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best head bolts

C

coondog240

Homing Pigeon
Joined
Mar 26, 2003
Location
St. Augustine FL
I did a search but couldn't find anything.
But it seems that I remember someone saying that pre '80 head bolts are the ones to use for high boost and a built motor, because they don't stretch or something. I was wondering if this is true why? And do you buy new ones or take them off a car?
Thanks,
Jeremy
 
yes, the head bolts to use are the ones with a female hex top, often called an allen-key-type head.

They have a fuller main diameter, shorter threading, and presumablely different material.

They are no longer available new.
 
I still can't understand why the new headbolts tighten the way they do. In my Haynes manual is says to tighten post-'80 headbolts to 15ft/lbs, then 45, then give each a 90* turn. What's up with the 90*? Is that just to squash the new HG properly? I can't really see how a quarter turn could be all that accurate, I'd think that a proper torque number would be more accurate. Thoughts?

And the pre-'80 headbolts are something like, tighten to 50ft/lbs, then bring the engine to operating temperature, then tighten to 80ft/lbs. (not exact numbers!) But this method makes sense to me.

John
 
90 degrees is to stretch the "torque-to-yield" bolts.

Rotational torque only approximates the desired stretch of any fastener, and is affected by the thread pitch, the materials used, the lube, the condition of the surfaces, etc.
Each normal non-stretch bolt will still stretch a certain amount prior to taking a set and not springing back, and will stretch a bit before failing.
To get the most clamping force, the best way to tighten is by measuring stretch, which is a pain, and most people would screw it up.
The next best way is to torque them to a set amount, but people still mess that up.
So the manufacturers use bolts that stretch a long way before breaking, and it evens out the clamping force nicely and holds that force a long time.

Studs with fine threads give much more clamping force than coarse threads in the block.

Moly lube is the best thread lube, loctite is OK, and Felpro grey bolt prep is a combination of the two.
 
All above is true. Also, the stud can be screwed all the way into the block. Torque applied to the fine threads on the other end give a more accurate torque reading.
 
Torque reading is a horrible way to tighten a bolt to a given clamping force. A given torque reading is affected by the type of lubricant present (or not) on the threads/bolt head, surface quality of the threads/bolt head, cleanliness, speed of rotation, etc. Just about anything will throw off a torque reading.

Measuring bolt stretch is about the best you can do with high-grade bolts short of instrumenting for a direct strain or clamping force reading. The problem with head bolts is that you can't access the other end to measure stretch and you likely won't find stretch specifications anyway.

A compromise is to measure angle. By knowing the thread pitch you can produce a approximate stretch by turning a certain angle. The problem with this method is when do you actually start measuring the angle? So far the easiest method is to use torque until you are pretty sure the gasket is compressed and all washers, etc have flattened out. The majority of the clamping force is then achieved by turning the bolt to the specified angle.

RT
 
To add to Richard's post, the low torque figure is used because the more torque you apply to the fastener, the more surface finish, lube, etc., have an affect on the friction on the threads. You torque the TTY bolts to a given value to take up all the slack and make sure they're even, (plus most click-style torque wrenches are only accurate above a certain value), and then you KNOW how much more they're going to stretch by turning them 90 degrees.

Thomas Fritz has some opinions on head bolts, and many of them are based on personal observations. Mainly, he's noticed that on cylinder heads where the gasket has failed, the area on the gasket surface around the hole for the head bolt has actually deformed, suggesting that installing a stud or any other style of head bolt wouldn't actually help prevent the gasket failure. I'm not sure I believe that 100%, but it IS clear that the head is permanently deforming somewhat around the head bolt holes.

Studs for (12 valve?) Cummins 5.9 litre engines are said to work in 8 valve redblock OHC motors. If you wanna give 'em a try...
 
"...on cylinder heads where the gasket has failed, the area on the gasket surface around the hole for the head bolt has actually deformed..."

The deformation is caused by bolts pulling up the metal as they are tightened. This is less likely to happen with studs since the stud is fully seated, using all the threads in the block. Much less torque is needed to reach the desired value since you are pulling on fine threads on the other end of the stud.

But, stretching bolts by degrees of rotation is the future for bolts. All new GM engines use this method. There is an attachment made by GM, that reads angularity, for use with a breaker bar.
 
