History repeats itself. The turbo car is broken again and will be for a while..

He's using a Chevrolet rocker conversion, which is the plate.uzzled:

 

Is that the Mark Burton conversion? I'd like to hear his views on the problem.

 

I am a little sceptiical about the plate needing to to thicker, and the bolts should be more than adequate.

Bob did some testing and things seem nice and have at over 600 HP.... Time will tell, however he has had no issues.

There are some good pics here:

http://www.v8buick.com/showthread.php?t=149569

The procharged 350 with this rocker conversion:

http://www.v8buick.com/showthread.php?t=200499

 

i dont disagree that higher spring pressures are needed with boost. BUT. Seans post said as i quoted

hp has nothing to do with the spring pressures, Boost or pressure against the backside of the valve does as well as camshaft requirements. i was just maiking an observation and not intentionally picking on Sean.

 

Seems to me the boost/something else/ is causing the valve to close too soon,which is causing the bent parts problem that he is having. The plate looks plenty thick. There has to be mechanical solution here, just need to be figured out.

 

My thoughts EXAXTLY.. Flexing and breaking. It's the original thread size, and there is 1/8" between the bottom of the rocker and the flat bar, which is 3/8" thick..

 

That plate looks pretty stout, could you machine a small recess (1/8", 1/4"?) in the plate for a standard bolt head?

I still like the idea of openning up the hole and heli-coiling the next bolt size up in there. 1/8" clearance doesn't leave room for a vertical brace on there.

This might be obvious, but because I've done it I have to ask. Are you sure the bolts on the plate are not too long? Two years ago I used bolts just slightly too long on the stock rocker shaft, everything was tight, looked good, then the shaft cracked and bent. Turned out I bottomed the bolt in the hole instead of tightening on the shaft.

 

I will try to answer all of the questions here..

I only have one part of the bolt right now. My camera won't take a close enough picture to tell anything..

BLUE Threadlocker was added to the screws from the manufacturer, and they were tight going in. I have 8 more of them.

I did not get a new plate assembly last time, I straightened it. But it is on the other head..

Sean. The quote above about me missing the locktite was in reference to the studs/shafts..

I will update the springs when the heads are off.

It's anyones guess why this is breaking, but it seems to me that stronger springs would only cause more stress on the area. The engine revs very cleanly to my 5000 or so shift point.. It just needs to be more firmly attached to the head at the ends of the bar. The stresses in the center two attachments are much different than they would be on the end.

 

I guess I can pre-face this with "I'm no engineer, and I'm a mediocre engine assembler at best" but I think the concern on springs is mis-leading as well, and stiffer springs would only complicate the problem unless harmonics are indeed playing a factor, and I'd think power would be dropping off substantially if the valve was floating.

When apart, I'd run one bolt in with the plate removed just to be sure it doesn't prematurely bottom out.

 

Just checked thread depth on the one hole that is open and I have 1/4' to spare..

The fasteners I used are at the bottom of this page.. #84254

I picked them because the were manufactured to ASTM F835 specs.. Whatever that means. Perhaps someone can pick a better fastener. Was told not to use stainless and could not find Grade 8

http://www.fastenal.com/web/search/...ket-cap-screws/_/N-gj4wbuZjuevz3Zjue0jq&Nty=0

 

Jay, that sucks bad. I think that there is something going on that is stressing the valvetrain unusually. Maybe pushrod length causing the rocker arm to be tipped back too far? James went through a lot of valvetrain trouble too (not with a roller conversion) and broke several rocker arms. He concluded (I think) that the valve seats were too far in the head throwing off the rocker arm angle.

Here's my $.02 on some of the suggestions. First, DON'T cut a recess in the shafts and use a standard bolt. The flathead fastener locates the shaft due to the taper, and adds off axis stability by spreading the clamping force out toward the perimiter. Here is some info about the shaft flex from Bobb at Finishline...

So guys I have read there was concern about shaft flex so I decided that I would do some testing to see what we could come up with. First I put a valve in place and locked it down. Then I installed the rocker arm. Once that was done I put my on head valve spring tester on it. The more you pull the more pressure it will shoow lbs it takes to move the spring. But with the valve locked down it will pull on the end of the shaft just like if it was running but worse because the force will be focused on the end of the shaft. I installed an indicator to give me a reading on movement. This is what I found.

100lbs 0 movement
200lbs 0 movement
300lbs 0 movement
350lbs .0005 movement
400lbs .001 movement

I did not go any higher due to that fact there isn't much point in higher than that unless you are going to run a roller and at that point you need to look at the higher end set up. But I really feel that this is a great budget minded set-up and shows no major down falls that I have seen yet I will run this set-up and pound it hard you can count on that.

