!!! 1990 Rm 125 Powervalve Problem !!!

Lukee_RM125

Member
May 31, 2012
4
0
Yo everyone, recently purchased an old 1990 RM 125..

when i first rode the bike i noticed it wasn't pulling as much as it should on the top end, like it wasnt hitting the powerband properly.. I'm new to the engine side of things so i got my mate to have a look for me to see what was going on inside. when we took the power valve cover off to our suprise there was no valves / acuator rod or anything inside !!! infact the previous owner of the bike had 'bodged' a mechanism inside the ports, in which case the valves werent opening fully, which i presume is why the powerband wasnt coming in properly..weve tried to rebuild it to how it should be but stuck on what the actuator rod connects to in the bottom end and how to assemble the governer! also there is not much compression in the kick, you can push it down with one hand but she kicks up first time easily, the piston and rings dont actually look that worn!

HELPP! cheers.
 

RM_guy

Moderator
Damn Yankees
LIFETIME SPONSOR
Nov 21, 2000
7,045
208
North East USA
Wow, where do I start? I’m a bit confused. You said there are no valves, etc but the previous owner “bodged” the repair and the valves weren’t fully opening. So are they there or not? If they are there and they aren’t opening (move upward) you won’t have any top end power. If they are not there at all it will be hard to start and you will have no bottom end…only top end. Bottom line is that you have to fix it right and avoid bodgeing it ;) Here’s a link to an exploded view of the power valve and governor. http://www.bikebandit.com/1990-suzuki-rm125-rm125l/o/m147885#sch278139

The compression issue could be because the cylinder is worn. Someone probably changed the piston and rings but never checked the wear on the cylinder wall. Check the ring end gap. It should be around .012”. A bike that old could very well have a very worn cylinder and if the ring gap is large it could be an indication of wear and you’ll need to have it measured. You can also look for wear through the plating.

I’m assuming the cylinder has the original plating but it could be sleeved but the wear problem would be the same. You can tell it it’s sleeved if a magnet sticks to it. A sleeve can be bored out if it hasn’t already been bored past its limit, if so it will need a new sleeve.

If it is plated, I’d advise getting it re-plated although it might be a bit pricey in the UK.
 

Lukee_RM125

Member
May 31, 2012
4
0
Sorry my mistake, the valves were in but bodged in a kind of half way position so they didnt move up or down, but the connection from the valves to the governer in the bottom end were missing! :o weve managed to get the parts and connect it up and have rebuilt it so the valves will open and close correctly.. the cylinder wall / sleeve didnt look too bad so gonna rebuild as it is, test it and see what happens, surely with the valves being in the correct postion this will create a little bit more compression?

cheers!
 

Lukee_RM125

Member
May 31, 2012
4
0
Must be the cylinder thats worn then, probably not worth even getting it re-skimmed if its pricey, havent tested it out after sorting the valve problem yet.
 
Top Bottom