Greetings
I have a DT1 engine that needs freshening up.  I have a 2nd over DT1MX piston and ring on hand.  It would save me the price of piston and rings if I could use what I have.  Is this possible?  Is it a bolt-on or is some modification of parts required?
Thanks for your experience/advice.
Chris Finlayson
Alexander NC 28701

Yep, goes straight in. Inlet skirt is a few mm shorter. Had one in mine & a 32mm 360 carb for a lifetime ya just reminded me. Goes extra good too.

Thanks for the speedy/authoritative/positive reply.

You've made my day!

Chris Finalyson

I should've said 'Welcome' from NZ down under. We mix n match all sorts of things down here lol, in my case because because i hate spending money if something will do. Think i've got a piston to take a pic of alongside original just for comparison.

My only thought beyond is to make sure both pistons are from either a piston port or a reed valve engine...  all 250's from 68-73 had engine numbers with the "DT1" prefix...  even the reed valve DT2 and DT3.  I don't think you'd want to put a reed valve piston in an earlier piston port or vice-versa.

 

Thanks for your advice and comparative photo.  Since the skirt of the single-ring MX piston is slightly shorter than that of the civilian model, it seems to me as if that will open/close the intake and exhaust ports slightly earlier/later.  Correct?  If so, how does this affect the performance characteristics of the motor?

I have noticed that the info and discussions on this forum are of a relatively high order compared with most others I have read.  Very refreshing.

Chris Finlayson
Alexander NC 28701

Yes, opens it sooner & closes it later so more duration by a little. Hasn't done mine any harm, only good. Bigger carb probably helped though. Could do what i did to my other & put a 360 crank in but i guess you're working on a customers bike. The MX cylinder has a larger-taller inlet port to match the piston so at tdc its equal to the skirt at tdc. So in your case "& mine" the piston skirt goes above the inlet at tdc by the amount of skirt difference. When i used the 360 70mm stroke crank in the DT1 MX cylinder "on other bike" it was a close to being a problem as at bdc the MX single ring gap was 'just' showing in the inlet port, not completely but close & 'just' safe. Anyway, ignore all that as irrelevant to your original worry. My bad habit of wandering off the case lol.

Agree on using the MX piston, paying proper attention to clearances and comments regarding reed valve vs. none reed.

The shop I worked at saw a lot of MX'ers get used in sand pits once the monoshockers came out. We would often (with their understanding) use the enduro piston to replace the MX piston. There was a price difference then, and the second ring would give them better wear and longevity, which was more desirable since they were by that time playbikes, and not real competitive.