OzVMX Forum
Marketplace => Wanted => Topic started by: firko on December 14, 2010, 08:16:04 pm
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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 :'(
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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.
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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}
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firko
send me the part nos and i will check for you on my zedder program
jim
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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..... ;D
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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.
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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 ?
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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
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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 ;)
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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
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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.).
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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. 8)
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.
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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
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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. ;)
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Wow, 2 on the front - that's Bathurst gearing ;D . That would take the sting out of sudden power delivery 8).
The old YZ musta had power to spare to pull 2 teeth and still be competitive on acceleration.
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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.).
Graeme, primary (& secondary) ratios certainly affect overall ratios, but don't affect % drop from gear to gear. Its simple maths.
Vandy, no criticism intended. I was just crunching the numbers so people could see what % drops tell you. Yr descriptions of how they feel when riding is exactly what I would have expected from the % drops. It works for your intended purpose. I might have used the 29T 5th gear from an MX box in the 360, to close up that top gear drop if it was mostly used for racing, but each to his own.
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Trust me, they rip....std gearing all they want to do is wheelspin and fishtail.....vandy's riden it....he cant work out why I'm so slow. ;D
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Boys...This is great stuff. It's an area that I fall a bit down on so I'm finding it all very interesting. I knew JC and Vandy would come up with valuable information....keep it coming guys ;D. In all of your opinions, what would be the best trans ratios for a piston port 360 RT1 Yamaha using what's available from the Yamaha range? I'm building another engine for my Cheney using the best I can muster. Lozza's doing the ports and supplying a 'Lozzatronic' CDI and Frank Stanborough is balancing the crank. If I'm going to the trouble to get it going fast, I'd like the best ratio spread available.
I've got a DT2MX trans in the engine currently fitted to the bike and have a YZ250A trans in my DT1 from Hell engine. The DT1 was/is perfect but going by your opinions, the DT2MX ratios might not be all that great for the 360. Because of the torque the 360 produces, would the stock ratios be better than the DT2MX? I'm starting to think they may be, even before I ride the bike.
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MY PP 360 honked along quite well, 1st was a bit of a screamer and then it was great till to hit top then it stopped.
It tended to load up the carby a bit, so maybe with a bit more power it would clean out. if i was do do anything to the gears i would stuff around with 1st and 5th. I cant start in 2nd and 1st needed a change metres of the line, so if you can back it down to just under 2nd i reckon that would be a good thing, then you can still pull sprocket changes.
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Use the DTI from hell gearbox Firko.
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Use the DTI from hell gearbox Firko.
I would John but I don't want to rat that engine. It's a bit sentimental to me plus it's still a goer (in need of a bigend).
But........if you could sell me a YZA trans from your extensive stash my problem would be solved ;D.
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Unfotunately I only have 1 spare g/box....old mate in the west has a few.
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Mark,
There's no question that if you want a FAST engine, the closer the ratios (eg YZ-A/B) the better. The simple reason is that when you change up it doesn't drop as low in rpm on a close ratio box so you are in a meatier part of the powerband. (Thats one major reason why YZA/Bs & VR Montesas are so fast.) But of course it requires a bit more tap-dancing on the shifter. (Hence my point about YZA/B ratios being a bit too close IMO, esp for a 360. Fine for Gary Jones back in the day, but for regular VMXers..?? Is it needed?)
A DT2M or MX-A gearset really needs a closer top gear for a fast engine, eg from YZ, as that std gap is really too big for a fast bike. Depending on the track, you may get away w gearing the bike to use 2nd to 5th, which means % drops of 24%, 21% & 14% (forgetting the 1-2 drop of 27%) w a YZ top gear. Not as fast as a full YZ gearset, but less tap-dancing
Using std DT/RT ratios, you'd also need a wider powerband & closer top gear, say from the DT2M, & likewise probably gear it to use 2nd to 5th, which means % drops of 27%, 23% & 21% (forgetting 1-2 drop of 29%) w the DT2M top gear (Only requires one gear changed IIRC). Still less fast than the above, but even less tap-dancing - a bit of a 'lazy-mans' race bike. With the right final drive ratio, you should be able to overcome Freaky's problem mentioned above (ie 1st too low; 2nd too hi) on his PP360 w this set-up.
