DT125R FORUM

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.

Tdr 250?

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

@SpookDog seriously think your massively over thinking this!
I've used many Athena head gaskets with no issues, shouldn't need to use any type of sealer on the gasket either. It's either something like your piston is hitting the head, or your cooling system isn't pressurising properly. I'd be looking very close at your radiator. Have you checked your water pump actually works?

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.

Welcome, your not too far away (NW Leicestershire), often over that way doing a little green Laning.

@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.

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.

Delorto 34mm vhsa is supposed to give good gains, a Honda rs125 carb inlet will fit the carb and bolt straight on to nsr engine. But it mounts the carb at a different angle, so on mine I'm looking at making a angled adapter to use between.
Make sure you have the full power cdi and power valve controller. Earlier jc20 barrels had more aggressive porting but are very rare now, and run slightly different power valves. Nsr150 engine is basically the same engine and top end will swap over onto the nsr engine.

@irongamer727 said in Opinions Honda NSR 125 1989:

@dtr-nsr soldering plastic? U mean melting the plastic together?

Yeah that's it, found it works best cleaning it back to bare plastic, then melting the two edges back together.

Got a 1992 nsr myself, there well built bikes to be honest. Is yours the full faired version or naked F model? The most expensive part to fix on the engines is the barrel as its a plated barrel as standard, so can't be rebored. Mechanically there the same as the later foxeye nsr, so spares are pretty easy to come by. Done about 8k miles on mine over last couple years regularly doing 70-80 mile journey's. Will happily sit at 90 all day.

I must have the only dtr that's speedo under reads lol. I thought it felt quicker than speedo showed, checked speed at 30 with gps, showed actual speed was 33mph.

@Calum said in H reg Dtr:

Yeah unfortunately that nut is connected to the output shaft

I wouldn't want to be hitting that with a hammer and chisel personally!!

Especially as that thing is going to be rotating at some silly speeds during operation.

With the nut drilled out, your only chiseling through about 1mm metal, with a nice sharp chisel it takes surprising little effort to split. Your tapping it rather than clouting it with a hammer.

might also explain the markings in the bore

rest of the engine came apart pretty easy

I've had the crank rebuilt and barrel rebored, and have bought all new bearings for the engine. Just in need of a intact power valve cap and temperture sender (engine has the warning light type fitted). Then can start building the engine up, when I get some spare time. Also looking at fitting road tyres to the standard dtr wheels, if anyone has any recomendations on size and make? Cheers John.

@SpookDog if your splitting the cases, I'd highly recommend using threebond sealant, on the case halves. Think it's 'yamabond1184' that the Yamaha service manual tells you to use, which is threebond1184.

Reason I ask about the head mount, is my Mick abbey modified head. Needed the bracket holes enlarging, because of how much had been skimmed off the head.

If you've been skimming the heads and barrels, the squish gap will have closed up. It may be a insignificant amount. But with how many times you've been doing it, it would be worth checking.
With how old these bikes are now, you can't guarantee things are to standard specs. Skimming your head and barrel will raise the compression ratio.
Also after reboring a cylinder and fitting oversize pistons, you increase the cc slightly also affecting the compression ratio.
All this will have a slight effect on jetting, add in newer ethanol fuels burn slightly leaner as well.
Not convinced these are the reasons for your issue's but worth ruling out.
Could the piston actually be making contact with the head?
I would pressure test your radiator with compressed air (don't need alot of psi) while submerging it in water, to check for leaks.