Well, it seems new rings have not made a difference.

I tried running her in for a day - very light loads, no static rpm for long, and no high rpm, and then today I did some more and a compression test. It is actually a bit lower than before. Although the cooling system is keeping temperatures in check, the engine is kicking out lots of heat, and I think the oil must be close to burning. One thing I dislike about these SYM is the lack of oil pressure warning/gauge etc.

Anyway, for sure it is not repaired and still has the feeling it could clunk out mid journey. I noticed in my pics a small longitudinal mark on the cylinder wall - it is visible in the top left of cylinder bore in the the pic above. It is more of a scuff - my fingers didn't feel any scratches. But whatever, I had previously thought the cylinder was without any such issue, but now it seems it is not so it is damaged to some degree. I'm pretty sure my attempt to use new rings was not enough and I will need to go with a new piston, rings, and cylinder repair if I try again. Now I've done it once, I know how to strip and rebuild so it should be somewhat more straightforward next time. I may even catch all the coolant next time :-)

I measured the outside barrel of the cylinder and it was 78.89mm and the hole in the engine block was 79.36mm. So I'll see if I can find someone selling a 278cc cylinder to measure it and work out if it will fit.

I have no time left for this now so the Citycom will be off the road until the summer. If the Z+ 300 becomes available soon, I'll buy that and perhaps not bother repairing the CC.

EDIT - I continued to try to break in the new rings but the heat turned out to be too much. It has eventually caused the camshaft to fail and the end of the shaft has sheared off. As some mechanic websites tell me, too much heat can cause the head to swell in the middle, and this shape change is enough to cause the shaft to bind so it doesn't want to turn, and then it breaks. So the engine now needs a new camshaft and bearings on top of the other parts, and the head would need to be stripped and rebuilt.

On the plus side, while stripping the engine a little to check out what had gone wrong (still in the frame), I did manage to catch all the coolant. The trick is simple - first drain the coolant from the drain screw and the remove the highest hose that connects to the thermostat - a second surge of coolant from the drain plug gives up all the coolant in the system.

Anyway, I won't be bothering with the repairs - too much time and money and I'm not confident it would work either. So, my Citycom is finished, just shy of 80,000kms. I reckon I could have got to 85,000kms and by then she'd have been such a heavy smoker that there would have been a "natural" end. Rest In Pieces Citycom. :-)

I followed the manual and the only part that caught me out was draining coolant. I drained it from the drain plug but then when other hoses got disconnected, more came out from the drain plug and elsewhere every time a hose was removed. Even knowing this beforehand wouldn't have made sure I collected all the coolant because it comes out of everywhere else, not just the drain plug. Apart from that, quite easy. I decided to use a couple of scissor jacks and a trolley jack to support the engine  and then lift the frame and front end up and forward to take it away from the engine unit. I have fitted the new rings by following the manual and copying what was installed, and how, and that was straightforward. So now I'm at the stage of scraping off old gasket before the slow process of cleaning and rebuilding.
Draining the coolant using an old orange juice bottle


Piston cleaned up with a knife.

new rings - the piston measurements are all within spec so it just needed a de-coke. It shows that oil has passed the oil ring as expected, but perhaps more than expected because it has burnt on as a crust, and the same is less true of the second ring. The cylinder head also has a lot of this kind of crust. I'm surprised I didn't notice any white smoke out of the exhaust. It made me wonder if something else besides rings might be the issue, or if the problem had not go that bad yet.

The residual gasket between the cyilnder and engine block is a pain to remove - soaked in solvent and scraped.

The cylinder bore looks very smooth and polished - there's some honing lines criss-crossing the bore and no signs of damage or unusual wear of any kind. I couldn't measure distortion but the bore measures within spec so it should be fine, assuming my vernier calipers and measurement method are up to the job - the tolerances are very small.

And the gasket has all gone after an hour of work on it...

De-coked the head


I took a break for a long lunch and then started again in the afternoon. I got the head etc reassembled and the engine back in the frame by the end of the day. Tomorrow I try to reconnect everything...

The parts arrived already!

I bought the gasket for the 278 as well as the 263 to compare and they are 100% identical except for the bore on the 278 is 1mm wider all the way round - so 2mm in diameter more. If I ever need to, it's certainly possible to fit the 263 head onto either the 249 or 278 cylinder/piston. For the 249, it would all bolt on and there'd be a little more squish. The 278 would require some machine shop work to fit but it's doable.
278 vs 263 head gaskets

All parts needed for piston ring replacement

Piston ring set for 263

I've also reached out to family in Taiwan to see if they can get the 263cc parts but since these models are export, it's unlikely.

My sister-in-law is a bloody legend - she has no clue about scooters but still she called around and eventually found a SYM dealer in Taipei who had them in stock. They became concerned that she was planning to do the repairs herself but she reassured them it was for an "experienced" mechanic. Actually, I've only ever once changed piston rings and it was on a real easy two stroke about 30 years ago! Anyway, she bought them today and is sending them on immediately - I doubt I'll get them in time to do the work over the Easter holiday but it isn't an emergency repair, yet. So I think I'll be fine to delay the repair until June when I have the time.

And the cost? Camcover gasket, US$5, head gasket and piston rings, US$20, cylinder/block gasket US$3. I'm not sure what shipping will be I'm sure the total cost is less than the cost of the piston rings alone on Ebay.

