Thread:

Another head gasket question

But we are going to studs now and torquing them to 70 ft lbs with arp lube.
Right?
Cuz I think bolts may have been a major player in all this....so cover that base.

This could all be you just did not have enough clamping force. The studs will make that better.

I don't know about the other MLS gaskets, but Cometic says they require at least a 50ra which is pretty smooth, but not "reflective". I've used them on worse with a layer of copper coat. I know they're far less tolerant of an out-of-flat surface than a questionable surface finish.

Originally Posted by steelcomp

Hmmm. Me thinks here might be part of your problem, thinks me.
5 lb increments is bad. Every time you start your pull, you're barely overcoming the breakaway torque. Besides, that would take forever. Big waste of time and probably not getting enough preload on the bolts...
...except to say I don't know of any 7/16 head bolt that gets torqued to 85#.


Here's what I prefer. Use the GM torque sequence. (I worry about the inner head studs later)
Start at 30...then 50...then 70. Go through the recommended torque sequence. Then do the inner head studs 30, then 50. If you want, you can add them to the end of the regular torque sequence as #17 and 18, but here's the most important thing:

Let the engine sit for about a half hour or longer, then come back and starting from #1 in the torque sequence, loosen the bolt (or nut) at least 1/2 turn, then in one smooth pull, go to full torque value...in this case, 70#. Then move to the next bolt/stud, do the same. Loosen, tighten to full value. Move to the next, and so on till you've gone through the entire torque sequence.
Using this method, I've never lost a head gasket, and never had to re-torque one either. FWIW, this method came from Felpro years and years ago. I think they claimed something like 80% improvement on head gasket sealing using this method.
Here's why.
1. when you wait a while, things settle, things compress. As this happens, the fasteners lose preload (stretch, clamping force, whatever you like). Re-torquing even without running the engine or using their full-value method is a good idea.
2. When you pull your torque wrench from 30 to 50#, or 50 to 70#, you have to overcome what's called break away torque. This puts the fastener in a preloaded torque condition that subtracts from the final value when you stop pulling. You are not rotating the nut or bolt as far as you should be to get the proper amount of preload. The result is less clamping force than was intended. The solution is to go from a zero value torque, to the full value torque in one movement, eliminating the breakaway torque. Of course, the reason you can't do this from the start is you want to bring the part down tight evenly, so we use increments, but once the part is flat and stable, you can go back and individually re-torque each bolt to it's full value, getting the designed preload and clamping force needed. The way to verify this is, put an index mark on the bolt or nut, and on the head next time you do your torque sequence. Then follow the above instructions and note that the second time you tightened the fastener with no break away torque, it actually turned further, getting that extra preload (more bolt or stud stretch).

Here's after completing the normal torque sequence to 70#, BB Chev, factory head bolts. Notice the white index mark:



Here's after doing the full value re-torque:

X2 on the half hour or longer....even overnight. I was taught it was the path around the pia re-torque.....and marking bolt heads was proof enough for me. Pretty sure it's mostly gasket smash, i had the occasion to remove a head from my deal several times
over something i refer to as 'improper valve guide break in procedure' an re-used the head/intake gasket and ckeck the the re-torque first time and nuts ended up in same place.

I do remember years ago putting a set of heads on a small block,late night cold...might have bee, 45*-50*...next day boss came in...maybe 80*...and 'checked my work' and every bolt turned a little before it would click the wrench.

Originally Posted by PS&B1

Well?
Machine work
gaskets
old head bolts
needs studs
o- ring block
copper head gasket
Inadequate torque
Come on guys Tom wants to go Racing

thats why you do it right the first time so you can go racing and enjoy yourself. year after year after year