Yamaha DT3 - Small Garage, large ambition

[TresCuatros]

I've had atv's and motorcycles on and off most my life. The two strokes were always the most fun but the four strokes always won the most trophy's. Given a recent back injury and lengthy recovery, I figured it was best to start a project more about the build process and the fun of the ride rather than trying to build a race-worthy bike for competition. What's more fun than a vintage 2T with a bonified California legal plate? - How about one I can track too
Enter this DT3 I acquired Saturday.

Current State:
1973 Yamaha DT3 (250cc)
Stock Mikuni Carb
Stock Wheels
Unk bore / piston
Starts first kick
Last street registered in 1985
Leaks a bit of oil from some yet-to-be-determined location
5yr old gave me the thumbs up.
Wife thinks it's good for me to start another project after selling the last one.
Wife has no idea what kind of habit she's supporting
Game on


Future State:
Deraked & plated stock frame
Disc Front
[Preferably] disc rear
[Preferably] 19" F/R wheels, Dirt Track Tires
Stock tank
Glass Seat section
Chromoly or Aluminum subframe
Chromoly Swing Arm
Flat Slide Carb
Updated reed cage (V301a, V4R01D)
Modern electrical (12v, CDI?)
Find the leak [preferably fix it too]

As she looks at her new home

Quite photogenic already

The Yami's get the sun while the Honda gets the bench

Great site for axle and fork tube dimensions for conversions: http://organ-donor.org/motorcycle-data/fork-tube-diameter-list/

 

[TresCuatros]

Before I tear into this and start parting it out - I'm not a savage and can appreciate a bike like this staying stock if the right circumstances come about. Please reach out immediately if you feel this bike is somehow worth keeping whole for the right buyer.
Alternatively - I'm looking to modernize a lot of bits, so if you need a DT3 stock part, please let me know.

En route already - 2017 35mm SR400 Fork tubes, axle, caliper, and an All Balls tapered bearing set

The biggest hurdle I'm facing is finding the right wheels. I'd love to convert to disc front and rear with a 19x2.5 rim, but I'm also hoping for a lightweight 1 piece alloy set if at all possible. Hard to find wide enough mag or alloy wheels in 19" variety. I may end up doing spoked wheels if I can find the right set.

 

[Maritime]

Sign me up. The CR450 you did was nice. This should be too.

 

[TresCuatros]

Not a ton of updates yet on the bikes, but I've been learning a boat load and need to record some notes.

Random bike dimension / info site: https://motoperf.com/
Axle Sizes: https://www.bajanopinch.com/bikes-axle-size-list/

Stock DT3 Steering Stem Bearing Sizes:
Top: 25mm ID, 43mm OD, 11.1mm Wide
Bottom: 30 mm ID, 48mm OD, 12mm Wide

BMW K75 Bearings:
Top: 28mm ID, 52mm OD, 16mm wide
Bottom: 28mm ID, 52mm OD, 16mm wide

Stock DT3 Rake / Trail: 30.5 Degrees, 135mm
Target: Closer to 26 degree, 95-100mm

Sr400 35mm Fork tubes - 8.6 lbs each VERY HEAVY for their 35mm size
(not going to use these, selling soon)

Newer 41mm Bonneville Fork tubes - 7.75 lbs each

Triumph Steering Stem / Lower clamp: P/N T2049003 (Supposed to be ~55mm offset, 41mm fork tube, just over 7" stem length)

Wheel Weights
2005 Suzuki DL1000 3 spoke cast front wheel - 19x2.5, 8lbs 13oz confirmed.
Strongest contender at the moment for wheels
https://www.stromtrooper.com/threads/wheels-cast-vs-spoke.431760/page-2

Sundance "PVM" 7 Spoke Morris Mag Replica (Mag) - 19x2.25, 7 lbs 9oz
Great wheel, not cheap. Save for Sporster build.
https://www.sundance.co.jp/original-parts/traktek-sundance-enkei-7-spoke-cast-alloy-wheelsトラックテック-サンダンスエンケイ7/

2015 Yamaha XVS950 C-Spec 12 spoke cast front wheel - 19x2.5, 15lbs VERY HEAVY

Ducati Bevel / Pantah Rear (twin 6 spoke / 12 spoke)wheel - 18x2.5, 13.2 lbs
Cool looking, but heavier than should be

1986 Suzuki Katana 750 Front Wheel - 18x2.5 - 10.1 lbs

1988 Suzuki GSXR 1100 Front Wheel - 18x2.75 - 11.05 lbs - RARE but good
https://www.gixxer.com/threads/lightweight-18-wheels.185455/

1986-1987 GSXR 750 Front, PN 54111-27A00-291 - 18x2.5" ~8lbs no bearings (I suspect closer to 9lbs)

