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

Or, if the fastener just isn't up to the task of the upward and torsional load placed upon it by the exhaust rocker hanging off the end of this shaft. On the stock rocker shaft, there is no torsional load, and the fastener is stronger..

 

I'll post it one more time, the fastener is rated for 7,340lbs proof load. That is right off the Allen Manufacturing Company cap screw card. There could only be torsional load applied to the point that the bolt broke if the shaft was able to wobble back and forth, virtually impossible unless the shaft mounting surface was machined warped. Even so, if torsional load was a factor, SBC folks wouldn't be able to keep their 3/8 studs standing up straight. With that out of the way, we can only contemplate leverage, as a function of distance from the point of failure. Let's for sake of argument say the valve is totally frozen stuck closed (or binds from guide clearance issues and/or spring bind as mentioned before). The rocker arm has a 1.6 leverage ratio, so it would still take some 4500lbs of force (at the pushrod tip) to pop the head off. Even with the exhaust stud being out toward the end of the shaft, we're talking about a massive spike in force. I'm amazed the pushrods or something else isn't failing too.

My point is that like Devon and others have said, something unusual, or too tight on clearances etc, is causing this. A bigger bolt might hold up a bit longer, but doesn't address the cause.

 

Bill made over 1000 hp and ran 8s in the quarter with his BUick 350 using the TA roller rockers so I think that these engines should be safe at the roughly 550 hp Jay was at. No reason that the Burton conversion would not handle 550 hp in my mind.... I guess we will find out when Bob M`s son gets some track time and miles on his 600+ HP Buick 350 witht he roller rockers. I think he has already ran over 20 dyno runs on it.

I know Jay had problems with the other head, however after getting it back together it has not failed even after bending the plate back... On that failure the bolt loosened off right? Then the plate bent? Then after all that and bending it back he has had no more trouble so I think the sysytem is working well except on that side that recently broke...

If the whole sysytem was bad then why are all the other valves not busting the bolts on the plate?

 

My thoughts as well. If there was a chronic problem with materials or design or both, I'd expect to see signs of failure on all four corners of the engine, all else being equal.

Devon

 

No.. It just broke.. Still had to use vise grips to get the remaining part out..

In both cases it has happend on the front or rear of the head and has broken right at the end of the taper of the screw.. Leaving plenty of it poking out to remove..

 

So far we have two corners..

 

Sorry Jay, I must have misunderstood...I thought this go around was a repeat in the same spot as the last. That's even worse news in my book.

Devon

 

Yep.. The spot I bent back on the pass. rear was still holding..

 

I think were really close to the answer here..... This is why i was interested to see pictures of the breaking point, so we could do a failure analysis on the bolt.


My hunch is, the bolt at the end is not breaking off in one shot, its probably breaking off due to fatigue or chatter or something, then leverage is doing the rest.

Mark im with you on this one, we are all so focused on the amount of force and pressures going on here, but im stunned the pushrods are still ok. If i understood this correctly, the failure has occured on the same spot, but the last time it was on the opposite head which is on the other side now and still holding. Id be suspect of the valve geometry in the failure spot. Is the block square? Is the lifter still good? that sorta stuff.

 

I don't have a way to get you pics of the bolt that are close enough to make an online decision...

You are correct about this being the second failure at an opposite corner..

It is waht it is. I knew going it that I was basically the R&D guy on this. Yeah.. It made some dyno pulls.. So what.. I've been full boost for 30-40 minutes on this setup. How many dyno pulls is that?? I balooned the TC also. It's making a little power.. Probably a good thing I pulled this all apart..

 

Sorry to here that this is not working out. Try checking some things.

How much valve guide clearance does the exhust valve have on these heads?
If they are too tight it will cause this type of a problem. Also check for spring bind. If the springs are too soft and a valve will hang open and bounce, pushrod drops out of cup in rocker. Check tis out at the machine shop.

what is interesting is that race cheves use shaft mount rokers to get rid of these stud mount setups.

