1979 RM125 Restoration Complete

[spicydave]

We'll my bike is now complete

I have a full set of original plastics if anyone is interested, including the tank (Secondhand)

Cool
SD

[monaro308]

Hey Monaro, i think you are correct. maybe i am thinking of rm100a and rm125a.

We are both right....lol   
RM125A 56 x 50mm and RM100A 50 x 50mm

[rocketfrog]

You are right rocketfrog...front mount to the rear and rear to the front.
My RM125T is running the 100 top end and crank as the previous owner blew the bigend and decided to put the RM100X bits onto it.....I got all the original bits with mine including the 100X bits and pieces,but i want to put it back as a 125.....so i'm chasing a rod kit or a good 125T crank.
I kept an eye on a 125N crank.....but T crank part numbers are different.....any idea why??
Anyway....spicy dave......nice job on the bike....i assume you are waiting on a new clutch cable as it should run behind the pipe up along the frame downtube like your original pics.
I like it

Monaro, I do not have an 'N' crank to compare the difference, but I do know that the 100 and the 125 "T" share the same con rod, the only difference in the crank seems to be the crank pin being positioned further toward the circumference of the counterweight by 2mm to give additional 4mm  stroke overall. Crank pin, bigend brg and rod are all the same part number items. If you still have the 125 crank then the rod, pin and brg are still available from Suzuki, a bit cheaper from Alpha sports than local, especially if you have a list of bits to complete the rebuild and make the additional shipping costs bearable.

[Marc.com]

little forward movement on my 78

[monaro308]

Thanks rocketfrog for the info.
I keep an eye out on and see NOS rods from the US but never find crank pins....i should get off me butt and just order the lot and get it assembled.....just gotta work out what to do with the bike and whats worth spending on it.
The 125C is still sitting in the lounge room unstarted and i will possibly have a PE175 floater coming in the next week or 2.
A mate is interested in the T as long as it goes back as a 125....then factor in the crank rebuild etc etc.

Hey marc...i thought a watercooled  was going in it??
Looking good though!

[lukeb1961]

little forward movement on my 78

Ouch! that Simons magneto cover is worth its weight in GOLD.

[spicydave]

little forward movement on my 78

Nice,

I like the rear swingarm

[oldyzman]

Nice swing arm!

[Marc.com]

Nice swing arm!

thank god someone does 

[Marc.com]

Ouch! that Simons magneto cover is worth its weight in GOLD.
[/quote]

its all in the detail stuff, plus I bought I good motor.

[BAHNZY]

Guys,
Sometime back the 100 Vs 125 engine issue was covered, basically advising that a 125 crank won't fit into a 100 case set. Whilst the 100 crank will fit into the 125 case set, the swept volume of the crankcase is all up the shizenhouzen and the bike would have no power. Whilst i am 100 correct on the C model (as i have both engines and have checked it) I am not sure about the N and T models, but i would suggest that you check before you go buying bits and fit i wont work.

Rod

[monaro308]

Thanks Bahnsy for that info,good to know that.
I reckon N and T model might be ok as both the 100 and 125 cases have the stroke dimensions of both capacities cast into the left side next to the c/s sprocket.

[BAHNZY]

monaro308,
Don’t use that casting as a guide, the C model has exactly the same information cast into the side but the cases were different internally.
At a guess, the castings start out exactly the same. The 125cc cases are machined to take a large diameter crank web and the 100 remains the base case. I looked into having the 100cc cases machined out to take the 125cc crank (it's only 2 or so mm) but i found it easier to track down a set of 125cc cases from the good old US of A.
Bought and shipped was less then the cost of the machine work.

And another warning. The N & T cases, whilst they may look the same as the B & C cases, the stud arrangement for the mounting of the barrel are completely different. Got burnt with that one as well.

Rod

[monaro308]

Yeah i had a play around with my 125 T barrel and head to compare on my C rebuild....stud pattern different and the spacing at the reed base area up the shite.....not only that,the rear case mount holes to mount an N,T engine into a C frame dont line up and vice versa.
I will take note of the crank diameter diff in the cases......actually now that you mention it....i have the 100 cases that came with the spare 100X and the 125T top end and crank that came out of the 125 bottom end.....i'll do that later as its about 43c outside....even the spiders in the tin shed have to move
out of their hiding spots and rest in their webs....lol
I will sit the 125T crank in the 100X case and see if it fits and note the clearance.
I will also report back on the 100 topend and crank that is on the bike when i pull it down (oneday) and note that too for info on here.
Thanks Rod
Cheers.....Mario

[BAHNZY]

Mario,
I was able to build a good engine from a 125 and a 100 engine for my RM125C, mainly because the gearboxes are the same, so never pass up on a cheap 100cc engine for that reason alone. The biggest issue that I found is locating a barrel that wasn’t completely rooted. I am 2.0mm o/s and only just at that. I will keep looking for a good barrel that will bring back to somewhere around the .05/1.0 o/s but I am not that fussed as I only use the bike for classic Dirt and Broadford type events.

Rod