Early Block Head Bolt Prep

[CTX-SLPR]

Howdy,

I tried searching but I can't find the thread where I think it was mentioned... Is it a good idea to counter sink the head bolts on an early block like the factory did on the 109's? I know it means different head studs and I don't want to buy the wrong ones if it's best to countersink them.

Thanks,

 

[earlbrown]

Yes, it's a good idea to countersink a few threads and break the edges with a 45* countersink. It most likely won't require the use of new studs though. Although a rule with these cars and studs is ALWAYS check!! Most of the time the studs are on the long side than short.

 

[turbodave231]

I don't think it is possible to sink the threads below the deck surface on an early block. The 109 blocks have the threads down deep in the block. The bolts in a 109 block have less influence on the deck surface when tightened.

 

[earlbrown]

It's possible. I've seen me do it.

 

[charlief1]

It's possible. I've seen me do it.

I've done it as well.

 

[CTX-SLPR]

Some guidance on what to tell the machine shop to do? I don't trust my setup abilities on my own mill, this is going to be one of a few things I don't try to DIY.

 

[dr_frankenstein]

personally I like to use a end mill for the procedure as it will square off the threads better then a drill, is much sharper and will be easier to align to the block if you use a transfer punch as a guide.

but a good drill bit with a stop collar can work really well if you take the bit to the grinder and shave some of the rake off to keep it from pulling. same again, use a transfer punch to align your drop.

needs to be dropped about an 1/8" of an inch below the deck, then touched real lightly with a chamfer cutter to remove the hard edge. then run a tap gently through all the holes to ensure there threads are clean and fit.

 

[earlbrown]

I just use a hand drill then follow up with a nice thick 45*. Takes all of about 2 minutes.

If using head bolts instead of studs chuck a wire brush in a drill motor and polish the hell out of the threads.

 

[CTX-SLPR]

Sounds like I could put it up on my mill, drop a stud in the hole (or a bolt with the head cut off) and align to that. I'm guessing that after I aligned 1 hole the rest would be good.

The other alternative is to use a hand drill (or that crappy old mini drill press I have if I could adapt it to the head bolt holes) with a stop and drill them 1/8in deep then hit it with the 45* counter sink bit to knock the edge off of the hole.

Unless I think I can convince myself that I can do more with my mill, such as surface the deck, I'll stick to the drill press on a piece of thick plywood (or scrap steel) bolted to the deck.

 

[dr_frankenstein]

just depends on how anal you are.

im super OCD (like really bad) so I have to do it on my mill in the most precise manner i can. but as you see above Earl and Charlie have gotten by just fine with hand punching it. And theres absolutly nuthing wrong with that! some guys can just "eye-ball" it good.

Id say do what you feel comfortable with, its an early block... so no tears if you make a mistake- plenty more can be had for cheap.

 

[earlbrown]

If you're going to put it on a mill. Set it up and indicate the the deck surface flat. No reason to get dead nuts exact, a few thou corner to corner will be plenty for what you're doing. Once the block is squared up, just put a large pointed somethingoranother in the collet to find center of the hole. Once again, you're just knocking a few threads out so a few thou out won't matter one bit.

You must have one hell of a mill at home if there's room for a block and fixture and a drill!

 

[dr_frankenstein]

If you're going to put it on a mill. Set it up and indicate the the deck surface flat. No reason to get dead nuts exact, a few thou corner to corner will be plenty for what you're doing. Once the block is squared up, just put a large pointed somethingoranother in the collet to find center of the hole. Once again, you're just knocking a few threads out so a few thou out won't matter one bit.

You must have one hell of a mill at home if there's room for a block and fixture and a drill!

me or him?

lol

 

[turbodave231]

I've never done this before and I have a question.

How deep do you plan to countersink? From my rough measurements on a 109 block, the threads don't start until .500 below the deck and then go to 1.75" . You will need to remove 7 full threads. How deep do the threads on an early production block go?

 

[ek02]

I use a hand drill with a bit slightly larger than the bolt and a 45 degree countersink bit to bevel the hole. I go less than about 3/16", then use a thread chaser.

 

[CTX-SLPR]

I have an RF-31 Mill/Drill. Should have enough Z room to put the block on the table and still be able to fit the bolt to align and a short endmill to cut the threads. I'd probably do the countersink by hand with a drill motor.

Dr. Frankenstien, do you use like a ball nose endmill to knock the hard edge off of the thread ends or are you talking about chamfering the deck with a countersink?

I was thinking that if I pulled the rods and pistons out but left the crank in, I could get the crank centerline parrell to the table. Then I'd put the stud or headless bolt in the collet and adjust the table and tighten the collet down to get the rotation around the crank axis correct. Then I'd lock the block to the table with fixturing off of the timing cover and bellhousing bolt holes. Check a few more headbolt holes to make sure I'd gotten it straight then use a flycutter to cut the deck. Then drill the holes. Since I'm planning on using steel shim gaskets of some kind with either the goop or spray sealants, how good of a finish do I need to put on the deck? Not that I have an RA meter.

Thanks,

 

[earlbrown]

use a coutersink. There's no benefit to having a concave bevel on the relief. All you want to do is widen the footprint on the actual clamping area, no reason for heroics.
If you're going to go through all the trouble to set the block up for decking, do some measuring before hand. Since you don't have a square decking fixture, you can get pretty close and straighten out some of the Generals handywork without one.

Measure the distance from the crank bore to the deck surface on all four corners. If one side is .002" taller, for instance, make that side .002" higher when you indicate the deck surface in. Find out what corner is the shortest and make all four of them match. (make sure to do the short side first so you won't have to do it three times).
If you can figure out a way to locate the imaginary line through the centerline of the crank and the centerline of the cam bore, then you can truly square deck the block. Based on my personal experience Buick v6 blocks are pretty close. When I decked my 4.1 block it was only out .0015 on the 4 corners.

On the finish for MLS gaskets, smoother is better. I used a 12" cutter with a CBN insert on my block, hit the holes with a counersink after decking, then went over the deck with the diamond stone I use on the ways of the surfacing machine. It leaves a nice matte finish on the machine surface. My .027" cometics seal good enough to crack pistons without leaking using that method

 

[Nick Micale]

I use a hand drill with a bit slightly larger than the bolt and a 45 degree countersink bit to bevel the hole. I go less than about 3/16", then use a thread chaser.

What is said here is way we do to the head bolt holes in an early block, and like Dave stated, why would you want to go deeper and remove threads?

From the few early block I have seen with cracks, they are very small from only one or 2 bolt holes which really do not affect anything, although we have welded up a few of them.

My opinion is to always use studs on early blocks and bevel the holes like mentioned above. Since the stud does not "pull" up on the threads especially during installation, it is unlikely this issue will happen. Even if it did, you would never know it until you removed the head.

 

[turbodave231]

I am fairly sure we are not talking about the same thing here.......there is no possible way you can countersink the head bolt threads on an early block to be the same as a 109 block. You would end up removing most of the threads. There would be no strength left to torque a bolt or stud. I believe what you are discussing is chamfering the bolt hole at the deck surface........ not countersinking the bolt hole.

Chamfering the bolt holes is a common practice after decking the block. You would still use bolts or studs for an early block.......the studs or bolts for a 109 block would be too long.

Dave