Although I have no hard facts as to the 2 failures this year, I was offered 2 good suggestions.

1. A valve hung up in the guide when the engine heated up (possible but not likely).
2. My choice of valves was wrong and the high lift cam and strong springs was just too much for the valves. The extreme forces slamming the valves closed actually broke the heads off the intakes. This sounds like the best reason so far for the failures.

The valves were a Manley offshore brand. Not true Manley valves.

My new Merlin heads will have good valves, springs etc so it won't happen again.




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87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

 

Hmm, The first seems fairly unlikely to me, Unless you were using a valve with a larger stem diamter than you should have been, but even then I wouldnt think it would cause that sort of instant catastrophic failure.


The second Sounds like a Winner, What was the rate on the springs you used ? It would be interested to know for future referance. Did the Valve manufacture give a rating of acceptable spring pressures ?

What may be interesting is to Look at the fracture on the valves themselves, and see how they broke, perhaps have one alalized by a materials engineer, if your that interested




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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver 14.82 @ 91.1
Reader's ride -> My Ride

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

Unknown rating on the valves. Springs are Comp 924. The ones recommended for the XE294-10 cam. 317 lb/in spring rate, 125 lb closed, 315 lb open.

The only parts of the valves that I have left is the head of an intake that's stuck in the head of a piston. You can't get a good look at what's left of the stem but it looks like a clean break. Pretty hard to tell after it was beat up inside the combustion chamber.

 

Any Idea When it broke, IE RPM wise ?


This was on the first Run, wasnt it ?


Was it the first Loaded WOT test of the Motor ?

it just " breaking" like that would Make sense, but only if it was the first time it was put under stress.


Those are some Hefty springs, but dosent seem like enough pressure to Clean snap the head of the valve off... But of course I am far from an expert here... or anywhere



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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver 14.82 @ 91.1
Reader's ride -> My Ride

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

1, Have you thought about calling Manley to see if they have anything to say?
2, Were/are the stems undercut?

What you are describing sounds right. When the valve slams closed it contacts the seat all at once. That would cause the break to be fairly clean and perpendicular to the stem.

 

The valves were an undercut style.

The first failure I was able to get 6 passes down the track. The second failure I only got 2 then blew up the engine working on it in the pits.

 

well, i can shed no light on your problem.. but thought i'd say sorry to hear that, I know its got to be dissapointing having it happen.. good luck finding the culprit

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• 83 Z28-- not a pretty site to look at, 200k miles and im sure it was treated like a rental car every day of its sad life(before i got it).. sold, thank the lord
• 74 Z28-- 383/400, green on black. pretty clean. FOR SALE!!!

 

Finding out what happened will probably never happen. The machine shop is rebuilding the bottom end this time and installing a set of Merlin heads. When they're done, all I'll have to do is install my intake, oil pump and pan, valve covers, and all the rest of the external attachments and it'll be ready to go. If they say all the machine work is correct then it shouldn't happen again. The machine shop is also changing the springs in the Merlin heads. The supplied springs are only good to .570 lift and my cam goes to .593. Sounds like a lot but it is a big block.

Other than the new heads with valve components, the engine also gets new push rods or at least replacing the bent ones and I'm switching from Crane Blazer rockers to Golds. The Blazers are cheaper but the trunion is also weaker. I'll throw the Blazers on my truck some day. It never gets above 5500 rpm.

 

I am assuming this is on your 454 big block. What size valve did you run. I am guessing right now that you jumped up to the L-88 valves. If so, I think you don't have enough spring tension. I have ran more pressure than that on small block 2.02/1.60" valves WITH undercut valve stems. Only problem I had was still encountering valve float at a little over 6000RPM. Given the heavy L-88 valves they would have probably floated badly at 6000RPM. Comp Cams seems to be using fairly light springs to be honest. Combine a marginal spring with a larger set of valves and next thing you know at 6000RPM its losing a valve.

Also...if a guide would have seized up hard enough to cause a failure it would be obvious looking at the guide and stem. Look at the other valves, chances of just 1 locking up bad enough to fail is small. The others would show scoring and problems. Never heard of this actually happening.

To back my spring claims I went to Crane. Crane has a little bit milder hydraulic cam listed, a few degrees smaller and about 0.010" lower lift or so. The recommended springs on that cam are 99893's. 165lbs on the seat and 426lbs open. Valve float sure will end an engine quickly, and is far more likely than breaking a big block valve under the sheer force of 300lbs.

[This message has been edited by Grand Prix (edited June 26, 2001).]

 

It doesnt sound like the springs are all that stiff, but you never know...

A long time ago, I was sitting in my dads cousins' (Dale) house watching TV, other side of the house from the garage. He had just finished up his car (32 Plymouth coupe) and was ready to fire it up. My dad was in the garage with him, and the car was so loud I couldnt hear anything but the car... and I was 80 feet away. Somehow through all that noise, Dale heard something and shut the car off right away. It snapped one of the valve heads clean off, took out a 59 Hemi head, and one of the pistons. It was an undercut swirl polished valve... IIRC it was a pretty new thing at the time. I see things havent changed much in 25 years.

May not be it, but I have seen the end results...

BTW, Dale swapped to a new head and NO undercut stems, and never had it happen again.