wrd1972

Well, I fixed my 5.5K RPM stumble, it was the ICM.
To celebrate I went out for a very spirited country drive. I made several 1/4 mile runs and on the way home just driving a normal 55 MPH I hear a loud banging noise.

The rev limiter is set to 6000 and the push rods I am using are Melling hardened rods that I got at Autozone when I did my LT4 spring and RR install.

I instantly knew it was somthing in the valve train. I pulled the cover and one exhaust roller rocker is cocked at an angle.

The rocker DID NOT come loose, I guess the push rod slowly bent over till the RR was unstable. After removing the RR I saw damage on the arm next to the roller tip, the guide plate is severly worn away and the tip of the valve is slightly beveled on the edges. I drove maybe 2 miles under these conditions to get it home. I also used a magnetic retriever to as many metal shavings out of the head as possible.

Here are some pix:





I smoothed out the damage on the RR, the tip spins freely:


My questions:
1. I know the guide plate is toast, but can a still use the re-dressed RR, or will Comp cams sell me just an individual?

2. What are the chances the exhaust valve is bent?

3. What are the chances the lifter is shot.

4. If the valve is NOT bent, can I still use the valve if the tip shows slight surface blemishes?

5. What exactly causes this to happen, rapid decell at high speed, other?.

6. What are the most reliable push rods that will not do this.

Black_Z28

I had this same problem last summer after putting some RRs on my car.






1. I know the guide plate is toast, but can a still use the re-dressed RR, or will Comp cams sell me just an individual? Comp does sell a single. I bought mine from Tunder Racing for something like $30.

2. What are the chances the exhaust valve is bent?
Mine was not bent, as I have put about 650 miles on the car and it has been fine. It could be different with yours though. The only sure way to find out is to remove your head and check.

3. What are the chances the lifter is shot.
See #2.

4. If the valve is NOT bent, can I still use the valve if the tip is a tad beveled? Not sure on this one.

5. What exactly causes this to happen.
Mine was caused by a loose rocker.

6. What are the most reliable push rods to ensure this does not happen again.
I guess just making sure that your rockers are set properly.

Guest47904

Look very carefully at the ratio. When I got my box of 1.6's from comp, one was shall we say not the same. If it was accidentally a higher ratio, it could have been in bind causing your problem.

wrd1972

The damaged RR is stamped 1.6.

I am very confident the rockers were set correctly. They performed well and ran quiet for several thousand miles. I seriously hope the valve and lifter are good, I dont want to yank the engine apart.

My plan is to replace the parts and fire it up and see what happens.

What are the best push rods?

Joe B

The Comp Hi-Tech pushrods are one of the best...summit has a pretty good price on them(about $130ish If I remember right).....they're a 4130 chromoly one piece pushrod with 80thou wall thickness in their thinnest spot.. Also, by their intended design, they give off less harmonics as we'll .....A high quality pushrod like these(and obviously some others) are really on a whole different level when compared to a regular advertised "hardened" pushrod....IMO, and experience, half of the hardened pushrods out there are nothing but cheap junk that have went thru a minimal heat treating process that dosn't add up to much (Point being, you get EXACTLY what you pay for with pushrod quality and strength)..........This "isn't" directed at anyone here one bit....but I could never understand why it is that so many people will spend thousands for highquality parts elsewhere and then buy some 35-50 dollar pushrods to be the structure for the whole valvetrain.....all I can think is that they don't understand the extreem conditions that a pushrod is under at 6000 plus RPM's.

wrd1972

Well said, i paid $40 for these. I will get the chromoly comp cams push rods tomorrow.

String

Hate to say this but it looks like that exhaust valve tip is rounded. If so, you will never get the rocker to stay centered.

Are you running into coil bind? How is the goemetry? Has it been making any strange noises? I would also suggest replacing that rocker. I think that you can buy them individually. I also agree. Buy cheap, buy twice.

Joe B

If it is too rounded.... a set of Lash caps should take care of that......

wrd1972

I dont think there is any coil bind. The tip of the valve is slightly "mushroomed", however it appears to be roundly uniform. I can also see excessive wear on some of the other guide plates. Starting to look bad.

What is a lash cap?

Joe B

A lash cap is a small hardened cap that you press(by hand) onto your valve stem tips......they can be used to protect your valve tips from wear as well as changing rocker geometry on the valve side, instead of the pushrod side of things......but in your current situation I would use them since your tip is a little mushroomed like you mentioned.....this will basicly give you a nice perfectly even surface (which it needs) for your roller rocker to ride on....they go for about 35 to 60 bucks for a good set of 16 from comp cams, crane, ECT.......www.summitracing.com then search for lash caps

Zeueses 97 RamAir

looks like a defective rocker I went with full roller shaft mounted rockers go to whiteperformance.com there shaft mounted 1.52s I didny=t want to put anymore stress on the engine r valvetrain...

wrd1972

Clearly what is going on here is the roller tips are running off center due to excess GM guideplate wear. This one guidplate simply was so bad the roller tip fell of the valve. I can see at least two more areas of concern that appear to have excess wear.

I am going to go ahead and get some lash caps, they are only $30.00 or so, you guys seem optimistic they will help.

What would cause these guide plates to do this to happen?

HardcoreRM125

There could be a few things that could cause it.

When you tightened down your rocker arm studs on top of the guide plate, how did you tighten them? You had to do one at a time and take them up slowly to the recomended torque. Do like 10-10-25-25-40-40-50-50 as you torque them down. If you just crank one down to the 50 ft lbs, then crank the other one down, it could pinch the guideplate and rotate it a tiny bit. You really have to watch how you tighten things as your torqueing them down for internal engine parts.

Also, using ****ty pushrods could do it too. They could be flexing so much that they are causing the odd wear on the guide plates. Go with ISKY Adjustables, their a great guide plate. High wuality. Adjustable. Simple. Slightly agrivating to set up as they are free to float to the left and right, but overall, they are sweet.

1racerdude

Ya probably don't have enough spring pressure to bend even a SOFT PR much less a 5/16 heat treated 4130 set. Something happened,either the valve hit the piston or the rocker came loose or the guide plates were not installed in line or the spring coil bind.
If ya get lash caps they will be about .060 thick and you need corresponding length PR's. Ya need to check your geometry and make sure that is correct also. That could/will lead to just what is happening.

ONLY GM guide plates will work on stock heads.

wrd1972

So what is the rule on push rod length if get the lash caps.
Do you simply increase the length of the rod proportionally to the height of the lash cap?