DT2MX transmission

[firko]

I desperately need a close ratio transmission to suit DT1/RT1 cases. Yamaha YZ A/B would be ideal but I don't like my chances of getting one. DT2MX or RT2MX will do. I'll pay you what you want for good usable gears. (within reason of course).  I don't like my chances though :'(

[Freakshow]

Vandy did some research and figured out the same ratio where in some MX 250/360 i think, never got the part numbers but he built the dt2mx box with the same ratios using the later gearsets. 

So you might want to ask him again for me, and then  write it down, make a copy and then give it to me as well :O)  i think it was 2nd and 5th but dont quote me.

[vandy010]

at 1.15am off the top of my head,
4th gear is the same so forget that.
1st gear is only for the pits so forget that.
a DT/RT 3rd gear is pretty good as is. excellent for the start straight as it's a slighty lower ratio than the MX/YZ. change it if you want to the MX/YZ.
grab the higest ratio 2nd gear you can lay your hands on. i think it was std in the first silver tank MX250/360.
5th gear can do with changing to the MX/YZ spec.

My RT1 runs,
std 1st
high 2nd
MX 3rd
4th is the same
std RT1 5th {only because i know the motor will pull it but it never winds out on any track}

My MX250 runs
the full MXgearset but has a DT 3rd gear fitted. ask Davey Crocket, my 250 gates well in 2nd and then when clicked into the DT3rd it hooks up and drives well because the revs don't drop.

in a nutshell, the part number teeth counting was all a big headf**k at the time and i don't remember specifics. there's usually a heap of gearsets on yankie ebay but getting them at a reasonable postage rate is the catch.
or, figure out what ratio's from the manuals you like and set about buying the individual gears.
good luck Firko!
DT/RT1,2,3 & DT/RT2MX & DT & MX250/360A, SC500 & YZ250/360A/B should all interchange
{ratio's galore!}. there are some subtle differences but nothing dramatic.
the later MX250/400B~YZ250/400C won't work so forget them.{they fit the shafts but not the shift forks}

[jimg1au]

firko
send me the part nos and i will check for you on my zedder program
jim

[firko]

Thanks Vandy, I wasn't aware the MX gears fitted the early cases. Are you sure they fit without any modification? I seem to recall trying this back when I build the DT1 from Hell and not going ahead with it for some reason or another. If they do fit it opens up my little world of possibilities by a motza.....back to my Yamaha book to check out ratios.....

[vandy010]

Thanks Vandy, I wasn't aware the MX gears fitted the early cases. Are you sure they fit without any modification?

i don't have any engines apart in front of me but when i did mt RT1 i bought a complete MX250 gearbox from ebay and used a mix n match. i know the shift drums/forks are different but the gears swap on the shafts no probs.
part numbers can get a little confusing but the cost of individual gears is not that much if shopped wisely.

[Freakshow]

I have both boxes  apart and they all look the same, but i have not tried one on the other for fear of forgetting what come from where.  I was saving this for Xmas break, and i was goiong to hassle vandy out again,  But if your onto it befor eme firko can you keep me up to speed with what you did.    If you need me to count some teeth or measure something tell me while im in peices  :O)


I think there was also mention you need to change over with its matching pinion ?? as the lash was linked ?

[Iain Cameron]

Hi guys beach yamaha in the us has a lot of the gears for dtmx rtmx in stock nos . I will be watching this thread guys please pm me with any ideas as a fellow dt/rt tradgic this is  very interesting

[Freakshow]

Firko, i found my peice of paper, so i can scan it and email it when im at work next if you like.  Basically i have all the teeth and part numbers for the Dt/Rt , Dt1-2mx/Rt1-2mx, and the YZa. 
Funny thing is some are the same some are little differant. 
Ill have to look in the MX250/360 book and write those down for you if we are going to look at them too.

With the Dt2/RT2  they went
1) 38T - 15T
2) 34T - 19T
3) 30T - 23T
4) 26T - 26T
5) 23T - 30T

then With a GYT gear kit they changed - main axle , 2nd wheel, 2nd pinion, 1st wheel, 3rd wheel, which then evolved to came out standard in the mx...

