Cycle News - Archive Issues - 1960's

eprinti 9 THE TD1-B By Bob Bravennan Pbotos by Dennis Greene A close eumination of World records and racing results over the :;j last couple of years would indicate that the TDIB is the most success~ ful production racer going. The same basic engine is used as a power ~ plant in the Ascot Oattrack bikes and the past and current perform- ~ ances of these machines speak for themselves. However, these successes have been fraught with frustration, dispair and in many cases financial hardship. If you own, or desire to on a 'l'DIB, there are a great many things you can do to improve the reliability and thereby realize a great deal more enjoYBIent from racing. And you'll spend a good deal less time and IIOney (and tears) in the bargain. , Blue Printing the TDl·B Let's start with the engine. AS you may know, there is more than II casual resemblance to the YDS3 road machine. Since the TDIB engine is based on the YDS3, a large number of their parts are interchangeable. So should the need arise for new parts, you don't alwa,ys have to go hunting for special nuts, bolts, gaskets, etc. etc. As a matter of fact you can lift a crank assembly out of a road bike and drop it into a TOIB. They're the same. The biggest difference is in the top end. Pistons, eyclinders, heads and carburetion are different. The pistons are fairly short and since one ring is used, it is mandatory that the piston rings be changed after every race. They're cheap, and the who I e job doesn't take more than a couple of hours, no matter how slowly you work. The parts are fairly well finished, but to achieve top performance it is necessary to match up the inside diameters of the carburetors, insulator blocks and the cylinders. Wnen finishing up the intake and exhaust ports, work UP to 1/16" from Improving tile Magneto The next thing to receive attention is the magneto. The mag is one of the best parts of this engine. It throw s a good strong spark even when being turned over very slowly. The problem is in making the timing s t a y put. The wa,y to solve this is as follows: directly behind the mag base plate there are two tapped holes in the crankcase. By drilling and slotting the mag base plate you can use these to install two 14 mm bolts in addition to tbe two screws provided for that purpose. It will be necessary to cut the bolt heads down so they don't interfere with the coils. Now take the point plates themselves and wash them thoroughly in clean sol vent. Mix a solution of25% rubber cement and and 75% solvent, and brush this on tbe back side of the plate. A thin film is all tbat is required. Let this dry thoroughly and put the points back on the mag. set the points at .010 to .012 and retime. the engine using a dial indicator in the spark plug hole. You'll find that if you've worked carefuJly, your timing prpblems are over. Once the engine is timed it won't slip again. The extra bolts on the base plate, plus the fiim of cement keeps everything immobile. .. Beefing the Clutch The clutch is another matter. This is one of the weak points of the machine. However, the clutch can be bee fed up by some reworking. The biggest problem area is the clutch hub itself. It just isn't strong enougb if you're really scratching. By removing the inner and outer plates and trueing UP the outer and inner parts on a lathe, plus making new. heavier plates (.150) this problem is eliminated. A local machine sbop should be able to do this for about $20.00. Be sure to assemble the clutch with socket-head screws as these can be pulled down very tight. Don't forget to use a small center punch to interrupt the threads where they come through the other side. This prevents the screws from loosening up and causing a lot of expensive noises. A metal band press-fitted onto the outer die cast clutch plate housing completes the clutch modifications. Since I've been using this type of clutch in my road and drag racers, I haven't had any clutch problems whatsoever. Before that well, let's not go into that. • .. .......=--~ Th. n'w rlne on the rleht Is considerably beefier, and the Installation 01 thase will .lImlnat. any lutur. hub probl.ms. Be sur. th. insulator block and Intak. port are match.d up car.fully, This Is v.ry Important, so try and do the b.st Job posslbll, It'll payoff, the cylinder, but no closer than that. The reason is that the eylinder bores are chrome plated, and there is danger of the plating peeling off or from the ring catching on a sharp edge (the exhaust port should have a chamfer all the way around to prevent this). 