Need a machinist for a motorcycle project

[dang472]

Hey guys, I need someone that has the capability of making a custom offset countershaft sprocket. It looks like an EDM is preferred for the inner splines. I’d be interested in 5-10 pieces to help offset the setup costs. Most oem sprockets are heat treated Chromoly that is also case hardened and surface treated. I can outsource all the treatments if the sprocket can be made by someone here.

 

[SONIC SAAMI]

Linn Gear Co.

Linn Gear manufactures stock and custom sprockets, gears and other mechanical power transmission components for industrial applications.

www.linngear.com

 

[sirhrmechanic]

Worcester Gear/Swiss Precision near Worcester, Ma. can handle that.

I have a specific contact there if you want to try them. Or PM me for an introduction.

Sirhr

PS Owner there is an old Indian and MC Fanatic. So they are going to be sympathetic to your project!

 

[dang472]

Awesome, I’ve got a local guy trying to make something happen. I’d like a proper one piece sprocket instead of something welded when I’m hitting a jump in 4th gear. I managed to put this Suzuki 125 into the newer aluminum frame but my last hang up is the chain alignment. Here are a few pics for reference. Hopefully the motoheads here will approve.

 

[PinesAndProjectiles]

What happened that you aren’t able to find a sprocket?

Couldn’t you find one for the model of bike the engine came out of?

 

[dang472]

I need the countershaft sprocket to be offset 3.5mm from the OEM position to line up with the RMZ rear wheel and swingarm. There isn’t another model that uses these output shaft splines. I’ve called every manufacturer.

 

[blues2o]

Sweet project! I can’t help with a sprocket but I do appreciate you sharing this project. I can smell klotz in the air.

 

[n2ishun]

What about just moving the engine over 3mm ?
It would be a helluva lot easier and cheaper too.
Just slot the mount holes, or weld in new mounts.
Add shims here....grind a mount there.
Lather rinse repeat.

 

[Drew M]

There would likely be a sprocket with an offset from something else that may work?

Could you machine the rear hub to move the rear sprocket in the required distance & use standard sprockets if that didn't put the chain to close to the tire ?

 

[dang472]

I could’ve done an offset rear sprocket or machined the rear hub but then I’m changing the chain guide alignment and chain slider as well. Plus I change rear sprocket sizes much more than front sprockets so that would be an extra cost as well.

The engine can’t be moved over anymore without cutting the Y brace off the frame. The exhaust is almost hitting the frame as is.

I talked with a custom sprocket company and they said there wasn’t another make or model that uses this spline count or shape.

 

[Sniperwannabee]

So what is the combination your working with here?
Yr Frame?
Yr Engine?

 

[Drew M]

I think it would be easier in the long run to machine the rear hub then move the slider & guide etc & use standard consumables.
(sprockets in this case)
Guide can be moved with simple spacers, top roller the same, either redrill the slider to move it or redrill & tap the mounting holes for it.

another way which is also probably more trouble than its worth would be to offset the swingarm then you need to move the wheel back & still machine the rear sprocket carrier anyway but it would leave guide & slider alone.

Cool project by the way,
Love the smell of 2 stroke in the morning

 

[dang472]

2005 RM125 with 144 kit
2020 RMZ250 rolling chassis from JGR Suzuki race team

 

[dang472]

Here is a zoomed in picture of another conversion that was done. This is the only other conversion that I’m aware of and this was done with the help of someone connected to Suzuki motorcycle division. They also used an offset front sprocket but they won’t respond to my email.

Here is a picture of the oem location

 

[ken226]

How thick is the sprocket in the splined portion?

Would it be possible to put it in a lathe and face a 3mm deep counterbore on the outboard side of the sprocket, then add a 3mm thick spacer to the inboard side. The counterbore diameter could easily be of a sufficient diameter to accommodate the snap ring.

That should offset the toothed part of the sprocket by the needed 3mm, and be easy to modify oem sprockets in the future, for replacements. As long as it's thick enough that 3mm of material removed wouldn't appreciably weaken he sprocket.

Anyone with a lathe could do that job in less than 10 minutes, including making the spacer.

That kinda looks like what they did in the first pic, with the counterbore anyway.

 

[dang472]

Yes, that’s what we’re trying right now. The sprocket is 7mm thick so you’re almost machining half of the strength out where it rides on the output shaft. I bought 2 new sprockets so I’m hoping we can sacrifice one to add material to the backside. He thinks we can heliarc weld the pieces together to add strength back. This will probably get me going until a 1 piece sprocket is made. At least this engine isn’t a high torque monster. I wish an engineer could look at this and say that 4mm of contact on that spline is plenty but I don’t think that’s going to happen. I also don’t want to find out on the takeoff of a 90’ triple either.

