Author Topic: Crank bolt torque / methods  (Read 215 times)

drooman

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Crank bolt torque / methods
« on: November 27, 2021, 20:32:41 »
I searched the site and the tech manual, found two conflicting pieces of data on the crank bolt torque.

Engine: 1969 280SL  with  Automatic trans

I replaced the crank seal (was hard as a rock might have been original)  I made the appropriate tools
to install the seal properly without folding it. There was a lot of info on here about that, and it was very helpful.

Ready to reassemble, what is the torque spec of the crank bolt? ( I read 150 AND 200 ft/lbs on here) this is a  significant difference.

Also, any particular stacking that is correct for the spring washers?  Some  Porsche designs using these types of washers call for “ front to back “ stacking.  Mine were stacked like you would stack dinner plates in a cabinet..with the high centers facing the bolt head.  “ front to back” washer stacks would be like if you stacked every other dinner plate upside down.  Which way do these go? I don’t trust how I they came out considering other former repair  “efforts” I have found on this car.

Finally, any tricks for Holding the crank for the torquing installation? I can make a holding tool but before I do I’d like to hear what others have done.

Thanks everyone!

ja17

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Re: Crank bolt torque / methods
« Reply #1 on: November 28, 2021, 07:58:06 »
The crankshaft bolt with threaded straight sides gets torqued 21+1 mkp or 151.62 ft/lbs. + 7.22 ft/lbs. (Factory Shop Manual Late BBB p. 00-0/2 and 03-1/20). Some engine use three heavy flat washers.  The cupped washers are actually "Belleville springs" .  The BBB refers to them as "plate springs". They must all be installed with the convex side outward against the bolt head. An upgrade modification was offered in which a crankshaft stretch bolt (partially threaded with tapered sides) was used with the three of these plate springs. With the stretch type bolt the torque is 160 ft/lbs. then 90 to 100 degrees of additional rotation. The Early BBB has diagrams and information on the stretch bolt versions page 03-10/2. As far as bracing the engine, the Factory BBB simply states "counter hold at flywheel" while applying the torque. Most likely a special factory tool is involved. Normally I can find a safe way to position a heavy pry bar so as to lock the engine from turning while removing or installing the bolt.
« Last Edit: November 28, 2021, 15:05:52 by ja17 »
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2006 Mercedes Sprinter Van
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1982 300TD Wagon turbo 4spd.
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback