Vintage Dirt Bike Q & A

On one of my MT250's Ive got what looks like a CR250 rim... has the special bearing retaining nut like the MT250, but the sprocket is held on with fixings that have tabs, which according to my manual means its a CR wheel. It does have a DID alloy rim but that could have come from anywhere of course LOL

Anyway, My problem is that whilst i can see that the sprocket is firmly bolted to the hub, with the axle bolted up on the bike i can wobble the sprocket and backplate, which cannot be right. I assumed it would be solid not rattly... can i sort this or is it worn out or something?

_________________
MT250 with CR250 top end & Bassani pipe... almost fully restored.

See more of my motorbike builds at my Honda MT250 and Yamaha RD and RZ website, 2Smoked.com

If you like watches, check out my websites: DeskDivers.com & PloProf.com

My guess it's a stock MT250 rim... in which case you have a cush drive behind the sprocket. The CR hubs are a 1 piece design, so the sprocket would be a solid mount...

The MT has a very large seal on the hub with a large snap-ring behind it which holds the cush drive on. Then behind that are metal tabs that engage rubber bumpers which, in turn, engage the hub.

Sounds to me that your rubber bumpers have worn out, or your washer behind the snap ring has worn down to allow excessive play.

Only solution... tear it apart! Look at what you're dealing with...

If it was a CR rim doing that, all you'd have to do is torque down your bolts and be done with it... but if the bolts are tight, the sprocket should be 100% solid.

_________________
I drink your milkshake!

Thanks Danny, Always good to have people who know these bikes chime in.

Yes, I agree the CR hub is one piece and this one is definitely not one piece and does appear to have the sprocket firmly bolted to a backing plate, it is this backing plate that rattles and turns, so yes it does sound like worn cush drive rubbers, hmmm. I will take the wheel off and see about that snap ring/clip, I also have a 'known MT' wheel on my bench so will have a look inside that one first.

Im guessing Cush drive rubbers are now NLA, but does anyone have a leads on replacments at all?

_________________
MT250 with CR250 top end & Bassani pipe... almost fully restored.

See more of my motorbike builds at my Honda MT250 and Yamaha RD and RZ website, 2Smoked.com

If you like watches, check out my websites: DeskDivers.com & PloProf.com

_________________
80 CR250Ra
80 CR250Ra
78 CR250R
80 CR80
82 Bultaco Sherpa 340
78 Bultaco Pursang 250 MK12
76 Bultaco Frontera 370 MK10
76 Bultaco Alpina 250
73 Bultaco Lobito 125 MK6
76 Suzuki RM125A
90 Kawasaki KX250

Thanks!

Ive got both my hubs apart now and one is MT and has the dust seal, the other has some kind of metal plate that is bolted on with the sprocket bolts and has no seal. I will try and do some pictures. The hub parts are the same, ie the spring clip, washer etc are all the same, just the sprocket plate is different.

_________________
MT250 with CR250 top end & Bassani pipe... almost fully restored.

See more of my motorbike builds at my Honda MT250 and Yamaha RD and RZ website, 2Smoked.com

If you like watches, check out my websites: DeskDivers.com & PloProf.com

So the cush drive absorbs some of the shock from accelration, so then why does the cr not have one and the mt does. I put a cr wheel on my mt. I was told on another site that it will damage the tranny but dont know that I buy that. I would think that the cr would be harder on the tranny and it didnt even use them, anyone know?

It seems to me that cush drives are used mainly on mellow-powerband street-oriented bikes, where 100% traction is nearly always available and a smooth drivetrain feel is desired. Obviously the CR250 doesn't fit this profile, and would probably kick the crap out of a cush drive eventually.

I don't think real-world transmission, chain, or sprocket life would be much affected either way.

Ray

_________________
'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Almost all road bikes have a cush drive, even modern ones. The rubber bumpers take out some of the stress in the transmission from the fact that the tyre is stuck well to the road, unlike an off road bike. Sure they soak up a few bhp, but on the road you can cope with that as it prolongs the tranny life, but on a MXer you want all the bhp and you have a loose road surface, so its no problem.

I have this hub apart now and its very similar to the MT, uses the same rubbers, same bearing retainer, same clip and washer, same bolt pattern for sprocket, same sprocket (ie no offset etc)... but... the plate where the sprocket sits is different and there is a metal plate that sits under the bolts that hold the sprocket on that runs up to the hub, but it doesnt have a seal like the MT does. I will do pics when I get a few mins, it would be good to know what its off.

_________________
MT250 with CR250 top end & Bassani pipe... almost fully restored.

See more of my motorbike builds at my Honda MT250 and Yamaha RD and RZ website, 2Smoked.com

If you like watches, check out my websites: DeskDivers.com & PloProf.com