: Head Bolt/Stud Placement

10-13-10, 06:21 PM
Head Bolt/Stud Placement

Do we have any High Performance Engine builders here?

Why did GM pput the head bolts threads down in the block and not at the top of the deck?

Why do performance builders relocate the threads lower in the block?

Why do performance builders cut the top section of the treads off?

I worked for an engine builder that got $30K for a Buick 3.8L and he sold a lot of them

10-13-10, 06:59 PM
Bolt/stud stretch, head/block movement, and avoidance of thread interference with gaskets and head bolt hole sizing. You torque down a bolt and you pull up a lump of metal at the top of the hole if the threads are at deck level.

In my Olds 455's (iron block/heads) the ARP stud threads start at .060" below the deck surface.

10-13-10, 07:31 PM
Torque Plate :yup:

10-13-10, 07:33 PM
Thanks SUB

Even LS1's have the thread sunk down in the block

10-14-10, 08:57 AM
Torque Plate :yup:

...........nobody needs a torque plate for a stock Northstar rebuild because we don't bore the cylinders..............now if I were CHRFAB and going .030 over for a sand rail engine, then maybe...............

10-14-10, 11:56 AM
The reason you Torque Plate is to compensate for Torquing Distortion.
Now on a Northstar the Cylinders have a water passage around them. On an old SBC the torquing of the head bolts can change the shape of the cylinder.

The bolts will also pull the material up around the bolts. That is why they most head bolt thread are deep in the block.
We all know how the Northstar Block are. They will pull the blocks deck up at the bolt hole and leave the cylinders low. Remember .004 is the rule of thumb for deck distortion.

10-14-10, 08:35 PM
I read the reason the bolts are deep in the blocks, as per General Motors wording.

AJ is there a particular reason this question is being asked?

My studs use the upper 2" of the bolt hole. There hasn't been one failure to date-

If the heads are securely clamping down on the block, cylinder bank flexing will not be an issue. If the heads are not torqued enough or improperly, then I would say there is a chance of flexing because of the open deck. Once the heads are torqued down, there's no chance.

Nevertheless - if there are still people that insist the threads be in the very bottom of the holes, I can run a special order of studs. I just won't warranty anything at that point. I know what works good and has a 100% track record of success. No cracked blocks, no pulled threads, no overheating when the job is complete.

This is actually an email I received tonight at roughly 7:00pm:

Just had your stud kit installed my 1998 Eldorado (base model - dark green) about a month ago. JD Auto Service in Fairfield Ct. did the work, actually you recommended them to me some months ago. I bought the car 2 yrs ago with 55,000 on it, when it hit 65,000 the head bolts pulled. I had Time-Serts installed, but the front bank failed. I got on the Internet and found your site. the rest is history - the car runs like it just came off the showroom- the car is mint - everything works...

Anyway, I know you guys are busy - 2 questions, you recommend the green low-silicate coolant - any particular brand? - also 1997 - 1998 being the worst years for Northstar head bolt failure should I use Seal Tabs as recommended by the factory?

Thanks in advance


Sorry Joe that I did not ask permission for posting this - but thank you for the email! :)

10-14-10, 08:40 PM
Another thing. If there was a chance that the cylinders would become lower than the portion around the head bolts holes, one can compensate by machining the exterior portion of the block deck below the cylinder bank by say, .002. I would never do this. I'd be afraid of exterior leaks- but I'm sure the cylinders would seal nicely!

The composite head gaskets have a fire-ring that is raised slightly compared to the rest of the head gasket. Don't forget, that fire-ring compresses too and conforms to the surfaces.

AJ are you having head gasket sealing issues?

10-14-10, 09:07 PM
I am doing some research. This was not directed to you and your product.
I am working on some very high HP engines and came across some information about the reason that manufactures moved the threads lower in the block.

10-14-10, 09:11 PM
Cool - high HP Northstars? Aluminum blocks? Iron? Fill us in - don't keep us in suspense AJ!

10-15-10, 08:18 AM
Cool - high HP Northstars? Aluminum blocks? Iron? Fill us in - don't keep us in suspense AJ!

I don't think AJ is working on high hp Northstars - right now or maybe any more.

Torque Plate: That huge, thick chunk of steel that is machined to the exact cylinder and bolt hole configuration of a particular engine. Before cylinder boring it is installed and torqued to cylinder head specs to simulate the distortions placed on the (completely assembled) block so the boring process machines the cylinders as they would be in a complete engine.

This thread started as a rumination on recessing the bolt/stud threads .060" to .100" into the block of a rebuilt high performance engine. The question has nothing to do with Northstars, and no, you don't want to bottom the threads of a stud in the hole - As an illustration, if the threaded hole was 2" deep and the threads on the stud were 1.75" long, you could recess the threads .060" into the block and still not have the stud touch bottom. That's the thrust of his (loaded) question.

Many of ARP's waisted studs accomplish the same thing. On some of those we don't use torque settings: a dial indicator is used to measure total stud stretch. (torque does not actually "tighten" a long stud or bolt - it stretches it.) Think about the differences between studs and bolts (block thread movement) when it comes to creating (and measuring) stretch.......

10-18-10, 10:47 PM
Well said Jim. Torque IS stretching a bolt/stud. A certain amount of stretch provides the clamping force. Too large of a fastener diameter would not allow any stretch, and too skinny of a fastener and you wouldn't get clamping pressure before too much stretch occurs.