2004-2006 Triump Tiger 955i alloy front - 19x2.5 - 12lbs 9oz


Carb:
Consider Keihin 35mm PWK (90's two-stroke KDX200, some KX125s, some other small bore 2-strokes).
Reed Cages: KX85 or YZ125

Engine Porting:
http://www.3wheelerworld.com/showthread.php/125151-yamaha-porting-book

Exhaust Parts
https://www.coneeng.com/

10/28/2020 Update: Wheel / Fork / Axle Dimensions
CB600F Axle: 20mm
- Stock Bearing Size: 20x45x17
DL1000 Axle: 20mm
- Stock Bearing Size: 20x47x14
https://www.motosport.com/oem-parts/part-number/54111-06G01-019?mmysource=SUZUKI;dl1000;2006&partgroup=front-wheel&mmy=clear

Triumph Bonneville T100 Axle (2008): 17mm
DL650 Axle: 17mm
- Stock Bearing Size: 17x40x12
- Spacer Between Bearings: 17.5x25x88
https://www.motosport.com/oem-parts/part-number/54111-27G30-019?mmy=suzuki;dl650;2008&group=front-wheel-(dl650k7~k8~k9)&qty=1

CB600F Axle with DL650 Wheel: Need a 20x40x12 Set of Wheel Bearings (Nonstandard)

FZR600 Axle: 15mm (basically use fork and ANY wheel option with a spacer)


Below: List of fork-spacing on some bikes. Note: the "mounting" dimension is for the fork brace, not a clamp size for the fork tube in the trees.

 

[teazer]

Great little bikes.

A few random thoughts:
YZ85 reed cages are great in an RD350 twin, but you might want to think larger. Try a Blaster reed cage. Blaster is a 200cc single but the reeds are much larger than YZ85. I use them on a TZ750 top half on our little RD350 drag bike and it is like a street bike to ride.

Look at FZR400 fork tubes if they can be fitted. Lightest I have looked at and conventional style. Added bonus is that the FZR400 has clipons above the top triple clamp, so it has long legs, and who doesn't like long shapely legs?

How about a supermoto look for the street, but don't go too fat on the wheels. Are there any Aprilia RS125 wheels around? 17" and wide enough and lighter than any big bike wheels.

Before you de-rake the steering head, try the longer swingarm and maybe slightly more swingarm droop and see where the numbers are with the taller rear end before you cut and weld.

 

[teazer]

And check the gear change shaft for that leak. Yamahas of all sizes tend to weep from there or the neutral light switch.

 

[TresCuatros]

Good point about the FZR Forks. I have FZR forks on my radar, as well as RZ350 and newer Bonneville forks. Probably going towards the bonneville forks since they're newer (easier to find without pitting) and I can save a couple bucks getting the front end with a lower clamp & stem as a package. The stem will require some modifications, but may fit the DT frame. If not, I can always press in a DT stem.

As far as stance go, this build will be a race-capable dirt track build with street credentials. I'm actually leaning towards 19" wheels a bit more now since I can find more rubber for them. The de-raking won't happen until after the forks and swingarm are sorted out. Like you said Teazer - the swingarm droop & length will affect the front, I might not have to cut if other dimensions fall into place.

Do you know if the blaster reeds have the same bolt pattern as these cylinder on the DT3 250?

 

[teazer]

I don't have a DT3 inlet to compare it to but if they are the same size as an RD350 the bolts are further out and the flange would have to be plugged and drilled assuming there's enough meat in the reed box.

If you sketch up your inlet, I can compare that to what I have here and see what might work.

 

[TresCuatros]

I don't have a DT3 inlet to compare it to but if they are the same size as an RD350 the bolts are further out and the flange would have to be plugged and drilled assuming there's enough meat in the reed box.

If you sketch up your inlet, I can compare that to what I have here and see what might work.

You got it!
(This was taken of the gasket)

 

[teazer]

Holes in the flange are the same as the Blaster cage and one year of YZ80
58T-13610-01-00 or 2HF-13610-00-01 the difference between those two is one has a full flange and the other is scalloped on the sides.

The reed cage itself is probably the same dimensions too. Time to pull the reed cage out and measure the reeds and openings to see what's different there.

What about a DT250 reed cage? It's 6 petal but I don't know the dimensions. It's six petals and may be too wide, but you could grab one off ebay and compare it. But in the meantime, can you measure and photograph the stock DT3 cage.

 

[TresCuatros]

Holes in the flange are the same as the Blaster cage and one year of YZ80
58T-13610-01-00 or 2HF-13610-00-01 the difference between those two is one has a full flange and the other is scalloped on the sides.

The reed cage itself is probably the same dimensions too. Time to pull the reed cage out and measure the reeds and openings to see what's different there.

