Can aftermarket roller rocker shafts be drilled to 3/8" ???

[yullose]

My heads are up at Andy Jensens shop to be repaired. (The shaft pedestals are cracked)

Andy wants to mill off the factory pedestals and make new ones out of steel. He asked if I could get a roller rocker setup with the shafts already drilled bigger for 3/8" studs, instead of the normal 5/16" fasteners. He seemed concerned that the aftermarket shafts may hardened and difficult to ream/drill.

Does anything like this exist ? or do I need to make a special request ?

Or... are the shafts soft enough to drill ?

Thanks in advance !

 

[Chuck Leeper]

Just my $.02..
I think that most shafts break where the hole is. I'd not be removing any more material.
I'd leave the holes alone.

 

[yullose]

I talked to TA Performance and they said the shafts couldn't be mfg'd with bigger holes.

Not a problem though... as Andy Jensen said he will make 'em bigger if they can't.

 

[bison]

Ive run heads with broken pedestals before. You can have the broken piece brazed on. Grind a fillet all the way around and bolt it down with the shaft as a locator. Then have it brazed in place. Then drill the hole beyond the break point about an inch, tap it, and use a longer bolt. One of the heads in my sig has this done and the engine has seen 6400rpm with Comp 941 springs and no problems. Its advisable to drill all the holes deeper, tap them, and run longer bolts for more thread engagement and strength.

 

[turbofabricator]

I would NOT reccomend drilling the shafts larger. You will severly weaken the shafts. 5/16" bolts are plenty strong. Do as Bison suggested, or mill the broken part off and build a new pedistal. I have steel pedistals that will work if you need a set. (I sent you info on them already, on your previous post: http://www.turbobuick.com/forums/engine-tech/285055-wtf-rockershaft-shims.html) Just need to mill the top off of the pedistal and slide these over the shafts. Shim as required for proper geometry. Your machinist MUST mill the pedistals at the correct angle to get a new pedistal to locate the shaft in the correct location. Mill the pedstal at the wrong angle, and it will move the shaft inboard or outboard of the correct location. He/she just needs to science it out BEFORE milling anything.

 

[yullose]

I have complete faith in Andy Jensen.

Google his name and you'll know why.

 

[SS_Sean]

Then why did you ask the question?

 

[ttypewe4jim]

Why do you want to increase the bolt size anyway? I can understand wanting to use a larger bolt.... but at the same time you are decreasing the surface area of the rocker shafts which IMO area already weak... You hear of alot more rocker shaft issues then you do pedestal issues.

 

[yullose]

Because the pedestals are cracked... one of which has a huge chunk broken off.

They will need to be milled almost all the way down and replaced with steel pedestals. The head will need to be drilled & tapped and a long stud will need to screw into the head, pass all the way through the fab'd pedestals and then through the rocker shafts.

The difference between 5/16" and 3/8" is .0625"... which is only .031" around the diameter of the hole. Big fvcking deal. Aftermarket roller setups have reinforcement supports on top of the shafts anyway.
The weakest link at this point would otherwise be 3 fasteners approx 3" long and no stronger than a carburetor stud. Increasing the stud diameter to 3/8" makes perfect sense to me.

I asked the question, wanting to know if anyone had done this before or if they knew if it could be done during the mfg process (prior to hardening)... instead of machining hardened shafts.

Since nobody could answer the question I asked... and only questioned me instead, fair enough. No harm no foul. I called TA and got an answer. As a result, my machinist will drill the damn holes himself.

I'll be sure to post pictures of the heads when they are done. :wink: