rm125 b or c

[noisy toy]

Hi there. I have just got an old mongrel rm125 which i am not sure is a b or c. The frame is rm125-60498.
I think it is a 77 125b, can anyone advise? It is currently fitted-poorly- with an rm250 engine.... not a good fit as i think the 125 frame is shorter than 250. eng no is rm250-21278. Anyone know what year/model it is from?Now do i look for a 250 roller or a 125 engine.....
Are there any useful forums that cover these bikes?
Cheers, shane

[BAHNZY]

Shane,
The frame number indicates a 77 RM125B, the engine also a B model but a 250cc.
It's gunna be a lot harder to track down a roller for the 250cc engine than it is going to be getting an engine and ancillary 125cc parts.
In addition you'll probably find that people may be interested in swapping a 250B motor for a 125 motor.

Rod

[bigk]

Reckon I'd have a 250 frame, forks & rear wheel and a 125 engine.
K

[noisy toy]

Thanks for the info Rod, I would like to make two bikes out of the one if possible but I will see what pans out. It would be an interesting pair of bikes to have in the shed and at VMX events!
I have already had a swap offer for the engine but not sure yet. I will get it running again first and see what the options are. I have to watch the secret funds for the IT 465 project.....

BIK K, I sent you a pm.

Cheers, Shane.

[noisy toy]

I have had a look at a few pics of b and c bikes, mine has an alloy swingarm and plastic tank, and a tapered/conical front brake. Could it be a b with c bits, or a late b? I dont want to restore to pristine or anything like that, but would be good to know for parts sourcing when the time comes. The little round tank rubbers are mounted on proper little posts,  and the mount in the frame for the angle tank brackets is there, do the metal(alloy?) tanks have the same thing? It seems more like a c but the serial number indicates b. Can anyone help with these little details?
Cheers, Shane

[BAHNZY]

Shane, post some pics and well have a look. If you are going to race the bike it is important to know as the "B" can be raced in pre78, but a "B" with "C" equipment would be a "Evo" machine. It's a big step up in class where pound for pound it is off the pace compared to the last twin shock offerings around 1980.

[monaro308]

Shane,rear wheels were different. B had smaller sprocket spigot,bolts had metal tabs to lock sprocket nuts,C had the now normal looking sprocket (with a pain in the arse I.D for sprockets
Check my rebuild and see what you can pick.

http://www.thumpertalk.com/forum/showthread.php?t=807100&page=2

I think the handle bar mounts were solid on the triples...C rubber mounted (i'll have to check that 1)

Plenty on here can help you.
cheers...mario

[noisy toy]

I have had a look at a couple of bottom ends at the local bike wrecker, i found two different types of rm125. one has a coarse splined kick shaft held on with a short bolt screwed in to the end, an integral intake flange, and the two rear barrel bolts were quite a small diam. eng no rm125-113190
The other had a fine spline kickshaft with a groove for a pinch bolt, a bolt on intake flange and the four rear barrel bolts were the same size.eng no rm125-41745, and another rm125-76644. These point to b and c engines, can anyone tell me what the other two mean? The numbers dont come up on the rm serial number site, but they seem to match the rm125m 1975 frame number. Can anyone help? There may have been a 125s barrel and head too, but not quite sure how to i.d it for sure.
Cheers, Shane

[monaro308]

The 79 RM125N was the start of the coarse spline centre bolt and small stud at the rear of the barrel.
Like you,my number list doesn't match those numbers you have...more home work to do!

[noisy toy]

I checked the alpha-sport suzuki parts site(vey good one!) and i can see that the coarse spline engine is from an n model, and the others are from a,b, and c. Thanks to everyone, i am learning a lot. As for the wierd engine numbers on the n engines, maybe the local dealer can help. I will look in to it and let you know. I found a couple of different chambers as well, hopefully one will suit the c. Not the bike i was looking for, but it has grown on me!

[oldfart]

This may be of some help. http://www.ozebook.com/compendium/suzi/engine-nos/engnos.htm
     

[cyclegod]

eng no rm125-113190 = RM125T (magneto taper different to 'N')

eng no rm125-41745 = RM125A different stroke and small end diameter to 'B" & 'C'

eng no rm125-76644 = RM125C much the same as 'B"

Here's my source  http://www.vintage-suzuki.com/rmnumbers.htm

[monaro308]

Hey thanks cyclegod i was wondering why the N and T cranks were different part# Been keeping an eye out for a 125 crank to go back into my RM125T which currently has the 100 crank and top end.
Thanks
noisy toy keep firing them questions....we don't mind helping get another Suzuki going

[noisy toy]

I have done a bit more homework on the old rm, but i am puzzled. The frame number says it is a 77 b, but it has the mounting bracket tube for the 78 c fuel tank. Did the b ever have the angle brackets under the tank? I thought they still had the front rubber strap thingy.
Maybe the later b frame had them getting ready for the new c model?
I dont mean to be picky about this but if it really is a b then i can run in pre 78 instead of evo.
Can anyone help?

[monaro308]

Do these pics help...this is my 125C frame.