What about a DT250 reed cage? It's 6 petal but I don't know the dimensions. It's six petals and may be too wide, but you could grab one off ebay and compare it. But in the meantime, can you measure and photograph the stock DT3 cage.

Rad. How'd you find those comparative dimension?

I'll revisit the reed size / dimensions at a later date. I already re-sealed them back in the cylinder. Most the work I'm doing at the moment has to do with online shopping for the right set of wheels/fork/stem combination. The chassis layout is my first priority since the bike already runs pretty reliably.

Speaking of the chassis -Does anyone have a cool tool for aligning the stem? I was looking at something like this and using a VERY long piece of all-thread that extended to the ground. That would allow me to measure centerline alignment I hope.

 

[teazer]

Rad. How'd you find those comparative dimension?

I cheated. I had a one in the shop for a project.

 

[TresCuatros]

Small update.

Suzuki America finally had some DL1000 fronts in inventory, so my rep from Motorsport placed the order to have em shipped to me. This only matters because I like the wheel's weight and size, but they were extremely hard to find on the used market and most places were charging real money for them; not the OEM money they're worth. Anyway, this settles me with 19"x2.50" F/R wheels that can accept a 20mm axle and damn near any brake caliper/rotor combo.

I'm looking for a good set of Bonneville, Thruston, or Scrambler forks (04-12 ish) but they're not popping up much at a reasonable price. Likely ordering CB600F Forks and used Bonneville upper and lower clamp with stem. This'll set me with ~30" long 41mm forks and plenty of work to do through Nov.


Starting to like the 34mm or 35mm Mikuni Flat Slide carbs after some keyboard jockying. Looks like I can get a flange-to-spigot style intake from Mikuni to convert the stock bolt-on carb to a spigot style. That'll bring the bike into the late 20th century at least.

Link to pwk airstriker carb details: https://motocrosshideout.com/cr250cr125-pwk-air-striker-conversion-throw-out-the-tmx/

 

[Luugo86]

That is a cool little bike, looking forward to see the build

 

[teazer]

I got my hands on a DT400 and YZ250 reed cages and they are quite large and six petals but they have very little effective port area. I haven't done the calculations but I'd bet that the Blaster has more effective port area in a more compact 4 petal cage.

 

[TresCuatros]

Ordered brand spankin new CB600 41mm forks with calipers off fleabay. No weight yet on them, but they're going to be better than stock and those SR400 forks in terms of performance. Now time to find a suitable triple clamp setup...


Update:
CB600 41mm Fork -8lbs 6.5oz
1 Caliper - 2lb 4.7oz

 

[TresCuatros]

Wheels came in!
Forks too but I haven't unboxed them for photos.
These babies are light for their size.
They're born a healthy 8lbs 13oz

 

[irk miller]

Watching closely. Been having lots of 2 stroke conversations with my friends. I have zero experience with them outside of little YZs when I was a young kid. There have been a number of these DTs come up for sale cheap near me recently.

 

[TresCuatros]

Progress had been a bit stalled.
I went on my honeymoon (that killed a week) and now I'm waiting on California Highway Patrol inspection December 8th to verify my VIN for the new title.
The bike didn't come with a title (lost by previous owner) so CHP needs to verify it's 1.) Not stolen and 2.) A dual sport intended for street use

Aside from those delays - I also hit snag with finding an affordable triple clamp / stem I like.
I'm looking for a set for 41mm forks that has ~55mm offset and 7" stem length and WIDE spacing (195-205mm)
Top on my search is P/N T2049003 from the T100 Bonnevilles and Scramblers. They're apparently sought after since they're nearly $200 for a lower w/stem and other bikes go for about $40.
Going full-custom is a $600 decision, but I'm hoping patience will pay off and a set pops up used.
I can always re-use my DT3 stem or make one, so the stem is less of a concern.

Anyone know of other bikes with 41mm forks, sizeable offset (45-60mm), and wide spacing (195-205mm)?

Edit: K100 BMW, 1998-2000 SV650 maybe?
https://www.k100-forum.com/t13270-stock-offset-of-the-triple-tree-clamp

Edit: Pulled the trigger on some K75 clamps. Hoping to confirm they're for 41mm not 41.3mm forks. Also hoping to confirm offset is 56mm and stem has 0* built in rake and 190mm fork spacing with a 176mm stem lenght. All of this is trial & error boondoggle with my CB600 axle coming in at 204mm wide and no known bearings to convert the DT frame to BMW stem; so some mods to the axle and a new (custom or pressed-in DT stem) will have to be employed.
https://www.motobrick.com/index.php?topic=7898.0

 

[pidjones]

You really get your taxes worth. It took all of 15 minutes for our Sheriff's office (in Tennessee) to check my RD400, and they came out to my house!