SYM Owners Forum

General => General Discussion => Topic started by: Thoppa on November 13, 2019, 07:34:21 PM

Title: Clutch pad thickness - how thick when new?
Post by: Thoppa on November 13, 2019, 07:34:21 PM

Does anyone know how thick clutch pads are when they are new for the SYM 250/300 models?

I have a Citycom 300 and the service manual says the wear limit for the pad "lining" is 3mm, and the pads measure 3.5mm thick after 62,000kms. If I know how thick they are when new, I can work out how much longer they should last.

The manual p.143 also says the thickness of the clutch "weight" is between 6mm and 3mm. Does it mean the weight is the lining? Anyone confirm the pads are 6mm thick when new? If so, it's 25,000kms per mm of wear for my commute, so another 12,500 or so left before I need new "clutch weights/lining".

I just changed the belt - lasted 40,000kms - so if I can avoid taking that section apart again for a while, that'd be great.

There were no other problems when I did the job yesterday - lots of black dust of course, and some minor wear on surfaces, but nothing problematic with clutch, variator, etc. The new belt has dropped the revs by about 10-15% for a given speed and the machine seems to be a little smoother, with noticeably less mechanical noise at idle. After 40k, the retired belt was 22.7mm wide, with the service limit being 22.5mm, and it was also showing some lateral cracking in the grooves.

Thanks for any help on the pad thickness :-)
Title: Re: Clutch pad thickness - how thick when new?
Post by: Thoppa on May 02, 2020, 11:18:26 PM
Update - it seems I measured the thickness incorrectly - I measured the outer top of the pad to the metal of the shoe/weight which is the the thickness of the material above the surface of the shoe - that was 3.5mm. However, the shoe has a 2mm recess which is only visible on one side of the weight, which I didn't notice before. This means the pad thickness is actually 5.5mm, not 3.5mm as I said before.
Here's a pic that shows the recess, although it looks much smaller here than it measures.

I found this out because I bought a replacement clutch assembly on Taobao and noticed the pad thickness of the new one, 6mm, wasn't significantly different to the original. So in fact, it didn't need replacing and probably won't for another 60,000kms of my mostly highway commuting - good for 100,000kms + of mixed highway/city riding.

About the replacement - I saw on expensive Ebay ads that the clutch from the Yamaha Majesty YP250 was the same as the Citycom 300, RV250, etc. I then hunted for a YP250 clutch on Taobao and found a China pattern part assembly for US$35 - that's the complete assembly including the outer drum. I figured it would be crap (and the metal is crude) but I only wanted the pads, and I can't get them easily otherwise, and if I ended up throwing most of it away and keeping the pads it would still be the cheapest option. Long story short, that's what happened - I ended up throwing it all away except the pads/weights, springs, and circlips.

So did it fit? well, yes and no.

The outer drum doesn't fit because although the shaft is the same diameter, it has larger and fewer teeth than the Citycom's shaft which has smaller and more teeth.

The rest of the clutch assembly fits (SYM part number 22300-HMB-000) BUT it needs an extra washer on the engine side - a very specific washer size and thickness so the back side is spaced outwards and doesn't interfere with a lump in the engine unit housing. I'm guessing the Yamaha doesn't have that lump. With just the right size spacer/washer, it fits on both inner and outer bearings, but only half of the outer bearing makes contact with the shaft. Without the washer, it fits exactly on both bearings, but fouls the housing. I only had one suitable washer - a standard part - a custom made spacer might be better, or just using the original drive plates would do it because they have a little spacer/riser designed into the shape. Maybe it was not that the Yamaha part was wrong, but the China pattern part was missing the riser and had located the outer bearing 3mm too far along the shaft.

It's shame this site doesn't host pics - one pic of the riser would show very clearly what to look for. Here's an online pic of what I'm talking about but it doesn't clearly show the rise at the centre. (!!337140760.jpg)

It seems it's possible to make it fit with some more involved modification so I tried to disassemble it to see if/what could be done to create a perfect fit. I used two large c-clamps as spring compressors and tried to undo the large (46mm) nut holding the assembly together. I failed. That nut has been put on so firmly I could not shift it either with torque or shock.

So, because I couldn't get a perfect fit, and there's no way to modify it, I just cut out the three shafts holding the weights, and removed them, the springs, etc and threw the rest in the bin. One day, I will try to get the SYM clutch assembly apart to replace the pads but it doesn't need doing anytime soon.