Crankshaft drill and tap

[vegetable]

hey all, just a quick question, am I able to drill out a hole and tap it to accept a bolt in my crankshaft? the shaft doesnt have a hole for one and I want to use a cvt drive with this engine. attached is the shaft, i do have a drill press if that makes things easier to start the drill

 

[Triley41395]

hey all, just a quick question, am I able to drill out a hole and tap it to accept a bolt in my crankshaft? the shaft doesnt have a hole for one and I want to use a cvt drive with this engine. attached is the shaft, i do have a drill press if that makes things easier to start the drill

Yes, one of the members here sells drill guides just for that.

 

[vegetable]

Yes, one of the members here sells drill guides just for that.

I saw that they only came in 5/8" and 3/4", this shaft is 1"
could I rig up the shaft on my press and then just eyeball it that way?

 

[Triley41395]

I saw that they only came in 5/8" and 3/4", this shaft is 1"
could I rig up the shaft on my press and then just eyeball it that way?

I'm sure you could, as long as everything is straight and centered.

 

[sparkwizard]

Yes, you can do that. I mounted a crank through the hole in my drill press table, made sure it was square to the table and drilled it just fine.
You already have a hole in the center to get you started. Be careful not to break a bit in there.

 

[KMC1]

Yes, the factory center drilled hole will serve you well to get it centered. 5/16-24 is common bolt size for this.

 

[creia]

FWIW, Heald Super Bronc engines came with a 1" crank and the crank bolt was a 3/8-24
Michael

 

[sparkwizard]

You could drill a one inch (or 15/16) hole in a 2x4, clamp it to your table, push the crank into the hole, swing the table to the side so your crank is centered under your bit...

 

[SAT]

I can make drill tap guides for just about any small engine. My bigger lathe is a 10x24 and the sky is pretty much the limit.
I would need some specifics and output shaft Outside Diameter, in several places with a micrometer.

 

[KMC1]

I can make drill tap guides for just about any small engine. My bigger lathe is a 10x24 and the sky is pretty much the limit.
I would need some specifics and output shaft Outside Diameter, in several places with a micrometer.

Output is 1" OD. Make it a slip fit and it will be plenty close enough for that job. The crank is already factory center drilled. What he needs to do is determine what size bolt he wants to use. Most of them use 5/16-24.

 

[sparkwizard]

Aren't most of the big, 1 inch cranks tapped for 3/8-24 bolts?

 

[SAT]

I’ve seen both 3/8” NF and 5/16 NF.
Probably depends on the size required for the CVT. But are the keys different ?

 

[DaddyJohn]

Heck, I’ve often just set the whole engine down on the drill press table recoil starter down and found that to be plenty perpendicular to get a straight hole drilled in the crank.

 

[sparkwizard]

I’ve seen both 3/8” NF and 5/16 NF.
Probably depends on the size required for the CVT. But are the keys different ?

I have never seen a one inch crank with anything but a1/4 inch key.

 

[creia]

I have never seen a one inch crank with anything but a1/4 inch key.

That has been my experience as well. I have a Tecumseh HM-80 and a Briggs 8HP (both with 1" cranks) that have a 1/4" slotted keyway.
Michael

 

[sparkwizard]

5/ 8 shaft, 1/8 key
3/4 shaft, 3/16 key
1 inch shaft, 1/4 inch key.
Seems to be the same system for axles and jackshaft stock.

 

[creia]

5/ 8 shaft, 1/8 key
3/4 shaft, 3/16 key
1 inch shaft, 1/4 inch key.
Seems to be the same system for axles and jackshaft stock.

Every 5/8" shaft crank Briggs or Tecumseh with a slotted keyway that I have seen was for a 3/16" key.
Michael

 

[KMC1]

Every 5/8" shaft crank Briggs or Tecumseh with a slotted keyway that I have seen was for a 3/16" key.
Michael

Same.

 

[sparkwizard]

Every 5/8" shaft crank Briggs or Tecumseh with a slotted keyway that I have seen was for a 3/16" key.
Michael

I just measured a couple of 5/8 cranks. I was wrong, you are correct. 3/16 keyways.