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

And so how does that make the fastener break???? And how do we know it isn't closing?? If it weren't closing it would ignight the unburned fuel in the intake and makle a big boom?? Right..

 

well if this is the problem. im sure there is something to cure it. unless your not having this problem. common sense to me would be a higher spring pressure. you might need some tips from a turbo guy. i was just throwing that out there.

 

I'm guessing maybe you didn't read the first post..

 

I am not trying to say that you need mega spring pressures however I do know that the stock springs at 40 years old are in no way suited to handle performance use let alone boost. if the valves were slapping around it could not be easy on the cam, lifters, or rockers.

I know I had terrible valve float with my 350 on the dyno, it was giving up at 4600 rpms and after valve spring swap it was peaking at 5600 rpms and this was under 400 hp NA.

Quoting from David Vizard's book:

"Take the area of the valve multiplied by PSI of boost and add 2/3 of number to the normal required valve spring seat pressure that the cam you are using would require when naturally aspirated."

"The intake valve is mostly operative during mostly prior to the overlap period when the exhaust backpressure is low. Thus the force available by the valve spring to prevent valve bounce has been cut by 50%"

"During the exhaust stroke the exhaust valve is pulled on by the exhaust pressures. Some additional force will be required to keep the exhaust valves seated"

"The situation of pressure balances existing at the valve during closing phase, which is the most important toward controlling seat bounce is somewhat complex. The least control of the valvetrain and the worst situation is at high rpm and from low throttle to full throttle"

 

the problem could be from valvetrain instability though is what i was suggesting. im not a boost expert but i would bet if your breaking stuff that normally wouldnt break in the rocker assembly and you have the stock springs that would be the first place i would look.. kinda like a ball joint or wheel bearing messing the alignment up causeing the inside of the tire to wear excessively. you wouldnt just change the tire. you would fix the problem

 

Oh come on Sean.. The car runs great. No one is breaking stock rocker assys.. no matter how far they turn them..

 

I plan to add an additional fastener at the point with the dot..

I have some new springs, but these were tested and within stock specs before installed, and run perfectly NA and boosted to 5200 RPM..

 

Could you machine a cast iron piece and weld that to the head, then re-machine the steel plate to fit to it, and bolt it to the new plate in a better, stronger fashion? Just thinking crazy thoughts here.... o No:

 

i think that will cause other problems since there will be less metal to resist bending in the area of the tapered hole.

 

wondering if it's possible to not have a recessed bolt and tapered hole in the plate. maybe a grade 8 bolt and hardened washer instead. that would allow for a smaller hole and a stronger plate. maybe even a stud in the head and a washer and nut

 

Absolutely.. There could be a recessed bolt without a washer. Maybe even a specialty bolt with a really thin head..There is only about 1/4" or less below the rockers. Maybe only 3/8".. I'll make it work because I have too..

Whatever it is is has to fit below the rockers..

 

It doesn't bend in the area of the 1st tapered hole. Once the bolt breaks it bends in the area of the NEXT hole.. Take a closer look at the first picture. If I can keep it connected to the head in any fashion it will work..

 

Jay;

Do you have a picture of the two sides of the broken bolt?? I think the cantilevered end seeing the load on the outside of the plate is causing the bolt to fatigue. Id like to see the break to see if its a fatigue failure or something else.


Did you get a new plate assembly last time to fix?

 

I hate to bring up your old posts however it seems relevant:

So if you forgot to blue locktight the bolts and they backed out and the plate bent then that may bring us up to date in this situation.

Today I broke free 11 bolts that were blue locktight secured, only the red caused stripped and broken parts and this is why I never use red.

 

So after the plate was bent you replaced it with a new one?

If you did not and re-used the bent plate I am saying you were asking for trouble using a fatigued and bent plate.

Again, I am not trying to come down on you just trying to get the facts on the situation.

 

I guess I have to ask.... Why not upgrade the springs when making double the HP of a stock 350?

 

Sean, in all fairness it's the cam that dictates the valve spring required. horsepower level has nothing to do with it.

 

Wrong. Running turbo's dictates increased spring pressures. It is a MUST to run stiffer springs on the GN's when running bigger turbo's and more boost than stock. Sean was correct in his earlier post.

Now, on to your problem. How much room do you have between the top of the "flat head cap screw"(not tapered head bolt) and your rocker arms? Those bars either need to be thicker, or it needs stiffeners built in to them. I would draw something out for you and post it, but I won't be able to until late Thursday or Friday. If there is enough room, I would almost use regular Allen head cap screws. BUT, IMO, I think the ends of those bars are flexing, causing them to bend the bar and then break the bolt.

But, this is all just the opinion of a machinist with 23 yrs experience.

So to recap, is the thread size of the flat head cap screws the same as the original rocker arm shaft bolt? How thick is the plate, and how much room between top of plate and rocker arms? I'll post back with some ideas on how to help fix this WITHOUT USING THAT F*%#ING JB-WELD!!!

BTW, try to use a little heat(like propane torch) on the lock-tited bolts to break the lock-tite loose. Needs to be good and hot to break them loose.

 

I can't give any specific advice or opinion since this is out of my league, but I can play the think things out game.

Why exactly do you need the plate there? What specifically is flexing that needs to be reinforced with the plate? If you can find a way to reinforce that area without using that plate then would you still be having these problems with everything coming apart?

I'd say start at square one and figure out exactly what the weak point is in the valvetrain and then figure out how to fix that spot with super strong parts instead of with additional reinforcements. Like when people go to thicker and stronger rocker studs to gain stability on the sbc motors. Maybe you can find a way to get the stability you need without having to use that plate at all o No:

 

The "plate" is there to mount the inexpensive Chevy style roller rockers. The Buick rocker arm shaft pedestals(sp?) were machined down to mount the plate.

Another thought, can anyone post a pic of the modded head without the plate installed? I got another idea on a possible fix.