DT250 piston for TY250a

[typarts-aus]

Fellas, this may have been tackled before but can anyone tell me why a dt250 piston kit will not suit a TY250a. Is there a difference in the skirt or ports. I realise that the ty has a top keystone ring but as for the rest????????????? Can anyone enlighten me.

[Stu]

I have a found out i have a 438 piston( I think its a DT250 piston) in my TY250a the hard way! The TY was used as a comp bike and a trail bike for many years. Ive ordered a new piston kit from TY Trials in the UK.

[David Lahey]

I haven't compared a Yamaha TY250 piston with a Yamaha DT250 piston, but have compared a Yamaha TY250 piston with a Wiseco DT250 piston. They have the same skirt length, but from memory, the holes in the rear of the piston are slightly different. The Wiseco DT250 pistons fitted to my TY250B and TY250D motors have seen years of use and both motors have run beautifully from the time of reassembly. Both motors ran more strongly than before they were rebored - probably because the old parts were worn.
If the holes are different in a DT250 piston, then it would not be much trouble to reshape them to suit the TY250 rear transfer port. Yamaha DT250 pistons are a high quality item, which I would have used in my bikes if I had been able to find some for sale at the time.

[Guy53]

You need to tell us more on that DT 250 piston: year, model ( DT or DTMX ) . I have a DT and a TY ( 434) original piston and apart from the " corner " that are cut on the TY they are the same. I will lookup the part number of the DT and come back to you.
Guy

[Guy53]

I just looked at the 2 piston that I have, the DT is a DT 2-3 and the TY is genuine. The port holes are the same, total height and pin height same.

Guy

[typarts-aus]

Thanks for reseach fellas. Yambits in the UK have a piston kit comprising of Yammy rings, pin and clips and Matika piston for a DT250 75-76. I contacted them and they claim this is not suitable for my TY250a. Can anyone tell me the major difference.

[David Lahey]

If Yambits can't answer that question then maybe they can provide dimensions so other people can decide for themselves?

[David Lahey]

One thing I just remembered about TY250A compared with the other TY250 twinshocks is that the conrod design is different on the A model. Maybe the Mitaki piston is too narrow between the gudgeon pin holes for the A model conrod? I'm only guessing here (the piston photo on the Yambits website shows a piston that looks just like a TY250 piston on the outside)

[Guy53]

I looked carefully at my DT piston, I knew the ring where different but I checked for the position of the ring stopper pins and they look similar, and from memory we installed at least 3 DT piston in TY with no problem. I don't remember the year of the DT piston we use, sorry.

Guy

[typarts-aus]

Yambits emailed me and although they couldn't give me the piston measurements they did say they will have a kit to suit the ty250a within the week.