1977 merc 500 driving me nuts! any help greatly appreciated

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Vintagenc

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ok guys here is my issue, i replaced the trigger and stator on a this new to me motor.
The flywheel nut had had it.( barely any thread left) I ve tried 3 oem nuts from different sources. and one from automotive fasteners here in town. NONE fit! threads look good on shaft
could the crank shaft have a different thread on mine for some crazy reason? maybe it had been rebuilt sometime.
ser # on motor 4579144.
Nut Merc is calling for is 5/8 18 this is a tad to small.
Im stumped. and running out of summer to use this boat ive been restoring for a year
 
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Moody Blue

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3,136
Re: 1977 merc 500 driving me nuts! any help greatly appreciated

If the outer hex size of the nut is 15/16", then it is a 5/8" thread size. What you need to determine now is, is it a coarse or fine thread? Coarse is 5/8-11 while fine is 5/8-18. Can't see Merc using a non-standard fastener.
 
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Vintagenc

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Re: 1977 merc 500 driving me nuts! any help greatly appreciated

Moody Blue said:
If the outer hex size of the bolt is 15/16", then it is a 5/8" thread size. What you need to determine now is, is it a coarse or fine thread? Coarse is 5/8-11 while fine is 5/8-18. Can't see Merc using a non-standard fastener.
Click to expand...

They say it's 5/8 18 I've tried 5/8 11 also. It really seems like its a tad larger than 5/8

This was my idea. To maybe help so it would start the thread.
I took an old 5/8 18 die cut it in half put it on the shaft clamp it together( on the crankshaft) back it off so I'd have a clean start of the treads. Die won't go around . Im
Stumped
 
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Moody Blue

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3,136
Re: 1977 merc 500 driving me nuts! any help greatly appreciated

It's possible that someone has hit the end of the crankshaft with a hammer trying to remove the flywheel, thereby swelling the end of the shaft just enough so that the nut will not start. My bet is that it is a fine thread.
 
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Vintagenc

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Jun 17, 2012
Messages
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Re: 1977 merc 500 driving me nuts! any help greatly appreciated

Moody Blue said:
It's possible that someone has hit the end of the crankshaft with a hammer trying to remove the flywheel, thereby swelling the end of the shaft just enough so that the nut will not start. My bet is that it is a fine thread.
Click to expand...

That's probably the case. Now.... How to fix it ? I guess file down a tad and keep trying
Or order a Nes External Thread Repair Tool prob only options... Thoughts?
 
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