My new Merlin 3 block has provisions for an extra head bolt for each cylinder. Our bigblocks lack a head bolt at 12 oclock on every second cylinder. The merlin block allows you to tap the cylinder head and add a extra head bolt in this location. My bordix heads also have provisions for doing this.
I can set the heads up on the mill, locate each hole and drill a tap the extra holes required after checking with Brodix that there is in fact NO water jacket in this location. You can see on the heads a dimple where they intended this extra bolt to go but I want to check with them first before drilling..

You can see the extra bosses added in the lifter gallery for an extra head bolt at 12 oclock on each cylinder



Here you can really see the cylinder on the left already has a 12 oclock head stud while the one on the right does not.
My question is do you guys that have done this do you add only head studs where they are missing in a cylinder or while you are at it add them to all 8 cylinders??
To add all 8 is not a problem with the head set on the mill but I am worried about the double studs cracking the head or warping the head from overtightening in one spot.
Jim what have you done???

 

Norval i called my alky blower buddy about those 8 bolts. He told me that they are not required unless your running high boost pressure like 30-60 pounds and alternative fuels like alki or nitro.

The added strength from thos 8 bolts is for blower explosions where the burst plate isn't enough and the whole blower, blows off and only the straps keep it in place.

 

Thank you George for calling your budy. For me it is a simple matter to set up the heads on the mill and drill and tap the holes for the extra studs. I have lifted a head before with my blower and don't want that happening agian. Every second cylinder has 6 head studs and the other half has 5. I feel this is not right and if I can correct it with a simple drilling and tapping of the heads why not do it??
I am running a blower motor, one capable of pulling about 12 pounds of boost and NO rpm and locked in 5th overdrive with 308 gears.
I think that is a tough situation for the motor, locked down in rpm and yet the boost level is high.
I did email brodix to get their opinon on drilling all 8 or just 4.
I actually am looking forward to the exercise in drilling the head.,

 

Personally i would just do the 4. It seems a little redundant to do a bolt outside of an existing bolt.

 

This is what I thought and would like to hear from Jim. He has the same block and will know

 

Norval, do you have the torque specs for the extra bolts?
I remember they aren't torqued down very much.
I'm thinking only 35 or so...

 

No Steve. I am hoping that Jim or Brodix would tell me what they should be. I never expected them to be so low.

 

I'll see if I can find the spec. I've got it in a book somewhere...

 

I can't find what I was thinking of but I found this:

Ed Staffel's "How to Build Max Performance Chevy Rat Motors"
has a page of torque specs. It has a listing for a "7/16-14
Valley Stud" of 55 ft lbs.

All the other values on the page are correct so it seems pretty reasonable...

 

From page 69 of Chevrolet High Performance Tips and Techniques (Copyright 1991) one Henry "Smokey" Yunick lists 25-35 Lbs/Ft as being sufficient for keeping the head gasket in place.

BigBlockk

Later.....

 

just out of morbid curiosity. do normal head gaskets have a hole for the extra stud?

 

You are either a research God or have a great memory!
I actually pulled that out but couldn't find the reference.

That's a cool old book. It's the first place I heard about Tom's Differentials.

 

The Dart Big M block has provisions for every other one, the ones that are normally missing. Fel Pro and Cometic head gaskets come with holes already there for those normally missing ones. AFR big block heads come already drilled and tapped for those normally missing ones. Do not double up those studs right next to each other. Fasteners that close together, don't even meet engineering requirements for fastener spacing, which could cause cracking between those fasteners. No engineer would design parts this way, that should tell you something right there. It will do nothing more for you in terms of clamp up, and may very well give you distortion issues you don't want, even if it doesn't crack between them. It doesn't make any sense why they would put those redundant holes in there anyway. First they had to catch up with Dart Big M blocks which had the extra bosses there all along, when World didn't. Maybe World thinks they are doing Dart one better this time, but they aren't doing you any favors here. Paul Pfaff Racing Engines told me to torque mine to 55 ft lbs, but good luck getting a torque wrench in there.

