Went for a ride today... will it hurt my bike?

[Graeme M]

Well, yesterday really. Finally got the RM125M back together and took it out for a test ride. It actually went very well, I was really surprised. I enjoyed it at a HEAVEN round last year, but with the fresh cylinder it ran even better. Plus I have the YSS shocks and PD valves fitted now, and the suspension was brilliant (well, for an old bike that is!).

I had a couple of laps around a fastish open oval track with a young guy there on a late model RM125 (05?), and after that we had a chat. He reckoned the old RM was a bit faster than he'd expected and wanted to know what it was like. I told him bloody hard work... I was totally stuffed but he hadn't raised a sweat... tho I didn't let him know that! But I have to say I really enjoyed it, it handles and steers real well. Far better than my TM.

I probably did about an hour on it, including one session of about 20 minutes where I pushed it along a bit. Never having owned a 125 before I'm wondering how these things hold up. Are they OK to be ridden that long at a time? How often do they need rings? Pistons? At this stage, my fresh bore, piston and rings have done 1 hours work, of which only the 20 minutes were hard work. I'm running 20:1 premium fuel with mineral based oil. Did a plug chop with a fresh plug and it's nice, just a touch dark. Feels a bit rich in the mid so will drop the needle a notch.

Anyone got some advice on how to take care of it?

[KB171]

HOLD it WFO

[Lozza]

That's not a bad start KB.
I'll assume that you measured the ring end gap,your port windows were chamfered properly and that you began with 0.05mm/2 thou clearence.
I would after 3 meetings take the top end off measure your ring end gap and piston to bore clearence.This will give you a guide to how the engine wears.Unfortunately more than 0.1mm piston to bore clearence(about halfway down the bore where the end of the skirt is with piston at TDC) will if left unchecked will end in tears.The upside is running 20:1 goes a long way in reducing heat build up and wear of the bore.When you get to the last oversize let me know.

[Graeme M]

WFO is easy...

Yep, end gap checked and right in spec, piston/cylinder clearance started at 3 thou, and port windows chamfered, tho whether 'properly' or not I don't know, but they looked and felt fine. Will take the advice and pop the top end after a couple of meetings (let's say 3 hours work including this past weekend).

[Doc]

Graeme, the little RM can be ridden all day long if you like without issue. That's how we rode bikes back then. Only time we stopped was for fuel and no-one suffered any ill effects mechanically. The rings last for ages. When released suzuki recommended replacing the rings every 3 hours for optimum performance in the M. What a lot of people didn't realize is the M and S came out with very very thin low friction rings no thicker than a single scraper ring from say a 3 piece 4 stroke oil ring (less than half the thickness of a normal TM ring). This combined with the thought that everyone rides as hard as Gaston set the precedence for this recommendation. You can safely double that and maybe even triple it for 'normal' TM/RM ringed pistons. Dodgee gets great life and reliability from his TM's/RM's..don;t think his TM or RM has had rings since well before Coff's last year, I don't ride mine enough to know yet but I'll be expecting about 6 hrs before I'd look at replacing them.

[Lozza]

I would take anymore rebores to that place if you were returned the barrel with 0.075mm/3thou clearence.Not sure if the S has the shocker T shaped exhaust port(like a TM) which is very hard on rings,because of the small radius at the intersection.It makes careful dressing of the port windows essential.It's easy done with diamond file, extends ring life by keeping the chamfer on the rings.Which is another tell for rings being past their use by date...no chamfer=no good