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Gen pulley diameter

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healeyboz

healeyboz

Jedi Knight
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A weird request, however, could someone measure the outer diameter of a 59 generator pulley if their mechanical tach reads correctly?
 
My tach is reading about twice as much as I imagine it should. It bounces all over the place. The only thing I can think of is that I have the wrong pulley on the generator. I am reading a 3" o.d.
 
Sounds like the cable is binding and releasing. This flicks the disc and causes higher readings. If I get out to the garage today I'll measure mine.
 
Thanks Trevor. I have checked the cable and it is not binding. I even changed the cable and it is doing the same thing. Still could be the problem, just wondering the if the pulley is the culprit.
 
I have no experience with this but it's hard to imagine a wrong sized pulley doing this - surely it would give a wrong reading - but a consistantly wrong reading - can't think why a round "input" would give an erratic or bouncing respone?

FWIW
 
Maybe there is binding in the Tach. Has it been rebuilt/serviced?
 
I took it in and had it checked--it checked out ok. I hooked up a drill to the end of the cable that would go into the rear of the generator and everything looks as it should, (no bouncing). The only thing I can think of is the pulley diameter, but you are right, it doesn't explain the bouncing.
 
I'm not sure a drill is the proper tool for checking the tach. It doesn't take much of a bind to make the needle jump all over. The drill probably wouldn't feel that at all. Better to try turning it slowly and carefully with a hand tool and no leverage.
 
...or hook the drill to the generator end of the drive cable and see if the tach reads smooth or bouncy.
Bill
 
oops,
I forgot, but I'll do it in about 1 hr.
 
OK,
The one I have is the old riveted version. It is 3 and 9/16 inches across the face. I'm not sure if that is of any help to you.
 
To answer the original question, the pulley on the generator of my '60 bugeye is 3 5/8" in diameter, measured at the outermost edge. However, it's hard to see how you could get the wrong size pulley, especially to give a reading of twice what you should get--it would have to be 2" in diameter! Also, if the pointer is bouncing a lot, that 2x estimate can't be very accurate, I suspect.

The cable follows a rather tortuous path between the generator and tach, and it can easily bind in the housing. Then, when it lets go, the pointer jumps, and maybe that's why it seems to indicate fast. Finally, if the pointer has been moved on its pin, that could cause the indication to be inaccurate.

I'd make sure that the cable is moving smoothly first--that might fix it completely.
 
I'm with Steve ... like I said in my original post.
 
This is a problem that arose in the spring when I first hooked everything up. I hear what you all are saying and I have already tested everything. The only thing left was the pulley and the belt. I have a smaller belt due to the pulley size. When I took the generator in to have it reconditioned they chose to put the later model pulley on. I can't remember the reason. I do remember something about making sure the belt lining up properly, that is how I know they swapped pulleys. I think it might have been slightly bent. My pulley reads at exactly 3". I tested the cable binding with a drill. I placed the drill at a very close position to where the generator is and ran the cable just like it is when hooked up. I even bought a second cable. The cable is not binding. I figured, roughly, twice as much--Who knows. I will try to locate the original and see what happens. Trevor, thanks for the measurement!
 
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