Dan

 

Here you go Jay

http://www.racingjunk.com/category/...390/SB-Chevy-1.5-Shaft-Mount-Rocker-Arms.html

Dave

 

Well where do I start. My car will go for long periods of time without breaking any rocker parts. Then all of a sudden it will break two or three parts. It has broken rocker cups, It has ripped the rockers right of the shaft. Hell it has broke the shaft once. It has done it on exhaust. It has done it on intake. every time it has been a different cylinder. Once it broke a rocker cup, then I let the car cool down and replaced the whole Assembly drove it two blocks down the street without ever getting the RPM's above 2000 and it broke another Rocker on the other side of the engine. Then I took it home fixed it and didn't have any more problems for a long time I think I drove it for 6 months and raced it 3 weekends before It broke a rocker again. Matter of fact here is a link to a post I made looking for roller rockers stating that I have broke the rocker Assembly many times. http://v8buick.com/showthread.php?t=213877

I am running stock heads with stock parts.

 

Would that fit??? Somehow..

 

Hmm. This is very interesting if this photo works..

http://www.probeindustries.com/PhotoDetails.asp?ShowDESC=N&ProductCode=11317

With this setup you could use a larger 3/8" grade 8 hex head fastener.. And then with this secured to the plate it would really stiffen things up..

That would mean fabbing up two more plates though..

 

:idea2:

 

In the end I believe you will find that something is hitting. Tubular pushrods, as long as they are straight, can take an incredible amount of pressure and abuse, but the symptoms as you describe them indicate that contact is there but the give in the valvetrain is enough to keep parts from breaking, usually. Then, when everything stacks up just right, with the right temperature, engine load, and lifter pump-up, something gives. That is what we were seeing in the 215.

You might try removing the timing chain and cranking the cam over by hand. (there should be a crank position that allows this without hitting the valves, where all the pistons are down somewhat in their bores) I don't know that this will do it, after all, without oil pressure the lifters will begin to bleed off and we're talking about very small clearances. But how much clearance do you have between the spring coils at full lift? Are you seeing any damage to the valve seals?

JB

 

I don't think there is any binding going on although the turbo'd engine may put more strain on the rockers than a normally aspirated engine with a comparable cam. But, neither of these guys is running a big cam, big boost, or high rpm compared to the Brand X cars that have troubles. Heck, who hasn't broken a stock shaft or rocker? If you haven't you haven't been at it long enough. Lots of times a used stock rocker gives up because a cam with more lift has been added which moves the rocker into positions it has never been before which takes it out of an area that has been work hardened.

It is obvious to me that the 5/16" flat heads are just plain being fatigued. Look at it this way. Chevy decided that each rocker needed a single 3/8" stud. The way the plate is made TWO 3/8" studs are now being held upright by ONE 5/16" bolt. The reason the end bolts break first is because under normal conditions the inner two bolts are being "helped" by the bolts on either side of it. Even a stock rocker shaft is the same way. Usually when a stock shaft breaks it is the outer one right at the bolt because it has no helper bolt on the outside.

When you want to break a long piece of metal what do you do? Keep bending it back and forth. In this case imagine if that piece of metal is the 5/16" flathead which continues up to the tip of the 3/8" studs. The pivot point of this lever is right where the 5/16" threads go into the head. At that point it can't move. However where the rocker is attached can and also the ends of the plate. It may be only rocking back and forth .0001"(or less) every time the rocker moves but it is doing it 1000's of times.

I did some drawings to show what is going on the way I see it.(Not done to any scale.)

Dan said it, guess what Chevies do to stabilize their rockers? Shafts! The only weak spot in the Buick shaft setup is that the outermost rocker doesn't have any outer support. In some really HP Chevy setups that use the stock studs they have a support girdle that connects all the 3/8" studs together. Now think of what that 5/16" bolt is going through again.

The Chevy shaft system is possible but the original idea here was to have a more cost effective solution to the expensive HP Buick rocker setup.

The only cheap solution is to get larger stabilizing bolts into the head on either side of the 5/16" locating bolt.

 

That was my thought but I got chastised for it. Simple physics.

 

I admitedly have a pushrod that is so slightly bent that I had to put it on glass to tell.. But I drove this with sh*t banging around in the valvecover for 30+ miles.. I had to pry the oil cap out..

I've brainstormed with others about a fastener outboard of the last rocker and come up short. You opinion is the same as I expressed at the start of this thread and has been conveyed to me by others confidentially.

Geeze.. That's what happens when you go outside the box. Sometimes you hit a home run, sometimes it doesn't go so well. My hat is still off to anyone that tries to design a better mouse trap.. Guys.. I still love you.. Maybe others will have better luck with this setup.

I still think this basic design will work with some tweaks.. Remember my exhaust lift is less that a TA 112 cam..