jimbotipler

Hi folks, I'm going to take the stock exhaust off of my Trailway and repaint it black. I also want to clean up the engine and repaint it. Any recommendations for paint woud be gratefully received :-)

Just flagging this up. Bike jumble and classic bikes at Ardingly Show Ground - Sussex tomorrow. It's a great little show if you're in the area. https://www.facebook.com/events/932382926832224/

Recently I changed a piston and rings on a 1999 TW125 (the same engine as a SR125 i understand). I bought a set from Wemoto which was not genuine Yamaha. There were no markings on the rings and I couldn't say for sure which of the two top rings was which. After much trawling around the internet and leaving a post in the workshop forum here (thanks Airhead for getting back to me), I did come across this site, which might be useful. http://www.dansmc.com/rings.htm Although obviously I can't substantiate it, it does look like the fella has looked into it.

Thanks airhead. Had to take a bit of a flyer as I couldn't find much info. So I fitted them in what seemed the most likely order according to a site I found re chinese piston rings http://www.dansmc.com/rings.htm. Seems ok. Certainly runs well and is currently starting first push of the button. So to recap it looks like it was a coked up exhaust valve causing poor compression, enough to cause bad starting but not enough for it to not run. I changed the piston and rings as a Chinese set was about £30. Not sure if yamaha do a genuine replacement any more. So I reground the valves and decoked the head. Hopefully that's it sorted unless I've screwed up in the reassembly somewhere. Thanks again for all the helpful advice.

Thanks mate. Rocker. Trying to work out which ring goes on top. Ive put the rings under a magnifying glass and there are no marks. Looking closely neither has a chamfered side - inner or outer. The only difference seems to be one has a bright outer. I've been trawling the internet and cannot find any info on this at all. The order out of the box was bright on top, then black, then the oil rings. I've put them in the piston in that order. What do we think? IMG_1829 by tiplerjim, on Flickr

The edge of the top one in the old piston looks possibly slightly chamfered. And the brighter one in the new set looks slightly chamfered also?

They certainly look the same. I haven't got a micrometer. There are no markings on them.

Thanks folks. A quick update. A local garage checked the cylinder bore and that's ok However the exhaust valve was quite heavily coked - including the seat. Inlet is ok, so it looks like the exhaust valve could be the problem. Lapped them both in anyway and de-coked I'm putting in new standard size piston set. Any tips with regards installing the new piston? I'm trying to work out which ring should go top and which on the middle. It's supplied with a metal one and a black one which looks like carbon or plastic of some sort. I can't find any info in the manual about this. I'm guessing metal on the top as that will take the most beating.

Well, I ran compression test with my brand new compression gauge and Its reading about 6 bars. Manual says should be at least 11, ideally 12. So I squirted a bit of oil in and it went up to about 8. So I'm thinking piston. Got it apart now but don't really know how to proceed. Pistons out and the cylinders off and I'm thinking I'll take both to a local bike shop and get them to check for wear so I can get the right piston kit. Valves look in good nick but is it worth having them out and regrinding you think while I've got it in bits or best left alone? They don't look particularly coked up and the collets look ok. Anything else worth doing while I've got the top off? As always any advice is hugely appreciated.

Name: Yamaha TW 125 (1999) Date Added: 12 January 2015 - 01:16 PM Owner: jimbotipler Short Description: Picked it up a few months back 2nd hand. Not terribly fast, but them, neither am I! suits my 6'2" height really well. Got a bit of a starting problem right now and a small dent in the tank which I might get sorted at some point - then again, I might not ;-) View Vehicle

New plug. I'll double check the right plug and gap. Yep, trimmed off some ht lead but haven't changed the cap. Looks ok though. Thanks folks. Will update once I've had it compression tested.

Yep, with new seals not so long ago.

I've only tested by compression by sticking my finger over the plug hole but I'm guessing a proper compression year would be the thing?

I'm wondering now if it's possibly something more fundamental. In fact I'm wondering if it's a couple of issues. Poss inlet valve prob and battery. When I get it running (quite easy to bump it), it's backfiring every once in a while Here's what I've checked: Carb (cleaned thoroughly by me and a local mechanic), reset carb to spec, carb join to the cylinder, air filter, spark, cut end off ht lead, plug gap, valve clearance, timing and a load of other bits and pieces. I've got a new battery on charge which I suspect may aid starting but not tick over. Can anyone suggest what I try next? I'm quite up for dropping the engine if necessary.