Drilling Rear Shaft for cotter pin...
 

Was pondering how to lock the castle nut in place on my GY6 rear shaft. I saw a bunch of posts that recommended Loctite and no drilling. Note: This posting is for those that bought an engine without the rear shaft cross drilled to retain the castle nut.

I didn't listen but soon found out one reason people like Loctite... Drilling that hardened steel is a real pain. I have a mixture of 1/8" bits, cobalt high speed steel titanium etc... Broke every last one of them trying to put a hole through this thing. Note: I maintain slight pressure on the drill at a slow speed and I center punched the shaft.

I about gave up until I read that someone was using masonry bits to go through hardened steel. I bought two bits and used a bit of cutting oil. Broke one bit because I failed to recognize when the bit was near the center of the shaft. Nothing a couple of dental picks and pin punches didn't take care of.

FWIW ... Did I truly need to drill the shaft for a cotter pin ? Lowe's sells them under the Bosch name item number 143555 about $ 3.48. Don't use it in hammer mode. Yes, it would have been nicer to set this up under the drill press but somehow convinced myself that a hand drill should be able to do the job.

sounds like a lesson learned and taught. lol

next time you need to lock a nut down, just use another nut like it and jam them together.

Great idea. Just couldn't use it for the shaft. Not enough room.

Drilling the shaft for a cotter key is the only way to go. I would have never thought a masonry bit would work on steel.

you could also grind a little flat spot where it needs to go and then center punch it.

I did center punch but didn't grind a spot on it. Probably would have prevented the punch from shifting across the metal. Thanks, hopefully I don't have to do this again for a while.

I've read up a bit on using masonry bits for hardened steel. The carbide tips have a drill type head to them but it's an inefficient grind angle on the tip. If ground more like a metal cutting bit the carbide bit will cut and not scrape a hole. Either way it goes the masonry bit is NOT the way to go IF accuracy is paramount. However, a cotter pin hole is okay. Now, what someone needs to tell us is how do we get what angle with a Drill Doctor because I don't have the skills to sharpen a drill properly by hand.

In most cases if something is hardened it's usually not hardened all the way through. It's usually just the surfaces that's hardened.

Grinding a little before you drill will ''usually'' get you into the softer material.

An efficient way if you don't have the tool for drilling the shaft. Know where you want your hole. Screw a regular nut on the shaft. Center punch where the nut meets the threads on the shaft but don't overdue it. This lightly locks the nut to the shaft holding it from turning while drilling. Punch the nut center of a flat. Using a cobalt bit drill though nut making sure your bit is straight so that you come out other end center of opposite flat on nut. Once you drill through the nut it will act as a guide when going through the shaft keeping the bit from walking. Keeping a pretty good pressure on the drill and low speed you will drill through the case hardened shaft. Once done remove the regular nut and install your castle nut. I have done this several times on case hardened bolts. Any drill doesn't do good on radius since they are ground to drill a flat surface.