I stumbled across an oddity in the garage the other day while organizing the parts heap. I have three DT360A cylinders, two are identical and the other is slightly different. The one that came with the bike and the one I have on the bike now have no external markings other than "351CC" on the clutch side of the jug. Jug number three is also marked "351CC" on the clutch side but also has "44500" on the stator side, at the base of the jug under the cooling fins.

The only significant difference I can see is the 44500 jug has all of the transfer ports opening at the same time, while the two other jugs open the main transfer ports about 1mm later than the aux transfers and the boost port. The intake and exhaust ports are the same as the other cylinders.

Does anyone else have a 44500 jug? I suspect these are what Yamaha sold as replacement cylinders and the non-marked jug was original equipment.

That's interesting & be good to hear from the knowledgeable.

I wonder if it runs any different. That change with the transfer timing is subtle but it would probably have a significant effect.

Too bad this jug is at .060" over already, I'd like to try it but I don't think it makes sense to bore it again just to run one more top end through it and scrap it.

445 looks like the number for that model. Maybe they ran out of stamps till late in "74--being silly. Seeing its out to +60 you could use a 2X5 YZ400F 1979 one year only long stroke small bore 400 piston 82mm or up to 83mm in yamaha .25 steps. Need about 5mm of the bottom of the skirt to be safe but i forgot on my last one & think its still going.
Sorry i did that on my RT2 but same bore & stroke as all 360's 80x70 std.

I've been running a Honda FL350 piston in this motor. I can get them in 82mm I just don't think the jug will have any more meat left in it for oversizes past that.

I've read that the MX360 has a thicker sleeve than the DT360 and can be bored significantly oversize. Haven't experimented with one myself.

What I could do is send this 44500 off to LA Sleeve and see if they could fit an 89mm sleeve into it. Personally I don't see why not. Then I could run CR500 pistons. That would make 435cc's with the 70mm stroke.

Over-bore sizes might be the clue. Port heights often change significantly as the bore is increased.

I agree, though I've never seen a port move up with an overbore, only down. .060" over is only half that per side as well, that shouldn't be enough to alter port timing.

I have a DT360 cylinder and an MX 360 cylinder and the big difference I saw was the intake and exhaust port size and the head had way mor volume on the DT360 for lower compression. When I get the gbike running good I am goig to try first the head on the DT cylinder and then the cylinder and head. I believe though that the big difference is in the pipe on both engines. The DT pipes and very restrictive in stock form
Doug

The MX360 cylinder is a whole different animal. On the one I have the exhaust port measured about 6mm higher than the DT. Must rev like crazy, seems risky for a big bore.

The stock DT360 pipe is garbage. Heavy, restrictive, not particularly quiet either. The MX360 pipe works much better, even with the DT porting and head.

60 over is only 1.5mm. piston i used 2x5 starts at 82mm which is +80 & takes that ok. I stuffed an rt2mx 360 cylinder by trying a yz400 85mm piston & alloy showed up. Still p--sd about that 47 years later lol. & even more p--sd off i dumped the cylinder when coulda sleeved it with available LA or Wiseco sleeves.