It should also be noted that Bobb's testing was of the original prototype plain steel shafts. The production parts are a higher grade tool steel, and are thicker, as well as have added meat due to incorporating the pushrod guides.

In short, the shaft isn't the weak link. This is just the opinion of 3 other machinists though.

Jay, one thing that pops into my mind is when you do get it apart, make sure the bolts aren't bottoming out in the head and the top of the cap screw sticking up at or near the thickness of the plate. That would prevent them from fully torquing to the plate. Also, make sure not to over torque them. I supppose going to a larger bolt is an option, and will add some beef to the bolt, but may also weaken the shaft some because of the larger hole and countersink. The proof load for a single 5/16 cap screw is 7,340lbs. Something unusual is causing it to fail.

 

Yeah I wasn't looking at the pictures correctly, I thought there was still part of the original head centering the plate, wasn't until I looked at the link to the screw I see the heads are tapered. I retract my recommendation on putting a recessed bolt in it. I'm out of ideas since it's not bottoming either. =/

 

Did you ever get in touch with a rep per your earlier thread? I'd ditch the nylon button feature and find out if they have another 5/16" fastener with a tensile strength greater than the 145,000 psi min for the one you chose. I'm also going to say ditch the threadlocker and use a decent thread lube, including under some smeared below the conical head and the countersunk plate. A lot of torque can get eaten up due to friction there.

Devon

 

Mark.. I checked the thread depth on the open hole I have and it's plenty deep assuming all are the same..

I wonder where Bobb checked the flex?? The very end of the plate where it hangs off unsupported would be far more likely to flex than any others..

The heads were assembled by an EXTREMELY knowledgeable Buick guy with 30+ years of experience..

The pushrods are just 39 year old stock stuff off an engine that appeared to have 40 years worth of gunk in it..

 

No.. I never actually called them, but I will be now..

 

Flex discussion: http://www.v8buick.com/showthread.php?t=149569

Devon

 

I am not truly sure the amount ...but do you not have to machine off the stock tower to accept the plate ?
Is this an exact amount ?....Could it be that the geometry has changed enough for the given length of pushrod you are using that it is causing the plate to " rock " the top of the tower surface to marr to a convexed shapethus causing over stress to the bolt itself.

 

mhgs, I wondered about that too. The amount machined off is .800", but isn't too critical because the adjustablility of the rocker arms covers the height variance. It is mostly just clearance for the rockers fulcrums. Only the pushrod length in relationship to the valve tip height would impact the geometry.

The rocking could happen, if the machining wasn't perfectly flat. It would take an absolute hack of a machinist to screw that up though. I suppose the flat that the shaft bolts to could be checked with an indicator to see though. That would gives us something to check off the suspects list!

 

I agree....what I am wondering is the amount of difference between using a "stock" length pushrod versus what you are using > Thats where I am not sure as I dont have knowledge of your stuff. BUT with any length change there is going to be a change in geometry....so..???

 

Looking at it all, I would agree that the plate is thick enough, especially after seeing the flex test results. I don't think I have ever seen the flat head cap screw like that with the nylon patch, but I'm assuming that it is there to retain the screw in the threads, like the nylon lock nuts. In that case, yes, they would go in tight, and you shouldn't need lock-tite on them.

As far as straightening the plates, personally, I would advise against it. Once you've stressed the metal, you just run into all sorts of problems. I would suggest replacing them.

The only thing that I can think of right now, is that with the flat head cap screws, you really have to start each one and just barely touch the countersink in the plate, and then just barely back it off, and then do that with all of them, and then go through and snug them down to locate and align the plate. Once they are all snuggled down, then take one off at a time, lock-tite it, and then torque it down. Then do the same with each one, one at a time. That is the only thing that I could think of that *might* cause the problem you had, was if the plate was misaligned slightly. When that happens, the tapers don't line up correctly, you run the motor some, vibrations shift it enough that the bolt loosen up, the plate bends and the bolt breaks. That's the way I see it.

Mark, when you machine the pedestals down, did you have to drill new holes for the plate mount bolts, or were there still existing holes that you may have had to drill deeper. My thought is if you had to drill fresh holes, that there shouldn't be any mismatch problems, but if you just deepened existing holes, that there may be some original GM machine tolerance stackup from cyl head to cyl head, so that if you make the plates identical to each other, then the bolt holes won't line up the same from head to head. Not criticizing or blaming, just throwing out some thoughts. Hopefully, we can all get this figured out. I for one, would like to know just how much power can be made with the turbo setup.

By the way, how much run-time on the motor before the problem hit?