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Head Torque Technique

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jnclem
Posts: 41
Joined: Sat Jul 04, 2020 7:56 pm

Head Torque Technique

Post by jnclem »

I have been told that when doing a retorque, such as after head gasket replacement, I should just barely crack the bolt or nut back, in other words barely loosen it a hair, then bring it back up to 25 ft/lbs. is that the recommended procedure?

I’m working on a '58 R60, but this would apply to any Airhead, and presumably any situation where you have to retorque a bolt periodically.

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schrader7032
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Joined: Fri Oct 27, 2006 3:00 am
Location: San Antonio, TX

Re: Head Torque Technique

Post by schrader7032 »

On a rebuild and/or replacement of a head gasket, that's it something that I would do. Of course, try and do the criss-cross torquing as well. However, whenever I'm checking torque on a bike that's been running for a long time, I don't do the un-torque approach. I usually just see if the head bolt will take 25 ft-lbs without moving. I realize that the torque is really a "moving" resistance, but I figure if it takes 25 ft-lbs without any movement, then it's probably pretty close.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

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srankin
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Joined: Fri Jul 14, 2017 8:45 pm
Location: Spencerport, NY USA

Re: Head Torque Technique

Post by srankin »

Not that I am a professional BMW mechanic but I back off the tension then in a criss cross pattern I torque to the proper setting.

Now that you have brought it up, I will check out some of the guys who are BMW mechanics and have websites. Snowbum, Brook Reams, Anton Largidaire. (forgive the spelling guys).

I may even get off my computer chair and check out my BMW factory books. LOL, it is a rainy cold day here, and it is warm in the house, not so in my garage.

Somewhere the answer will be found. Who knows, I could have been doing things wrong for a long time. St.
Owner of a 84, R80RT and 78, R100RS

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schrader7032
Posts: 8467
Joined: Fri Oct 27, 2006 3:00 am
Location: San Antonio, TX

Re: Head Torque Technique

Post by schrader7032 »

I wonder if something like this would even be mentioned in the factory repair manual...I checked my /7 for a bit and couldn't find anything. These manuals are meant for technicians who already have been to tech school...many steps and tips are left out because they "already know that"!!
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

dardaris2725
Posts: 51
Joined: Fri Oct 27, 2006 3:00 am

Re: Head Torque Technique

Post by dardaris2725 »

The Barrington "Singles" book has a tip which makes a lot of sense to me. Especially for bikes where the head bolts may have
sat a long time; One at a time, loosen 1/4 turn and re-torque to spec.using the pattern required.

jnclem
Posts: 41
Joined: Sat Jul 04, 2020 7:56 pm

Re: Head Torque Technique

Post by jnclem »

Thanks for all the feedback. I have always used the back off a bit and torque to spec method. I was taught that by a lifelong BMW tech that I trust explicitly. I was just curious to see if there were other opinions or methods out there, but this seems to be the consensus. His comment was that, especially if the bolts have been sitting a while, or the head gaskets had been leaking, they will become somewhat stuck in place. So, you need to break them loose and then retighten.

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schrader7032
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Location: San Antonio, TX

Re: Head Torque Technique

Post by schrader7032 »

My only concern on backing off the tension is that you're doing exactly that. The loosen-tighten process just adds more tension cycles to the bolt as well as what it's bolted into. On the /2s, I believe we're talking about a steel bolt into the steel cylinder. On a /5-on, the steel bolt goes into the aluminum case. Yes there are tension cycles I suspect just from starting the bike and bringing it up to temperature. I'd be curious about the extra tension created when the spark plug fires...how much does that add to the tension over time.

I guess my point is, if there's no visible issues with leakage or indications of changing valve clearances, I just go with the test to see if it doesn't turn at the required torque...I know there's stiction involved, but if it doesn't turn, that gives me some confidence.

Maybe the small loosen once every couple of years is peanuts to the larger number of tension cycles going on! :D
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

lauffer6996
Posts: 81
Joined: Fri Oct 27, 2006 3:00 am

Re: Head Torque Technique

Post by lauffer6996 »

I torque like Kurt.
Scott

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Twocams
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Joined: Sun Mar 16, 2014 8:42 pm

Re: Head Torque Technique

Post by Twocams »

I never loosen head bolts either. Just check the torque is correct on all bolts, then check valve clearance. Checking head bolts on cars the same way. I had a 1985 Toyota Cressida for 12 yrs. Everyone complained about blowing head gasket on the aluminum head. Book said to loosen and retorque head every so often. Why? I just checked they were correct. Never blew one in 12 yrs & 150,000 miles. Go figure. Something a little common sense goes a long way. :shock:
Twocams
92 R100RT/69 R69S
2004 Aprilia Atlantic 500cc single cylinder Scooter
83 Honda V65 Magna, fastest production bike in1983
2015 Can Am Spider SE6 1,688 miles
2018 Moto Guzzi V711 Special

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