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Is retorquing the head advisable?
https://slantsix.org/forum/viewtopic.php?t=46410		 Page 1 of 2
Author:  Sam Powell [ Wed Sep 21, 2011 5:33 pm ]
Post subject:  Is retorquing the head advisable?
While I have the valve cover off to adjust valves is it OK to re-torque the head bolts, or is this a real bad idea?

Sam
Author:  olafla [ Wed Sep 21, 2011 7:14 pm ]
Post subject: 
Sam, if you retorque, do it before adjusting the valves.

Olaf.
Author:  kielbasa [ Wed Sep 21, 2011 7:37 pm ]
Post subject: 
ive never heard of retorqing the head on a v8.... ermmm american car motors. its a common thing on vw's since the case is mag, and the skinny 8mm head studs which are almost a foot long like to stretch a little.
Author:  Reed [ Wed Sep 21, 2011 7:58 pm ]
Post subject: 
I've never retorqued head bolts on a slant.
Author:  SlantSixDan [ Wed Sep 21, 2011 8:17 pm ]
Post subject: 
Retorquing is necessary with certain kinds of head gaskets (e.g., the original shim-steel variety) a fairly short number of miles after the original installation. Periodic retorquing isn't necessary with any kind of gasket. I'd say "don't".
Author:  olafla [ Wed Sep 21, 2011 11:10 pm ]
Post subject: 
If you decide to retorque, some words from Doc in an old post:
Quote:
The engine must be hot.

Once valve cover is off, I check the torque on the head bolts, if they don't move ("crack" loose and turn more) by 75 ft.lbs, go to the next, follow the "center-outward" sequence.
Doc also used 80 ft.lbs. for the same procedure in a post. Question is, if retorque is necessary - i.e. did some bolts come loose when checked at 75 ft.lbs., should the retorque best be done with a hot or cold engine, are there thermal expansion issues to consider with some of the bolts?

Olaf.
Author:  Sam Powell [ Thu Sep 22, 2011 1:17 am ]
Post subject: 
The head bolts are just sitting right there staring up at me, and if it is a useful practice, why not? If it is harmful in any way, than I won't. It is easy to put a wrench on them and check. You know, stuff gets loose. Especially in a turbo application. I did not know if head bolts needed checking. Even though it is not mentioned in the service manual, I thought the engine gurus might take things a step "better". Or maybe not. Thanks for the feedback so far. I really appreciated the quote from Doc. "Cracking" loose could have scared the you-know-what out of me.

Sam
Author:  Sam Powell [ Thu Sep 22, 2011 4:35 am ]
Post subject: 
Quote:
If you decide to retorque, some words from Doc in an old post:
Quote:
The engine must be hot.

Once valve cover is off, I check the torque on the head bolts, if they don't move ("crack" loose and turn more) by 75 ft.lbs, go to the next, follow the "center-outward" sequence.
Doc also used 80 ft.lbs. for the same procedure in a post. Question is, if retorque is necessary - i.e. did some bolts come loose when checked at 75 ft.lbs., should the retorque best be done with a hot or cold engine, are there thermal expansion issues to consider with some of the bolts?

Olaf.
Olaf, I was wondering about that "hot" thing too. Not challenging Doug's wisdom, just wondering in a curious way why this is better.

So here is a basic question to all torque specs. I have an old flex beam type torque wrench. It is analogue in nature, not digital, and requires a good eye and the correct angle of viewing. On many applications, the specified torque can be reached with this wrench while the bolt is still turning. Is it time to stop then, or does one continue to pull at the specified torque number until the bolt stops moving. In some cases there seems to be a big difference between when then wrench reaches this setting and when the bolt stops moving.

Sam
Author:  wjajr [ Thu Sep 22, 2011 5:37 am ]
Post subject: 
Quote:
I have an old flex beam type torque wrench. It is analogue in nature, not digital, and requires a good eye and the correct angle of viewing.
Yeah me too Sam, it’s a dust collector now.

Both click & beam are analog. Just one is designed to stop applying force once torque setting is reached. The flex beam can over torque if not used properly.

It may be time to upgrade your equipment to something that will produce consistent torque each time. That beam type is ok for a tie rod nut, but ten bolts clamping down a casting that goes through thermal and pressure cycling is a different can of worms.

As for a bolt turning as specified torque is achieved, that is how it is; bolt turns until tangential force need to turn it reaches desired level. Turn it more, it becomes over tightened, turn it less its under tightened. Either way bolt is always turning.

Conditions that can change realized torque on a threaded fastener are cleanliness of threads, lubricant present if any, reused stretched bolts vs. new bolts, and consistency of the above conditions of all bolts to be torqued.

In other words, it is good practice to chase threads with tap & die to clean them up uniformly, lube or not to lube depends on application, and a torque wrench capable of consistent results within a small percentage of its setting is of great importance.

Bill
Author:  madmax/6 [ Thu Sep 22, 2011 9:40 am ]
Post subject: 
I re torque or check them every time I have the valve cover off.I am running 12.5 compression on a composite gasket and havent blown one yet.Will bee testing the gasket with Nitrous.
Author:  Sam Powell [ Thu Sep 22, 2011 11:08 am ]
Post subject: 
Quote:
I re torque or check them every time I have the valve cover off.I am running 12.5 compression on a composite gasket and havent blown one yet.Will bee testing the gasket with Nitrous.
Do you do this hot or cold? Do you use stock specs, or higher as Doug recommends? Thanks.

Sam
Author:  Doc [ Thu Sep 22, 2011 1:25 pm ]
Post subject: 
The head bolts seem to "take a set" once the engine has been in service for a while. You then have to exceed the stated torque, before getting any movement and the movement usually starts with a "snap" sound. (yes, that is somewhat "nerve-wracking")

Once the bolt breaks-free, you get a true torque reading. I find that this "breaks-free" point happens a little sooner when the engine is warm.
I will get the engine hot, turn it off for 10-15 minutes so it starts to cool, then check the head bolt torque.
DD
Author:  olafla [ Thu Sep 22, 2011 3:12 pm ]
Post subject: 
Hi Doc, do you then loosen the out-of-torque bolt a bit and retorque while hot?

Do you use a different torque setting for hot and cold?

I have seen aluminum heads that carried warning not to torque while hot, but those were relatively complex castings/pressings.
Is this an issue with the SL6 cylinder head at all?

Olaf.
Author:  Doc [ Thu Sep 22, 2011 3:32 pm ]
Post subject: 
No, I never loosen, just go tighter.
I commonly torque cast iron SL6 head to cast iron block to 80 ftlbs.
No on different reading hot vs cold.
Aluminum blocks & heads use a different process and torque rating.
DD
Author:  olafla [ Thu Sep 22, 2011 5:18 pm ]
Post subject: 
Relevant info, thanks. I had a bolt by cyl. #5 go loose twice.

Olaf.
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