Anyone know where to get a 3rd oversize piston and rings for a 74 Yamaha dt360?

If no luck on fleabay, then Enduronut and/or DEET on this forum might have some. 

bought my dt360 3 rd over from enduronut

Greetings from Tennessee. 

I previously bought one from CMSNL for around $200 in Jan-2020 when I had a meltdown. I just scanned CMSNL and eBay now and don't see any....would seem that these are getting really rare, if you can find and afford you prob should jump on it

I bought a RT3 last winter that needed a new piston and had a heck of a time finding one fourth over, in the end I just got lucky and found a new cylinder and a new piston both standard bore in separate places on eBay. Took a solid few weeks of searching and they were expensive but the bikes back running. I wish someone would reproduce pistons for these, seems they make them for a lot of the other vintage Japanese bikes, given the popularity of these old enduros I would think someone would start reproducing them. Good luck in your search! 

When I rebuilt my '74 360A a few years back I discovered that the DT360A really is that very rare, one-year-only model. The DT400B & C model cylinders do NOT go one those cases, and one can NOT retrofit a 250A cylinder when disaster strikes. Aftermarket sources probably discovered this fact in 1974/5 and figured why make piston/ring sets for just one year, not much money to be made. Thus you are pushed to OEM, and as we are discovering they are now rather 'thin on the ground'. Enduronut helped me out, as did eBay, but expect to pay more $$ for the bits.

A second solution for those with the 360A would be to replace the entire motor with either a 250 or 400, which seem to have more bits available. Just sayin'

As far as "NOS" supply, it might be more that since it was "one year only" not as much supply was ever produced.  The earlier bikes had a lot more parts in common for a lot more years...  and many more of those models were sold. 

As far as aftermarket today, Wiseco will make pistons for anyone... at least they did a few years ago when I spoke to them.  You just need to buy a minimum run of like 10 or 12 is what they told me.  Someone back east commissioned a Wiseco run for the TS400...  which fits the Suzuki TM400 and TS400 models for about 7 years...  not just "one year only".  I bought a couple as funds would permit.  When he ran out I contacted him and he said it took him over a year to recover his investment and it wasn't worth the hassle and dealing with selling them for virtually no profit and listening to people bitch.  I was one of the very few that was happy just to be able to get a new piston kit. 

At such a low volume the price you get is more or less retail... "modern" retail... he said his cost was near $200 per piston set...  and he said too many vintage bike people out there consider a $200 piston kit  "highway robbery".  I just looked it up and a factory piston kit for a two stroke 2022 KTM 250 retails for $228. (a 2022 KTM 450 four stroke piston is $554!!!)

If you bought a couple hundred piston kits your purchase price per kit would come down but you might never be able to sell them all.

Apparently very few people want to pay modern prices for old bikes so if they can't buy a piston kit for $59 for their old bike they think it's a ripoff and either won't buy and/or will complain to the seller.  (He said he had a lot of people complain and cuss him out for "being a crook" and not buy. )

In other words, if more people that owned DT360's would be willing to pay $250 to $300 for a brand new piston kit and there was decent demand for them, someone probably would be selling them.  (That someone could be actually be you.)

Wossner would probably make piston kits too if someone commissioned a run.

In the meantime, Enduronut might still have a few DT360 NOS piston and ring sets, you'll have to contact him.