Torquing Head Bolts

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Torquing Head Bolts

Post #1 by Whiskerfish » Tue Sep 04, 2007 5:00 pm

Here is a link I borrowed from Exavid over on the Saunders board. It describes the effects that torques have on head bolts and head clamping pressures. Some interesting reading if you are so inclined.

http://www.babcox.com/editorial/ar/eb70536.htm

I think the link above died try this one.

http://www.enginebuildermag.com/Article/1126/perfect_engine_sealing_starts_with_proper_head_bolt_use.aspx





I bring this up due to the recent rash of head gasket failures that we have seen discussed here. The note (Below) from the Manual is there for a reason. This step is critical to achieving proper head clamping pressure. According to the article (above) lubricated bolts can achieve 20-25% more clamping pressure than non lubricated bolts. Any decent Moly Grease will suffice but make sure the threads of the head bolts are cleaned then lightly lubed along with the undersides of the bolt heads before torquing them.

So basically not lubing the bolts is ensuring that your head is not properly torqued and is a sure fire way to have a head gasket failure before it's time.

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Also make sure to observe the new torque values (42-45 foot lbs) per the service bulletin http://www.ngwclub.com/File%20Share/100 ... 0%2314.pdf
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Post #2 by RAT » Tue Sep 04, 2007 5:07 pm

Useful stuff,

Hope I never need it.

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Post #3 by RebelRouser » Tue Sep 04, 2007 5:12 pm

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Post #4 by ElPiloto » Tue Sep 04, 2007 5:16 pm

I prefer studs to bolts for heads.
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Post #5 by dodger889 » Tue Sep 04, 2007 10:20 pm

Here is something that was taught in shop class years ago always tighten in steps like 50% then at 75% then to th total and read the manual and see if the torque values are lubed or dry different manufactures uses differnt ways to torque a head or any bolts. If dry then use a degreaser on the bolts and holes if wet then use light oil like 3 in one , motor oil or assy. grease . nothing else a heavey gear lube will not work right nor a heavey grease. Sorry if I step on some toes but old school way for old school bikes.
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So you guys don't retorque?

Post #6 by Cookie » Sat Oct 27, 2007 11:16 pm

I hope you are correct.
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Post #7 by Victorious1 » Sun Nov 11, 2007 2:29 pm

Good information at the top. I always grease head bolts when torquing because I work on old stuff. Old head bolts lose their elasticity and need all the help they can get to stretch the correct amount to hold the head down against compression. Grease under the bolt head and on the threads gives the bolts that chance to stretch whereas no grease might mean changing another head gasket a short time later. Remember, it's the stretch of the bolt that holds the head on securely, not the rotational torque therefore the bolt needs to spin in freely and stop at the correct torque reading. Tightening the bolt dry interferes with that process.

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Well basically, I was trained 30 years ago

Post #8 by Cookie » Sun Nov 11, 2007 9:52 pm

and I'm sure things have changed. We were taught to ensure bolts were clean, usually by the wire brush mounted to a grinder motor method. Wash in solvent, dry, and lube lightly with 30 wt.
Check each head bolt hole carefully, blow out with air, make sure it is clean to the bottom, and run a tap down if any damage. Make sure no threads protrude from the block surface and if so file and level them.
Then torque to 1/3 of spec, half spec, and full spec. If you have no pattern available go from the center of the head and work your way out to lay it flat. They will all work that way. If you have no spec go by bolt size specs and be sure to torque small outlying (fix) bolt to spec in pattern by size. Fix bolts are usually there because somebody made an error that caused gasket problems in testing, they should have gotten it right the first time.
By the way, we are not yet using in production the maximum gasket cures developed during ww2 for the piston gas engine.
After you are done it does not hurt to come back the next day and re torque.
Run the engine to normal operating temp for a time, this depends on what you read. I like an hour or so, and re torque, then re torque at 1,000 miles and forget it. I've only had two consistent failures in a large number of engines so this works in most cases.
All the above instructions are superseded by specific gasket instructions in a manual or with a gasket kit.
Many errors are made and it is not unusual for revisions so check for the latest stuff.
For example Subaru has had six gaskets for their 2.5 engine. I'm running revision six, and I'm not sure they have it 100% right yet. Sometimes the after market does better than the manufacturers so the more knowledge the better.
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Post #9 by Victorious1 » Mon Nov 12, 2007 1:53 am

That's darn good advice. Always check the kit instructions these because you never know from one gasket to the next what changes have been made and with the price of gaskets today you only want to change them once.

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Post #10 by Victour » Fri Mar 27, 2009 1:15 am

Cookie , You went to a slightly different Old School than I did.. You can't re-torque head bolts unless you loosen them first, once properly torqued they are properly Stretched and if you put the torque wrench on the Bolt you will have to exceed the Proper torque by at least 10 ft lbs.. to even move the bolt.. I was a ford mechanic and the boss better never catch you putting used head bolts back on a engine because like you say the Stretch of the bolt is what holds the head on. and they are designed to only stretch one time. reused bolt will never torque properly. that may be the reason for a rash of blown head gaskets.. I admit I don't replace them like I should and have gotten away with reusing the bolts..

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Post #11 by Cookie » Fri Mar 27, 2009 1:37 am

Vic,

That's the modern way. In the old days we often reused bolts on Diesel engines several times. Bolts and studs like that are very expensive and for some time they have been using one use bolts. Like you say one can get away using them again most of the time.
It is true when you re torque you back off a bit. I guess a lot of modern gaskets don't even want a re torque but I've used many that would blow if you did not. Sometimes I'd get another turn on the suckers after 500 miles or so.
I guess that's why I try to stick with directions if I can, I like to avoid being the test pilot.
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Post #12 by bum » Fri Mar 27, 2009 2:23 am

that's right cookie , old school.......................gotta love it 8)
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Post #13 by Morriscatt » Tue Sep 29, 2009 10:57 am

So are you guys saying I need to loosen my head bolts and then tighten again at 100 and 1000 miles? I already checked at 100 miles and I simply put on the wrench and turned until I heard the click. Barely saw any of them move/tighten at all.
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Post #14 by Victour » Wed Sep 30, 2009 1:03 am

Well I just Torqued my old Bolts to spec.. I used Anti Seize instead of grease or Oil. nice and slick and worked great.. I also torqued all the other bolts I put on. better safe than sorry. It is very important to use the proper length bolt. If you use a shorter one you can pull the threads right out of the block while torquing them..



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Post #15 by ajc » Wed Sep 30, 2009 1:28 am

The old-time mechanic I learned from, my undergraduate automotive professor, and my NIASE wrenching experience all said: clean and lightly lube; torque in increments up the the spec in a center-to-outside pattern (unless mfg has specified a torque sequence, as the GL does); recheck in a couple hundred miles.

On cast iron block & heads, I usually reuse the head bolts. On aluminum heads/blocks I would use new head bolts. However, I will admit I've done it both ways and have never had a comeback.


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