OzVMX Forum
Marque Remarks => Yamaha => Topic started by: Mick22 on April 02, 2008, 11:19:52 pm
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G'day fellas, just after a basic explanation of the differences of the above 3 bikes.
I've always mucked around with Hondas so i know bugger all about the 360's
I know the RT1 will never be a MX360 but can they be brought up to similar spec for racing or am I wasting my time??
I'm just looking for a cheapish bike to build for the over 250cc pre 75 class, and a XL350 doesn't float my boat, and the euro big bores are big dosh...
Any help would be great
Cheers
Mick
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hey mick,
if it's pre-75 your chasing and you'd like to be on a yamaha, go the mx360 or bring a dt360 up to the MX spec.
i have both the RT1 and a dt360 {that will be brought up to mx spec but havn't ridden yet}
the only difference between the RT1 and the RT2/3 is the addition of the reed valve and some cosmetics.
but the difference from those to the MX360 or a modified DT is huge. mostly in the handling department.
Firko's often talked about a mod to the RT1 frame by lowering the engine in order to lower the centre of gravity. another bike here in brisbane has had the same mod and mine will get it around xmas time. from the moment i first rode it and came to my first corner it just felt top heavy and when that beautiful 360 two stroke motor steps the back end out it just feels unstable, so i reckon the RT1 frame mod is a must.
while the MX360 won't need it.
cheers,
Mick.
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Are you doing mx or Dt ? if your doing MX i would assume all you need is a MXA frame as the 250/360 where the same and you ight be able to build up your own on the cheap using the bits you have onto a 74 frame, if your doing Dt hunt down a trackmaster/champion frame and stuff your motor straight in that.
IF you stick in the Dt/RT engine mould you may not win races, but you should still get heaps of parts for it cheap, when you venture into MX or yz territory you might find you have to open you wallet wider. IFd it was me and you have the Rt already just build it up to race, see how you feel about the class, then you can get a feel for what you want to do. Based on the current market i think there are some bargins out there to be had, and thats a race ready bike under $2000. ID hold out til you know if your going to enjoy the class ands then decide which direction your going in. FWIW
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Mick it all depends what you've got. If you've got an RT1 and you prepare it properly you will end up with a pretty decent pre 70 class bike. As Vandy said you will need to modify the frame by lowering the engine cradle 1"-2". If you are prepared to do that, you might as well lengthen the swingarm 1 1/2 ", preferably to a stronger early DT1 rectangular section swing arm. I can advise you off the forum if you're fair dinkum about these mods as it's a bit involved to relate here .
The RT1 engine is one of the more under rated engines in motocross history. It was equally as powerful and efficient as any of the pukka euro open class engines of the day but was overlooked as a serious mount because of the ordinary chassis it came in. The clutch and transmission are as good as anything else but you'd need to look for wear in selector fork and gear dogs as the engine is forty years old and will undoubtably need at least a looking at. If you want to race in pre 70 which is the RT1s spiritual homebase, you'll need an early piston port barrel as the later reed RT2 barrels are not accepted for the class. They respond well to a later model 32mm Mikuni using a TM Suzuki rubber manifold and there are plenty of pipes, both period up pipes like GYT, Bassani or Hooker available on eBay or you could get a more modern pipe like something from GMC or Lozzas Institute. You could opt for up market PVL ignition or if you're on a budget you could use later DT400 CDI which has an external flywheel rotor similar in weight to the original RT1 points unit, or you could use internal rotor MX250/360 CDI. The close ratio DT2MX or YZ250 A gearbox goes straight in. I have a YZ250 A trans in my modified DT1 and a DT2 MX version in the RT1 engine I'm building for my Cheney. The stock transmission and ratios are fine though. The stock porting is fairly ordinary but it doesn't take much port work to get them revving a bit harder. Once again, I'd have to look up my specs and advise you offline. The engine responds to some head work and the reshaping of the combustion chamber or you can use a Webco head or an ACK like I'm using. Unfortunately these things are going through a price spurt at the moment and it's hard to find one for under $300. The stock wheels are extremely heavy and I used an MX250 back wheel on mine (still heavy but lighter than stock) and I use an OSSA Stilleto front wheel purely because it fitted to OSSA Betor forks I use. The best class legal wheels to use are CZ or rare as shit Rickman like I'm using on my RT1/Cheney. For a budget I'd use the stock front brake with an alloy rim and the MX250 back wheel because it looks like the RT1 unit but is much lighter.
