Pre-65 YDS VMX project.

[Nathan S]

For those that haven't been paying attention: After being disappointed by the low numbers of pre-65 bikes at the Crawford River Classic, I bought a $200 YDS3(?) from Ebay. I know that I'm trying to make a silk purse from a sow's ear, but until I can afford a twin-pipe CZ, then this is the best compromise between cost, performance and which side the gear lever is on....
Turns out that its actually a YM1, which is the 305cc brother to the 250cc YDS - from what I've found, this is a good thing - the bigger bike had a lot more torque.

This thread will be a mix of questions and semi-regular project updates...

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=150345477458&viewitem=&sspagename=STRK%3AMEWNX%3AIT

 
So I finally got it home at 2:30am today... Thanks to Matt and the Ebay seller for their help!


First impression: Its tiny! Short, low, and short. OK, so the motor is long and wide, but the bike is little - kinda like an LT1 with a big motor in it. Honestly, an AT1 has more presence!
Second impression: F#$k, the motor is empty... oh wait, hang-on, here's all of the internals in a seperate box.
Third impression: Its a little brick shithouse - the rear frame members are larger diameter and thicker walled than many other bikes' backbones.

Random points:
1. The crank is rooted - one side has been sitting in water. It might be save-able with a new rod kit, but I am not holding my breath. Hopefully, air-cooled RD bits are similar.
2. The frame number (as in the in the Ebay ad) looks like nonsense, but the pic in this link suggests that its a legit, Yamaha supplied number. http://www.classic-motorbikes.com/stock.asp?Ref=FA62&Lang=en
3. I'm not too sure what to do about the front brake/hub. YA5/6 front hubs are pre-65 legal and look very similar to DT175A bits. This would be ideal, as DT175s have good brakes, and are definitely strong enough for MX. And are cheap and easy to get.
YA brakes look different (see previous link), but the Ebay ad suggests that they're very similar to DT parts.
Rear hub will probably remain standard, although I'd be happy with a smaller/lighter hub if something else is common and pre-65 legal.
4. If anyone (Graeme R, most likely), has any use for standard YDs front end, rear rim, chain guide, head-light bucket and/or fuel tank, then let me know before they hit Ebay.

Pics in the next day or three.

[paul]

GOT YOUR WORK CUT OUT THERE  NATHAN  GOOD LUCK WITH IT

[VMX247]

Welcome to the clan-good stuff 
as my stars said for this week "you have to walk before ya can run"
enjoy 
cheers

[jimg1au]

looking at yamaha cross reference dosent do back that far bub dose have ym2c big bear scrambler 305 cc 1967 so may be able to sorce come parts

[Lozza]

Check the bore centres and main bearing size and get back to me(most air cooled RD stuf is still available. Crank will be the least of your worries, a good ignition and then everyone will forget about those czech things.

[mx250]

[email protected]

Nathan, try your detailed technical questions with this group - just say its a resto, I'm not sure they would welcome a bastardised mx'er  .
 
Its a bummer that internal condition of the engine wasn't clearly described  . I hope all the gearbox/clutch etc is there. The clutch is going to be unique to the YSD3/YM1. I'm not certain about gearbox bits (ratio) and other bits like c/cases and c/c covers. Obviously the clutch side is gonna be very different.

Talk to the guys above and they might be able to help you out. I've got a number of YDS5 250 motors and I have in the back of my mind I'll convert one to a 305 for road use. Pistons are regularly offered on ebay in a range of sizes at cheap prices. I'm not quite certain about crank bits. I'm 98% certain done of the RD series crank bits swap over. But either correct bits or alternatives/availability/sources might be known by the guys. Ask the guys in the group. There seems to be a surprising amount of stuff still about, and interest in, the YDS/YM's.

I didn't quite describe it as a 'brick shit house', very adapt, but I told you it was heavy and over-engineered. But then every thing in that period was  . Out with the angle grinder and hack off every unnecessary over-engineered bracket will make a difference

The weight will be offset by class leading HP, even pre-Lozza  and left close to stock. I think your suspension mods will make it manageable and even competitive - if you are trophy hunting   .

You know my opinion of front brake. I think a well set up AT/CT1 brake/wheel would be the go, particularly if you already have one. I would err for lightweight. I would hook up a standard AT/CT1 wheel and keep an eye on the spokes. They may have to be re-spoked with heavier spokes - suck it and see  .

