Hi, been lurking on the forum a while, but finally got round to registering. Over last 6 months or so been returning a H reg dt125r to the road. It sailed through it's mot back in february, but the engine is currently apart, being rebuilt to bring it up to the standard of the rest of the bike. I also own a K-reg honda nsr125rk, so like my 2 strokes Will start a project thread when I get some photo's worth posting, John.

You normally check the squish by feeding a small length of solder down the spark plug hole, so the edge of the solder touches the edge of the bore. Then turning the engine over by hand then measuring the squashed end of the solder with a micrometer or similar. The squish on my dtr was 0.6mm when I bought it, which seems to be on the tight side.

From experience it tends to be running too lean that kills two strokes. Though a 2 stroke makes more power the leaner it runs. At 57mm you often have to modify the power valve for clearance. And the head gasket will need opening up. When the barrel 1st seized they might have replaced it with a 'good' second hand barrel that had already been taken out a few sizes.

If yours has got the reed switch in the speedo it wont have the black/green wire. Pretty sure fitting the zeel would do away with that restriction anyway.

Freshly powdercoated parts going back together

starting to look more like a bike again next to my nsr125rk

and after a little light offroading

Piston rings have a hard life in a 2 stroke travelling over the open ports. I've seen the pins that stop the rings rotating on the piston move, allowing the ring to spin and open end catch on a port. With it being under load at time it failed (going up a steep hill), I wouldn't be surprised if piston expanded due to heat build up and pinched the rings. May have been running on the lean side aswell.

@gilerasc125 at 57mm bore it could well be catching powervalve and/or head gasket. I'd whip the powervalve out and check for any witness marks.

Tdr 250?

Big chain and padlock gets my vote. Preferably chained, with the chain and lock away from the ground. Makes it harder to attack with a hammer or cutters. Also if you can lock the padlock to part of the bike (as well as both ends of the chain obviously), it prevents them manouvring it into a position it's easier for them to attack.
Yes determined theifs will still try, but I don't believe you should make it easy for them.

@calum yeah it certainly wasn't a happy piston, also was a dark heat spot on the underside of the crown.

Pictures of a dt piston that heat seized due to lean mixture, from the base gasket blowing. You can see the classic 4 point seize and a little detonation damage to the piston crown nearest the exhaust port. Believe it or not, pistons aren't perfectly round, And are normally narrower along the line of the gudgeon pin, so it would be very unlikely to get a heat seizure at that point on the piston.

@spookdog that's not a 4 point heat seizure from running lean though. The side of piston above the gudgeon pin see's very little load. Only time I've seen damage to the side of a piston similar, was when a gudgeon pin clip had come loose.

If it was only one side I'd say bent rod, what was the little end bearing like? And what does the plating look like near the transfer ports?

@karumaspt I may have miss understood what you've put, but sounds like mixing the parts might be causing your problems. I know some bikes have two pickups one for low rpm timing and one for high rpm. So joining the two would very likely cause issues.
And the impedance of the different year pickups could be different, causing them to burn out.
I'd try get one matching setup, all from the same year to remove those variables.

@arild I think they were 50mm longer than stock. That was for road use though, but did seem ok green Laning at the weekend.

I've fitted longer spacers in my front forks, which has made them stiffer. Much better for road use. With out, the front end used to dive a stupid amount under hard braking, often causing the rear to lock with the weight transfer (road tyres). And that was on freshly rebuilt forks.
Also not all grades of fork oil are equal, one brands 10w might be anothers 15w. Your best looking at the cst rating of the oil to compare them.

@arild said in Engine tuning/ bike build:

@DTR-NSR as i said above im planning on 3d printing a pair if i get spare time for that, i might make a batch and sell them for 5 pounds or something

I'd definitely be interested in a set!

There's quite a few guides out there, on doing it on banshee engines, which are very similar to ours. They tap and bolt the two half's together. Nearly every basket I've had in my hands has had excessive play. Problem for us is getting the rubber parts unless someone can 3d print them.

@DTMAN sorry to here that pal. You only need to remove the clutch cover and clutch basket to remove the selector shaft. Only problem is you'be got to either straighten the shaft at least a bit to remove it from the engine. Or cut it flush with engine, and slide the remains out the clutch side. Might be worth removing the knackered lever. Then sliding a length of steel tube over the bent selector shaft and applying a bit of gentle leverage. Heat would help but you'd fry the selector shaft seal. : /