DT1-2MX and the RT1-2mxer is this
1) 36T - 16T
2) 33T - 20T
3) 29T - 23T
4) 26T - 26T
5) 23T - 29T

YZA was way differant except 4th and used they're own cogs
1) 34T - 19T main axle
2) 31T - 22T
3) 28T - 24T
4) 26T - 26T
5) 24T - 28T

MX - MXA alternates are as follows:

1) 36T (31)     - 16T
2) 32T (33,28) - 22T (20,19)
3) 29T (28)     - 24T (24)
4) 26T - 26T
5) 24T (23) - 28T (29T)

Firko, So if you suss out the ratios, maybe we can work out a few options and co develope somthing data wise, i got a box here i was going to put togheter over xmas so happy to work on it with you rather than both of us pulling boxes apart a few times before we get it right  :O)

this could be a fun and interesting project.  Seems like there are heaps of variations you could come up with, Might even learn somthing tricky 

[JC]

I've looked at these options myself a fair bit. I find it helps to consider the % drop between each gear (ratio).

Ideally what you want is a 3 or 4% drop from gear to gear. If you don't, it generally feels a bit of an odd spacing when racing

eg for DT2/3 (RT2/3 & later D/RT1 same IIRC)
1-2 29%
2-3 27%
3-4 23%
4-5 23%  (longer jump than ideal gives a bit of a car-type overdrive effect for cruising)

D/RT2MX & MX250A

27%
24%
21%
21%  a bit longer jump than ideal for racing

YZ250/360A (these are a bit too close IMO; Yam must have thot so too - the YZ250D had wider ratios)
23%
17%
14%
14%
Some DT2Ms came w these ratios too: IIRC it was an option in USA

Vandy's MX250
27%
21%
23%
21%

Vandy's 360 (assuming 2nd is most likely GYT/DT2M ratio)
35%
21%
23%
23%

Yamaha liked the same drop for 3-4 & 4-5. It kept production costs down as it meant they could often run the same gears for 3rd & 5th, just the other way around on the shafts



 

[mx250]

Although these percentages is some guide don't you also have to calculate the primary drive ratio. Doesn't the primary drive ratio impact on the overall and the % drop between gears.

This ain't my expertise (very dodgy actually ). And isn't there a difference in the primary drive ratio difference between the 250's and the 360/400's (clutch basket etc.).

[vandy010]

cool JC,
but it can all get pretty techo this ratio/percentage thing.
the seat of the pants riding for my 2 bikes are,

My MX250 std g/box with DT 3rd {lower ratio 3rd}
it gets off the line well due to the short jump from 2nd to 3rd but the gap from 3rd to 4th is now DT bigger.
3rd gear on the track seems pretty good it's just when you come onto the main straight you lose a little.
no biggy. {the DT3rd was the only decent 3rd gear i had when i built the motor and is the only reason i used it} i kinda like it as it's not a problem.

My RT1 with the close ratio box & std RT1 {tall} top gear,
the box shifts better than my MX250. lower gears are perfect, top is too tall for MX but it's not a problem. where it really came into it's own was at the masters games Vinduro.
i left the stock gearing on and out on the trails there were a few sections where it could be wound out and top gear was perfect for that.
when i built the box on this one, i always had it in mind that i'd like to trail ride it, so i left the tall std RT1 5th gear ratio as is. it's a trade off that i deliberately went for but i wouldn't recomend it for serious racing.

[Freakshow]

OK had a look at the mx and mxa and shit there is like 5 differant pinion wheels for 2nd ?? and as many variations for the others as well.  the Main axle (8 choices of them) ( all 16T) looks like the same part so all the gears must be able to sit on a normal 214 main axle.

With the MX250B there are no variants so you get no choice, however if i list the numbers your able to see the ratios and hence figure out what the spread is and use it as a benchmark if that mxB was considered a nice gearbox spreed.

they are as follows:
1) 33T - 16T
2) 32T - 22T
3) 29T - 24T
4) 26T - 26T
5) 24T - 28T

have added the MX- MXa gear sets to the top post

[Davey Crocket]

JC, the YZ250/360A's gearbox ratios are spot on. ...you just play with the sprocket sizes to get what you want....remember these things only have 4 inches of travel and you have to get power to the ground....talking to Gary Jones at the nats and he said they ran std engines, just went 2 up on the front sprocket and perfectamondo!!...and you know what?...he's spot on, but I had already worked that one out.

[mx250]

Wow, 2 on the front - that's Bathurst gearing  . That would take the sting out of sudden power delivery .

The old YZ musta had power to spare to pull 2 teeth and still be competitive on acceleration.