139FMB gear issues

DrKassler · 09-13-2024, 04:40 AM

Hi!
We've got a Romet Division 50cc with a 139FMB 4-speed manual.
It has only done about 1500 km's but are showing issues with the gears.

Issue 1:
It's really tricky to get it into neutral.
From 2'nd to neutral you can barely put your foot on the gear selector. If just a bit more force is used it will go into 1st.
From 1st you most of the time end up in 2nd instead of neutral.
--
Issue 2:
At standstill and in neutral it's tricky to get into 1st and sometimes it's impossible until you switch the engine off.
--
Issue 3:
It goes from 1'st or 2'nd into neutral while riding by itself. Not very common but it happens once or twice at each ride.
--

The clutch is adjusted and releases properly and has no slip while driving.
Can anyone give me some advice on what to do?

How hard is it to split the engine and replace the gearbox barrel if it is faulty for example? Is there good videos available for example?
I'm a quite experienced mechanic but new to bike engines.

Thanks in advance!

Crossbar · 09-13-2024, 09:25 PM

When I read your issue one and two I'd say sometimes you just have to get used to the transmission. Most of the time if it's a 1 down, x up, I always go to first then neutral. On some of my bikes I have to let the clutch out just a little, pull it back in and then try for neutral. If it goes to 2nd instead I go back to 1st and try again. There's a ground off lope in between the 1st and 2nd gear lope that lets the roller rest/lock in the neutral position. It's just a matter of learning what your particular trans likes.

Your issue 3 however throws that out the window. It shouldn't be popping out of gear like that unless for some reason it wasn't fully in gear or maybe your foot slightly hit the shifter by mistake. There's some youtube videos on how a mc trans works to give you a visual on what's going on when shifting.

It almost sounds as if your clutch could be slightly dragging (not fully disengaging). That would make it hard to shift into gears from neutral.

DrKassler · Today, 06:23 AM

Thanks for your answers!
I think you might be right, when I tested the bike yesterday I agree that there might be something going on with the clutch. It´s our sons bike.
When we 1st got the bike it had only done 250km´s but had been standing still for a long time. The previous owner had changed the oil to 20/50w for vintage cars. The clutch worked poorly and at one point it stopped releasing at all even though we adjusted it as in the ws manual. After contact with the original distributor we got the info to change to 20w50 oil specificly for bikes and after that the clutch worked again.
The bike has though always been a bit strange with the gears so maybe the clutch is still off in a way.
We are supposed to change the oil now again according to the service interval so that´s the plan and then adjust the clutch again.
According to the service interval we are also supposed to clean the oil filter. It is done by removing the whole RHS engine crankcase cover right? Any knowledge about this?

https://photos.app.goo.gl/sxbfGXeN3dLBUieDA

Appreciating all and any help.

Crossbar · Today, 09:41 AM

Sorry, not familiar with that motor but if it's a mesh flat screen it is probably under the clutch cover. I would make sure the clutch cable is correctly adjusted so it's properly disengaging the clutch. I'd be tempted to try a 15w40 oil. Many on this site run the common Shell Rotella 15W40 and works well with the wet clutches. I run that in all mine but I don't have any 50cc engines.

DrKassler · Today, 10:33 AM

Checked the clutch cable and adjusted the clutch, no improvement. Wonder if the clutch sticks a bit from the friction parts being perhaps damaged from using the wrong oil. Will change complete clutch to rule it out, just about 30 euros and easy job so willing to take a gamble. Will look into different oil viscosity if needed.
Hopefully it will work without changing the gear selector barrel or something a like.

krat · Today, 06:22 PM

If this is a manual transmission with the gears sharing the engine space 20/50 car oil is not what you need to be running. Auto oil does not contain the additives a motorcycle transmission/wet clutch needs.

You need oil blended for motorcycle use with anti-slip agents incorporated. 99% sure that is what is causing your problem.

You can get it at most auto supply outlets. It will be labeled for motorcycle use.