[firko]

I've been giving Nathans DS3 pre 65 project a bit of thought and reckon he may be onto a good thing once a number of inherent problems are overcome. To my mind, the main obstacles preventing the bike being a successful motocross bike are !: Weight and 2: Chassis geometry. To achieve a ridable bike using the original YDS chassis will require a deft hand with a hacksaw and welder and even if you could get the chassis dynamics within a cooee of being motocross (or dirt track for that matter) friendly you'd still be stuck with a heavyweight.

To solve the weight and geometry problems I believe the easiest and in the end most satisfying solution is to use a frame designed for off road use. The choices are as varied as your imagination but to keep the bike withing Nathans tight budget I'd be lookijng towards some of the following.

*Sprite: I've been flying the Sprite flag quite a bit in recent times (Budget Bikes and Sprite threads) but they are the cheapest way of finding a lightweight chrome moly frame that's pre 65 legal. The frame has a large cradle that'll handle most conversions, the only clearance problem I forsee being the exhausts fouling the twin downtubes.

*Husqvarna: The pre 1967 "bolt up" Husky frame is pre 65 legal, light, reasonably obtainable and being single downtube,
suitable for twin cylinder or sideport engine swaps.

*Greeves. The cast alloy 'downtube' Greeves Challenger frame goes back to the late fifties and has laid host to all sorts of engines from Triumph and BSA twins through to Brit singles. I've seen one fitted with an adler 2 stroke twin which is of similar dimensions to the Yamaha.

*Cotton: Another Reynolds tube Brit frame. These things can handle all sorts of engines. I saw one with a 650 Beeza motor and I've had Triumph and Honda twin engines in mine.

*Honda: The Honda CL72 frame is a fairly handy frame that can be made pretty light. The geometry is much closer than that of the Yamaha.

*Bultaco Sherpa S. The little Bully frames are a bit on the heavier side but still a lot less than the Yammy original. The gemoetry is good and the forks and wheels are ideal. The Bultaco M11 "Metisse" is also a nice little donor and how cool would a YDS3 Metisse look!

The Suspension and wheels are fairly easy options. It's cool to keep it with as many Yamaha components as possible so I'd use Graemes AT1 front wheel option which I'm also using on my Maico Metisse project. The back hub is a bit more difficult but to keep it pre 65 I'd be looking for as early a lightweight Yamaha hub as will fit. Perhaps the matching rear hub to the front from a Yamaha 80 or similar. The cush drive original YDS hub may be too heavy to use.

The engine is a bit out of my area but I reckon it'd respond well to a "twingle" conversion. Lozza will be more up on that area. There are all sorts of tuning options using later Yamaha parts but the key to the engine is to turn it into a tractor rather than a road race style revver. Twingling the crank and porting and pipes to achieve torque would be the key.

My ideas may seem a bit difficult and probably away from Nathans wish to keep it all Yamaha but after building a number of specials and attempting to convert road bikes into motocrossers (the illfated Jawa Californian project) I reckon I've shown the easier method to get the DS3 competitive. The forum/old mate network/eBay/swap meet system will come up with a suitable frame if time isn't an essence.
 
It's very reassuring to see one of the younger generation vintage racers be prepared to do something different to help save a class that's in need of a boost. Good one Nathan.

[mx250]

Firko you make some interesting specials and have some interesting ideas but I really don't think the YM motor is worth a classic period frame. If I had a classic period frame and a YM engine I think I would trash the YM engine and look for a different period engine. ( I also think the size and weight of the YDS engine would make an engine swap an engineering challenge).

I would be prepared to pursue the use of the yds frame as an MXer. I don't think it is that far off in the handling dept/basic geometry. I cite the success of the Ascot and the Yamaha Catalina 'experiment'. I think the biggest limitation is the weight of the engine, the general weight and the suspension.  I don't think there is a great deal that can be done about the weight of the engine and the resulting general weight. I think Nathan's Betors and new modern rear shock would be an easy, effective and as 'good as can be expected' fix for the suspension. I think the frame geometry will get an improvement when Nathan swaps to the Betor triples during the front end swap. I suspect that they will give a shorter trail speeding up the steering responce.

