DT125R Build
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@SpookDog Do you know if the cylinder is nikasil coated on the 3MB engine or could anyone doing work on cylinders fix it? Cheapest alternative would be to get just a new piston, keep the cylinder, and maybe send the crank off to be rebuilt, smack new seals on everywhere an change the oil...
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@TBthegr81 Steel liner on the 3MB so just needs a rebore.
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@Calum Right, good, then I should be able to look for any company in the area doing engine restorations.
Instantly found a pair on google saying they do motorcycles, for boring out a MC cylinder they wanted 1100 SEK or ~110 Euro
Googling for pistons they seem to go for about 100 Euro, CMSNL seem to stock oversized ones as well which I suppose I would need for a bored out cylinder...
However it's just a step up to the Athena 125cc Cylinder kit (~450 euro) including a new top, pins an gaskets as well.
(Though if the bottom end needs rebuilding as well one might wanna go the longer route, and relocating some budget to the crank) -
I was gonna take the bottom end apart but instantly got stuck at the flywheel. I have a box of pullers but none of them deep enuff to catch the threading of the flywheel before engaging the crank. I tried looking in my Haynees manual, and googling "DTR 125 R flywheel puller" but I didn't find anything in the book, an got conflicting results online.
My best guess is that I need M27x1 Righthand thread, is that correct?Also looking closer at my engine I saw that the case is a 3NB while the cylinder and head is 3MB, so a previous owner have already swapped the cylinder at least once.
After reading some threads here about the difference that seems like a good thing?As @SpookDog said I also checked the head and gasket for any signs of blowby but couldn't see anything suspicious.
Checking for play on the conrod it seems to move a fair bit side-to-side, but nothing front-to-back, I think it's good enuff to use, though I will still need to remove the sides to check the gaskets.
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PJME did the best rebore I’ve had, £30 + postage if I remember right. Plus the cost of piston. I’ve run Mitaka and Namura with no problems that I didn’t create 🥴
The work was A1, especially compared to others I’ve seen from well known ‘tuners’...PS only the first early 1988 bikes had 3bn barrels. You want a 3mb piston for your barrel...
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@TBthegr81 you need a special flywheel puller if you look on yambits you should be able to pick one up for the 125
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@mhbikesnbits Early '88 models in the UK ran a 3BN barrel which has a slightly larger bore and shorter stroke.
But 3MB is the norm. Also the 3BN bottom end is the usual crankcase stamping.
This is the flywheel puller:
https://www.ebay.co.uk/itm/193259707118?hash=item2cff2d1aee:g:eVwAAOSwz5pd97Mi
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@SpookDog
This is an 1989 bike from Sweden, registered as a 3MB with 3MB in the chassi-number, but the engine says:
If I keep the cylinder I will get a 3MB piston yes.
@Calum Ya sure? The picture shows 2 of them, but the text says 18X1,5Mm, and it's def bigger than that. With the set I had either a 26mm or 27mm would fit, though they where not deep enuff to let me screw them into the flywheel without also screwing it onto the crankshaft.
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@SpookDog
The center bolt on the puller used the exact same thread size and pitch as the crankshaft, so I could screw on a much too small puller (for that flywheel) that fits nicely on the shaft.After further testing I could confirm it was M27 x P1.0 L so I'l order one such as that, but deeper than the one I already have... But with easter being a national holiday nothing will ship until earliest tuesday.
Also emailed a Swedish firm doing work on cylinders an they could bore it out an supply a new piston for a decent enuff price, I'm ready to pay a bit more just so I can actually ride the bike these few months of the year with good weather xD
Meanwhile I am also working on my 2 other bikes, the daily-driver scooter have a clogged mainjet so it's real slow on it's acceleration... Need to get it on the lift an clean the carb.
And the big heavy bike is being prepped for summer MC wacay, getting some sidebags for it, an swapping the bearings for the stearing, it keeps locking itself into a bad position an makes it hard to drive safely.. -
@TBthegr81
I just assumed you were UK based, hence the PJME suggestion. They’re good. I’ve brought a rebored cylinder that was done by a well known UK ‘reputable Tuner’ and it looked like dogshit...Notchy steering is well annoying! And yes, dangerous!...
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