[Darren 639]

So with the interest that has been floating around made me open up my block that I got back from the machine shop. I specifically asked for the best cooling possible for extended heavy street use and occasional track rental. I think they may have missed drilled the 421 hole as the drilled hole heads into the threaded head bolt hole. it goes halfway up from bottom of the threaded hole in the block then it passes at a different angle into the water jacket kind of wondering when I put the stud in place it’s going to either leak cooling up through like the Chevys would without some sort of pipe sealant or The head stud is going to block the hole off making it completely useless ?? only thing I could think of is indexing the stud and make sure the stud has a counter sink notch in the location so the hole should not get blocked with the stud. The bottom of the threads don’t seem like they’ll do very much with half of the thread missing now. Any idea’s has anybody else ever run into this issue? Thank you for helping.

[cgeise]

it looks like the hole goes to the bottom of the bolt hole -- correct??

[Darren 639]

Yes one side looks like a complete misfire came out about three threads up from the bottom of the hole then the hole was re-drilled straight down through the threaded head stud hole to make some water passage connection. that’s on the left side but it’s worse on the right side I could count about six threads up from the bottom where the drill poked through almost looks like a 45° angle from the top of block into the bolt hole.

[Darren 639]

Way worse On the right hand side it looks like the drill bit pushed through 9 1/2 threads from the top of the block. I can count 20 threads in total on the opposite side that same hole didn’t get any miss guided drilling . 1.860 is the total depth of the 1/2” threaded hole. 0.671 is The depth before the drilled hole pokes through on the inside of the threaded hole. Yikes I can’t even understand what I just said.

[Darren 639]

In my opinion the drilled whole should’ve poked through , (staying away from the threads) and landed and this area where this dot from a magic marker is.

[ID67goat]

So you are building an IA2 with 389/421 iron heads? That's interesting if you are..

I am by no means an expert on this stuff, but I would think that you will need to use head studs and trim them so the hole is not blocked and use sealant (like the Chevy stuff).

I am not familiar with the earlier Pontiac stuff...is that hole absolutely necessary?

Interesting to see what others with more experience say...

[chuckies76ta]

I'm just a novice here. We didn't drill any (421) hole for the center coolant in our IA2 block. I have read lots about it. I read post that say to drill it on an angle so as to stay away from the head bolt hole. Haven't had any coolant issues so far. Engine stays around 160*-175*. My heart goes out to you on this as these blocks are not cheap. Other more qualified members I'm sure will offer advice.

[mgarblik]

I will be drilling the water pattern today in an aluminum IA II. I saw the possibility of a breakthrough drilling the "421 Hole" yesterday and decided not to drill that hole. Just too close to the head bolt boss and only room for a tiny hole to stay off the sleeves. Your situation isn't a big deal IMO. IF your running studs, I would just load the threads with pipe sealant with teflon and install it . If using head bolts or for double protection I would do the following. Run a bottoming tap in the 1/2-13 head bolt hole. Clean it out. Get a shallow set screw and load it with pipe sealant. Bury the set screw. Install the stud or head bolt. Just make sure the head bolt has enough clamp length and doesn't bottom out. Your "421 hole" should still pass some water through it. Good luck, it should be fine.

[Darren 639]

MGARBLIK
Thank you for your reply Im probably over concerned. I am running head studs. I did not want to hijack your water jacket drilling post but when I saw the mess I had I just wanted to make sure nobody else wound up with the same issue. Drilling definitely will compromise integrity of the threats even if they hadn’t hit the block stud hole. It’s just too tight for that hole. I didn’t specifically ask for the 421 hole I just told the Machine Shop please make sure you do your best with your Pontiac experience. I guess I should’ve had a close look at it just as soon as I picked up the block. but it was put back in the A2 box and screwed tight figured everything would’ve been perfect.

[Skip Fix]

IA drills a hole in the bottom of the main cap stud for the accessory oil feed hole.

[Tom Vaught]

Originally Posted by Skip Fix

IA drills a hole in the bottom of the main cap stud for the accessory oil feed hole.

Originally that oil feed drilling was supposed to be a location for feeding oil to a Boosted Engine device, if I remember correctly:
Vortech Supercharger, Turbocharger, 2 Turbos, etc.

When most people were not going boosted then the oil drilling near the front main was used to add even more oil to the front of the block.

Tom V.

[Darren 639]

They notch the bottom of one stud make sure that stud goes back in the same hole if you’re going to use the feed oil feed port from the front. The splayed main studs seem a little short I twisted them up a little so the nuts would have flush on the top but I had to turn them up a good 1/4”. Anybody have any ideas ? I know ARP recommends 2 to 3 threads protruding past the nut.

[Darren 639]

Picture the difference
I didn’t torque the nut on the stud that was low.

[67Fbird]

not sure how many threads you have engaged in the block but the basic rule of thumb is MAXIMUM thread holding capability is achieved at 1 1/2 X major diameter. So 1/2" stud only needs 1 1/2" worth of thread engagement to achieve max holding...anything more is wasted. Yeah that stud is short as you do typically want 1-2 threads visible above the nut.???? Outside of my knowledge working with IA block stuff ..for sure.

[grandville455]

When I bought my IA2 , I pondered having that hole drilled too, but after talking to my machine shop guy we decided not to, cause
we needed some magic to drill it properly! My engine doesn't overheat and it made 800 hp on pump gas!

[mgarblik]

Originally Posted by Darren 639

Picture the difference
I didn’t torque the nut on the stud that was low.

As long as you have plenty of thread engagement in the 7/16" splayed holes, I recommend the following. I install a hardened steel ball bearing in those holes and then tighten the stud against it. That makes a nice solid connection there. Tighten it to 10 ft. lbs or so. If you need some, PM me and I will send them to you for postage.

[Darren 639]

Ahh thank you good idea. I didn’t see any 4” available on arp site. I have a drawer full of random ball bearings. I’ll measure 6 of them out and install. I didn’t like the idea of leaving the stud loose. Never crossed my mind to do that thank you