Yamaha YZ125 rear wheel offset

[ChrisACT]

Hi guys,

I have put a DT100D engine in a DT175a frame, and I now need a rear wheel which will fit the DT175A swingarm but has the same sprocket offset as the DT100D (70mm from the centre of the hub to the centre of the sprocket).  The DT175A rear wheel puts the sprocket way too far wide of the mark.

I'm thinking that a 70's YZ125 or DT125 wheel might be about right.  I'm happy to lose the DT100D cush drive anyway.  A 12mm axle would be good as it saves me having to mod the swingarm.

Anyone know what the sprocket offset is on those bikes?

Thanks,
Chris

[TT5 Matt]

why not space the 100 motors countershaft spocket to match the 175 rear wheel ???could be easier then trying to make the wheel work with the 100 motor

[ChrisACT]

I'm not really sure how I could do that.  The countershaft doesn't have enough length to space the sprocket 6mm further out.

As it is, if I go with the DT175 rear wheel, I'll have to run a 428 chain instead of the 420 and the extra thickness of the front sprocket will take up any of the shaft that is left.

So, unless an offset front sprocket exists which would fit the counter shaft, it'll probably have to happen at the rear wheel.

But thanks for your reply.

[TT5 Matt]

ok got you with the lack of countershaft length so why not machine the desired amount off the hub or cush drive hub where the spocket bolts on to get everything to line up again

[vandy010]

Not totally sure but off the top of my head the DT100 cush drive should fit into the DT175 rear wheel.
Or,
The MX/YZ125A/B rear wheel should be a close fit/offset.
Im currently putting a DT100 donk into a TY175 frame and the MX/YZa wheel is a good fit/offset etc
I thought the rear axle was 15mm not 12...

[OverTheHill]

Hi, might be thinking back to front, but would a 'dished' AG100 type front sprocket get it close to working [ie' in line with rear], or if you were real desperate [i'd do it haha], machine the teeth off the dished front & weld another sprocket outside that to step it out even further after machining the middle out of it so as to get at the nut. Agy's are 428 as are DT175 of course but if you wanted a 420 & found a rear i'm sure you could organise a front 420 to weld on too. [I'd stick with 428] Good luck. ps, like i said, hope i'm thinking right & not got story back to front.

[Gerard De Ruyter (Twistandshout)]

Chris, the hub centre to sprocket distance did differ across early YZ125 hubs.  Nathan S knows all the details, and may (may) be able to help you with a hub with the right amount of offset.

[Nathan S]

Chris, you should ring me.

Super shortened version:
YZ125A/C have a dished rear sprocket.
YZ125X has a flat sprocket and more meat on the hub to put the sprocket in the same spot as an A/C.
DT175 mono shock has even more meat, to move the sprocket further to the left.

0400023847.

[OverTheHill]

I'm sure you've seen these but here's a pic of a worn out one. Is AG100 but would have to be the same spline as a DT100. Have an XR200 type motor [made up from bucket racing leftovers] which is in a PE250 frame & had to do the sprocket "step out" thing to get it somewhere near lining up with rear. Been ok for 10+ years.

[ChrisACT]

Hi guys,

Thanks for all your comments.

The AG100 sprocket might fit the bill if I can get them in a 15 or 16 tooth.

Matt, the part of the DT175 hub on which the sprocket mounts is 10mm thick.  Machining 6mm off that wouldn't leave much left of it for the sprocket to hang onto.  This is an odd project involving methanol and much higher speeds than the old DT's were ever designed for.  I'd hate to lose a rear sprocket along the way.

Vandy, you're absolutely correct.  The DT175A has a 15mm rear axle.  Oops.  But the DT100D cush drive will definitely not fit the DT175A rear wheel.  Although the DT100D did have a totally different frame and swingarm compared to the DT100A - C so potentially the rear wheel and hub was also different.

Nathan, what I need if I'm going to change the rear wheel, is less meat under the rear sprocket.  YZ125A might do it.  I'll call you tomorrow.

[Lozza]

Where have you been Chris, uni finished and back into the shed? 

[ChrisACT]

LOZZA!!

Yeah, mate.  Uni is all done and I'm gainfully employed again.  I'm writing software for mainframes these days.  It's very nice to have an income after three years in the financial wilderness.  I can get back to building silly motorcycles.  I have plans to visit Lake Gairdner next year (which is what this thread is all about).  It could be hilarious.   

You still up Newcastle way?

[Lozza]

A friend is off to the salt very soon actualy everyone is pumped after 2 yrs of being washed out. Yep still in Newcastle. Good to hear you have some play money.

[ChrisACT]

Yeah the poor buggers have been pretty unhappy with the weather out there.  But still, this year should be a big event.  Obviously, I won't be ready by then so next year is the go.  Lots of prep to do on the bike, dyno work etc. and I have to get the scrutineers to look it over before I set off.  Running methanol requires a fuel shutoff and they want a bombproof chain guard etc. Lots of rules.  Luckily the chief scrutineer for bikes lives near Canberra.

[Lozza]

What class?