Hey Lynn;
I have a question for you.
Jeff Whaley and I ended up installing and tightening some bolts to
normal torque the other day in cold weather - approximately 0 F.  As
opposed to 70F.
The thought occurred that stresses due to thermal expansion will be now
be a bit higher.  We should probably have used lower values and
re-torqued later.
Any thoughts or rules of thumb based on deltaT from absolute zero.
Have you had any similar problems with field repairs in the cold?

Thanks
Cary

Aluminum adds about .001" per inch per 100 degrees. So, in theory you would expect about a .012" of growth going from zero degrees to about 190 degrees. If there were no tension bolts.  However, with the bolts torqued up perhaps a number of tons of pressure are applied to the stack, and any growth will be drastically limited.

 

Note that a column of aluminum is cast in place around each bolt hole to prevent bolt loadings from deforming the housings. In effect each bolt hole is a very thick walled aluminum tube.

 

The torque numbers provided are for clean dry threads. There is an assumption here that all machining is accurate in the bolt holes and bolt threads. And is it "dry" after the cleaning tank and car wash? Vapor degreasing yes. Home shop no.

 

Racing Beat says to use anti-seize on the threads. I add it to the heads and washers, as well.

Use the factory sequence and go at it to 8 pounds-12 pounds-16 pounds-and end at 24 pounds unless its a high HP, Turbo or Racing unit, then end up at 32 pounds. This will be well into the elastic range and if a bolt seems to turn without adding torque, just discard that bolt. At this point I make a Sharpie mark on each bolt head and the iron next to the mark on the bolt. Wait 24 hours. go around the pattern again, and several bolts will pull up a bit more to get to the torque number. If the engine is out or the rear iron is exposed for any reason, re-torque the case bolts. Several will pull down.

 

The reason for all of this multi step procedure is that the rotor housings are just not very stiff in torsion. The shallow torque steps and sequence is to pull the stack together nice and flat, and end up with a nice square engine.

 

With a higher torque load, the engine will be more stable in torsion. It will be stiffer in bending (Beam). Stiffer means more power and less noise and less heat. Stiffer is better.  

 

The answer if we start from absolute zero is: Finger tight will be fine, but your fingers will break off, so don't do that........Got back from Daytona yesterday. Got my screaming 3 rotor fix. Dreamed about them last night. I got a sun burn. Got to wear my No-pistons Tee shirt.

 

Lynn E. Hanover 

From Zephyrhills

Florida