66 427-425 Head Bolts....function & judging

[Craig S.]

Well, it seems that my machine shop is suddenly making substantial progress on my engine and I am rapidly nearing the stage where I need to get the head bolts figured out if I want them to hone my cylinders with my bolts in the deck plate. I am torn on this topic, my engine has none at the moment since the heads and block came from different sources. Per Joe L's posts, Paragon does have the correct original headmark bolts for sale. I don't know if anyone has seen these, or had any experince with them....I trust ARP like no other brand, and while it may be many moons until I ever have this car judged, since they are externally visible I am wondering if I should get the bolts from Paragon or go with the Hex head ARP's. I don't know anything about the quality of the Paragon parts, if they are US made, import, strength, etc...but I do know a lot about the quality of ARP. This is no place to scrimp, and I want the quality of the bolts to be there first and foremost. Any thoughts? Thx!...Craig

[Clem Z.]

Re: 66 427-425 Head Bolts....function & judging

if the bolts hold torque there should be no problem. what are the head bolt marks as i have some orignal BBC head bolts here. for street engines even used bolts will be OK as long as they pull up to torque.

[Craig S.]

Re: 66 427-425 Head Bolts....function & judging

Clem - sent you an email through the send email function here....but I would be very interested in your bolts. I can't find the headmarks listed in the TIM&JG, but the Paragon catalog says all BB head bolts from 65-74 have an 'M" headmark. Thx for checking!....Craig

[Craig S.]

Re: 66 427-425 Head Bolts....function & judging

Clem - my machine shop felt if I was going to use stock bolts, he has some for the torque plates. But if I use ARP, he wants the ARP's used since they have greater clamping force, and would affect block distortion for the honing operation. Thx again!...Craig

[Patrick H.]

Re: 66 427-425 Head Bolts....function & judging

Craig,

I'll leave myself wide open here for criticism, but how could a stock bolt vs. an ARP bolt, both torqued with the same method and to the same values, yield different "clamping forces?"

I'll fully admit I may be missing something here, but I don't know what it is. The only way I could imagine a difference is if the thread portion of an ARP bolt is significantly longer than a stock bolt, potentially reulting in slightly different distortion down the cylinder.

Either way, I don't think there is any way it will make any difference whatsoever. You won't get an extra 100,000 miles out of the rebuild just because of the bolt you used in clamping down this fixture.

Just my $0.02

Patrick

[John H.]

Re: 66 427-425 Head Bolts....function & judging

Craig -

I'm with Patrick - makes no difference whose bolts you use for the deck plate; torqued to the same level, either one will exert the same clamping force (assuming they don't yield). For long-term reliability, I always use ARP head bolts (and main and rod bolts) too at engine assembly.

[Craig S.]

Re: 66 427-425 Head Bolts....function & judging

John and Patrick - I think his comment relates to the higher tensile strengh bolts that have a torque specification higher than the stock values. If I recall, all ARP fasteners have their own torque specification, and, if I remember correctly, they supply their moly lube, and indicate that there is far more clamping force at a given value than with motor oil at the same value. Anyway, a 220,000psi fastener can take more torque to yield than a 150,000 psi grade 8 fastener. This is what I am guessing is behind his comment. I would agree that given the same lubricants and the same torque, the clamping force is the same. But, I know you have to stretch a fastener for it to work correctly, and I am just assuming that when the bolt stretch of a 220,000 PSI ARP fastener is has reached the same stretch length as a lesser psi fastener, it takes more torque to reach that stretch length, generating a higher clamping force. Same principle as going by bolt length for rods instead of torque value, the stretch is the real indicator of proper installation of a fastener. ARP makes a big deal out of this in their master fastener catalog. Anyway, bottom line is the variable is increased clamping is caused by a higher torque value on the fastener, to reach the specified stretch on the fastener. Hope this makes sense....Craig

[Patrick H.]

Re: 66 427-425 Head Bolts....and semantics.

Craig,

I think you're getting into a LOT of semantics at this point. I'd still say that if a fastener is torqued to, say, 55 lbs-ft, it doesn't matter how much it has stretched - the force exerted downward will be the same as the next fastener. Whether it has to stretch .0001 inches or .0002 inches is a moot point, as long as the breaking point is .001 inches (or some similar arrangement of numbers). I think it's more likely your engine guy doesn't want you to BLAME him for anything that MIGHT go wrong, so he's doing some "CYA."

If the car is going to be judged and run on cruise nights, use some stock bolts and enjoy it. For a slightly better idea, use new GM bolts under the valve cover where you won't see them, and originals where you will.

If you plan on spending a lot of life above 6000 rpm (can big blocks do that? ) then go with the ARP's. I know John uses ARP's and doesn't care about lost points, but I take my (small block) motor to 6000 rpm once a year or so and don't have any problems. Your rod bolts are MUCH more important to engine longevity than your head bolts.

Patrick

[Craig S.]

Re: 66 427-425 Head Bolts....and semantics.

Patrick - you are probably right...but I do know a fastener has to be stretched a certain amount to insure correct clamping, or it cam come loose. I am sure my use doesn't really dictate the ARP....and I agree that rod bolts are FAR more critical. Knowing me, that BB will see 6000 grand every now and then, probably right before I see red and blue flashing lights in the rear view... thx for the input!...Craig

[Clem Z.]

Re: 66 427-425 Head Bolts....and semantics.

using the same type head gasket under the plate that you will use with the heads is just as important as the type of bolts because the gasket also loads the block. i always used stock chevy head bolts and used heavy wall tubing the correct length around the long bolts to get the correct load. on the short bolt side of the head i counterbored the plates to the same thickness as the heads so i could use the stock chevy bolts. if you want to really get anal make sure they do the final hone with hot water flowing thru the block. we use fitting that went into the soft plug holes in the block to run hot water thru when we honed. we used a electric water heater and a small pump to move the water thru the block and back thru the water heater,crude but it worked. i wanted to get to 190/200 degrees temp but the best we could do was about 160 degrees with our setup. the bore at 160 degrees is anywhere from .0006 to .0010 different than room temp and this could be in the same cylinder.

[Craig S.]

Re: 66 427-425 Head Bolts....and semantics.

Clem - I was planning to use the Felpro head gaskets under the deck plates. However, the hot water hone idea, while is makes good sense, is probably not practical for my machinist, although maybe he does do it as he builds mostly high performance racing engines, occasionally the standard stuff but lots of local racing guys use him. I am not trying to get too crazy here, just do a basic stock rebuild to exacting specs....but with a few goodies such as 7115 crank, GM white dimple rods with ARP Prowave bolts, etc. Thx for the insight!...Craig