs always breaking at the same height from the head casting? Where are they breaking?