DT1 250 pre 70 legal BArrel

[Freakshow]

Howdy i want to run one of my bikes next year in the pre 75 class, as i understand it i can put a non reed barrell on a DT1F and its pre 70 ?  does anyone have one for sale or swap ?  also do i need to run the 19 inch front or the 21" front ?   id prefer to track down a 19" front and hub/ brake etc to slot in if any one also has one for sale of swap.  what the story with the forks ? whats size or style does the pre 70 Dt need to have to be legal ?

[Nathan S]

The basic DT1F bike can be legally 'back-specced' into a pre-70 bike. The rules say that any DT1 is pre-70 legal when fitted with a non-reed-valve top end - and that's all you need to  do. You can, of course, fit any/all of the older model parts if you wish - including the 19" front wheel.

The hub and brake are common to DT1/RT1/DT250/360A, although with a 21" rim. A 19" front wheel with smaller brake from an early DT175 (or a late CT1) might also be a possibility for dirt track, but the skinny little axle on the 175 means that its not just a bolt in.

If you fit a piston port top end to a reed bottom end, you'll discover that the reed conrod is 5mm shorter - so you have to put the barrel into a lathe and take 5mm off the bottom. You'll also have to remove a couple of millimetres from the bottom corners of the piston so that it clears the crank halves.
Of course, all of this buggers up the port timing, but the DT1MX specs are freely available and easily replicated (let me know if you can't find them, and I'll dig them out).

The DT1F also has a slightly wider ratio gearbox than the PP models. I haven't gotten mine running right yet, but as it currently is (not revving out), the closer ratios would be a real help.

Sorry, I can't help you out with parts.

[vandy010]

Hmmm?
thats pretty interesting on the conrod Nathan as i thought all DT1/2/3 and RT1/2/3 shared the same
214 prefix rod.

anyway,
after a dig through the shed Freaky, i've unearthed a very usable
DT1 piston port barrel, 3rd o/s,
a DT360a front hub with brake plate, no axle,
and a NOS set of 19" spokes.
theres definately a dollar bill attatched to the barrel and spokes, so let me know and we'll go from there.
cheers.

[Freakshow]

check ya pm

[vandy010]

PM recieved, checked and replyed to.

on this Rod Bizo that Nathans mentioned, i've never heard of differing length rods between the DT1/2/3, can anyone else reading this shed any light on the topic?

[Nathan S]

I'd not heard of it either.

I went to bolt the non-reed top end on, and discovered that the piston sat 5mm down at TDC (and that the piston hit on the crank before BDC).

Then I spoke to Nifty (who runs a 'proper' early DT1), and he said that his barrel had obviously had the same thing done, and that he hadn't been able to figure out why.

Finally, the more recent motor that I acquired was the same again - its had the base machined down by about 5mm. Its a DT1F engine number, but has the PP top end and clutch cover.
I'm now somewhat regretting cutting my original barrel, but them's the breaks.

Both of my motors have genuine Yamaha pistons, and I believe that Nifty's does too.

[JC]

Are you sure its the rod thats shorter, & not the piston deck height?

I have some old Yam pistons from that era & some are about 5mm taller than others.

[Nathan S]

Definitely a possibility, but doesn't explain the piston hitting the crank.
I'll pull the top end off the second motor and work out what rod is in it.

[firko]

I've been playing around with DT1s for years and wasn't aware that there was any difference between a reed or piston port rod or anything else other than the actual reed valve itself. It's been a while now but I'm certain the DT2MX crank in my DT1 from Hell has the original rod and I'm certain my barrel hasn't been decked. I'm curious now as I've just bought a DT1 F basket case in Qld purely for the engine to use in my Metisse.

