I recently lost cylinder 1 due to a bent exhaust valve. Sent the heads back to ARE for warranty work. The existing springs have 115 pounds of pressure on the seat, when they were installed there was 125.

I am not sure what caused the valve to bend. I have not missed a shift or did any 3-2 or 2-1 type of accidental shifts that would lead to a mechanical over-rev. I have not hit the rev limiter, set at 7k either.

Upon inspection at ARE, they said I have 5 bent valves?! They then asked me what I have done to the motor, what I have changed etc. I have not changed a thing. I only had the passenger side valve cover off one time to look at the shiny new yella-terra's, and did not take any off.

The tips of the valves were also worn funny, like the 'wipe' pattern was not quite right.

Could a batch of 'bad' valves be the cause? Not sure what could have caused this. I am concerned because I do not want it to happen again.

Here is my setup:

422 (4.100 x 4)
diamond -7 cc dished pistons
6.125 rods
7.4 hardened pushrods
248/248 .345/.345 @ 110+2
1.8 Yella Terra's bringing lift to .621/.621
I believe the springs were comp 977's, possibly 987's. They had a red stripe on them.
LS6 heads with ~ 62 cc chambers. 2.055/1.57 valves (ARE says these make more power than 2.08/1.60's on a big bore motor?!)

ARE is replacing (under warranty) all the springs with Patriot Golds (I think), and new valves also. I am concerned what caused it, and that it may happen again.

The funny thing is, the car was 'fine', I drove to my parents, washed it, ate lunch etc, then when I started it again, it was missing bad.

 

If the wear pattern was not centered on the valve tip, look at the valvetrain geometry, especially the pushrod length.

 

piston to valve contact bends valves.
inspect your piston tops very closely to see the little smile shaped markes where they touched.
Cam being out of time can cause this kind of contact, as will valve-float.
That's the main cause of bent valves.

The only other very remote possibility I could think of is if rocker tips where going off the side of the valve tip due to bad geometry... and even then I doubt it would bend the valves.

 

"248/248 .345/.345 @ 110+2
1.8 Yella Terra's bringing lift to .621/.621
I believe the springs were comp 977's, possibly 987's. "

I didn't see this part at first.
Long duration with high lift can cause piston/valve contact. that's why a lot of people fly-cut valve reliefs into the piston tops for clearance.
You may have been running closer than you thought.
Did someone mock up your engine with clay on the piston top and test for clearance with the valves before you fired it up?

If there was NO piston/valve contact, then I'd look towards the rocker geometry being off with those stock length 7.4" pushrods.
Converting to the rollers may require a different length.

 

i would lean to p to v clearance issues

 

ARE built the motor. It has valve reliefs in the piston. There is a mark on piston one where the exhaust valve hit.

I am not sure if they did a clay mock up.

 

ooopsie, no wonder they are fixing it under warranty

The easy way is to just get the reliefs recut in the pistons to a point that works. You can guess on where and how deep to go, but clay mock-up is ideal IMO. There's no substitute for bolting it together and measuring actual clearance.
I'd triple check the cam timing first though.

 

I remember them telling me that there should be plenty of piston-valve clearance. I wonder if a clay mock up was done.

 

with 7 cc reliefs? I find p-v clearance pretty sufficient even with a 248 duration cam. I would think it is builder error.

Nate

 

I just got off the phone with Nick A. ARE is changing all the valves, all the springs (to Pat Golds), new retainers, new valve guides/seats etc. He said all the hardware is going to be replaced.

I think when the motor went together, the heads were not 100% and just got bolted on. He saw conclusive evidence of valve float in the seats. I had had problems with my 346 setup, and it seems the heads just went together in a flawed state.

I am happy with the actions taken to correct this, and should make a bit more power too with no valve float! ARE has honored the warranty and have a happy customer.

 

you have to remember that he is using 1.8 ratio rockers bringing lift to .620

 

Greg, are you sure you are calculating the lift properly? I think you mean the base list is in the 500's right?

I run a 236/246 cam and the exhaust lift is .632 with 1.7's, but I know the GM cup cam has big duration and low lift, but I thought it was in the 550 range.

 

PSJ, I think your cam would be .371 base lift. The GM cup cam may sho .550 but that may be with the assumption of a 1.7 rocker arm ratio, which is what is standard.

 

I am assuming you are talking about lobe lift, PSJ.