You finally got to me Firko :-)

[Tahitian_Red]

mainline,

I was thinking the same thing. 


Firko,

I found those photos in my web searching and the newer forks are on both of them.  Our rules are slanted too much towards the Euros and not the era (Kawis, Suzis and Yamahas were modified).
 

Was the1970 DT-1MX bore chrome or steel?

[firko]

I was thinking the same thing.  Cheesy

Thank fu*k someone got it .

I found those photos in my web searching and the newer forks are on both of them.  Our rules are slanted too much towards the Euros and not the era (Kawis, Suzis and Yamahas were modified).
 Sad

I think both of those bikes have stock forks Jay....Your bike is a appears to be 1969 DT1B which came with the candy tangerine tank, square swingarm and steel fork legs. Why can't you fit forks from the next model, the 1970 C? The only major differences are the colour (Candy Apple red), round swingarm and alloy forks. Everything else is pretty much the same. I have steel legs in my DT1 resto but I've got later internals which bolted straight in as Vandy said. Surely your rules aren't that strict?

Was the1970 DT-1MX bore chrome or steel?

Here's one of the great DT1 anomalies. From what I'be managed to find out, the DT1MX's that came already set up from the factory, had a chrome bore cylinder. However, if you bought a GYT kit from your Yamaha dealer, the cylinder had matching porting but had a cast iron barrel. Not a lot of genuine DTMX barrels survive today because back in the day when a chrome bore was damaged the technology to rechrome it was in its infancy making businesses that were capable of doing it hard to find and expensive. The cheaper alternative was to go to the dealer and buy a GYT cylinder (or port a stock enduro barrel to GYT specs). That's why you almost never see chrome bore DT1 cylinders but there are plenty of stock bore GYT pistons available on eBay because there aren't any chrome barrels for them. You'll be a very lucky fella if yours still has the chrome bore
 

[farmpro]

Firko !!!

I think the DT1MX's in the states had the cast iron cylinder as I have an original bike and it is cast iron
It was the GYT kit cylinders that were chrome over here.
They also had RT1 GYT chrome cylinders but were quite rare.
Chrome bore rings are still out there.You can tell them as they have 70 as the 9 & 10th part number.
214-11601-70-00,364-11601-70-00,363-11601-70-00


Bill Davis          Texas Vintage Racing Club

[Tahitian_Red]

Thanks Bill,

I was getting confused looking at pistons on eBay!  I'll pull the cylinder this weekend to be sure before buying anything

Bill are you a Bultaco guy?

[farmpro]

Hey Tahitian !!!
I rode one for about 6 months in 1974.Loved the way it ran & handled but I couldn't stop it as it had no brakes.

I'm a Yamaha guy.
Take care.

[firko]

Bills correct.....I got it arse about . I was thinking of what an old Yamaha dealer told me back in the day but I remember him to be pretty brain fuddled too . I wasn't sure but when you think of it the chrome bored MX version makes more sense. I've never seen a chrome bore DT1 barrel but I've seen a few cast iron GYT barrels yet very few DT1MX's were sold here. Plenty of kits were however. Looking closely at the kit below however,  it would appear that the cylinder is a chrome bore version...I can't see the liner outline on the top.

I should've checked with Bill first, he's a pretty smart Yamaha fella!

They also had RT1 GYT chrome cylinders but were quite rare.

I've got a cast iron GYT RT1 cylinder and remember that my RT1MX had a chrome bore back in the day...go figure Maybe that helped confuse me! Here's my DT1B

[Iain Cameron]

Mark both my 68 and 69 have alloy sliders when I got them ?

[firko]

Mark both my 68 and 69 have alloy sliders when I got them

If you look at the early ads and magazine pieces you'll find that both the original white '68 DT1 and orange '69 DT1B both had steel sliders Iain. My all original '68 had steel sliders so I'd suspect that maybe they'd been replaced over time. Here's my DT1 with steel sliders (TOP) and a  bike '69 model in the USA..also with steel sliders.(bottom) Yeah, I know I've got the front mudguard mounting bracket on upside down .
                               
             

[Tahitian_Red]

Will the DT-1 and RT-1 GYT pipes interchange?  I see pipes on eBay all the time and the heading says "DT-1,RT-1 pipe".  The reason I ask is because I have found and aftermarket pipe labeled RT-1.

 

[firko]

Yep, they're the same pipe Jay. There may be a difference but I'm fu*ked if I can see it. I haven't checked but I'm fairly confident they're the same part #.

Jay, check out the latest on the American Eagle/Sprite/Alron thread, we've uncovered another anomoly with the single and twin plug GYT heads. I've never seen a single plug GYT head before...Maybe Bill Davis can help with some info .