 

Thank you 540Rat. I thought they would be too close but I wanted to hear someone stay it. I also assume that I use a 7/16 x 14 bolt? As for torquing to 55 foot pounds it I have a problem I could tighten a head bolt to say 50 and see how much force it takes with a wrench and extension and then try to duplicate the feel on the 4 valley bolts. I will pick up some grade 8 bolts for this purpose.
My heads are NOT drilled and taped but I can see a dimple in the heads where they are suppose to be. I can set the heads up on the mill and use my head gasket as a reference after checking it on the block and use transfer punches to mark the new location. The mill will drill and tap straight.'
Thanks again 540 Rat

 

This spec makes more sense then 25-35. For a 7/16 bolt that is not very tight.

 

I noticed that nice hone job on your cylinders, I assume the block was
honed with head plates using the original bolting?
Would that be an issue with a blown motor?

 

Center column of print, last line at the very bottom of the page. I really don't have a great memory but I listen when people smarter than myself (just 'bout everybody) are talking. I knew it was there, just took a few minutes to find it.

BigBlockk

Later.....

 

First off...Pretty stuff there Norval!!

You're ahead of me...my Merlin block is an early one that didn't come with the extra bolt holes. Dart wasn't making them back when I bought mine. It was Bowtie or Merlin and both were extremely hard to find at the time.

All that said, I WOULD use the studs on your boosted application. As you mentioned, you have the tools and skill to do it as well as the need..no reason not to. I'm not sure why they put all 8 boss's on there either. I think just using 4 will do all you will need just like Rick said.

Looking at the boss...is it machined flat on the underside? It doesn't appear to be.

I've seen the bolts handled several ways. I think the best would be to drill and tap the heads and install a stud in them and then put a nut in the lifter valley with a flat washer under it. Seems like that would be the easiest on the head casting.

I've also seen the hole drilled all the way through and a flat head bolt installed through the port with a nut in the lifter valley. That takes some fancy machine work to make a recess in the bottom of the port for the bolt head to drop down into. Plus you always have the sealing issue. Probably done when someone messed up the first version listed above!!

Then I've seen the head tapped and just a bolt installed and TQ'd up. That works too...but I would just feel better with a stud in there.

I'd have to go look up the TQ specs too, but I know they don't take too much really. See what Brodixs says. You might even consider installing a Helicoil or steel insert in them to make sure things hold well.

Good luck...looking forward to how that bad boy runs!! We still need to line up a *dyno day* for that puppy!!


JIM

 

the previously-available GM older-style (not ancient-style) alum open chamber heads (e.g. PN14011076) used to come with those two particular bolt holes already drilled into the intake port, to mate with those extra hold-down bolts in the lifter valley. it was two (2) per head. The purpose was to provide some extra clamping for that long stretch of head-gasket between the 10 o'clock and 2 o'clock head bolt/stud. I guess in older technology castings in those days of yore, the head casting may have had a weakness there (metallurgy and/or casting design). I suspect modern aftermarket BBC head castings (and gasket technology) are improved in that aspect. Old pictures of Can-Am blocks show the extra hold-downs. The old Chevrolet Power Manual used to remind folks to not to forget to plug those holes in the intake port bottom if their block didn't have these accommodations and those extra hold-down features weren't be used.

 

Jim you have planted a idea.
I will drill and tap the head for a helicoil. I will then install a stud with loctite. The stud protrudes into the intake port which I don't mind. When the loctite sets up I will then take the grinder and report the runner so the steel stud blends into the port and not disturb flow.
It is a great idea you planted.
Yes I think the bottom of the bosses are machined but have to look closer tonight.
I will use a stud like you suggested, a hardened washer and a nut.
Jim I am not going all out for horsepower, I am not interested. I just want a super torquey motor and 540 cubes and a blower should get me that.
At the local shop they have a test mule for checking the dyno. It is a blown bigblock putting out exactly 1000 horse, they have it on wheels and roll it in to check the dyno from time to time , comparing the horespower curve against each other to see if the dyno has changed. I will talk to them about a cam choice.
I am looking for about 1000 horse but don't intend to abuse the engine.
Just a nice smooth running street car.
I do intend to really brace the front end more when the motor is out. Before pulling it I intend to really take picture, measure and figure out how I can add more bracing while it is appart.
I am busy file fitting the rings today.
Thanks Jim for your input.