Engine rebuild Dt125 Page 2

[MugenSeiki]

Well it's been a year now and i've been having no probs till yesterday

Quick reminder of my project on here that started 2 years ago

HD

https://www.youtube.com/watch?v=eg5f2N0-nBI&hd=1

Anyways on way to do my MOT and it starts screeching etc and breaks down right on Yamaha's forcourt. Crank ceased, piston screwed, bearings screwed. Looks like the oil pump packed in or something as everything was bone dry despite me always keeping it topped up.

SHOULD have rebuilt it last year when I was doing the bike but it ran a whole year fine so I call lucky.

So back upstairs the bike came today and the engine's getting sent off to Bob Farnham to rebuild and race tune. Cannot be asked to do it myself and i wouldnt mind the extra pony's

Few little mods i'll be doing to frae while it's stripped so stay tuned

so far ive just cleaned it


https://i39.photobucket.com/albums/e179/mina-patel/IMG_1306.jpg

https://i39.photobucket.com/albums/e179/mina-patel/IMG_1308.jpg

https://i39.photobucket.com/albums/e179/mina-patel/IMG_1309.jpg

https://i39.photobucket.com/albums/e179/mina-patel/IMG_1310.jpg


Goop on exhaust is gone and its clean

https://i39.photobucket.com/albums/e179/mina-patel/SDC10887.jpg

https://i39.photobucket.com/albums/e179/mina-patel/SDC10888.jpg

https://i39.photobucket.com/albums/e179/mina-patel/SDC10889.jpg

https://i39.photobucket.com/albums/e179/mina-patel/SDC10890.jpg


In here was black with crud

https://i39.photobucket.com/albums/e179/mina-patel/SDC10891.jpg
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www.dt125.co.uk

[The Artist]

That rear tyre is soooooooooooo square

[MugenSeiki]

Sunday rider, every 3 months
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[Devans]

Nice too see the bike a year later, shame about the engine but it couldn't have gone at a better time xD

[clancy]

to the bike being in the house, and can i ask what was on tv lol

looks tidy i like the rim tape
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KLX 300r

[Billing]

It's Avatar in at least one of them
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'84 TS50X, '91 TZR125, '89 CBR400RR, '91 VFR400R NC30, '98 R1
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[swiftb]

Welcome back dude good to see the bike still looking clean a year on and your still riding. I see you still like taking the same photo from a few different angles too

[Ol]

WTF were you watching on TV ????


https://i39.photobucket.com/albums/e179/mina-patel/IMG_1310.jpg
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Previous: Cub50, NRG50, TS50, YB100, CB125, NSR125, ZZR600, CBF1000, SV650s, ZX6R B1H, XT250, Mito Powered Crosser, WRF450, , FZ600, VN800, GSXR600 - Currently CB1000R

[clancy]

[waffles]

This was definately one of my favourite bike projects to follow, shame about the engine but I guess every cloud....
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Theory test - 19/8/09, CBT - 11/10/09, MOD 1 - 16/8/10, MOD 2 - 27/10/10
Past rides Yamaha XT125X, Triumph TT600, Honda XR250
Current rides Suzuki GSXR 600, Honda MSX125

[Billing]

[MugenSeiki]

Yup Avatar


Got a little done today ..

My LH switch has been annoying me all year so bought a second hand one and i'll swop over the internals. Also treated myself to some new grips and bit more SM stylee. Yammy want £130 for a new switch btw.

https://i39.photobucket.com/albums/e179/mina-patel/SDC10898.jpg

https://i39.photobucket.com/albums/e179/mina-patel/SDC10899.jpg

Then been thinking about moving the front fender down and styling the front end a bit more like a streetfighter. Might use a MT03 headlight as I hate my current one.

Few pics of the idea and i'll photoshop the headlights on in a while

https://i39.photobucket.com/albums/e179/mina-patel/SDC10909.jpg

https://i39.photobucket.com/albums/e179/mina-patel/SDC10900.jpg

https://i39.photobucket.com/albums/e179/mina-patel/SDC10904.jpg

https://i39.photobucket.com/albums/e179/mina-patel/SDC10903.jpg


Really liking the idea as i've always hated the front end, not sure how i'm going to mount the fender that low so need to think about that one, open to ideas! <<< Ignore all this, it was a stupid idea

New grips match the bars better (details lol)


Old

https://i39.photobucket.com/albums/e179/mina-patel/SDC10895.jpg


New

https://i39.photobucket.com/albums/e179/mina-patel/SDC10907.jpg

https://i39.photobucket.com/albums/e179/mina-patel/SDC10905.jpg
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[stevo as b4]

Shame about the motor going pop Mugen. These things can happen though, and you might have had no reason to re-build or replace the oil pump before.

Still it's really cool to see the bike a year or so on from that epic build, and it is still an awesome 125cc Motard! It's really stayed clean and in great condition too, and i guess that proves that doing a quality resto job and keeping it clean after can make any bike stay nice for a long time!

