[Squidward]

Since I have a number of less than desireable lo-po heads (i.e., small valve and press in studs) I thought I would convert over to screw in studs. I'm sharing these pix and information here to help any other intermediate level dude who wants to save some coin in upgrading their factory heads.

I tried the Comp Cams 5306 stud pulller/tap guide since it was advertised as Chevy and Pontiac compatible. It is NOT. So I returned that, and made my own puller/tap guide.

I started out with a 4" piece of 1.25" 304 stainless steel square bar. It cost me $10.64 from a local metal supply company. I then went to a local machine shop where I paid $20 to have a pair of 1/2" holes drilled 1.925" apart (stud to stud distance I measured), 1" from one end, and centered in the bar at .625". I requested only the dimensions above and that the holes be true perpendicular to the deck surface. So far, total of $30.64. I spent another couple of bucks at the Depot getting some washers and a bolt, so the grand total comes out to around $33.

1st pic is untouched #47 head. I probably should have started on my 7H1's, but I forgot and dove right in on the set of heads I plan on using soon.

After pulling off the guide plate and cleaning the stud boss surface of any crud, I put the jig over the first pair of studs and secured using an old rocker nut and a washer. See 2nd pic. I had to put the nut upside down to maximize thread engagement so it didn't strip. This happens easier than you might think.

I cranked on the nut, which takes less torque than you might think to start pulling. I then used varying combos of washers to continue pulling the stud. See 3rd pic for fully pulled stud.

After pulling the first stud, I then tapped the hole. Piece of advice: Don't go hog wild and pull all of your studs at once, because you need the adjacent stud to secure your jig for tapping. You'll have to pound a removed stud partially back in.

I used a washer and rocker nut to hold the jig in place. The jig hole is 1/2" in diameter while the stud base diameter is 7/16", so there will be a little slop that will need to be accounted for. Use a tapered starting tap, and put it in the other 1/2" hole. Wiggle it around a bit while turning it CCW so that you are able to center the tap in the hole and get the jig aligned before snugging up the rocker nut. Commence tapping. See pics 4 and 5.

I counted about 10 full turns before the tap hit bottom. Be careful, and don't go too far or you might risk breaking a tap or messing up your newly cut threads. The final few threads near the bottom should be cut with a bottom tap anyways.

[Squidward]

I then cleaned out my newly tapped hole, because I used it as a threaded guide hole to anchor the jig while tapping the adjacent hole. I pulled the adjacent stud, set up to tap that hole while anchoring the jig with a 1/2-13 bolt I prepped for the job. I took a bolt, and left the bottom 3/4" of threads untouched. I then took a grinder, and ground down the bolt threads almost smooth for the next 1.25" or so. There was a reason for this: I didn't TOTALLY trust that my 1.925" stud spacing measurement was accurate, and my jig didn't have a lot of play to allow for tap alignment. Rather than hogging out one of my holes to allow for alignment I reduced part of the bolt diameter so that the jig could be moved more freely on the bolt and allow better tap alignment. See pic 6.

After starting the bolt into the threaded boss, finger snug the nut and washers down on the jig to hold it loosely while centering the nose of the nose of the tap. And once again, wiggle the nose of the tap in the hole while turning so that it centers itself and the jig. Snug up the nut to hold the jig in place, and start tapping. See pic 7. During this phase I realized that I should've used a shorter 1/2-13 bolt for anchoring. I used something like a 4" bolt, and a 2 1/2" length bolt would've been better. I could have avoided using the nut to hold down the jig, and I would've avoided having to pull my tap wrench off every 1/4 turn because it was hitting the anchor bolt. Oh, well, live and learn. But it worked regardless, just more PITA.

And final pic of threaded stud holes, see pic 8! Next step is to do the final tapping with a bottoming tap that will cut threads down to the bottom of the hole, and then install ARP 290-7201 studs. I hear that the stud base might need to be trimmed back a bit, and since the stud hole is almost an inch deep, this sounds about right because the 290-7201 base thread is 1" long. When combined with hole depth of just about 1" and the thickness of the guideplate, it's going to be a close fit. I'll report back after I install studs.

[Squidward]

My jig specs again: 4" cut piece of 304 stainless 1.25" square bar stock. First 1/2" hole is drilled 1" from end, centered lengthwise at .625". The next hole is drilled 1.925" from the center of the first hole. I measured 1.925 as the stud to stud spacing. Maybe someone has a more exact measurement. Here's a pic before drilling.


Thanks to all of the people on here who gave me the puzzle pieces to put this together and give me the know how and confidence to do this. Now I will now do this to a set of big valve 061 heads, another set of 47's, and 7H1's. Altogether this took me about 3 1/2 hours to pull/tap a pair of heads start to finish. Hundreds of $$$ saved!

[mechanic17]

Thanks Squidward for documenting this. I'm "practicing" on some SBC heads with my Proform tool.

[dmorg1]

Nice job Squidward,

The stud to stud spacing on one of the heads I checked on a milling machine with an indicator had some pretty varied spacings. If memory is correct there was up to .015" deviation.

You can also use a stepped shaft to align your tap block with the hole you are tapping and not even be concerned about the spacing deviation. Just drill the securing hole a bit larger. The stepped shaft makes alignment a bit easier.



Dave

[Squidward]

Originally Posted by dmorg1

Nice job Squidward,

The stud to stud spacing on one of the heads I checked on a milling machine with an indicator had some pretty varied spacings. If memory is correct there was up to .015" deviation.

