Size needed for bolt to hold clutch & pulley on Tecumseh 5hp engine

Doubtful Bob

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  • / Size needed for bolt to hold clutch & pulley on Tecumseh 5hp engine
I have a Super Tomahawk 5-8-2G/C chipper from approx 1983. with a Tecumseh 5hp engine Model H50-65484N Ser 4180D sold by W-W Grinder, (who is no longer in business). The crankshaft outside is 3/4", what I need is the correct end bolt size to hold clutch and pulley on the crankshaft, 5/16" 24 is too small and 3/8 either 18 or 24 threads per inch will advance no more than a turn. The threads are visible and clean. I have the key and allen head set screws. Thanks in advance.
 

BlazNT

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  • / Size needed for bolt to hold clutch & pulley on Tecumseh 5hp engine
Have you tried an M10 1.00 or M10 1.25?
 

Boobala

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  • / Size needed for bolt to hold clutch & pulley on Tecumseh 5hp engine
Have you tried an M10 1.00 or M10 1.25?

I wouldn't think a Tecumseh THAT old would have Metric threads, (unless someone ran a metric tap into it, ) I would take a small drill-bit to check the depth of the hole and then blow-out the threads with an air nozzle then try to retap the threads to the correct size ( 3/8 ...?? ) ..:confused2:
 

BlazNT

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  • / Size needed for bolt to hold clutch & pulley on Tecumseh 5hp engine
I wouldn't think a Tecumseh THAT old would have Metric threads, (unless someone ran a metric tap into it, ) I would take a small drill-bit to check the depth of the hole and then blow-out the threads with an air nozzle then try to retap the threads to the correct size ( 3/8 ...?? ) ..:confused2:

I agree with you on this but I have seen crazier things. That is why I asked if he had tried it. I have seen a crank drilled out so much the sidewall was not 2mm thick. Stripped that engine down for parts.
 

Doubtful Bob

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  • / Size needed for bolt to hold clutch & pulley on Tecumseh 5hp engine
Have you tried an M10 1.00 or M10 1.25?
I think this is a good suggestion which I intend to try, I noticed that 3/8" = .375 inch and 10mm = .3937 inch; Do you think the pitch could over come this? Thanks.
 

Doubtful Bob

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  • / Size needed for bolt to hold clutch & pulley on Tecumseh 5hp engine
I wouldn't think a Tecumseh THAT old would have Metric threads, (unless someone ran a metric tap into it, ) I would take a small drill-bit to check the depth of the hole and then blow-out the threads with an air nozzle then try to retap the threads to the correct size ( 3/8 ...?? ) ..:confused2:

I am the second owner of this machine but do not believe it has been retapped, but perhaps W-W Grinder requested it that way. The depth of hole is 1 1/2" and the threads appear very fine like 24. I can blow out the threads but they do appear clean. Is it hard or risky to retap to 3/8" and would you suggest 24 or 18 threads per inch. can this be done while the crankshaft is mounted in the engine? PS(W-W Grinder parts diagram only gives a part# and I don't know any cross references since they are out of business). Thank you.
 

cpurvis

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  • / Size needed for bolt to hold clutch & pulley on Tecumseh 5hp engine
Technically, you should be "chasing" the threads, not re-tapping.

Chasing threads is the act of using a tap to repair damaged threads and remove dirt, etc., from them, not create new ones. If you try to re-tap a threaded hole using the wrong tap say, a 3/8"-24 tap in an M10-1 hole, you'll be left with a very weak threaded hole that you'll probably strip the first time you try to tighten a bolt in it.

If you don't know what the thread is (and in this case, you don't), use a T-handle to hold the tap and turn it using very light hand pressure only. If you feel serious resistance, stop--that means you're cutting metal and probably don't have the right tap.

Use what is called a 'bottoming' tap as they will chase more threads in a blind hole and offer more resistance when the tap's threads don't match the hole's threads.

If you can't repair the threads this way, you can use a threaded insert to repair the threads. Auto parts stores sell these; if you ask for a Heli-coil repair kit they'll know what you need.

Just a FWIW, probably not applicable in this case, there are other thread types. Whitworth is one but you usually don't see this in American equipment. Only place I've encountered Whitworth is in old English motorcycles.
 

Doubtful Bob

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  • / Size needed for bolt to hold clutch & pulley on Tecumseh 5hp engine
OK, appreciate all the answers. It turns out with the use of the suggested thread gauge I found out 24 was the number of threads. Since I had used a 3/8 16 bolt before even though it wouldn't advance much this had messed up the first 2 threads enough but I didn't realize it was wrong. With the 3/8 24 tap I was able to chase the threads and fix this situation with all your help. Now my 35 year old chipper is restored and I can give it to my son, who needs it. Thanks again.
 

bertsmobile1

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  • / Size needed for bolt to hold clutch & pulley on Tecumseh 5hp engine
Thank you for the "job done " post.
As it closes the thread or those who might read it latter on.

In future when you have a problem like this wind a piece of dowel into the hole .
Wind it out the count the groves cut into the wood.
 
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