Broken Gn1 rocker stand

[jpwalt1987]

Try making a call to Tom and get the correct height. I remember typically needing .090" of shim under the rocker mounts on the t&d jesel style setup on GN1 heads. If it was machined ideally you wouldnt need any shims. I also had to mill the pushrod holes out on the intake side to prevent interference. Once this setup is done you will have a very strong and stable rocker setup.

So are you saying that its still not a good idea to use the style roller rockers that I have even if the aluminum stands are milled off and the bolt on stands from T/A are installed? Really didn't want to spend $850 on new rockers. What is the downside of keeping the rocker assembly I have?
I am also thinking that I may run a +.050 valve lock to decrease some of the spring pressure.

 

[bison]

So are you saying that its still not a good idea to use the style roller rockers that I have even if the aluminum stands are milled off and the bolt on stands from T/A are installed? Really didn't want to spend $850 on new rockers. What is the downside of keeping the rocker assembly I have?
I am also thinking that I may run a +.050 valve lock to decrease some of the spring pressure.

I've never run the stock style rocker/shaft assembly on a hard running engines because I wasn't to confident in having 3 bolts/studs holding everything down. I'm sure it's probably not a big deal though. A +.050 lock won't do much. Those springs have a decent rate for what they are. I've got them on one of my engines with some very aggressive lobes and about .040" more lift. They have about 25 quarter passes, 40 dyno hits, 6000 miles, and hundreds of 6000 rpm blasts on the street. I haven't had a valvetrain problem with this engine.

 

[BEATAV8]

Really didn't want to spend $850 on new rockers.

the Scorpion stud mount style rockers are quite a bit cheaper if i remember correctly.

 

[TurboBuRick]

Did you pull rocker assembly and look at the bolts yet?

IMHO there would not be a problem had the bolts been the proper length.

 

[jpwalt1987]

Did you pull rocker assembly and look at the bolts yet?

IMHO there would not be a problem had the bolts been the proper length.

I pulled the rocker assembly yesterday to check bolt length. There is 3/8-1/2 inch of bolt sticking out past the broken part of the rocker stand. I did my best to measure how much longer the bolt could have been. 1/4 inch at the most. It looks like the helicoil insert was not all the way to the bottom though. I am thinking that where the helicoil stopped is where it broke. The broken price of rocker stand is still tight to the shaft. It did break the shaft at the middle hold down bolt though. Not sure how deep the bolt hole could be drilled to but I can see that it needs to be deeper and the inserts need to go to the bottom of the hole. I'll post up a picture soon.

 

[bison]

I pulled the rocker assembly yesterday to check bolt length. There is 3/8-1/2 inch of bolt sticking out past the broken part of the rocker stand. I did my best to measure how much longer the bolt could have been. 1/4 inch at the most. It looks like the helicoil insert was not all the way to the bottom though. I am thinking that where the helicoil stopped is where it broke. The broken price of rocker stand is still tight to the shaft. It did break the shaft at the middle hold down bolt though. Not sure how deep the bolt hole could be drilled to but I can see that it needs to be deeper and the inserts need to go to the bottom of the hole. I'll post up a picture soon.

The larger size hole used for the heli-coil removed some integrity from the stand. There's no way to get the heli coil all the way to the bottom of the hole. The end of the tap is slightly tapered as all taps are. Typically heli coil taps go fairly deep though. If you're going to keep the pedestals I'd remove the heli coil and drill deeper and go deeper with the tap. Once you get the hole tapped grind the end of the tap almost square and carefully bottom tap the hole and use long heli coils. Then use studs instead of bolts

 

[jpwalt1987]

Here are the pics.

It's almost 5/16ths of bolt sticking out.

 

[The Radius Kid]

So why do I see damage on the first turn of the bolt thread in the first picture?
That bolt almost looks like it hit bottom.
That could cause the breakage you see.

 

[jpwalt1987]

From what I can see it looks like it broke where the helicoil ended. There are threads in the head but they are not for a 5/16ths bolt. Looks like the threads are for the od of the helicoil. Going off of some rough measurements I can't see how the bolt would have bottomed out but I do see what you are saying. Probably going to order the adapters from T/A and a new shaft and then have the towers milled off.

 

[TurboBuRick]

Not knowing there was a prior repair and helicoil in the stand, the first thing that came to my mind was the bolts were too short. From the pics that's obviously not the problem but it might as well have been. The helicoil not deep enough had the exact same effect. Like Bison said, some special care needed to be taken to ensure the helicoil went deep enough. Drilling the stand for the coil defiantly took integrity away. Another reason it's important to get the coil deep down inside.

Live and learn. This Turbo Buick stuff will make you nuts.

RL

 

[jpwalt1987]

Thing is, I don't think there was ever a prior repair. I have had these heads since new. I never did anything to them. So they either came with the insert, it was done at McKenzie cylinder head when they were ported or when the whole engine was built at DLS. It looks like all the rocker shaft holes have inserts.

 

[TurboBuRick]

I just went out to the garage. I have a set of heads here that are helicoiled as well. They must come from Champion that way although these coils go all the way to the bottom of the hole.

How do your other holes look? Do the coils go all the way down?

 

[jpwalt1987]

Went out and did some measuring. Here is what I found : it was a regular short helicoil in all of the rocker stand holes. But the hole is almost inch deep!!! Damn the bad luck.

 

[TurboBuRick]

Unbelievable.

 

[DoubleD]

Wow, that is some pretty bad carnage. Sorry for your misfortune! I had 4 of 6 threads pull out in my Iron heads last time I had the rockers off, but no broken pedestal. Helicoils are working well so far, went ahead and did all 6, but now I'm a little worried...

 

[jpwalt1987]

Right now the plan is to pull the motor , remove all the short inserts, tap the insert threads as deep as possible, order helicoils from MSC that are about .975 long, order new shaft, and have the rocker tower welded back on. I think that with using studs that are reaching down into the meat of the heads I will be ok. Gotta find the right studs now. I can get grade 8 fully threaded studs but am not sure if a stud that has a non-threaded portion to go inside the rocker shaft would be better or not. Anyone have a link for some studs that would be best?

 

[aminga]

What about timesert's instead of helicoil's

 

[jpwalt1987]

What about timesert's instead of helicoil's

The timeserts look good except the longest I saw for 5/16 was .750. Helicoil has one that is .925 or so. I wonder if the external threaded portion would be the same also?? Never used them but I like the way they look.

 

[aminga]

The timeserts look good except the longest I saw for 5/16 was .750. Helicoil has one that is .925 or so. I wonder if the external threaded portion would be the same also?? Never used them but I like the way they look.

I know the LS1 guys around here sure dig them.

 

[ek02]

Call ARP to see if they have studs that will work. You will need the exact measurements of the studs shoulder and the thread lengths and pitch.

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