DT125R Build
-
1.5 years later...
I did get the bike together an rode it quite a lot last summer.We got some sunny weather a few weeks ago so I took it out for the first time this year for a day-trip, on the way back it all went down-hill though!
Was doing about 110kmh on the motorway when I suddenly felt like someone applied my brakes, the engine shot out a whole lotta oil through the breather tube so I thought some seal had broken. Immediately applied clutch an pulled over. Heat gauge showed max-temp, and before i turned the engine off it made a real racket.
Since I was kinda stuck where I was, I waited for the engine to cool down and it actually started, I drove to the next exit witch was only a few hundred meters ahead, at a very slow speed.
Actually drove it home but kept a bare minimum speed, all the while making a real bad grinding noice.Back home in the garage I could take it apart and instantly found this removing the top:
Removing the cylinder the piston didn't look very nice...
Checking the cylinder it looked a whole lot better:
Looking at the crankshaft I could see a spot where it got real hot:
Bluing the metal.Now I am not sure why this happened an where to go from here.
Have been looking at a buncha different options like aftermarket cylinderkits, local shops specialising in repairing cylinders an pistons, original pistons...
But not sure what to do, or even if there is more damage, have yet to split the case.
Any tips here would be apriciated, both how to fix this and if anyone has insight in why it happened in the first place. (Not enuff cooling? Not enuff 2stroke oil? Just bad luck?)@TBthegr81 holy smokes that’s some piston damage what barrel have you got ? I’ve got a barrel and crank here spare if it would be any good to you would want silly money
-
It looks like a heat seazure, whether from no 2stroke oil (??) or failed head gasket (did you check the radiator still full of coolant before rear down?)
It looks like not enough oil if it cooked the crank/big end (you might find the clutch side main seal failed/melted, hence the oil out of the breather) If it is you’ll have to get a rebore & piston, big end bearings & con rod replaced. Also whatever damage to main bearings & seals...
It’s all doable and you get an ‘as new’ rebuilt engine!
...Until you split the bottom end you won’t know for sure though...
@SpookDog I poured a lot of coolingwater on the floor when dissasembling so that should'nt have been the problem...
But I had problems last summer with the water cooking off, so maybe that was just a precursor to this. I thought it had to do with me running tapwater for a while until I bought a bottle of premix an swapped it out, but maybe the engine was just always running too hot.
Right didn't think of the seals on the crank... I turned the engine over with a drill, without the cylinder an whatnot to listen for noices. It sounded allright to me but broken seals would not make any sound so I should def check that.@Calum Lean eh... So should have used a bigger mainjet then...
@mhbikesnbits Barrel? Like cylinder? This should be the original cylinder and piston, I've never changed them and power feels like what I would expect from a stock engine. Original exhaust and carb as well.
Edit:
Off course when I removed the top one of the screws for the waterpipe broke off, so now I also goto deal with that. Another reason I was looking at cylinder-kits that includes a new top, I don't have the correct tools to do this correctly, any time I have tried drilling a broken off screw before the hole always end up off-center...
-
@SpookDog I poured a lot of coolingwater on the floor when dissasembling so that should'nt have been the problem...
But I had problems last summer with the water cooking off, so maybe that was just a precursor to this. I thought it had to do with me running tapwater for a while until I bought a bottle of premix an swapped it out, but maybe the engine was just always running too hot.
Right didn't think of the seals on the crank... I turned the engine over with a drill, without the cylinder an whatnot to listen for noices. It sounded allright to me but broken seals would not make any sound so I should def check that.@Calum Lean eh... So should have used a bigger mainjet then...
@mhbikesnbits Barrel? Like cylinder? This should be the original cylinder and piston, I've never changed them and power feels like what I would expect from a stock engine. Original exhaust and carb as well.
Edit:
Off course when I removed the top one of the screws for the waterpipe broke off, so now I also goto deal with that. Another reason I was looking at cylinder-kits that includes a new top, I don't have the correct tools to do this correctly, any time I have tried drilling a broken off screw before the hole always end up off-center...
Sounds like you had an ongoing head gasket leak. Check the head and gasket for signs of ‘blow past’ black wet/oily marks leading to the water channels...
Take the head to an engineer or bike shop near you. A helicoil only cost £20 or so...
Check for play on the big end now, as well...
Luck!!...
-
Sounds like you had an ongoing head gasket leak. Check the head and gasket for signs of ‘blow past’ black wet/oily marks leading to the water channels...
Take the head to an engineer or bike shop near you. A helicoil only cost £20 or so...
Check for play on the big end now, as well...
Luck!!...
@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...
-
@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...
-
@TBthegr81 Steel liner on the 3MB so just needs a rebore.
@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) -
@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.
-
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.
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...
-
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.
@TBthegr81 you need a special flywheel puller if you look on yambits you should be able to pick one up for the 125
-
@TBthegr81 you need a special flywheel puller if you look on yambits you should be able to pick one up for the 125
@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
-
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...
@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.
-
@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.
@TBthegr81 All the bottom ends say 3BN-XXX
-
@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.
@TBthegr81
Ditto! They all have bn on the cases AFAIKYou did unscrew the centre bolt on the puller, yeah?
It’s M27 x P1.0 L
Left Hand thread...(I have a m27 p1 R if anyone wants one?
) -
@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.. -
@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!...