09-13-2024, 04:40 AM	#1
DrKassler Join Date: Sep 2024 Posts: 3	139FMB gear issues Hi! We've got a Romet Division 50cc with a 139FMB 4-speed manual. It has only done about 1500 km's but are showing issues with the gears. Issue 1: It's really tricky to get it into neutral. From 2'nd to neutral you can barely put your foot on the gear selector. If just a bit more force is used it will go into 1st. From 1st you most of the time end up in 2nd instead of neutral. -- Issue 2: At standstill and in neutral it's tricky to get into 1st and sometimes it's impossible until you switch the engine off. -- Issue 3: It goes from 1'st or 2'nd into neutral while riding by itself. Not very common but it happens once or twice at each ride. -- The clutch is adjusted and releases properly and has no slip while driving. Can anyone give me some advice on what to do? How hard is it to split the engine and replace the gearbox barrel if it is faulty for example? Is there good videos available for example? I'm a quite experienced mechanic but new to bike engines. Thanks in advance!
	0

Today, 06:22 PM	#6
krat Join Date: Nov 2019 Location: KY Posts: 276	If this is a manual transmission with the gears sharing the engine space 20/50 car oil is not what you need to be running. Auto oil does not contain the additives a motorcycle transmission/wet clutch needs. You need oil blended for motorcycle use with anti-slip agents incorporated. 99% sure that is what is causing your problem. You can get it at most auto supply outlets. It will be labeled for motorcycle use. __________________ %90 of the Chinese motorbikes ever made are still on the road. The other %10 made it back home.
	0

09-13-2024, 09:25 PM	#2
Crossbar Join Date: Jun 2024 Posts: 65	When I read your issue one and two I'd say sometimes you just have to get used to the transmission. Most of the time if it's a 1 down, x up, I always go to first then neutral. On some of my bikes I have to let the clutch out just a little, pull it back in and then try for neutral. If it goes to 2nd instead I go back to 1st and try again. There's a ground off lope in between the 1st and 2nd gear lope that lets the roller rest/lock in the neutral position. It's just a matter of learning what your particular trans likes. Your issue 3 however throws that out the window. It shouldn't be popping out of gear like that unless for some reason it wasn't fully in gear or maybe your foot slightly hit the shifter by mistake. There's some youtube videos on how a mc trans works to give you a visual on what's going on when shifting. It almost sounds as if your clutch could be slightly dragging (not fully disengaging). That would make it hard to shift into gears from neutral.
	0

Today, 06:23 AM	#3
DrKassler Join Date: Sep 2024 Posts: 3	Thanks for your answers! I think you might be right, when I tested the bike yesterday I agree that there might be something going on with the clutch. It´s our sons bike. When we 1st got the bike it had only done 250km´s but had been standing still for a long time. The previous owner had changed the oil to 20/50w for vintage cars. The clutch worked poorly and at one point it stopped releasing at all even though we adjusted it as in the ws manual. After contact with the original distributor we got the info to change to 20w50 oil specificly for bikes and after that the clutch worked again. The bike has though always been a bit strange with the gears so maybe the clutch is still off in a way. We are supposed to change the oil now again according to the service interval so that´s the plan and then adjust the clutch again. According to the service interval we are also supposed to clean the oil filter. It is done by removing the whole RHS engine crankcase cover right? Any knowledge about this? https://photos.app.goo.gl/sxbfGXeN3dLBUieDA Appreciating all and any help.
	0

Today, 09:41 AM	#4
Crossbar Join Date: Jun 2024 Posts: 65	Sorry, not familiar with that motor but if it's a mesh flat screen it is probably under the clutch cover. I would make sure the clutch cable is correctly adjusted so it's properly disengaging the clutch. I'd be tempted to try a 15w40 oil. Many on this site run the common Shell Rotella 15W40 and works well with the wet clutches. I run that in all mine but I don't have any 50cc engines.
	0

Today, 10:33 AM	#5
DrKassler Join Date: Sep 2024 Posts: 3	Checked the clutch cable and adjusted the clutch, no improvement. Wonder if the clutch sticks a bit from the friction parts being perhaps damaged from using the wrong oil. Will change complete clutch to rule it out, just about 30 euros and easy job so willing to take a gamble. Will look into different oil viscosity if needed. Hopefully it will work without changing the gear selector barrel or something a like.
	1