I've got a set of Green Dreams I'm trying to figure out. One machine is on 1st OV and the other is on STD. bore.
Mainly I don't see a way through on a Piston or Rod/Crank replacement parts since Yamaha doesn't support thees parts.
Seems all the aftermarket parts designations are for 74' up or not 73' model year. For the rod, I'm almost 100% I have a 125mm center to center, 22mm small end, 25mm crank pin...I haven't pressed the crank apart to measure the big end.
I find it interesting Yamaha calls for the same part numbers for 74' and 73' Pistons but Wiseco and Wossner only have pistons for 74' up.
I purchased Wiseco 234M07000 / 234M0705 pistons to measure and compare to my Yamaha pistons and find them to be different in key areas.
If anyone has technical suggestions I'd be very grateful.
 

Looks like Yamaha superseded the original part number for the 1972/1973 DT2/3 piston to that for the 1974-1976 (and 1977 TY250) part. I believe that the initial part number started 311- and the superseded one 438-. Look for the piston part numbers on Partzilla/CMSNL, substitute 311 for 438 and then search fleabay for these - there are a handful of expensive nos available there.

Enduronut here might have some, but I'll leave it to him to volunteer any for sale!

I don't know why Yamaha changed the part number, but my logic dictates that the 1974 aftermarket parts should fit the 1972 and 1973 ones. Saying that, there is always the chance that it is a genuine Yamaha cock up (they do happen! ).

It's true what Als saying as i have bought a couple of pistons in different sizes for my DT 3.
I found a genuine TY 250 piston kit for £80 here in the UK . Getting a rod is the hard work. Try to get the correct measurements for the rod. Some aftermarket rods are fractionally shorter. Some of the crank pins are the same.
As they say where i work though " you can only piss with the cock you've got " !
Hard to find certain the parts for the DT 2 & 3 .

Contact Enduronut and/or DEET here.  Both are very likely to have the parts or may be able to help find them.

Hey thanks guys...I don't feel all alone as much.
As I first started the search for parts for these Dreams, I was astounded at the lack of support in general for older bikes. The after market AUTO world is supported almost as 'deep' as OE.
Now I am actually pissed off about the lack of support. I love a challenge as one poster mentioned in his post...the restoration in 'funner' than riding the bike.
If we could walk up to a Yamaha counter today and buy a DT3 250 piston, it would be in the same bin as a 74' 250... I think.
At one point in time Wiseco had to do the same, look at part numbers AND buy parts to reverse engineer their products. BUT for some odd reason Wiseco tells us today their 1974 product won't fit the 1973 product, for which Yamaha says IS THE EXACT SAME PRODUCT!!!
Measuring a rod / crank pin / etc is a straight forward endeavor. Measuring a piston on the other hand is a bit more complex. There's squish clearance, dome shape, transfer port timing/size, wrist pin depth etc.

Is there anyone we know of that has used the Wiseco 234M07xx pistons for the DT3 250's???


 

One other reason could be the ring end gap locating pins. 

For example, an IT175 and an DT175 piston are "almost" interchangeable except the ring gaps are pinned in different locations.  IT transfer port layout is significantly different and using that piston in a DT could be a disaster if a ring catches in a port.

Skirt window sizes and skirt lengths can change too....  doesn't mean you can use one for the other but they are the same.  And you know that if a manufacturer sold it as the "same" some idiot someplace would sue them because a detail was off. 

Wiseco will also make any piston you want.  Just have to order 10 or 12.  So why aren't they out there?  Because there's not enough demand and/or the people that want them won't buy them unless they can pay 1970's prices.  Rods can easily be made too.  Nobody does because it's simply a bad investment. 

Plus parts are available.  Lots of NOS still out there.  Just contact DEET and Enduronut and you can probably get exactly what you want.  Pistons almost certainly.

 

Thanks MarkT.
Good point about ring locating pins.
I took a couple of pics of the OE and Wiseco 234M07xx I have here.
Looks exactly the same pin locations.
See attached photos.

I've messaged DEET and Enduro.

DEET might not receive your message, therefore maybe also email him at This email address is being protected from spambots. You need JavaScript enabled to view it.