ElPiloto said:
But, stretching bolts by degrees of rotation is the future for bolts. All new GM engines use this method. There is an attachment made by GM, that reads angularity, for use with a breaker bar.
Click to expand...

You can buy one at Sears, too. At least you could a while back. It has an inner and outer part, and they rotate relative to one another. The outer part has degrees marked on it, and a little arm that you place against something stationary. The inner part has a needle on it which you read against the outer part. The inner part also has connections for your 1/2" socket stuff. So you can turn the socket and see how many degrees it turned.

(Just describing it for those who haven't seen it.)

Greg
 
ElPiloto said:
"...on cylinder heads where the gasket has failed, the area on the gasket surface around the hole for the head bolt has actually deformed..."

The deformation is caused by bolts pulling up the metal as they are tightened. This is less likely to happen with studs since the stud is fully seated, using all the threads in the block. Much less torque is needed to reach the desired value since you are pulling on fine threads on the other end of the stud.

But, stretching bolts by degrees of rotation is the future for bolts. All new GM engines use this method. There is an attachment made by GM, that reads angularity, for use with a breaker bar.
Click to expand...

The comment related to deformed head, not deformed block. There are no threads in the head and such the stud would be of no help in this case (or so it would appear).

RT
 
I tend to agree with CNG's last comment- headgasket failures in that case are head deformation- not block. IMO the early bolts are strong enough and accurate enough that when used properly failure will be either the headgasket itself or the head deforming.
Are the early bolts "old school"? Yeah. Are there more accurate, high tech, fancy-boy ways of bolting the head on? Totally.

But, the "early bolts overtorqued 10 ftlbs" recipe is pretty well proven imo. Clean 'em, chease the block threads, lube 'em up good with 15-40 and fire away. Just my opinion. I'm sure I sound old and etc but it seems to work. Oh and used ones are fine just make sure they don't look rusty or stretched or whatever.
 
CNGBrick, I don't see how a head could be deformed by torqueing the head bolts. Does he say how the holes are deformed? Was he referring to aluminum or iron heads?

I'm not disputing this, only curious how the head bolt holes got deformed.
 
hmmm...

coondog240 said:
Sweet thanks for the info. I am going to pull the head on my '78 gt and keep the bolts for my new motor. I am sure these will be fine.
Thanks,
Jeremy
Click to expand...

if you are somehow convinced that 26 year old bolts that have been in tension for 26 years are somehow better than new TTY head bolts...then go for it.

Since the 'Duck alluded to it, I'll post the link:

www.pbase.com/stealthfti/goodaluminum

in that gallery, I show where the aluminum of the head gets deformed by the head bolt tension...irregardless of any head gasket failure. And, that deformation was with the "weak" TTY head bolts. My point there was if the heads deform with those wussy TTYs, then overtorqueing old style bolts will only accelerate the problem. But, there is a lot more to it than just that. [and since I am in the middle of finishing up an L block, I'll let my gallery tell the story]

back in the good old days of the old style head bolts, head gaskets had a habit of just 'leaking out the side all of a sudden'. it was a fairly common problem.

Volvo went with TTY head bolts because TTYs provide a more uniform clamping force throughout the thermal cycle of engine operation; especially on engines with aluminum heads.

Don't believe me. Do a search on TTY bolts.

Are studs good? Sure...depending on the use. I have them in my SBC 4 bolt main truck motor: holding the main caps and the World Products S/R 202/160 iron heads on. I love them...in that application.

Cappy, I am gonna have to totally disagree with you on this; cuz there ain't no way that 20+ year old used bolts are better than new TTYs. And, cuz if you are really worried about handling "high boost", then you will Oring the block....AFTER you deck the block and the head to get them both abso-f'n-lutely flat. That is, IF you are truly worried about holding high boost.

And. as always: it's your money, your motor, and your problems when it craps out.

later,

Thomas Fritz
...the stealth FTi
 
I'm sure new TTY (at whatever rediculous price Volvo wants for them) would work well.
In fact, unstretched, brand new ones will definitely work great, but as I've said before, once they've "yielded" once, I think you lose a LOT of their benefit second time through. The earlies are consistent use after use which I like- and the dozens of 400hp'ish swedes who swear by them are enough to keep me rooted in my camp. :)
As always, everyone's choice is everyone's choice. ;-)
 
you are right about re-using the TTY bolts - they are one use and toss technically. They are spec'd to use once - not multiple times
 
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