 

[ken226]

Yes, that’s what we’re trying right now. The sprocket is 7mm thick so you’re almost machining half of the strength out where it rides on the output shaft. I bought 2 new sprockets so I’m hoping we can sacrifice one to add material to the backside. He thinks we can heliarc weld the pieces together to add strength back. This will probably get me going until a 1 piece sprocket is made. At least this engine isn’t a high torque monster. I wish an engineer could look at this and say that 4mm of contact on that spline is plenty but I don’t think that’s going to happen. I also don’t want to find out on the takeoff of a 90’ triple either.

Ouch! Yea, no way I'd run a 4mm thick splined drive sprocket.

While the area in shear would certainly be enough for the torque of a 125 two stroke, the nature of the slip-fit clearance requirement means friction, and the reduced contact area would wear, much faster. On both the sprocket, and the shaft.

I bet it would suck to have to replace that shaft after every race or two.

Sacrificing a sprocket and Tig welding it to the backside of another, then facing and counterbore g to the correct thickness would probably work very well. There's no way a 125cc engine is going to break 3ish inches of circumferentially welded steel with torque.

A quick Google search shows the RM125 puts out 26hp and 12.3 ft lbs of torque. There are welds not much bigger than that on the CV axles of front wheel drive cars.

 

[Eostech]

Any chance you would thread the splined shaft and use a bolt and washer on the front of the sprocket with a spacer on the back?

 

[ken226]

Any chance you would thread the splined shaft and use a bolt and washer on the front of the sprocket with a spacer on the back?

While there are oem applications that have used that method, I havn't seen it in a long time. I'd use plenty of locktight! it's been used on bikes with alot more HP than that RM125 though.

How bout turning another snap ring groove on the countershaft, 3mm further out. It would require splitting the crankcase, but you'd only have to do it once. Then you could use oem sprockets with a spacer, for the life of the engine. Looks like you might not have 3mm of shaft to use though.

 

[dang472]

I thought about threading the output shaft. Honda used this method on their 125 and 250 2 strokes with a 8mm bolt and conical? washer. Yes it’s locktited but it’s also rotating in the direction to constantly tighten the bolt. The shaft is extremely hard and there’s less material than a Honda. I would have to use a 10mm bolt at the smallest and probably use special tooling to thread it. Then I’d be worried I weakened the transmission shaft.

There definitely not enough material to machine another groove. The face of the sprocket needs to be flush with the outside of the shaft.

 

[ken226]

I went out and looked at my Speed Triple front sprocket.





My speed triple is a 1050cc with 140hp.

 

[gigamortis]

Any chance you would thread the splined shaft and use a bolt and washer on the front of the sprocket with a spacer on the back?

Seems like I remember building a bottom end for a fellow rider's CR250 many years ago that had the bolt and a bellville washer that retained the front sprocket to the countershaft.

As far as the OP's issue with the proprietary splines, how about start by buying two sprockets. Take one and cut off the chain teeth to where you are left with just a splined center. Bore out the other sprocket to have a slip fit over the OD of the first modified one. Then TIG weld the two pieces together at your desired offset.

 

[Eostech]

While there are oem applications that have used that method, I havn't seen it in a long time. I'd use plenty of locktight! it's been used on bikes with alot more HP than that RM125 though.

Yes all CBR1000RRs for the last fourteen years, most other liter sports bikes use a male thread and nut.
These bikes make a fair bit of power.

Obviously it's situational and no one should go cutting threads willy-nilly.

 

[ken226]

I thought about threading the output shaft. Honda used this method on their 125 and 250 2 strokes with a 8mm bolt and conical? washer. Yes it’s locktited but it’s also rotating in the direction to constantly tighten the bolt. The shaft is extremely hard and there’s less material than a Honda. I would have to use a 10mm bolt at the smallest and probably use special tooling to thread it. Then I’d be worried I weakened the transmission shaft.

I see no reason that it wouldn't work. Personally, I'd try the welded sprocket idea first though.



Drilling and tapping hardened still is something I have plenty of experience with. The hardened shaft may require a carbide tap and tap drill.

Trying it with a HSS tap would probably ruin your whole day. I wouldn't even consider trying it with a carbon steel hardware store tap.

Like this one. Not cheap:

M10 X 1.25 SOLID CARBIDE HAND TAP - North American Tool | A GWS Tool Group Company

SOLID CARBIDE HAND TAP

www.natool.com

 

[sgtsmmiii]

Chad Dixon at Longrifles, Inc. perhaps? He does unique projects every now and then.

 

[thejeep]

Instead of machining the rear hub, couldn’t you just shorten one axle spacer and make the other longer?

 

[dang472]

Well guys, we’ve got a working sprocket. We went with the original idea of turning 2 sprockets into 1. The long-term solution is to find a place to build several 1 piece sprockets from scratch, but this will get me moving and prove the concept. Thanks for the responses.