Yes, ports can drop as bore increases... they would not go up.

I've seen the steeply angled rear boost port drop over a mm with just a third over bore.

This is the marking. None of the others, DT or MX360 have this.

I was measuring ports this evening and it looks like one of the main transfers opens about .020" later than the rest of them. Not good. The first measurement was on the good side, I assumed the other would be the same. I've actually never seen that in a Japanese two stroke, usually they do a better job.

Re-sleeving is actually possible with these cylinders? I have one that appears to have been bored 'crooked'. I was able to get one from Enduronut and have him bore it for me so I could save the rebuild project. But I would love to send this one out if it could be saved. It was/is at 2nd oversize now. The machine shop did not think even a 1.0mm oversize would correct the 'tilt' from the overbore to 2nd (it's kind a of a long story there, won't go into it........... )

Can you post photos of the cylinders?

just check mine, vin 4427, only stamped 351cc

Yes NHSTEVE, there are shops that do this. In the case of a DT360 an appropriate plain sleeve (no ports) would need to be obtained from someone like LA Sleeve, the ports would need to be cut, the cylinder bored to accept the sleeve and the sleeve installed and ports cleaned up. An expensive process but a way to save a cylinder. I have NOT used this process, only investigated and inquired.

On one of these bikes, IMHO sleeving would be a waste of time and money.... find another cylinder.

One of the Yamaha features is on most models they "cast in" the iron sleeve. This results in great heat transfer and a good product... downside is not really meant to be re-sleeved.

So what you have to do is install a fairly thin new sleeve into the original "cast in" sleeve.... many years ago LA Sleeve made affordable repair sleeves for many engines... Sleeving was half the cost of a new cylinder from the dealer. I know of a few that were done and the engines didn't seem to have as much power especially after they warmed up. We always theorized the thin sleeve would heat up and warp under hard use. This was consistent... it wasn't porting... we were racing and the ports were professionally matched.

Now today the sleeves are not that cheap and good used cylinders are usually not that hard to find... I just wouldn't mess with sleeving on an engine with "cast in" sleeves. Unless you maybe had a rare cylinder or something.

Now an engine that had a pressed sleeve originally? (I think maybe the R5 was made that way). On those you can cut the original sleeve out and replace with a new full thickness sleeve... that works fine.

Hey guys, this conversation is a bit over my head but since my cylinder has the same 44500 marking being discussed I'll get in here anyway.

I took some measurements with the crude measuring tools that I have and here is what I came with on mine. Not knowing how to measure and so you'll know what I did, I took the measurements from the bottom of the cylinder to the bottom of each transfer port.

On the intake side with the shorter squarish ports I came up with approximately 1 25/32" on both.

On the exhaust side with the longer rectangular ports I came up with approximately 1 28/32" also both.

I have no experience with any other 360s so cant make any comparisons but I do know that this port arrangement seemed to work well on my bike. It was the best and the most fun bike to ride I ever had which is why I couldn't bring myself to get rid of it even after being told ( pre internet days) I couldn't get engine parts for it anymore.

Any areas in particular? I could get any shot you like.

Thanks for the clarifications guys. I was only 'kinda' aware of the differences in the sleeving process. When the machine shop doing
my cylinder the second time around found that it was crooked, initially I had a problem finding a cylinder that wasn't already out to second O/S already.