DT125R ARCHIVE

scrimsmustang · DTR Mechanic

90 YZ125 topend onto DTR

Calum122 · Guru

RE: 91 YZ125 topend onto DTR

scrimsmustang · DTR Mechanic

I duno it might be OK with the YZ airbox on and if I can get the fuel in OK. Ile give it a try and see what happens.

Calum122 · Guru

I'm wondering in terms of actual crank case volume. And the vacuum pressure...

scrimsmustang · DTR Mechanic

I don't know nothing about any of that type of stuff Cal, that's way to complicated for me. I'm just going by eye and what I can see and it all looks very very similar save for the DT,s heavy flywheel but that shouldn't be a problem it will just make the bottom end a bit better. It should just be like some people adding a flywheel weight to a motocrosser when converting to an enduro in theory. For me the airbox and exhaust is the main thing so you can get the jetting sorted properly with the old YZ,s TMX 35.

dan28 · DTR Senior Member

I was looking on google a few weeks ago an someone has already done this
he has since sold the bike but by all accounts it did work the topic was on the Yamaha owners forum an another forum I cant remember

Calum122 · Guru

It's interesting for sure. But I'm concerned about the port timings and compression ratios. Could go well with a proper setup.

scrimsmustang · DTR Mechanic

Port timing should be bang on as they both have the same stroke length that's the only reason im going to try it, I think I can convert the YPVS from mechanical to servo without to much trouble as they both use the same type of roller cam YPVS but the YZ,s is operated from the right and not the left so the servo will need to be switched to the right but facing the original way with the pulley wheel reversed if you get me. The airbox will need a couple of little brackets making and the rest im hoping wont be to bad. Inlet manifold might be a straight swap if im lucky and the YPVS cover will need drilling and threads tapping for the YPVS cables. Set up should be as the standard 91 YZ125 then go from there. That doesn't worry me though I've set up the fuelling on more 2t mx bikes than I care to remember the worst being a brand new 04 YZ250 but I stuck with it and ended up with it perfect that's how I learned. I had my K7 RM125 set up so sweet you could potter round the streets on it short shifting like a DT with no bother but crack the throttle and she was off like a scalded cat instantly.

scrimsmustang · DTR Mechanic

OK ive got most of the stuff I need to do this now, still need an exhaust but need to save some pennys for a brand new one FMF Pro Circuit or HGS etc depending on the price "cheaper the better" and I might need dual rads but I will run it with a single first and see what its like.

Got the correct TMX35 carb airbox and inlet from ebay, the carb should be easy enough to fit with the correct airbox will need a bit of fiddling about few brackets etc but shouldn't be to bad. Probably be harder trying to get the battery box back on than anything else.

in man.jpg

Need to modify the powervalve cover, nothing major just drill the top to get the DT cables in and slice the round bit off the top and ad 2 small brackets held with a couple of M3,s so it can be removed to set the cables. Then trim the bottom off where it sits over the YZ crankcase covering the powervalve actuator arm that I don't need as it needs replacing with a slightly modified cable pully wheel but the cover needs to sit flush with the DT crankcases to fit, its made of plastic so should be even easier than I thought.

If you see the next picture you can see what I mean.

scrimsmustang · DTR Mechanic

dan28 wrote:
I was looking on google a few weeks ago an someone has already done this
he has since sold the bike but by all accounts it did work the topic was on the Yamaha owners forum an another forum I cant remember

Be nice if you could find it again Dan, tried googling but cant find nowt anywhere

scrimsmustang · DTR Mechanic

Dropping my flywheel in to be lightened and balanced today at a local engineering shop, it will give it better throttle response and rev out a lot quicker more like an mx bike. Trial fitted up the airbox yesterday its going to need a slight bit of modding to get the battery box fitted but nothing to bad.

