Getting to know my newly acquired DT400, and half way though a short ride, it decided to stop.


I planned on giving the bike a full engine rebuild, just not this quickly......
The gudgeon pin clip had failed.

Ouch...!! What does the cylinder bore look like ?

I wonder if clip was in groove properly? Is that a Wossner piston?

Something to check is pin length. I had a 400 where I vaguely remember a piston pin and piston combo I had with a pin that was slightly too long and the clip could not quite seat in the groove. It was a Yamaha pin and aftermarket piston.

Luckily I figured it out during assembly and...
ground the pin down a little shorter
...so clip would seat, but it was hard to spot and could have been a disaster.

They say don't re-use circlips, but i always have if no other option on the day when playing with old stuff & its going to catch me out oneday for sure. Real shame when that happens. I feel your pain. Had a 400 twin suzuki at work 30 years ago where i think part of the clip broke but stayed in the gudgeon pin hole area as the pin hole came out to the cylinder wall so not recessed. & broken bit whizzed up & down randomly for maybe a very long time & channeled the cylinder wall way beyond reboring to clean up. Probably smoking bought it in to be fixed but that was a first & never seen it again since.

Nasty

If someone can correct me, I’m assuming it’s standard, I measured the bore and its 85mm, which from my understanding is original?
It’s been sent away already, so I’m just waiting to here back.

DT Tim, thanks for sharing cylinder pic. I hope those grooves are not as deep as they appear because they look beyond boring out. Hope I'm wrong and your machine shop guys can recover it. Good luck and fingers crossed.

Does it have any markings on the top?

DT Tim sorry about your failure but if you enjoy working on these amazing parts of our childhoods then you will have huge fun and a great machine when done!

Hopefully finding pistons and other critical parts is cheaper and easier than for my Dt360. I want to do a Dt400 next that requires resurrection so please share your progress so I can learn from you.

Good luck !

Non that I can see, I’ll clean the carbon off and see.