jon v8 Posted June 25, 2015 Report Share Posted June 25, 2015 (edited) Just a thought.... Back in about 2007 I bought a TY250 twinshock as a non runner / spares bike. It has sat at the back of the pile of bikes since then totally untouched, a couple of weeks ago I spent a day digging it out and making it into a trial ready ratty hack... I rode the first Golden Valley evening trial on it and it went well.This afternoon I took it up in the woods for a play practice with a mate and had trouble shifting down through the gears - from any gear shifting to a lower one.I got around it by lifting the lever slightly before pushing down.Feels like a weak detent spring or similar to me,it doesn't jump out of any gears once selected. I'm using Land Rover MTF94 oil in the box,which I used without problems in one of my other TY250's for the last 9 years, and the clutch is in good shape, freeing cleanly and taking up drive very smoothly. I've never had a TY250 clutch/gearbox problem before so have no previous memories of them,just a reliable / abusable bike... Edited June 25, 2015 by jon v8 Quote Link to comment Share on other sites More sharing options...
tony27 Posted June 25, 2015 Report Share Posted June 25, 2015 From memory the detent is under the motor, possible it has had sludge build up in the spring under the piston. Lie it on the clutch side & pull it out, check, clean & refit & see if that helps. By lying it on the clutch side you shouldn't lose any oil Quote Link to comment Share on other sites More sharing options...
feetupfun Posted June 25, 2015 Report Share Posted June 25, 2015 It might be what Tony says, or it may may be the shift mechanism centring spring. There is a centring spring for the shift mechanism that lifts the shift lever back up after you shift down a gear. It is visible when you take the clutch cover off Quote Link to comment Share on other sites More sharing options...
tony27 Posted June 26, 2015 Report Share Posted June 26, 2015 Had forgotten about that 1 David, that is a remove the clutch job though. I can hopefully scan the photo out of my B manual & post it up if needed Quote Link to comment Share on other sites More sharing options...
jon v8 Posted June 26, 2015 Author Report Share Posted June 26, 2015 Thank you both for the suggestions, my son tore it apart this morning while I was busy fixing my minders Range Rover... (The detent plunger was clean, unworn and free to move) He found that the crankcase has been welded in the usual place around where the pivot pin for the gearshift centring spring sits.(But the pivot was loose) And also the end of the shift drum has suffered a botched repair to a broken pin. Luckily my spare motors have enough bits to get it all back together without having to wait for stuff to arrive - or spend money ! There is a lot of gunge hanging around in the bottom of the gearbox, which I will flush out, its clearly chased a lot of dairy cows into the parlour from the fields.(And been spannered by the farmer that rode it) The motor does have a very healthy Yam rattle, but has plenty of go, so I don't really want to have to split the cases and do a full rebuild. I'll post a photo up of the mess when I get back to it over the weekend. 2 Quote Link to comment Share on other sites More sharing options...
jon v8 Posted June 29, 2015 Author Report Share Posted June 29, 2015 This has not gone well... The motor is now completely stripped after replacing a bent shift shaft,and return spring post.I also got rid of a horrible bodge where one of the pins was welded into the end of the selector drum. On reassembly it refused to select anything but neutral and first gear. The selector drum refused to rotate clockwise to select second or any higher gears.So it came apart tonight, with me expecting to find bent selectors or a damaged drum. Nothing, its all in very good shape.Selectors are straight,no wear in the drum grooves,no collapsed bearings or chipped teeth. Nothing... Going to replace the drum with an undamaged one and build the box back together without the crank, see if I can encourage it to work. I couldn't see any option but to split it,with the selector arm right off the box and the detent plunger out, I couldn't rotate the drum clockwise beyond neutral. Good thing is that the motor is in fairly good shape,just worn rings. Quote Link to comment Share on other sites More sharing options...
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