The MX360 is a good bike as it comes. I wouldn't touch it too much other than fitting a more modern tapered header pipe PVL ignition and a decent set of new generation reeds. I'd fit a set of YSS shocks and fork emulators to either bike.
These old Yamahas are good old bikes that will give you years of trouble free racing. The reliability factor does decrease the more you modify them (or any bike) so if you want trouble free motoring, keep the mods down to a minimum, limiting them to better ignition, carburetion and exhaust.
Below is my DT1 that has all of the chassis mods I describe. The frame has the lowered engine cradle but I took it one step further and grafted an Ossa Stilletto front frame section which gave me a steeper steering angle and tapered timken bearing steering head. Unless you are posessed by the devil, there is no sane reason to do this yourself.
(http://img.villagephotos.com/p/2005-8/1062154/Cus.jpg)
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Get yourself an MX frame and bolt as much of the usable DT stuff to it. I did check out what I have done so far...
http://ozvmx.com/community/index.php?topic=1561.0
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God, whats that rear brake stay off ?
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God, whats that rear brake stay off ?
Home made special (not by me) that came with the DT250A bits I started with.
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ooh looks very factory. Nice one :O)
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Thanks heaps for the responses guys.
Just the sort of info I was after, A bloke near me has one for sale for $300, complete, turns over but not running so I thought it kight be a cheap option for the big bore MX class. I've already got a CR250M as my "serious" race bike which I spend all my dosh on so just looking for something to get an extra couple of races on.
Didn't realise they were eligible for pre 70 so thats a real bonus, thanks for the info Firko, I might hold off on the frame mods for now, I'll just get her running and do a couple of rounds first and see where its at
Thanks again
Mick
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mine still handles pretty well without the frame mod Mick. it's just, i know it can be better.
the motor is a sheer delight in my opinion and mine runs a stock barrel and i will probably leave it that way.
definately, definately, get rid of the points and go to a CDI or the kickstart lever will kill you. mine has a dt400 unit with the big flywheel and it feels spot on.
good luck with it and for $300 bucks, you can't got wrong.
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mine still handles pretty well without the frame mod Mick.
:o :o :o
DT1 and RT1's are evil bastards that actively work against you, conspiring at every corner, every undulation, every jump and even in the straight ahead, to kill you. Particularly that front end. (But shit they are exciting and good fun ;D)
Modern shocks and modded forks would go a long way toward taming the beast but I'm pretty sure there are some basic compromises in the chassis that limit the 'go fast safely' of the old dog.
(I 'cut my teeth' on AT, DT and RT1's, trail riding, enduros, Club DT and MX. I've got a restored RT1 and I'm thinking of prep'ing one for Vinenduro.)
To remind you.....
http://www.youtube.com/watch?v=Cta94FE3Fek
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Lowering the engine in an RT/DT1,2,3 frame and lengthening the swingarm produces a frame with the same geometry as the DT360 and MX360 and makes it feel quite enjoyable to ride - something that cannot be said for the evil monstrosity that is the standard arrangement. I helped my riding buddy do the frame mods to his RT3 back in 1977 and it was a revelation to ride it afterwards. The motor was always a treat. The motor had a standard carby with increased throat diameter, added flywheel weight on standard flywheel, minor porting changes and a well made expansion chamber and easily pulled 90MPH on knobbies.
I reckon my (standard) DT2 was the worst handling motorbike I have ever ridden at speed off-road.
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What frame/engine number id a MX360?
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365-xxxxxx
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but the 250 is the same fram, just prefixes with the 364. infact iQuicky f you turn up anything with 363, 364, 365 hell even 431,432 give me a yell quickly :O)
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;D ;D ;D
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Hey fellas, I picked up the old beast today its rough but Its good enough to make a race bike out of. Un fortunately its not a piston port so won't be able to use it in pre 70.
Its got a reed block and it looks like some sort of decomp on the front of the barrel connected to a lever on the left handle bar??? the Eng # is RT1-135947. So would this be the orig barrel or has someone fitted a later model top end to an early motor?? Any idea what year it would be
I've had a good look around on the internet but can't find much info on the 360's, like I said earlier I don't know a lot about old yammies so still working it all out. from what I've figured out-
RT/DT is the enduro model, I thought MX was the motocross model but it seems they made MX and YZ at the same time and I'm sure the YZ is a motocross model..... so I'm confused can anyone shed any light on this
Cheers
Mick
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RoAd/ trail, - enduro/track, - track/ competition
or you could say the mx was the WR to the YZ.