MIGHTYMAN · DTR Senior Member

Do you reckon Norfe would still do it?

scrimsmustang · DTR Mechanic

Do what ?

scrimsmustang · DTR Mechanic

Lighten the flywheel ? I duno you would have to pm and ask him. Duno if he could balance it though another thing u would need to ask him. The only type I would really try is the 99/03 type on the kick start bikes as they split in two with a heavy outer plate with plenty of meat on that can be removed

Sam M · DTR Respected Member

Sweet idea i was thinking about trying this a while ago with a 89 barrel of ebay but never got around to it as my bike is my only transport so didnt fancy taking it apart to find out it will take a few days/weeks to sort. Be a nice conversion if it all works with not to much messing and i may have to immitate you if it does :)

Calum122 · Guru

scrimsmustang wrote:
Lighten the flywheel ? I duno you would have to pm and ask him. Duno if he could balance it though another thing u would need to ask him. The only type I would really try is the 99/03 type on the kick start bikes as they split in two with a heavy outer plate with plenty of meat on that can be removed

I spoke to the specialist at Yamaha Skellerns about lightening my flywheel. He was adament about not touching it with a barge pole. That was him hinself. He said magical things happen at 12'000 rpm, black magic was the word used to describe it, and he said he wouldn't even pretend to know what he was doing.

This guy as said many manu times very experienced two stroke bike engineer. And they turned down work that they could have botched and I wouldn't know any different.

Something to do with actually balancing the other side of the crank. When the engine is whirling round the crank will flex causing mass distortion and possible damage to the engine.

Anyway just saying.

If you're going for an ignition system I highly rate the Zeel with the programmer. Gives you absolute control over the jgnition system. Lovely chaps to ask questions for. Very helpful and responds to emails like lightening. Despite not being english. Top blokes. Skellerns can order them in for you if you want one but don't want to deal directly. Can get it cheaper else where mind you. I did have to send mine back but they sent me a new one first and then I swapped out and sent the old one back.

scrimsmustang · DTR Mechanic

The flywheel on the 88 to 98 is lighter than the 99 to 03 flywheel, so I will take my chances mate. The clutch on the old early 90,s YZ is more or less the same as the DT but the flywheel weighs nothing Cal. The only thing lightening the flywheel will do is let the engine spin up faster and make it more peaky at the topend. The exact opposite of weighting a flywheel on an mx bike to smooth them out at the bottom end.

I worked in motorbike shops myself nearly all my life till about 2 years ago mate so if I f**k it up ive got no one to blame but myself. Hopefully I will end up with good power with a wider ratio gearbox than the YZ using the DT bottom end, im just going to use a 4DL cdi with a 3 wire servo for now and see what its like as it will just plug in the DT loom with a little mod for the neutral light.

Calum122 · Guru

So sick build Scrim can't wait to see this finished :D

Dt Danny · Guru

ino i cant wait i think its going to be a monster

scrimsmustang · DTR Mechanic

We will see, im going to use a good conrod kit aswell in it Prox racing or something similar. Its going on my bike that I got brand new in 89 so im keeping its original engine and just going to see what happens with an 02 engine ive got kicking about that needs new mains anyway. I just want a little project to keep for myself.

Calum122 · Guru

I use Wossner forged rods in mine. Very nice rod.

scrimsmustang · DTR Mechanic

Yeah anything like that Cal, something with a bit of strength to it.

Calum122 · Guru

Costly though and I'm not sure whether it's over kill. PJME use and recommend Long rods. They're a good price too.

scrimsmustang · DTR Mechanic

I need something like this for the temp sender also but cant find one with a small enough diameter for the DT hoses.

$(KGrHqN,!q8FHnLMpzdsBSCkk6)tFw~~60_12.jpg

I cant remember if the plastic ones you get with a Trailtech are a single wire job but im thinking not as they need to earth one of them would do nicely. Ile av to have a look on my KTM

Calum122 · Guru

Trial tech sell them mate. But It'll be for their senders. I actually may have one spare if you want it

scrimsmustang · DTR Mechanic

Calum122 wrote:
Costly though and I'm not sure whether it's over kill. PJME use and recommend Long rods. They're a good price too.

Maybe a bit but very safe

Calum122 · Guru

Basically this but I accidentally snapped the wire so you will have to put your own temp in there.

http://www.ebay.co.uk/itm/Trail-Tech-Vapor-Vector-Water-Temperature-Sensor-for-Radiator-Hose-Insertion-/251678234070?pt=Motorcycles_Parts_Accessories&hash=item3a993115d6

-- Edited by Calum122 on Saturday 15th of November 2014 08:05:48 PM

scrimsmustang · DTR Mechanic

Calum122 wrote:
Trial tech sell them mate. But It'll be for their senders. I actually may have one spare if you want it

Yeah the sender will be in the plastic thing, should be OK

scrimsmustang · DTR Mechanic

Does the sender screw out of them Cal ? I cant remember never tried to be honest.

Calum122 · Guru

I would have to find it mate. Not even sure I still have it. Might have binned it when I snapped the cable...