[Tahitian_Red]

Thanks Firko!  I found a Bassani pipe for an RT-1 and I wanted to know if it might work.  Hopefully Bassani didn't make any changes between his DT-1 and RT-1 pipes.

I've been following the Eagle/Sprite/Alron thread. 

[Iain Cameron]

In the Yamaha tuning book covering the dt1s and rt1s the pipes are identical . It also gives the porting and carb mods its worth getting it IF you can find it .

[firko]

I found this on http://articles.superhunky.com/4/99
1971 DT1MX

LAST OF THE BREED

By Matt Cuddy

                   

1971 DT1MX Yamaha

The 1971 DT1MX Yamaha was the last of a breed that started in 1967-68, with the first Yamaha DT1 250 Enduro. Never remembered for good handling qualities, the DT1 did have reliability and strength that made it a natural for dirt biking.

This fact was not lost on the go-fast crowd, and soon the DT1 was the object of desire for many a dirt rider in the early nineteen seventies, since all of us were inveterate tinkerers and modifiers, because that’s how it was if you wanted to go fast. And we were getting sick of our BSAs and Bultacos blowing up underneath us. Enter the Yamaha DT1.

This was the last of the GYT kitted enduro MX line that started in 1968. When you purchased a Yamaha MX what you got was a stripped enduro with a GYT kit (GYT stood for Genuine Yamaha Tuning). The GYT kit comprised of a different cylinder, head, piston, carburetor and expansion chamber. The rest of the machine was an enduro, devoid of lighting equipment, and sported big white square number plates on the forks, and the flanks of the bike.

The machine was over-built, with crankshaft bearings twice the size of other 250s, and a seemingly indestructible transmission/clutch assembly that took serious abuse and came back for more.

The 1971 was also the year Yamaha started getting serious about producing a real off-road motorcycle, with different spring rates in the forks, and a 21” front wheel. This bike also had some pretty radical porting in its piston-port motor; with a one ring piston and 32mm flange Mikuni carburetor (stock on the enduro was a 28 mm). Also, you could see that the GYT kit was somewhat hand fitted, with ports hand shaped, polished and matched. Neat stuff when you think of the reputation Japanese products had back after WWII.

This was the bike that caught the attention of anyone who raced or rode a dirt bike. For $895.00 out the door, you got a fast, reliable and with minor modifications, a decent handling motorcycle that didn’t blow up every other race, and set a new standard for dirt bikes in general. The motorcycle factories in old Europe scoffed at the DT1, until they closed their doors a few short years later that is.

My 1971 DT1MX was modified with a stretched and lowered frame, Curnutt rear shocks, a No1 Products fork kit with top out springs removed, and spacers installed. A 36mm Mikuni carb, with porting and pipe done by EC Burt of Precision Cycles in Lawndale California, a Filtron Air cleaner and Preston Petty fenders completed the package. For less than $1000.00 I had a bike that could run with the Maicos and Huskys of the day, without the ridiculous maintenance rituals the Euro bikes required. The modifications made it a fast, forgiving motorcycle that was reliable too, something unheard of back then.

In 1972 Yamaha designed a completely new motocross machine that shared none of the parts from the Enduro line. The ’72 DT2MX is one of the most sought after vintage dirt bikes on the market, as it was the breakthrough year for Yamaha, abandoning the Enduro design for a real race machine.
               
But for my money the ’71 was the best, and embodied what dirt biking was all about back then. When you had to modify your dirt motorcycle to be competitive, and loved every minute doing it.

[Tahitian_Red]

Thanks Firko,

I've read that article before and it is one of the things that inspired me to get a DT-1MX.  They were just a little before my time, as I got the "itch" in 1973, reading about "Flying Mike" Brown, in the Mini-Cycle magazines, at our elementary school library.

The historical significance of the DT-1 and especially the DT-1MX are not lost on me.  The builder/racer in me wants to "Hot Rod" my bike, but I kind of like the idea of leaving it mostly stock, even if that leaves me at a disadvantage.  I always love to root for the underdog.

 

The RT-1 pipe is just a slight miss fit.  I will post pics later.  I guess I could have someone adjust it, but maybe I should sell it as is to someone else (Need to find out exactly what it fits first).  And it looks like I have a regular DT-1 cylinder and not the GYT cylinder that should be on it, but everything else is DT-1MX.

 

Could the GYT cylinder have a slightly different exhaust port angle?  Looking at the online Yamaha parts catalogs, every RT-1 pipe (stock or GYT) fits DT-1's 1968-71.  It doesn't cross through the frame, so I don't think it is for a DT-2 or later.  Maybe a later 360 enduro???
 

[Tahitian_Red]

Here is a pic of the GYT pipe and the Bassani:



The Bassani pipe is laying flat on the ground while the first quarter of the GYT is curving upward.