Rebuilding an alternator

[dguy]

If there's a recommended amount of torque to apply to the pulley nut on these things, Haynes doesn't mention it.

Is there such a thing, or should "damn tight" be sufficient?   

[aaron88]

There is a formula for that.  I need to know:

the size and thread of the bolt
How many threads will be in the the material
what is the type of material the thread is in, or what is the tensile strength of the material
finally will you be using locktite, anti-seize or nothing?


Aaron

.

[fiero308]

got me on that one, Don.
I wonder if one of the electrical houses in town might divulge that..... they might.
Otherwise, it is the BFH principle except you need a BFPipewrench to hold the armature  while you crank on it.......
good luck!

[Sentinel]

typically the give point is the fins on the alt ( if you use the jam something and torque method) not recommended, my friend swears by an impact wrench as the only method... not much of a help but....

[dguy]

There is a formula for that.  I need to know:

   When it comes to mechanical engineering, is there any formula you don't have? 

Don't worry about it.  I've asked around in a few other places, and the popular method is to crank it on as tight as it'll go with an impact wrench.  So methink's I'll be using an allen key/wrench/cheater bar combo, with a side order of loctite.

One of these days I really have to finish building that air compressor...   

[aaron88]

In my line of work it’s not just what you know it’s also what you can find out given time to research.  However; something as basic as thread strengths sits in my library at work.

With an impact it depends on the gun the socket and the air pressure.  Most people have little cheap 250 lb impact guns at 90 psi (air pressure).  But something else you have to take into consideration is that most people also don’t use the right socket or clean up the nuts properly, so although the impact gun is 250 ft-lb they don’t turn them on until the nut stops turning all together so in the end they really are only tightening to somewhere 37 ft-lb or something.  It sounds out there but those are the facts.  The other thing is; some people have much better impact guns, for example mine is 650 ft-lb.  If I tighten on that nut until it’s tight I’ll snap the bolt right off.


Aaron

.

[dguy]

Interesting!  The only reason I turned down your offer to calculate the thread strength BTW is that I have no clue what grade of steel the armature shaft and/or the nut are.

For what it's worth, after cleaning the threads up I can tighten the nut down to about 70ft-lbs by hand before the allen key starts threatening to slip out its hole in the shaft.  I can probably go a bit higher if I spend some more time cleaning up the hole in the end of the shaft.  Hopefully that will be enough to prevent the pulley from slipping against the shaft under normal loads.

...at this point I can't help but wonder why the pulley & shaft aren't splined?     It would make a lot more sense in some ways.  At least it would to me. 

The other thing is; some people have much better impact guns, for example mine is 650 ft-lb.  If I tighten on that nut until it’s tight I’ll snap the bolt right off.

Hey now getting those broken bolts out of the housing was enough work.  You keep that impact gun of yours well away from Sacha's alternator!