Although the flat track guys loved the RT/DT and the MX cause they had better roll on power over a wider band. it depends what you are gong to use it for i guess as to how good it will sui that use. Just enjoy regardless, you own somones history :P
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arn't I kind to ya ;D.
(http://i96.photobucket.com/albums/l187/mx250a/3b8b_1.jpg)
http://cgi.ebay.com/ebaymotors/YAMAHA-DT1-RT1-MX-250-360-FRAME-LOWERING-KIT-FLAT-TRACK_W0QQitemZ140222621522QQcmdZViewItem?hash=item140222621522
Either bid or use the picie to make your own. ;) 8)
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... but it seems they made MX and YZ at the same time and I'm sure the YZ is a motocross model..... so I'm confused can anyone shed any light on this
Initially MX and YZ were both MX models with the MX been 'softer' and cheaper and aimed at the masses. The YZ was a much sharper weapon, more expensive, and aimed at the professional rider (Yamaha Dealer sponored been typical). That changed after '75 (?) when all MX'er got the YZ tag.
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Mick,
all the RT models run the RT1-prefix, so my guess is you've got either the RT2 or 3
which is the exact same machine apart from the reed block. build it up and keep your eyes open for a non-reed barrel as you go. they are rare but do exist. i got mine from ebay in the states for US$35
do your ebay searches as yamaha RT, and then check the US ebay, pistons are pretty cheap, engine seals are easy to get as are bearings, most everything else needed for moto-x is a pretty close relative to all the early yammies, so anything Dt,mx,yz can bolt over.
any hassles, give us a yell.
good luck with it.
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MX250 how do the spacers work there is only three and the frame has four down tubes :-\ jimson
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MX250 how do the spacers work there is only three and the frame has four down tubes :-\ jimson
Good question ???. If you are interested ask the seller. May be the other is 'not in frame' ::).
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The two smaller diameter tubes go into the front down tubes just above the engine mounts and the larger dia tube goes into the single rear downtube above the rear engine mount.
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Firko what happens to the two smaller tubes coming down from the back supporting the rear of the frame or have I got it wrong ::) jimson
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Hey fellas, I picked up the old beast today its rough but Its good enough to make a race bike out of. Un fortunately its not a piston port so won't be able to use it in pre 70.
Its got a reed block and it looks like some sort of decomp on the front of the barrel connected to a lever on the left handle bar??? the Eng # is RT1-135947. So would this be the orig barrel or has someone fitted a later model top end to an early motor?? Any idea what year it would be
I've had a good look around on the internet but can't find much info on the 360's, like I said earlier I don't know a lot about old yammies so still working it all out. from what I've figured out-
RT/DT is the enduro model, I thought MX was the motocross model but it seems they made MX and YZ at the same time and I'm sure the YZ is a motocross model..... so I'm confused can anyone shed any light on this
Cheers
Mick
Here's your Pre72 barrel...
http://cgi.ebay.com/ebaymotors/1971-Yamaha-RT1-RT-1-360-Cylinder_W0QQitemZ320238209042QQcmdZViewItem
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Spewing!! missed out on the barrell.... didn't see your post until too late thanks anyway. Hey Vandy are you going to use it or resell it??
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Vandy i reckon i have a piston for that overbore
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freaky, i'll wait till it gets here and measure it up before i decide what size i need. thanks anyway.
Mick, PM on the way!
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I think I got the barrel I need ???
Is this the right one, I was reasonably sure when I bid on it but looking at it now I realised it doen't have the decomp..... anyone know what its off??
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=016&sspagename=STRK%3AMEWN%3AIT&viewitem=&item=260229672130&rd=1 (http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=016&sspagename=STRK%3AMEWN%3AIT&viewitem=&item=260229672130&rd=1)
Got another question for the Yammie experts, I've got a couple of LT2 100's that I'm going to make into classic bucket racers, one of them I want to cut all the excess brackets off the frame, before I bastardise them I want to make sure that by some chance they have become collectable??
Cheers
Mick
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Mick i think you've done well with the barrel. i did some running out to the garage and comparing to mine from the photo's and she looks to be the goods. the de-comp is a bit of a mystery though. most people usually plug them up anyway as i have. with a decent CDI fitted, you won't need the de-comp anyway.
the exhaust manifold and head from your other barrel will bolt straight over but you'll still need to source an intake manifold and the dowels.
well done!
as for the LT1's, collectable?
hmmm, don't really know. i looked at one a while back but shy'ed away from it as i was hoping to put a 125 top end on it but found they run a different stroke to the 125/175.
if you've got a use for it, just do it.
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Thats an RT1M barrel, good score.
Keep a look out for a matching head.