I think the YDS frame and engine with the Betor front end will make an interesting easy period MXer and I think a good rider could use the extra hp's to good effect on a period sympathetic (smoothish) circuit.  That would most certainly be my starting point. If that combination proved exceptional competitive but limited by the handling I might then think about a change in frame.

[firko]

Graeme....You're probably right as far as the weight of the engine but I hark back to the late 60s when I tried to turn a YDS3 into some sort of paddock basher and remember with a nostalgic smile just how big and ungainly a lump it was. Even my mates rooted Bridgestone 90 would whoop it in the bush. Ground clearance was a problem as was the width of the frame and lets not forget the fact that the engine only came on the pipe from half throttle on. Then it was that unmistakable "Whooo whooo Whaaaa" engine note and hold on for grim death!

Using say..my Cotton frame would remove all of the geometry, ground clearance and weight problems in one fell swoop.
The Betors will go pretty much straight in as would the back wheel. I'd use a DT1 tank painted in the YDS two tone style, and the DT1 seat as you'd get away with them as they're not considered 'major components'. The key is to keep the bike looking as much like a Yamaha as possible which is easily achievable using Yamaha bits and bobs.

As I've got three years worth of projects on the production line (including myself), I may be willing to part with the Cotton frame if it's to be used for a pre 65 project and someone has something interesting or usable to swap. I reckon it'd be perfect for Nathans YDS3 project (barring any exhaust clearance problems) or may fit into Mainlines pre 65 plans. I've only just now decided (since starting this reply) to offer it up and would like to see it used to strengthen the pre 65 class. I don't want it used for pre 70 or later classes or see it chopped up beyond recognition to make something fit. Over to you guys.

[mx250]

Interesting to hear of your first Bush Bashing on a YDS3. My first off roading was done on the YDS5 at Menai. My riding was mainly 'cowtrailing' in the American vernacular, (bushwalking on a motorcycle).   I don't think the limitations of chassis were pushed. I found the '5 extremely capable within this limitation, and given traction, that 5 took me to many hidden corners of the Sydney bushlands - from Menai, to Otford Falls to the Wheelborrow Ridge Road and a shit load in between - all with a ribbed Avon on the front and a street tyre on the rear. (Ah, the memories of a youth well spent ).

The '5 had the same mid range 'power hit' together with a hair trigger clutch. The choose was careful feeding in of the clutch or an involuntary wheelie across the intersection ('Honest Officer' ). By reputation the YM1 didn't have the same hit. The YM only produced 2 hp more and was obvious tuned for lots of bottom to mid range torque. I believe it makes the YM a much more enjoyable and relaxed ride compared to the 250. I don't know if was romanticizing, an exaggeration or a leg pull but I heard the YM being favourably compared to 500 four stroke twins of the period.

As much as my fond memories and loyalty of the YDS is I think I would rather see an engine other than the YM in your Cotton frame. It sounds an interesting offer for someone .

[Nathan S]

Thanks for the input guys.

Apparently the thing to do is to make it a 90* (or 270* if you'd prefer) split for MX. The cranks are splined together, so its not as silly/difficult as it sounds.


Good and bad discovered today:

Bores are standard. 
Bores also have quite heavy rust, and will require more than one over-bore to clean up. 

The engine cases have some fairly significant cosmetic corrosion, so the idea of polished cases is out.
The badly flaking chrome plating on the alloy clutch and ignition covers (that's the big side covers, not just the steel inspection covers) comes off in the bead blaster at work.

[Nathan S]

Pics are here:
http://s46.photobucket.com/albums/f128/annaandnathan/Bikestuff/YM1/

Pretty dry ATM - just motor stuff, mostly showing the less than ideal bits...
The other crank is from an air-cooled RD. Apart from the clutch problem it could be made to work in the earlier bike if need be.

 

[mx250]

The other crank is from an air-cooled RD. Apart from the clutch problem it could be made to work in the earlier bike if need be.

Ya reckon??

[Nathan S]

Yep.
The cases would need about 1.5mm removed to give room for the slightly larger crank webs.
Bore centres are the same (or very similar).
Ignition side is virtually identical.
Bearings are the same.

Clutch side is the killer.

[firko]

There aren't a lot of ports in there. It looks to be a Dremel drivers ultimate challenge. Lozza?