Hello, hopefully everyone is having a good day!  I am curious if anyone knows the dimensions of an rt1mx piston?  I am getting ready to install this top end, but I realized it's a regular rt1 piston in an rt1mx cylinder.  I was going to cut the skirts down to match the rt1mx piston.  Any help is greatly appreciated!

I'm guessing a bit but at tdc the skirt should be at the top of the inlet port so thinking along those lines your std skirt should show in the port by a few mm. My DT1 has an MX piston so i'll measure the difference in skirt as might be a similar difference.
If you had to shorten it 'too much' it might fractionaly alter the piston clearance as they taper up, but probably way beyond the amount were talking & don't alter untill about 20mm up. As i said--guessing a bit.
How lucky are 'you' to have an RT1MX piston port bike. I assembled my bosses one new in "70 & then much later i borrowed his motor for my DT1 race bike for one meeting [think he was away overseas haha]. Was a blast!!.

Ok, i'm a little confused [old & confused lol] so at the moment its got the RT2MX top end [so a piston with windows].
I 'think' the trail 360 piston & the RT2MX skirt are the same length.
I have an RT2MX top end on my old relic RT2 mixture with an RT2 machined head to get the compression up as don't have a genuine rt2mx head.
That said, i have an 82mm YZ400F piston fitted.
But the pipe is all wrong & peaky to the extreme.
So i've made a washer to fit behind the gasket in the exhaust port & made it so the top of the hole is lower to try & trick it into thinking the port top in lower.
Definitely changed it for the better but not perfect with the terrible trail ratios & big step between gears.
I've got an underneath pipe on now that works better [one i made years ago].
But i had a fatter RM250 high pipe on which made it rev crazy & had little low & midrange power.
Might have a pic of what i did so i'll go looking.
Love projects like yours.

Great news. Now i want an piston port mx cylinder & head for mine haha.
One point [& don't dwell on it] but by memory the mx with high compression timing goes back to 2.3btdc.
Hey if its going good & not detonating then ya must be doing someting right.

Hate to bore you lol but here's mine as an RT2 with a 250 crank just to confuse.

More boring stuff, just drag it on.
Then this'd be earlier this year with short suspension & RT2MX top end plus underneath homemade pipe. [& no mag cover haha]. Looks like march this year, i was only 76 then lol.

Pic below, forgotten which one, think on the trailer.
photos.app.goo.gl/fTUYfMw9FRrcPfuL7
Here it is with RT1 piston port cylinder.
Confused--hell, i am.
photos.app.goo.gl/aHYkXeoroGLweiPD9
High pipe justr sent the RT2MX cylinder wild like a roadracer which was hopeless with the wide ratio trail trans.
Have another motor somewhere as a 250 using a 360 crank & makes it about 280cc. Has a dt1MX cylinder.
Enough bull S#^t for now. Be great to see pics of yours & even a video if possible sometime.

I have an RT2 MX barrel and head on an RT1 bottom end on the shelf at home . Gives me ideas.

Thanks, i think lol, but look forward to seeing yours running sometime.

youtube.com/shorts/ET98Ach7GfE?si=wkEgkhHGLHtC90ya

That's the beast with the rt2mx top end.  Uploading the rt1mx top end video now

youtube.com/shorts/pxQeXtJQrGo?si=eWkuKi5DWWuqJ9KA

There is the rt1mx top end.  Dont mind the rt3 tank, the badge tank is in safe keeping (until I fix the fuel leak.)  I'll try to get someone to record me riding it around, best I can do today is some rev video's.  It's quite a difference, I think you'll hear that.