DT125R FORUM

@Nottsbiker I am going to use it, to be honest it’s not that bad there’s actually a small flat spot on the threads only about 2-3 threads, and it’s not at the end it’s about 15mm in from that so it’s not actually where the nut does up more where the washer goes so I’m happy to run it, I only was going to change it cause I got the 3MB crank cheap.

@SpookDog thanks for the help much appreciated, I’ll be getting the correct crank just makes sense.
As for the pv, again iv basically got the wrong servo for my engine electrics cause iv brought a 5 wire Could just pin it but that’s no fun.

I will say the engine isn’t actually going in a DT so I won’t need the loom, I have read that I will need to hook up a battery tho if I want to run the servo as they can act erratically without one.

@Calum Good work! this makes sense as the extra length on the left hand side would accommodate the flywheel/starter ring that goes on the back of said magneto.
Rookie mistake there. It’s not a major issue as I do need a new stator side cover and the wiring on the stator I have has been butchered abit so could replace the lot.

Either that or get a different crank again

Is there a “best” or “better” model of ignition system?

Back to my second point will the cdi unit/ electrics I have support a 5 wire pv servo?
If not again what would I need? 3 wire or different cdi? And would that mean I need a different stator &or magneto?

I really do despise electrics

Hi all, hoping someone can help fill in the gaps for me here. I appreciate all and any help.

I’m currently rebuilding a dtr 125 motor, now the bottom end is stamped 4BL But the top end is 3MB (cylinder and head). Iv purchased a new (used) crank marked 3MB as the one I removed had slightly chewed threads stator side, this is where I meet my first issue.

The crank spindle on the stator side of my new crank is about 15mm longer and by tho looks of it the magneto (marked 3NC)once fitted if the tapers actually match might not go inside the casing cover. Can’t see the code on the old crank as yet to remove the bearings so I’ll know that soon.

Can anyone enlighten me as to wether I need a different magneto/stator set up?

2nd issue would be that iv also purchased a pv servo with pulleys and cables but not sure now if this will work with my cdi unit? (Marked 3NC)

Even the stator plate has a different code 3BN..

Some clarification on what will and will it work together would be greatly appreciated or any advice will be well received as I’m not familiar with this particular engine nor do I like electrics.

Regards, Alex.

Can’t seem to upload any pictures either

Haha no. Copy, but it’s a good one or I wouldn’t have it lol

@declan mine was totally free so win win really, does need a new crank + the parts I mentioned earlier so probably still cost me a good £300-£400 to get it running nicely. Then I’ll figure out what to put it in, got a nice crf70 rolling chassis that needs a power plant.

@NINJA hi and thanks. It’s not a bike just the engine, I was actually given it for free as it’s been sitting I a shed for about 5 years after it blew the top end and seized up. My pal just brought another one with the intention of rebuilding this one but never did.

The only parts I haven’t got are the cylinder and pv assembly as he transferred those to the new engine after having the cylinder bored.

Iv already completely stripped the engine all seems to be in order, so I’m now looking for parts to complete it then rebuild time!

Not sure what it’s going in yet, probably one of the project bikes. Although i have always wanted to make some kind of mini cross kart type deal.

@Calum thanks very much, I’d like to think I can figure out most stuff or find it out myself lol see how I go I guess.

Hi to all, just picked up a nice little 3MB engine for a bargain of a price with a seized crank (which iv actually already un-seized) but I'll get to that later.

I have have several Honda CR’s, Yamaha YZ’s an RM or 3 and plenty in between over the years.
I know my way around most small-ish bike and quad engines but you never get help and Info better than the forums so her I am for the knowledge and wisdom you all contain.

I’m sure I’ll have some issues I need help with so I’ll get using the search function before I ask the usual run of the mill questions and annoy some people, if anyone could advise me if there’s a policy about digging up old threads that’s be great.

Best regards.