YZa - questions of why

[Freakshow]

i was looking closer at a Yza motor i was talking to a guy about how he nikasiled the barrel, the closer i looked the stranger it seemed, the cases are 431 from what i know are YZA, but the side covers are dt1, even the oil line hole is filled in, the sproket cover is dt1, the barrel and the head, im no guru by a lonf stretch but what i cant get my head around is if everything other than the cases are yza, Why would you do that to the bike ? looks bloody stupid with 2 side covers that say yamaha.

Am i right in thinking the Dt1/rt1 stuff all just fits other then maybe the ports being differant and maybe the gear ratios, are they that similar that every thing just bolt up ? including the barrel ?

and can they only use the serial side to make it look like a 431, but use the other crank case be a dt1 ? perfect crime potential ?

[DJRacing]

Basically YES.

I'm no expert either but as I know it the RT1/DT1 bikes are the daddy of the YZ-A and the cases etc are inter-changeable.

[vandy010]

i vaguely remember adam saying in the old forum that the barrell bolts for the 360 were different from RT to YZ and therefore on those bikes the barrels didn't swap over. don't know about the 250 though.
i do wonder sometimes if a dt barrel could be ported to yz specs and what about the reed block? are they the same size? or is the yza bigger?

[Freakshow]

i have no idea thats why im asking, to me if the barell just slips on and the geabox etc all fit in how would you know what actually other than outside appearances is YZa? you could be on the bad end of a deal there and never no it ?

adam you still around - get in here now you got some explaining to do, talk us through my pics, cuase im confused its a 431 case, but im guessing nothing else is ?

[Nathan S]

What's the barrel? Vandy's right about the YZ360A vs RT1 barrels - someone (Adam?) said that on the old forum.

From my reading, internally the YZ250A has a different primary drive (straight cut vs helical), clutch (unsprung hub), gears (closer ratios), piston/barrel, and ignition compared to the DT1 bits.

But AFAIK, everything is interchangable between the two.

[Freakshow]

its like a barrel but only shorter.  or if you werent taking the piss out of my spelling its a Dt1 - which is how i got onto discussing stuff with the guy and the pics as he was telling me its got a nikasel bore .

[YZ360A]

HI guy's been away from the forum for a while. No chance that motor or most of it is a YZ250A.
 The head and Barrel look to me like DT2MX (note horizontal fins no notches) with a bit of a fin mod to the head and the side covers look like your run of the mill DT / RT trail bike pieces. YZ250A/B and dt stuff will fit together but YZ360A is a totally different matter.
The sprocket cover has had a bit of a mod to the rear and the reed intake and carbie due to the choke lever also the carb would have stamping of 431 as well (very small even the carbie should match the designated prefix) are not YZ250A either. I bet the cases probably ain't YZ250A either probably been restamped DT1 as usual. So internals who knows?
 On these cases these no small ribbing in the engine number like on later models and DT1 RT2 look very similar.
 Best to get a close up of the stamping on the cases and I can tell you if the cases are YZ250A if they are genuine or not.
The letter stamps they used are different in size from the 431-  to the serial number. The 431 model prefix is usually larger etc.
I can also tell by the way they have been stamped.
Only way to really get these right is on a CNC machine or very old letter stamps not like the ones you buy these days at Hardware House or Gasweld.

Best to get a few more picture of the stamping.
Could have a chrome or a nika bore as this was a yamaha option for the DT2MX even up till yz250c you could buy a racing barrel (competition) with a chrome bore.

What's the rest of the bike look like.

Cya Adam

[Freakshow]

well its actually in a flat tracker frame so the rest of the bikes kinda erririvant,

yep i have seen the stamping and its definately 431-, and the bloke said it was a dt1 barrel and head,  my question was basically other than the stamp on the left case, could every thing inside it including the right case be just plain old Dt1, like how would you really know ? the sprocket and mag side are not yz, thats easy to pic, but what about the right case and the interanals do they just all bolt up, so unless it was in bits how could you tell if it was the real deal inside , square cut, clutch etc ?

Although if you look closely there is a output on the right case with a right shift pin coming out and they only usually did that mode with the yz flat track cases, too expensive for a palin old dt.



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[vandy010]

freaky,
with the gear change, see the clutch cover has the yamaha as a "raised" word yet the other side has yamaha recessed into the case.
recessed is dt/rt2 onwards, raised is early dt1 which had the gear shaft exposed standard.
someone may correct me on this but it could be handy for the flat track as an option.

[Nathan S]

Indeed. The raised lettering (and availability of RHS shifting - note plug down low) was for the first year or two of DT1 production only.

[YZ360A]

The right shifting was also avaible on a YZ250A aswell I think. The early DT1 stuff for this just slips right in. I have also seen on ebay YZ250A motors with the right hand shift also alot of the euro riders from Husky riding for yamaha prefered this option.
Check Torsen Hallmans 1971 YZ250 on http://www.mxworksbike.com/1971%20YZ250%20reed%20valve_2.htm
Not all of the YZ250A clutch cover have this hole though as I have a few on bikes and a few NOS items and they ain't all the same.
I have seen like extended shifter shafts so you can have left and right shift would this help for dirt track?

Adam

[Freakshow]

yep i got dual change on my YZa tracker, being able to flick with your right means you can have your foot our and dont need to try to slide your boot under the change  and chance going ontop by accident, i like the option it rocks



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[paul]

hey freaky   have you run this bad boy yet 

[Freakshow]

fast edit mate but not fast enough 

she is a badgirl.  this puppy is about half the length of a standard MXA, its so short in the frame it turns on a 5 cent peice, sweet pipe and handles like nothing you have ever ridden, this thing is everything it promises, you ride it and you know why it was such a successful bike.  the tyres on the front are so fat im sure it could stand off the stand.

I have ridden it on the track, but am not convinced about racing it, its hand painted , yes all that pinstriping and the Yamaha, the last thing i want is to have sum tool pass it on the inside and shower it with rocks.  i just couldnt bare it if it happend,  but lets see if i cant hold back foreva. 

I have ridden it on a loam/dolimite base flat track by itself, last time i was allowed 10 laps "run in time" solo , and the thing is so nibble, you cant help but let it drift, i could have ridden all day, it was just like standing up on your first wave, or learning to ride a bike, it had perfect equilibruim of the forces... even now remebering it i get a stiffy.  Bit hard to explain really.  maybe one day i can post a video or somthing, but the sweet sound, the balance and the motion in this bike can only be captured in the saddle. and holding onto the cow horn bars.

In its day this thing would have been a weapon with your mamola's and eckland's, and with an A grade rider i think this thing would still smoke today.  IF you have ever ridden a perfectly set up bike you know exactly what i mean, they virtuall ride themselves no matter how bad you try to ride 

[Freakshow]

Indeed. The raised lettering (and availability of RHS shifting - note plug down low) was for the first year or two of DT1 production only.

if you look close at the first set of pics nat thats a Rubber hose on the Dual shaft with a zip tie not a plug.  Its already set up for dual shift, but for some reason he isnt using it, its in a trackmaster frame and im sur eits for a bigger motor, so i kinda supect the guy is a nutter, but i posted the motor pics cause it was all kinda weird, i always get spun out by out of the ordinary things and kinda wanted to know if there was a special trick reason , or it was just a bitsa ? i mean if you had a 431 case wouldnt you go out of your way to keep it or get it back to correct it would surely be worth 10 times the money and probally twice as fast ? unless somthing tricky is going on inside there ? hmmmmm... nope bitsa