Bolt torque.....

Any of us who have been into the 6.2/6.5 engines are quite familiar with the TTY (Torque to yield) head bolts..

Use once and then toss them in the trash.....

Then there is the "Torque angle" procedure......

Confusing ???? Not really.....

Torque to yield is a type of fastener
Torque angle is a procedure to tighten a fastener to achieve optimal clamping force....

I recently sat in on a seminar at a large shop .......
Very interesting.....And it all makes perfect sense......

As a bolt is tightened the friction between the bolt head as well as the friction in the threads changes (Increases)

Factors such as...CLEAN THREADS, DIRTY THREADS, TYPE OF LUBRICANT USED..IF ANY can all have a major effect on the final result as far as the actual holding power of the bolt.....


The TTY bolt is actually taken to the point where it stretches to give optimal holding power as the engine warms up or cools down.

A TTY bolt is usually tightened using a "Torque angle" A BASE TORQUE SPEC PLUS 1/2 TURN OR WHATEVER IS SPECIFIED to place the bolt at the point that it is stretched into the elastic zone and provides the optimal holding power......


NON TTY bolts can and in many cases today are tightened using the TORQUE ANGLE PROCEDURE

The bolt is tightened to a low torque spec to provide a baseline and then will be tightened to a specific amount farther usually specified in degrees.....

For example.....A cylinder head bolt set will be tightened to 20# using the specified sequence.....then the second time through the bolt will be tightened to +80 degrees....Or some specific number (ANGLE)

There are torque angle meters that work with a standard breaker bar....The meter is a simple device that has a small rod attached that can be allowed to touch a nearby part to hold the meter...meter set to zero and then the bolt tightened until the meter reads the angle required..

The angle is simply a computation of the thread pitch and how far the bolt is actually "Moving" to apply clamping force......Vs friction of the bolt head on the mating surface and also the friction of the threads...

Torque wrenches can be all over the map.....There can be a lot of variables in torque wrenches......

Combine this with..

Were the threads all cleaned with a tap before reassembly
Were the threads lubricated
What sort of lube was used
Were the bolts new, used.....Some threads not in good shape and have nicks and burs on the threads.

Do the bolts have a dry sealer on them out of the box.....


The Torque angle procedure make absolutely perfect sense......The torque value that is actually the end result (Clamping force) will be far more accurate than simply wrenching the bolts down in three steps and calling it good...

The Torque angle procedure has come about to lessen gasket failures and other torque related issues....

My one question is HOW DID WE MAKE IT THIS FAR AND NOT HAVE ANY REAL ISSUES ?????

I got involved with this little quest while working on the engine for the snow cat.

A 1980 Small block Chevy 400 that we are fitting 1998 L31 Vortec heads to...

I have 1986, 1993, 1994, 1995 and 1998 GM manuals on the various V8 engines

The 6.5 definitely uses TTY head bolts....All other fasteners are just the standard grade 5 or 8 stuff with a given torque value.......


Now the gasser stuff like the LS engines use TTY stuff on the heads and the rods.....

The old school GEN 1 small block are standard bolts NOT TTY.....
The later stuff like the L31 vortec DO specify TORQUE ANGLE procedures when tightening the bolts.....


Simple answer.....A more accurate holding power of the bolts ......

Just because Torque angle is specified DOES NOT MEAN that the bolts are TTY

Now that you are totally confused.....

The TTY head bolts "Usually" have an area between the head and the thread on the shank that is smaller in diameter....TTY

"Most" standard head bolts will have a straight shank from head to the threaded area.

BUTTTTTTTTTTTTTTTTTTTT.....These two descriptions MAY NOT always be 100% true.

Confused yet......UH HUH.....

Always consult the factory manual OR a good trusted spec sheet to fully understand what you are dealing with

In looking for a head bolt set for my 406 SBC I found many brand names that offer bolt sets.....Some mentioned that the bolts fit all SBC from the 50's all the way to 2000....

Digging deeper....There were tightening specs on some that had both the multi stage torque value AND the Torque Angle value

This subject is still a tad vague.....but I hope this helps clear the air a little bit..


NOW TO MUDDY THE WATER EVEN MORE

I grabbed the 1998 Chevy shop manual........

The head bolt sequence is given in a few ways (5.7 gasser)

22 pounds first pass.....then the angle on the second pass

THEN....OPTIONAL "IN CAR PROCEDURE"
22 POUNDS....25 POUNDS THEN 45 POUNDS

NOW TO REALLY MAKE YOU WONDER (5.7)
Older GM books spec "Starting through the sequence" A LITTLE AT A TIME and finish at 65 pounds.

THE 6.5 ENGINE
20 pounds...35 pounds...55 pounds and then 90 degrees

NO OPTIONAL PROCEDURES ON THE 6.5 (TTY BOLTS)

The 7.4 (454) uses a 3 pass torque value only NO ANGLE REFERENCE IN THE GM MANUAL...

Best part was....I got to sit in on the seminar at the dealership and not fork over $$$$$$$$$ or drive very far....I was at the dealership anyway....

Back in the late '60's an early '70's during my SAAB 2-stroke days we wrenched down the head bolts on those 3-bangers using torque plus angle, but we didn't replace the bolts. The blocks were iron and the heads aluminum.

YUP

DKW was the same way.....I could not read the German service manual....So we just gave them what felt good and called it a day....

I also recommend allowing the head bolts to sit at 55-ft/lbs overnight (before applying the torque angle), then apply the 55 again the next morning. I found that the gaskets relax a little overnight. Spotlessly clean deck surfaces... Only handle the gaskets by their edges. Use bolt thread sealant on the bolt threads and a small dab under the bolt head (the GM sealant is a Teflon paste - only use a little).

I really prefer/like/recommend the Fel-Pro gaskets. I used their +0.010" over gaskets in our recent 6.5 build because the block decks had been machined about 0.007".

All good stuff Jim......
Tricks of the trade maybe ???