You can also use a stepped shaft to align your tap block with the hole you are tapping and not even be concerned about the spacing deviation. Just drill the securing hole a bit larger. The stepped shaft makes alignment a bit easier.



Dave

The spacing deviation was my big concern. With a stock stud as the anchor it gives 1/16" slop to allow for tap alignment. When I used the 1/2" bolt to anchor with an already threaded hole I realized I had to "skinny" it up to allow for slop and account for factory variations, as well as my own measurement inaccuracy.

I thought about hogging out one of the holes, but I hesitated to do that in case I messed up the 1/2" hole being used as the tap guide. By keeping the holes untouched, I can use either as the tap guide.

Stepped shaft is a good idea. I might refine one later for jig centering - 1/2" body with 7/16 tip that will just slide into an untapped hole.

[Icefan71]

Very nice work, Squid. I'll be saving this for future reference.

[Squidward]

Just an update: When using the bottoming tap, I was able to get about another 2 1/2 turns before it bottomed out. When installing the the ARP 290-7201 studs on top of the pushrod guideplate, it left about an extra 1/16" -ish of thread. I knew it was going to be close.

So yes, the stud needs to be trimmed down about 1/16" on the base so that it will fully seat into the newly threaded hole. I suppose I could put a washer under it, but then I don't know what kind of geometry issues I might create that I might have to crutch later (washer under polylock?). I just have to bite down and get out the cutoff wheel.

[Squidward]

Hmm... never finished the update.

Yes, I did have to cut down the studs. I trimmed maybe 1/8" off the bottom of the stud so that they would thread all the way down. I used my miter saw with a metal cutting wheel. I would never recommend trying to cut them down with a hand held cutoff tool. I drilled a hole into the end of a piece of 2x4 and threaded the top of the stud into it so that only the bottom was exposed. This held the stud firmly in place while I did my chopping.

The last item was to hog out a couple of the guideplate holes to fit the 1/2" base of the studs.

[67gtospud]

I posted in my thread but thought it might be a good idea to post here too for future reference.

For a stepped shaft for tap alignment would 1/16" under 7/16 and 1/2 be enough off the total diameter of both steps to move freely in the head but yet tight enough to properly center?

[dmorg1]

Turn the small diameter of the shaft to .429" max and the larger diameter to .507" or so to fit your tap block.

The hole in the tap block should be about .510"

1/16" under the nominal diameter is going to be very loose.





Dave

[Squidward]

OK, now that jig is pretty killer. I never thought of using the guideplate bolt holes for holding the whole getup together. Nice, Dave!

BTW, what did you measure for stud spacing?

[67gtospud]

Originally Posted by dmorg1

Turn the small diameter of the shaft to .429" max and the larger diameter to .507" or so to fit your tap block.

The hole in the tap block should be about .510"

1/16" under the nominal diameter is going to be very loose.


Attachment 342107


Dave

I meant to say 1/64th under 1/2 and 7/16, not 1/16. You are correct, that would be much too loose.

[dmorg1]

Squidward,

The spacing on the tap block is 1.935" but this spacing did not fit each set of holes.

The securing hole is drilled at 23/64" this allowed enough movement of the tap block to do both holes without completely removing the block.

Line up one hole with the pin and tighten the securing screw, start the tap 3 or 4 turns and remove the tap then loosen the screw and align the second hole, tighten the screw and start your tap.

My original plan was to set the heads up on a milling machine and simply run a Tapping Head down the length. Unfortunately the spacing deviation would require each hole to be indicated out as the tapping head has only a small amount of float.


67gtospud,

1/64" is much better and should work fine but the closer the fit of the pin and the tap to tap block the straighter you tap will be.

Dave

[rohrt]

Nice informative thread.

[67gtospud]

I went about measuring my press in studs center to center (using the small nipple on top center of each stud) and I have a total variance of 0.013". The smallest distance being 1.964" and the largest being 1.977". With this said, my average distance is 1.971" so if I drill my holes 1.971" apart I will have 0.0625" (1/16") to move my block to align each hole. Correct?

I'm throwing these up here so hopefully if I'm figuring something incorrectly someone will catch it

Here's a picture of the numbers I got, front cylinders to back:

[dmorg1]

You will get a much more accurate measurement if you measure to the outside of two studs close to the boss and then subtract the stud diameter (as long as both studs are the same diameter) from this measurement.

your average 1.971 distance is a bit a longer than the 1.935" distance I used on my tap block but there may have been different spacings used on different head castings.

Dave

[67gtospud]

Originally Posted by dmorg1

You will get a much more accurate measurement if you measure to the outside of two studs close to the boss and then subtract the stud diameter (as long as both studs are the same diameter) from this measurement.

your average 1.971 distance is a bit a longer than the 1.935" distance I used on my tap block but there may have been different spacings used on different head castings.

Dave

I was also thinking that it was a little longer as I went about measuring but all the measurements are "similar" so I'm not too worried about it plus with 1/16" of space to move the alignment block I'm thinking ill have enough space. I will go about making another measurement the way you stated and see what it results.

Thanks,
Spud

[Tom Vaught]

I found the extra package of MR GASKET "screw-in Rocjker arm studs. (without the hex nut) The part Number was 1077. The "Head Thread" was .700" long and 1/2-13 thread. The "collar" was .125" The upper Rocker Arm Thread was 7/16" thread and was .800" long. Total length was about 2.25" long but did not want to tear open the package further.

The listing says: Pontiac 1966-1968 (without oil hole)

Tom Vaught