Need advice on torquing M12x1.75 class 10.9 bolt connecting a NV4500 transmission to an aluminum 1

[bigfoote]

Need advice on torquing M12x1.75 class 10.9 bolt connecting a NV4500 transmission to an aluminum Bell housing

I do not know if this is the proper forum. If not please advise.

I have a 1994 K3500 Chevy truck 6.5 Turbo Diesel

The books call for 74 ft lbs of torque with no mention of thread locker or anti-seez.

74 lbs torque sounds a little high to me, since the bolt goes to an aluminum threaded bellhousing. It also seems to me that since it is a steel bolt going to aluminum that it should have something on it.

Please advise.

Thank you much

 

[MikeHalloran]

The GM factory shop manuals usually state, somewhere in the general notes section, that torques given are for clean, oiled, NEW threads. (the only kind they have at the factory)

I personally use Never-Seez on everything that doesn't involve plastic, and work to or below the low end of the torque range given.



Mike Halloran
Pembroke Pines, FL, USA

 

[TonyDeRamo]

Although aluminum and iron are not good friends in regards to corrosion, there is very little exposure to an electrolyte in this scenario. OEMs have been using aluminum bolts on iron blocks for a long time. I presume they expect the life of the car to not be longer than the time it would take for the bolt to corrode. Vice versa using steel bolts in an aluminum case.

"Research is what I'm doing when I don't know what I'm doing."

 

[mfgenggear]

Bigfoote

good call, 74LBs will strip the threads,keep digging until you have the correct torque.

ref only
chev 350 trans to bell housing 25-30 ft lbs. use with caution went using un-calibrated torque wrench.
I like using thread locker for bolts to prevent it from vibrating loose.

mfgenggear

 

[Tmoose]

As others said, I'd double check that spec.
Are any of the books official GM?

Generically that torque spec may not be out line for the bolt.

http://www.imperialsupplies.com/pdf/A_FastenerTorqueCharts.pdf

If there are 2 full diameters of thread engagement in the aluminum and there is plenty of meat (aluminum, really) around the tapped hole it >may< not be too much for the aluminum, either.

pages 66-68 here

http://www.dalecompany.com/pdf/UNBRAKO.pdf

 

[bigfoote]

Thanks.
Actually it was 2 different GM books and a Chiltons

The GM book can sometimes be hard to follow and I've had to really look to confirm that certain bolts called for sealer.

On my mind any bolt that goes to aluminum needs something on it. They are only assembled with a certain lifespan in mind. I frequently exceed that by decades and 100's of thousands of miles.

I've dealt with steel frozen in aluminum on far to many occasions to use nothing when they come in contact

Thanks for the advice.

I did torque to 74 lbs. But my torque wrench hasn't been double checked in a few years. I don't get it calibrated. I jus compare to somebody's new torque wrench on a torqued bolt

 

[mfgenggear]

bigfoot

hopefully the threads where not damaged.
that amount of torque is normally on the the nut that holds the engine harmonic balancer with steel threads.
was there Inserts in the Aluminum?


any way good luck

Mfgenggear

 

[Tmoose]

This says 200 lb-fts for a '96's damper bolt may be appropriate

http://www.thedieselgarage.com/forums/showthread.php?t=48097

Almost certainly larger than 12 mm

No mention of trans to bell housing

For corrosion sealing concerns and precautionary locking of assembled fasteners Loctite wicking green 290 is pretty slick if you can reach the end of the bolt/screw

 

[bigfoote]

No inserts in the aluminum

 

[chief]

The old DC3 Dakota aircraft had an aluminum engine block. They had constant problems with cylinder head bolts 'pulling out ' of the block. An old Scottish Engineer told me he solved the problem by fitting Heli-Coil inserts in the block threads. Reckoned they lasted for ever after.

Offshore Engineering&Design

 

[Tmoose]

http://upload.wikimedia.org/wikipedia/commons/e/eb/Buffalo_Airways_DC3_engine.jpg

When I zoom in and look at the base of the cylinders it looks like there are a brazilian large bolts securing the cylinder flange to the crankcase. I'm guessing those bolts haved sculptured, waisted shanks. Still, Bolts with a short "grip length" like that can bring on a variety of problems in a hard working joint.

The MIL spec recommendation of designing with at least 7 bolt diameters provides flexibility that goes a long way toward avoiding problems with loss of preload, and having to balance thermal expansion effects.