Another important consideration is overall gear-ratio spread (bottom ratio divided by top ratio). You typically need about 2.2 - 2.3 in a 250 racebike; perhaps a little less for big-bore. (eg 4sp Maicos were 2.0 IIRC)
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Another factor that occured to me is the ignition curve and flywheel weight and their relationship to gear ratios. We know that the difference between the heavy external flywheel DT400 cdi unit and the internal flywheel lightweight YZ or PVL style ignition will produce different power characteristics and therefore different gear spacing needs. I realise I'm putting an over complicated take on it but I know from my DT1 that the ignition differences make dramatic changes to the engines power to the point that a corner taken in second with one ignition can be taken in third with the other. Am I reading too much into the importance of this in relationship to the transmission ratio? Am I morphing into Ji Gantor? ;D
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In all of your opinions, what would be the best trans ratios for a piston port 360 RT1 Yamaha using what's available from the Yamaha range? I'm building another engine for my Cheney using the best I can muster.
If I'm going to the trouble to get it going fast, I'd like the best ratio spread available.
Firko,
for an MX race motor, any of the close ratio MX/YZ or DT2MX boxes will be fine.
in the 360 donk, i'd be aiming for the tallest ratio 2nd gear i could lay my hands on as starts are gennerally done in 2nd and a tall 2nd will allow the motor to pull it for just that bit longer and if your silly enough to go back to 2nd out on the track it won't rev its tits off quite so much.
Daveys YZ250A is flat amazing.
it felt like a bigger motor to me but my RT1 makes smoother torque.
when young Davey's done with it, he reckons he's gonna wrap it in shiny plasticy stuff and leave it under my tree :)
what a mate ;)
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Another factor that occured to me is the ignition curve and flywheel weight and their relationship to gear ratios. We know that the difference between the heavy external flywheel DT400 cdi unit and the internal flywheel lightweight YZ or PVL style ignition will produce different power characteristics and therefore different gear spacing needs. I realise I'm putting an over complicated take on it but I know from my DT1 that the ignition differences make dramatic changes to the engines power to the point that a corner taken in second with one ignition can be taken in third with the other. Am I reading too much into the importance of this in relationship to the transmission ratio? Am I morphing into Ji Gantor? ;D
STD DT400 monoshock flywheel wieghs 1800grams
RT/DT1,2,3 " " 1650grams
my RT1 is using a YZ490 " " 1450grams.
the 1650grams flywheel gives a good torque/rev mix for my liking ;)
as to how it all ties in with gear ratio's?
we need beer and a good pub after a good days ride... :D
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Change the flywheel weight changes the feel of the power delivery not the amount of power - general makes power delivery easier to control, smoother.
Taller gearing also changes the feel of the power delivery reducing the multiplier effect of the gear ratio, reduces torque applied, and also means you can hold the gear longer, over a greater speed range, which can also be a handy 'tuning tool' for specific situation (but would only normally be applied at the highest levels of motor sport).
Normally a heavy flywheel goes well with a w/r gear box. Even the most viscous 2t can be made like a 4t with enough flywheel weight 8).
I would use either for one or the other rather than both. But that's me :P.
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I left a key word out of the sentence in my post "differences make dramatic changes to the engines power characteristics". I like the DT400 flywheel on my DT1 as it's fairly radically ported and the heavy flywheel tended to soften the 'on/off' type power delivery that hindered it when the MX250 internal flywheel ignition was being used. The extra inherrent torque of the 360 puts a different slant on it though. I'll initially be using 'Lozzatronic' ignition....not sure of the flywheel weight......... Lozza?
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I had a PVl on mine so you would be thinking similar rotor to a lozza knock up, so refer PP360 info above again .
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I have a complete NOS gearbox but not sure what its from RT1 i think includes shafts and shift folks all in original packaging 5 speed close ratio dont know what its worth make me an offer
regards
Martin