OzVMX Forum
Clubroom => General Discussion => Topic started by: firko on March 06, 2013, 10:45:04 pm
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As those of you who know me are all too aware, I love building trick vintage motocrossers. That flaw in my personality goes right back to the early seventies and reading Barry Watkins Cycle Guide articles on building sub 200 lb DT1's, TM400 Suzukis and the like. I'd always wanted to build really trick bikes when I was seriously racing but couldn't afford all of the much needed exotica so I took the next best option and raced Maicos. Now I'm basking in self funded retirement bliss with a bit of disposable income and plenty of time on my hands I now get to build the bikes that Barry Watkins imgrained into my psyche 40 years ago.
http://www.mattwolf.com/watkins/history3.html (http://www.mattwolf.com/watkins/history3.html)
(http://i1112.photobucket.com/albums/k495/firko2/Yamaha20AZ20a_640_zps6bf9f99f.jpg)
http://www.eurospares.com/graphics.htm (http://www.eurospares.com/graphics.htm) Scan down the page until you get to Vintage Dirt Bikes and you'll find downloads of the Cycle Guide articles on the Watkins DT1 (above),Cheney TM400 and super lightweight RT2MX Yamaha. Good reading for those who like trick hot rod pre 75 iron.
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Another interesting legend read,nice truck on page 2.
He's had his fingers in many pies 8)
cheers A
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Yeh they were great articles. I pined for one as well but it was way beyond me too.
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I just re-read all three articles and it's interesting to see how Barry got his 237 lb RT2MX down to a featherweight 197lb. I'm taking a different tack to Barry to acheive a similar weight loss on my RT2MX. Barry used the stock frame with a Boyd and Stellings swingarm and got 36lb off the bike with a careful choice of components. I'm using the same philosophy on my RT2MX but I'm taking a slightly easier route by using a nickel plated Harry Hindall chro-mo frame/swingarm over the lumpy, evil handling original. Where Watkins skimmed down the original forks YZ-A style, I'm using magnesium Ceriani's with YSS PD valves and Pro-Fab magnesium triple clamps. I'm using alloy bodied Works Performance rear shocks. Like Barry I'm sticking with the stock front wheel as there are none lighter that stop as well as the Yam conical. I will however be using a Mag backing plate from a later YZ (not sure which model) instead of drilling the shitter out of the stocker as Barry did. I was going to use the stock RT2MX rear wheel but after reading the article I can see that they're way too heavy. I did consider a Montesa VR Cappra rear hub but it's too wide to fit the Hindall swingarm. I think I'll now use a Rickman Monty hub/Takasago mudcatcher rim combo. Takasago mudcatchers are a tad lighter than Akronts and Borrani's (plus they polish up much shinier 8). Both Barry and I are using the stock seat with its light but strong base. I've had half a dozen different tanks on the bike and have decided that because I want the bike to look as close to a stock RT2MX as possible, an almost identical MX250 steel tank will be used. My mate in Pennsylvania Michael McCook has donated a YZ250A tank to the project which will save a substantial amount of weight but it still hasn't left New Hope,PA so I'll proceed with the original look until it gets here and then I might make the change. I'm using DC Plastic front and rear mudguards to suit an MX250 and a stock fibreglass side panel on one side and a home made alloy oval number plate on the other side. I was going to keep the mudguards in transluscent white but I'm now going to fit repro RT2MX tank and fender stripes and paint the lot in coarse metallic silver with clear pearl top coat....a custom take on the stock setup.
The engine is fairly basic...using a stock cylinder and 2nd over piston, Boyesen 2 stage reeds and 6mm reed spacer, 38mm Mikuni, ACK radial head, Franks Cranks balanced crank, Barnett carbon fibre clutch kit, lightened clutch basket and stock transmission with undercut dogs. I'm not sure which ignition will end up in the finished product, I've got a choice of stock internal rotor mx250 CDI, external rotor DT400 CDI, PVL or "Lozzatronic" custom setup I got from Lozza for my Cheney's 360 RT1 motor but never used. Whichever works best in testing will get the gig. But there may still be some swapping and changing for different track conditions. Wheras Watkins used a Bassani pipe, I'm using a cool period Torque Industries "Whisperin' Smith'' pipe with inbuilt silencer.
I was hoping to debut the bike at the Bonanza but as Jonesy and I are travelling together I only get to take one bike so the Hindall RT2MX misses out, as does the Cheney RT1. I'd like to have the bike up for jetting plug chops and running in at the May Nepean practice day. I'll weigh the finished product on Jonesy's industrial scales and I really hope it does come in under 200lb as my Boyd and Stellings TM400 does.
I've also got another almost identical Hindall frame so I may make a 250 version of the bike down the line.
(http://i1112.photobucket.com/albums/k495/firko2/HindallDT1252-1_zps35b68f4e.jpg)
The under construction Hindall in its first guise as a trick DT1. I've actually built this bike three times with different engines and styling....never happy with any of the results. The current concept is the closest to what I envisioned in my minds eye. I'm pretty pleased with it so far.
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Ive found that the alloy TY250 tank fits and its a nice shape too .
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I'm finally using an MX250 tank as it's pretty close to the DT2MX, bar the filler hole location. I'm using the MX250 seat I got off you Iain.....thanks so much matey. The intent is for the bike to look like a tricked up RT2MX rather than an RT2MX powered Hindall. The tank weighs a ton but seeing that everything else is super light I can get away with it. I've got a TY tank but it's on my basket case TY...funny, I always thought it was made from steel ???.
I actually made a major change on the above Hindall build today. Rather than use the magnesium Ceriani's which need a shitload of work (meaning big money) I've decided to use a set of Can-Am TNT 250 Betors and because it's a major job converting the Yamaha wheel to those forks I decided on using the Can-Am conical wheel as well. The C-A wheel has a steel rim but I've got a 40 hole Borrani rim that I'll start changing over tomorrow. This decision is going to save me a bunch of time and money as the forks are pristine.
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Ian which model TY had the alloy tank have only seen steel ones an alloy one would be great to get hold of.
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(http://i1134.photobucket.com/albums/m612/Iain_Cameron/Yamaha-1972-DT-250.jpg)The Alloy tanks came out from the 75 B model 250 and they where a bit smaller than the steel ones . not 100% but my 75 B came standard with an alloy tank . The photo is a alloy TY tank on a DT2MX
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cheers Ian Ill have to keep an eye out for one
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All the '74 TY250 tanks I've found on eBay have rust in them. ???
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TY250A tanks are steel, TY250 B/C/D are alloy.