Size of flywheel pulling bolts

[Evinrude Boater]

I've buggered up the threads using the wrong bolts to pull the flywheel off my 1964 Speedifour. Don't worry, I didn't actually try to pull it since the bolts didn't thread in all the way.
Can someone confirm the number of threads per inch so that I can buy a tap to clean up the top few threads? I tried counting the threads but I'm still not sure. Is it 16 or 18 threads per inch?

 

[Tim Frank]

Re: Size of flywheel pulling bolts

I tried counting the threads but I'm still not sure. Is it 16 or 18 threads per inch?

It will be a standard thread and so is determined by the root diameter....if it is a 3/8" bolt it will have 16 TPI, if 5/16" it will be 18 TPI. These are coarse threads.
If by chance this is a fine thread, both 3/8" and 5/16" fine threads are 20 TPI.

 

[Evinrude Boater]

Re: Size of flywheel pulling bolts

Thanks Tim. Princess Auto had a 12 piece tap & die set on sale today for $7.99. The 5/16 bolt holes are 18 TPI and I was able to clean up the threads and get the flywheel removed. It actually popped when I was tightening the bolts down on the puller. I didn't have to turn the center bolt of the puller. The 5/16 bolts that I bought are indeed a finer thread but not 20. I'm wondering now if I bought metric bolts by mistake but you would think they would mark them as 10M

 

[samo_ott]

Re: Size of flywheel pulling bolts

The older engines are 1/4" 20TPI. I'm surprised yours is 5/16.

And user grade 8 hardened bolts or it will bugger up.

 

[tx1961whaler]

Re: Size of flywheel pulling bolts

All of mine are 1/4 - 20 also (1958 3 HP, 1969 40 HP, 1970 6 HP).

 

[Tim Frank]

Re: Size of flywheel pulling bolts

Thanks Tim. Princess Auto had a 12 piece tap & die set on sale today for $7.99. The 5/16 bolt holes are 18 TPI and I was able to clean up the threads and get the flywheel removed. It actually popped when I was tightening the bolts down on the puller. I didn't have to turn the center bolt of the puller. The 5/16 bolts that I bought are indeed a finer thread but not 20. I'm wondering now if I bought metric bolts by mistake but you would think they would mark them as 10M

Typo.... 3/8 and 5/16 fine thread are 24 TPI, looking back i had 20 TPI.

Closest metric to 5/16 would be 8mm.

 

[Evinrude Boater]

Re: Size of flywheel pulling bolts

The older engines are 1/4" 20TPI. I'm surprised yours is 5/16.

My '63 Starflite flywheel uses 5/16 fine thread and my '64 Speedifour uses course thread. I've found a few other differences during my engine block swap.