[jimg1au]

mark you are right the rod is the same one used from 1968 to 1974 mx360a.that is acording to zedder
Part # = 431-11651-00-00
Part Description = ROD,CONNECTING
Model Count = 29
DT1 1968 250 DT1 Dual Purpose
DT1B 1969 250 DT1 Dual Purpose
DT1C 1970 250 DT1 Dual Purpose
DT1C-MX 1970 250 DT1MX Dual Purpose
DT1E 1971 250 DT1 Dual Purpose
DT1MX 1971 250 DT1MX Dual Purpose
DT1S 1969 250 DT1S Dual Purpose
DT2 1973 250 DT2 Dual Purpose
DT2MX 1972 250 DT2MX Dual Purpose
DT3 1973 250 DT3 Dual Purpose
DT360A 1974 360 DT360 Dual Purpose
IT400C 1976 400 IT400 Dual-Purpose
IT400D 1977 400 IT400 Dual-Purpose
IT400E 1978 400 IT400 Dual-Purpose
MX250A 1974 250 MX250 Off-Road
RT1 1970 360 RT1 Off-Road
RT1B 1971 360 RT1 Off-Road
RT1M 1970 360 RT1M Off-Road
RT1MX 1971 360 RT1MX Off-Road
RT2 1973 360 RT2 Off-Road
RT2MX 1972 360 RT2MX Off-Road
RT3 1973 360 RT3 Off-Road
YZ250A 1974 250 YZ250 Competition Motocross
YZ250B 1975 250 YZ250 Competition Motocross
YZ360A 1974 360 YZ360 Competition Motocross
YZ360B 1975 360 YZ360 Competition Motocross
YZ400C 1976 400 YZ400 Competition Motocross
YZ400D 1977 400 YZ400 Competition Motocross
YZ400E 1978 400 YZ400 Competition Motocross

[vandy010]

Jim, i think i'm in love with your Zedder...

[Hoony]

Jim, i think i'm in love with your Zedder...

does it work with Honda?

[Freakshow]

Back in the day Neil keen used to run a 1/4 inch spacer on the dt1's he was building up for the Japs 2 stroke assult on track, so they where going up with the barrell not down.  

Maybe JC is onto somthing, maybe for some reason Dt1 ealry piston where scarce in the Act area and they just used later piston and skimed them ?

Hoony, im sure you know but are just being silly, zeeder software comes per maker table, so when you buy it  bout $40 online you DL the manufacturer you want , yam , honda suzy etc, the application just looks up tables they cross referance in the specific data base, thats the only differance. 

Best money you can spend, you be ammazed at the price differance of the same part with a differant sticker, Zedder keeps you on the cheap :O) and bountiful  (also has the supperceeded codes up) 

[JC]

This has got me intrigued too.  When I got my YZB engine it had a 5mm Al spacer under the barrell & unidentified wiseco piston. I figured at the time it was a piston from another engine that was a bit taller than std Yam piston.

Then I noticed DT1 pistons had diff deck ht to reed valve pistons I have (not sure what models they came from except one is IT250D). Just remeasured them all - 19mm for DT1 piston, 24.3mm for everything else, incl the Wiseco one that was in my YZB w the spacer.

So I tho't the barrell hts maybe 5mm diff. Just measured DT1M, DT2M, YZB, several DT2/3, & DT/MX/IT barrells. All are 110mm tall.

I've always been under the impression they used the same (214?) rod, as Zedder shows. So what gives?

The only thing I can think of is the cases may be 5mm lower at the base gasket surface on DT1 & YZ engines, but I no longer have YZ & never had DT1 engine (tho I do have a DT1F of DT2/3 models) to measure. I always tho't they used same cases tho. Might have to pull the barrell on DT1F to check piston deck ht.

Just checked early wiseco catalogues. They list same pistons for YZC-F, DT2/3, MX & IT but NOT incl YZa/b. In the superceded list, 74-75 YZ has separate numbers for it alone. I've found Wiseco listings aren't always accurate, but its the same in 2 diff catalogues.

Can anyone else shed more light?

[Freakshow]

i got a stack of YZ and mx piston that are wiseco at home NOS, they are all 234 prefix and say yz 74-76 and i know thay are the same as the mx250a as i used one from that box recently ?    they are all reed pistons the only thing i have noticed is the windows shapes changes through the differant piston makes in there as i have some Genuine Yamaha as well.   

 i have never seen a Yam piston port slug, so cant say on that one, maybe thats what we need to find and suss one of them out.