Author Topic: drill and tap front countershaft to hold on wider front sprocket  (Read 324 times)

Offline ams14

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I've seen this discussed/proposed on a lot of posts over the past years but has anyone successfully done it?

I need to move my front sprocket out about 0.3" so the circlip method of holding the sprocket on won't work.  If i drill/tap a bolt in the end I can put a washer/retainer on to hold the sprocket from sliding off the shaft.

I ordered cobolt and carbide drill bits and am going to give it a try.  I assume the shaft is hardened steel because I already tried with a regular drill bit and it didn't do anything.

Another option would be an offset sprocket but i couldn't find any for sale and figure the drilling would be easier than me making my own offset sprocket.


Offline mr72

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Re: drill and tap front countershaft to hold on wider front sprocket
« Reply #1 on: March 30, 2020, 08:37:03 PM »
Are you pulling the shaft? How are you going to drill that straight and absolutely centered?

Even with a cobalt drill I bet you will have an incredibly hard time drilling it. And then how are you going to tap it? A hardened steel tap is not going to work, and you are going to have a blind hole, so you'll have to basically make a hollow shaft to get a tap in deep enough to fully cut the threads, we're talking tapping a 1" deep hole in hardened steel. You ever tried to tap even 1/4" thick plain steel? I've broken taps many times in 1/8" thick plain steel.

I think you'd be better off with a replacement countershaft taken to a machine shop and have it done there.

IMHO, but good luck anyway :)

Offline ams14

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Re: drill and tap front countershaft to hold on wider front sprocket
« Reply #2 on: April 01, 2020, 07:29:04 PM »
Thanks for the reply, all good points you make, I am now skeptical:-(

I am going to do it in-place without removing the shaft.  I plan to lay down my drill press and put it underneath the bike and line it up. 

there is a small dimple in the center that will help me align and get the hole going.

I will try it this weekend and will report back.  If it doesn't work i will move on to a different plan.

Offline ams14

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Re: drill and tap front countershaft to hold on wider front sprocket
« Reply #3 on: April 05, 2020, 02:28:02 PM »
Well I drilled it successfully to about 1". Got through the first 1/4" with a carbide bit before breaking it.  Luckily i was able to extract the broken pieces.  Finished it off with a cobalt bit.  The steel was really tough for the first 0.1" or 0.2" or so and then softened up, so must be a type of case hardening.

Weird thing, once i hit about 1" deep I appear to have hit a void?  Looking at diagrams, i don't see any reason the shaft would be hollow or have an oil passage in there or anything?

Will work on the tapping next.

Offline The Buddha

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Re: drill and tap front countershaft to hold on wider front sprocket
« Reply #4 on: April 05, 2020, 06:02:13 PM »
I've dreamed about this. You can get it center easily - the counter shaft was dimpled in the center. You could drill it and the tapping part will be very very hard. But if you manage it its a very fine solution.
The stupid circlip has bothered me for years, I want to fit a belt drive in it, but the hurdle has been the drill and tap situation as well as the fact that a poly chain belt cant be turned tighter than a 4.9" and the clearance to the stupid clutch push rod is only 4.4 at best
You're going to a 530 chain - all the best for your endeavor, I love it.
Cool.
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Offline ams14

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Re: drill and tap front countershaft to hold on wider front sprocket
« Reply #5 on: April 06, 2020, 05:17:26 PM »
You're right, the dimple helped in centering the hole for drilling. 
My current tap is pretty old so i ordered a fresh one, should have in a few days.
Here is the setup, I laid my drill press down underneath the bike and shimmed it to the correct height.
BTW, I'm using the GS500 as a donor motor for a cafe project.
« Last Edit: April 06, 2020, 05:25:06 PM by ams14 »

Offline ams14

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Re: drill and tap front countershaft to hold on wider front sprocket
« Reply #6 on: April 10, 2020, 03:18:03 AM »
The deed is done, it went fairly smooth.  I drilled about 1" deep with a 17/64" drill size (used a carbide and a cobalt).  The outer part was a lot tougher than the inner.  Then I put on a 5/16" cobalt drill bit and went back and drilled in only about 0.1" so my tap wouldn't have to cut through the tough outer section.  I tapped with a 5/16-18, moving nice and slow.  I should be able to use a 1" long bolt with a large washer to hold on the sprocket.

Offline The Buddha

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Re: drill and tap front countershaft to hold on wider front sprocket
« Reply #7 on: April 10, 2020, 11:28:03 AM »
Brilliant work. Now I better do this and do a belt drive GS500 like I've been dreaming of.
Cool.
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