RM125C sprockets help.

[monaro308]

Hi all,can any of you RM125C owners/racers tell me where are you getting your sprockets from?
From what i can see the 59 tooth rear sprocket is pretty much an RM125C only kinda thing.
I'm leaning towards the 428 chain set-up for my restore or if i have to go 520 then that will do.

I can get the genuine 59t NOS (428) from the states @ around $100 US+postage,going to a 57t brings this down to $60.00.
The $40.00 difference because its the "genuine" standard ratio is peeing me off,add in the front sprocket and chain and its pushing the $200 US barrier.
Soooo the question is...anyone in Melbourne/OZ still make this size sprocket??
Was there any other model Suzuki or kwaka,honda,yamaha that has this PCD.

Almost at the end of the rebuild and the last thing that i thought would be holding me up was the simple sprocket and 132 link chain. 

Cheers....mario

[lukeb1961]

Vintage Suzuki has them
http://www.vintage-suzuki.com/sprockets.htm

have you tried your local dealers?

Ray at Suziparts   
  http://www.suziparts.com.au/

another great South Australia dealer - Kessner's.
  http://kessnersuzuki.com.au/

Steve in Victoria
 http://www.mickhone.com.au

perhaps?

Luke

[bazza]

Dealer in Queensland??  sells blank sprockets and reasonable price.Got one for BSA will see if i can find contact

[firko]

I think this is who you mean Mikey..........http://www.jtr.com.au/

[DR]

The original alloy rears were always very expensive. I remember paying around $80 for a new sprocket on my 400C over 25 years ago and since then have run steel except on the 125's. The list price for the 125C 59T sprocket is around $115 but they weigh absolutely nothing and postage should only be $10 or so from wherever in the world. To have a sprocket punched out locally maybe a little cheaper but on the whole I'd say the $100 original option is the go especially if it's the last thing holding you up and especially if you wish to retain the original appearance.

 Everything seems to go up in hundreds these days, swingarm bearings/bushes $100 steering head bearings $100 spokes $100 piston kit $100 bigend kit $100 new tyres $100 new seat $100 new stickers $100 new cables $100 chain $100 so $100 for a rear sprocket isn't out of the norm you need to use this reverse psychology on yourself in order to press that buy now button and be done with it

[BAHNZY]

If your looking for the resto job, then go the expensive 428 route. If it's a regular rider, then go the 520 conversion. Sprockets are easy to get and cheap. I have a 520 JT conversion set on my 125C and she's all good.

[Lozza]

A 520 will suck some HP out of the engine, I would be going 428, John Titman has aluminium blank sprockets that need the centre machined and holes drilled

[BAHNZY]

Lozza,
On the dyno there maybe a difference, but i was unable to pick the difference on the track. If you where to use a Enduro spec or O ring chain then you would probably pick it, but a quality low friction 520 motocross chain you'd struggle (if at all) to pick the performance difference.

Bahnsy

[motomaniac]

Mario , go to Byrners in Frankston.Max has been running  520 gear on his B all year ,bought from them.I just got some also .See parts girl Amy.

[DR]

no doubt a heavier chain would sap a little but then the last hollow plate 520 RK chain I purchased for my 400 was near as light as a HD 428 and safely rated to 80hp. I run 428 on all the 125's not only because they're 'usually' cheaper but because personally I think anything bigger on a 125 is an overkill..I nor anyone I know has ever snapped a chain in 40 odd years of riding it does happen no doubt about it but there are usually very extrenuating circumstances involved..you may also get longer life from a 520 and they may also seem to throw less due to the larger pitch but there's trade-off's either way just out of curiosity, is there a formula for working out the equivalent when converting 428 to 520?? Obviously you wouldn't run a 59T 520.. or would you??

[monaro308]

Thanks everyone,my bike came with 46/13 520 setup which must have been for bonneville salt flats 
Doc....i've had my finger on the "buy it now" several times at paul millers....but always do the "theres gotta be someone else out there with a 59T."
Brent is "max" running the 59 rear? I did visit Byrners this morning (i live just behind them)and Kerry and Amy weren't working today.
Kerry has helped me bigtime with genuine parts.
Bahnsy where did you get your 520 jt conversion from?
I'll do some home work during the week.
Cheers all....mario

[Lozza]

Smaller chains can take tighter turns , there is a big weight difference between 520 and 428 chains, even if it were 2 HP that's two FREE HP. A 45HP 125GP bike runs a 415 chain, for a reason. 125's don't have enough torque to destroy chains.

[BAHNZY]

When you change ratios within a 520 chain then you can calculate the ratio using teeth. Simple stuff.

When it comes to the 520 conversion you throw the teeth calculation out the door and come back to a diameter calculation. ie: the 428 sprockets should be the same diameter as the 520 sprockets. Just think of them as pulleys. (At least that's what i did)
I'll check mine, i think it is a 12/53 combination.

Any bike shop that deal's in JT Sprockets will have a reference book that will have the part numbers. As it is a 125 the base steel units and a quality MX chain, like they would use on a CRF250 & YZ250F, will do the job fine and cost you around the $150 mark.

[LWC82PE]

Blank and custom made sprockets available from here http://www.completedrives.com.au/home.htm. Good for old bikes you cant get sprockets for or in the case of bikes with the sprockets permanantly attached to the brake drum ( a lot of old british bikes) they can machine off the old one and fit a new one. Also good for half chain links as found on Nortons/AJS etc.

[BAHNZY]

Checked the bike and it is running 12/50. Depending on the track it could go to a 51 or 52 if i could be bothered. Seems to haul my 6'2 110kg frame around alright.

Also noted that the sprockets are steel SuperSprox which are distributed via BirdMan Accessories. Most shops will deal with BirdMan. I am running a Regina GP chain (i think it may have been a freebie) which is a low friction light weight unit.