Question for a machinest about head work
 

Ive been working at a machine shop for almost 2 years now and we don't get many Pontiacs this is the 2nd since ive been here. Its a 389 .030 over with 092 heads the customer wants roller rockers after the motor is already finished. Yesterday I took the heads off and pulled the studs out. Today I had the heads on the dcm machine and my boss told me we had to cut the stud bosses down and drill and tap the hole. well doing what he said Ive drilled into all the intake ports and 2 water ports in the center. My question is was it right by cutting the stud bosses down and we are using bbc studs and crane 1.65 rockers

why mill stud boss down??? ok, he,s the boss!!

Im sure because he wanted to use shouldered studs.The boss needs to be cut the thicknes of the shoulder BUT you have to use studs with short thread length.Tom

sounds like you drilled a little to far..

you're probably also going to have to clearance the pushrod hole towards the stud for the 1.65 rocker. It might be a little tricky as I don't believe that head uses guide plates. I believe the valves are closer together, so I don't think normal guide plates would work if you wanted to add them.

Because of the valve tip to stud distance, you may find a SB Ford 1.6 rocker fits better than the 1.5 or 1.65 Pontiac rockers which fit better on later engines[350,400,428,455]. Make sure the pushrod guide holes in the head are still oval and not worn on the sides. If worn on the sides, you will need to figure out some sort of guide plate. You generally just need to tap the holes and install the correct stud with 1/2" bottom thread.

SB Chevy stud holes break into the water jacket and intake ports all the time. They are not a problem, so neither should this as long as you left enough meat to thread. Just be sure to use a good Teflon thread sealer.

On a 389, you need custom studs made. All the aftermarket ones are too long on both sides. I bought ARP studs and had them cut down on both sides. Machining a flat surface on the bosses sounds normal to me.

I seem to remember I got the 1/2" ones because there is not much depth on the 389 bosses.

well someone all ready opened up the pushrod holes but it was running stock rockers when it came in. My boss its a 70 year old chevy man and trying to explane this to him is like speaking Spanish. He just orders ****** with out checking a lot of stuff out to see if it will even work

i had my 345 heads done with 7/16" arp bolts with short threads on the head side. My builder got pontiac guide plates that were too wide. He slit the guide plate down the middle and tack welded it back together. the width is correct for the pushrods and i am using 1.5 scorpion rollers. I think there might be a photo in my album. if not i will put one there

389 Studs/Guide Plates
 

I believe the "093" heads are the same configuration as the "092's", recently delivered a pair with this setup.

Fairly easy deal, used ARP studs (134-7103), Isky adjustable plates (AGP-200), and some Comp's roller rockers. Comp also has the guide plates available now (4835-8).

You drill the OEM stud holes to 1.000" deep, same size as original (7/16"), then machine .250" off the original boss heights, and finally, heli-coil (7/16"-14) all the original rocker stud holes.

I placed this info up here a while back, a "search" might locate it??

The final machining is open up the OEM pushrod holes in the heads, they aren't needed at this point!

Thanks, Gary in N.Y.

P.S. Here's a before/during/after shot of the studs/plates. Wasn't all that bad. We also did exh seats with no issues, but did require "custom" sized inserts with a large corner radius!

Yes, the only difference is the chamber size. The 092's are 70cc & the 093's are 68 cc's (10.5 vs 10.75 ) compression

Don

Be sure to use thread sealer on any that are drilled into ports or water passages!

We ended up going with some studs that are 1/2 at the bottom and 7/16 at the top just waiting for them to come in. I told him today we should cut guides down, its got an erson cam I think lift was somewhere around .460-.470 With stock 1.5. So with 1.65 rockers I feel like it would hit the top of the guides.

Your retainer to seal clearance may even be close with just .460" lift and the stock instaled height?

Gosfast has described the process very well. It should be noted, it is to be done on a machine, in a precision manner, NOT for a "hand" drill. The tap for the HeliCoil should also be at least "started" in the machine to insure it's straight. Power-tapping will leave the best threads.

The adjustable guideplates do work well. They're listed for the small block, but the engine doesn't have to know that. Be certain to enlarge the entire hole for the pushrod to pass through.

Using the "short" BBC stud works without having to trim it down. We use Permatex "Aviation" as the thread sealer.

Jim

When I tapped mine, I used 290-7201 studs, 1/2-13 on bottom, 7/16 on top. I had to chop about .15" off each stud bottom to get them to fully thread into the hole without any drilling.

Same ones as I used also. I seem to remember taking unequal material off both sides, but it has been 15 years.

I had Super Duty-like one-piece guide plates custom made by Fulper. They have an indent which faces towards cover bolt hole.

With big Norris 1.6 SS rockers, everything fits under my stock 389 GTO covers.