You might think the price doesn't matter that much but I'm planning to buy the Z+ 300 so this repair is just for "fun" - to see what state the cylinder/rings are in after so many years, and who knows, maybe get her near to full power again? Wish me luck!

Hi everyone,

Has anyone tried swapping cylinders/pistons from the different SYM engine sizes? How about using different piston rings? I might have to 'cos of a parts availability issue so if anyone has looked into this, or done it themselves, please let me know. As far as I can see, swapping the 249cc and 263cc parts is straightforward, albeit time-consuming, but the 278cc might need major modifications.

So why do I ask? My 12 year old Citycom is just shy of 50,000 miles and is using oil (300ml extra needed between changes), has low compression, 10kg/cm2, and makes a knock noise when the engine is cold. It all points to worn piston rings/cylinder.

At the moment, it's looking like I'm going to have to fit a new piston, cylinder, etc from the 249cc engine, not the current 263cc, because that's all that's available at reasonable prices. It's no more expensive to convert than it is to repair, and the conversion would include a new cylinder too, so it might last longer/seal better than a repair. I don't think the 278cc cylinder will fit the engine block, although I'm in the process of checking for sure.

My problem is that I cannot get new piston rings locally - part no 13010-LEA-000 (the numbers denote a piston ring set, the letters denote the model) - the dealer doesn't stock them and won't order them. I can only get a complete cylinder and top end build and the dealer wants to charge me big bucks for this. Ebay is a similar story with 500% overpriced parts; however, I can buy a piston, cylinder, rings and gaskets for both the 249cc and 278cc engines, and for US$150 for either set - by far the best value. I've also reached out to family in Taiwan to see if they can get the 263cc parts but since these models are export, it's unlikely.

All the 249/263/278 engines have the same stroke but 2mm bigger bores - 71/73/75. The Citycom is 263cc - 73mm bore x 63mm stroke, and the cylinder/engine block gasket is the exact same part as the 249cc engine - both HMA. This means the smaller cylinder and its piston and rings should be fine. The piston will probably be lighter, which will reduce the load on the rod and big end. The issue will be whether the head from the 263 works efficiently with the 249 piston. I'm guessing they used the same design and sleeved the cylinder an extra 2mm for the smaller piston, with only a slightly different head shape. For example, the inlet pipe assembly, the camshaft, the valves... all the exact same parts for both. I've not been able to check exhaust, except for the gasket, which is the same. However, the head gasket is different - LEA for the 263cc and HMA for the 249cc. I will need to disassemble and measure to see which gasket would work best for the smaller diameter piston, assuming everything else mates up, as I think it will. Probably the bigger one, the LEA, is better to create a seal.

The 278cc is 75mm bore, same stroke - it has a different engine block/cylinder gasket part code (RFA not HMA) so the 278 cylinder might not fit the 263/249 engine block. The 278cc engines appear to be all RFA code parts for all gaskets and either L3A (GTS300i) or L9L (Z300) for piston rings/cylinder - 2 codes 'cos the latest 278cc cylinder is ceramic not steel lined.

Parts numbers are here: https://goparts.eu/en/genuine-oem/sym/scooter/joymax-z-300i-abs-l9-eu/2019/cylinder-kit

The other option is to look into rings from a machine with a 73mm bore (Honda GX240 for example).

Here's some pics of the 2 troublesome parts that are specific to the 263cc engine - the rings and the head gasket. The other parts I need are the same (HMA) as the 249cc engine.





I can get this gasket for US$35 locally - the price in Taiwan is around US$10. The piston rings are on Ebay and they are about 5x the Taiwan price.



Cheers!

 

Hi
rang motogb the uk importer and aked if there was any intention to bring the Z+ or cruisym alpha to the UK, they said no at the moment unless SYM agree an attractive price agreement

That's a shame - but at least it means they know the new models exist so they might be available at some point.

It's the lunar new year here (Year of the Ox) so most shops are shut for a holiday. They'll reopen late next week and then I'll ask the importer here.

Great job - it's not easy fixing multiple electrical problems... it can be very frustrating!

I have had a starter relay die on another machine - I reckon lots of cranking in cold weather was the cause.

How did you identify that you were getting no fuel? I guess you tested the pump? Another thing to check is fuel lines - maybe they got gummed up from the machine sitting for too long?

Let us know if it turns out that was all - starter relay and fuel pump.

I saw that SYM had updated the Cruisym, now called an alpha, i think. It seems they have introduced an electronic dash panel and changed the halogen headlights to L.E.D. That was one of my niggles, having the speedo in Km instead of M.P.H. My Cruisym 300 will be three years old in May, so i will not be changing it just yet. I got my info from You Tube.

Yes, a Cruisym alpha - dunno when this was updated - do you know?

The other change appears to be traction control so that will mean a small bump in the price I guess. I would like traction control but I wouldn't buy a new scooter to get it, especially not if mine was only 3 years old - save the money for when they release a significant model upgrade.

My Citycom is 2009 though, and looking fairly tatty. It seems to be doing okay at 73,000kms but top speed is now about 120kmh (GPS) when she was capable of a little over 130kmh before, and fuel economy is 10% less (usually 32kml but now 30kml) so I guess it is wearing out slowly. I told myself I'd run it until it died but I'm hankering after a new machine!