Have you thought about either trying to locate a 200R engine or fitting a 170cc Athena big bore kit to your motor? I think the factory 200 engine would give you far more overall performance and ridability with much less of a peaky powerband than a serious tune to you 125cc engine will.

The big bore kit would probably work well too especially on a new bottom end, and carefully run in. More cc is IMO nearly always the best first mod you can make for decent performance gains. You will then find that things like a bigger carb will make more of an improvement to the 200 or a 170 big bore kitted engine, than they do on a 125.

[MugenSeiki]

[tvchimp]

You know you want to
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Bike: Currently Bikeless... Gahh

[N cee thirty]

[tvchimp]

[MugenSeiki]

But would it work
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[stevo as b4]

Yeah the DT200R engine would make for a fantastic street moto, having an easy 30bhp at 8500rpm. More would not be hard to find, and you can get aftermarket pipes for the 200R as well. Shame we never got them in the uk, as i guess it makes finding one a nightmare. Have you tried any Grey bike breakers, or BAT motorcycles maybe? Also worth ringing DK breakers just in case too.

You could look at an alternative engine, but then more work is involved and getting a different engine to fit in would be possible but could involve a bit of hassle with engine mounts, swingarm bearings, and in a worst case even having to cut and modify you lower frame rails, which would be so wrong on such a mint bike IMO. A Honda MTX200 or KMX200 engine might also fit, but again finding either in decent running condition is going to be real mission and thats before you start trying to get it into the frame.

I think the DT230 Lanza engine might well go into the DTR frame without much work as the engine looks very similar. The WR250R engine or even a YZ motor could probably fit with minor alterations too, but no MX engine is suited well to a street ridden motard, and it's really not worth losing your oil injection system for a more powerful engine with a less street friendly nature.

The 170cc Kit does seem to work well on the DTR and i expect that its the midrange it improves and makes much sharper as much if not more so than the top end power. I think alot of the bad rep with people fitting big bore kit's to 125cc strokers is due to poor installation, and also fitting them to part worn and already abused engines with wear to the bottom end already. I expect that with a new crank and bearings that a properly fitted big bore kit could be almost as long lived as the original 125cc engine would, if treated well and run on quality oil.

A professionally ported and tuned 125 DTR engine would probably make 4-5bhp more at the back wheel, but you will possibly lose some midrange performance, and still be within the limitations of the std carb and other parts. I think a pro re-built and tuned engine would work very nicely especially if you have the YPVS system fitted and working, but the bigger capacity route will normally always feel like more of a difference to the way the bike rides.

There are some people who like an MX like more peaky than std powerband, but i can't see that for road riding most of the time that it would make the bike faster or more satisfying to ride.

[MugenSeiki]

You've managed to change my mind mate ..

First off ignore this streetfighter idea please, it was a stupid thought.

Second I picked my engine back up today and will rebuild myself. I've never really bothered to figure out the workings of it but im forced to now.

Bottom end I'm guessing is just a straight rebuild, old bearings, seals, collars out, new ones in. I'll probably replace the crank as well with this

https://www.adrenalin-pedstop.co.uk/p-Top_Racing_original_crankshaft_for_Yamaha_DTR_125cc-3890.aspx

Then I'm hoping to get the Athena like you suggest. After thinking about it I remember Bob saying he'd bore it out to about 140 which is still under the Athena. So I think I'll see more of a difference with the kit.

The bottom end will be fresh and Yammy will help me rebuild so everything SHOULD go smoothly.
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[Shaft]

[MugenSeiki]

An unecessary change and wouldnt be that easy to do tbh. I still like the idea but I want to concntrate on getting it going again now.
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[Shaft]

Fair enough, just seems a shame not to do it while you've got it apart.

Looks to me like the hardest part would be working out which bits would look right.
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[iSinBlood]

I've always loved watching your Project video, very inspiring to be honest. If you put a 125 back in there can i buy it plox plox .

[stevo as b4]

Yeah i think that the 170cc kit if fitted properly to a nice fully re-built DT125R bottom end will give you similar performance to a DT200R or KMX200, and have a decent much better than std midrange, and still keep good reliability too. Id definately get the crank re-built to a high standard or replace it, along with the main bearings and all the oil seals too.

The one thing i would suggest if your going to be spending quite a bit on your engine, is to get the oil pump properly re-built or just replace it with a brand new one if possible? Id also replace all the oil lines from the pump to carb and from the tank to pump, and all the throttle/oil pump cables if you havn't already done so. Id could be a good idea to test out the pump first before you fit it to your re-built engine, by hooking it all up to the tank and running it with an electric drill to make sure it deliver's the required and specified quantity of oil stated in the manual, and then get someone who really knows what they are doing to set up the oil pump properly when you get the new motor running.

It would be worth finding out if you can from Athena what size jets you should be using, and what grade spark plug needs fitting to the big bore motor. I expect you will need a fair bit of re-jetting to get it to run spot on, and it probably will need a cooler plug, and depending on th compression ratio you might have to run it on 98RON fuel.