1 take a round abrasive stone and very carefully stroke the port edges to remove any trace of rotighness. The importance of this cannot be over - emphasized enough. If the chrome starts to peel around the exhaust port you might as well tbrow it awa,y and put on a new barreL It only will get worse. The heads of the pistons and combustion chambers should be brightly polished also. This helps discourage the carbon from building up and causing detonation and consequent overheating. The latest type of top end needle bearings are the best ones to use. The older type had a nasty ha bit of breaking the cage and dropping the needles into the lower end. What us nally happened then was that the needles would find their wa,y up into the combustion chamber and promptly pulverize the head of the piston and cylinder head. The new-type needle hearings will prevent this. If you have the latest type TDIB, these needles are already installed. The rest of the engine as It comes from tbe factory is fine. Frame & Suspension The front end is fine just as it comes out of the box and barring any head-on collisions a long time should elapse before the bushings need to be replaced. I would replace the brake linings with latest type as they are much better. These linings come standard on the new l>ikAS. "I'YI com' to tbe conclusion that tiler. reali, _ ' t any speed IIcreta for the Yamaha TD1-B. Tbe key to success Is attention to detail _ neat· DlSS and wwtuunllk. constr1lctlon.· So sa,s Boll BraverJllan, a mati well quail ned to 'JIlIlaln the blueprfntlne pr_s as It Is applied to the Yamaha production ra_. Bob Is the cunent holder of the world's 550cc Drae record with a TD1-B. In addition, a Yamalla _Ill by Ilab was rfddell to victory In the 250cc class by St... 61 bSOll In a recent Carlsbad road race. T1te noted tuner said: "Tbe .xtra effort spent on the SOIall, apparentI, Inslpllflcant details makes the dill... ence between wI ....rs and losers." Addition of two Ixtra bolts on th. mae back· Ine plat. will rosult in thl mae staylne put. Don't loreet to paint rubber c.m.nt on the backside 01 point platos. If these thlnes are done car.'ully your mae problems aro alhlne of the past. Always UII a dial Indicator and a point checker for seltlne the tlmlne. This Is th. most accurate way of dolne the Job. Be sur. the points are pr.set at .010-.012. Tum th. eneln. clockwls. wilen settlne the tlmlne. The frame is pretty good but it could stand being beefed up in several places. The rear frame tube where the right rear engine mount is welded has a nasty habit of breaking every now and then. Welding additional plates on each side of tbe tube is a good idea. By strengthening this area this problem can be eliminated. An.other problem experienced by many TD 1B owners is the front engine mOWlts breaking. Tbe mounts are too thin. If you've ever removed the engine from the frame you'll notice there is quite a large gap (comparatively speaking) between the frame and engine once the mounting bolts were removed. When the engine was reinstalled the bolts were once more tightened up and tbe frame was pulled in to meet the engine. Since the front engine mounts are the weak link this tension, p lu s the vibration, would eventually crack the mounts. However, this is easy to remedY. Install the engine with a .005 shim on each side between the engine and mount. Now cut a piece of tubing to fit between the two front down tubes just ahead of the sump on the bottom of the transmission. Now weld this tube in place and you're all set. By doing this you're not using the engine as a crossmember and also you're not putting a large load on the front mounts. I put an additional tube just above the exhaust piPes on my own bikes, but the one on the bottom will do the job. The additional tube I install above the pipes helps to stiffen things up. While on the subject of vibration it is worth mentioning that all nuts and bolts shonld be safety wired Or an application of Super 3M applied. There is a great deal of high frequency vibration on any two stroke. and the TD1B is no exception. If you take a few extra pains here yOU may save yourself some pain later on should something come adrift at high speed.. That pavement is pretty bard stuff. And So Forth.. , The tires that come as standard equipment are just fair. If you intend to do any real scratching then the new Dunlop tires will be a good inve stment. Goodyear also offers a new tire that may be worth looking at. Just remember tbat your tires are the only contact you have with the ground, so the best rubber you use can't be good enough. The Yamaha bas a tendency to get rather sloppy quickly so by cleaning the bike thoroughly after every race you can detect any small problems before they become big ones. I make a practice or wiping down the bike between heats just as a precaution. And it's paid off. I could go on writing for hours on this subject but I think this information will enable tbe average privateer to go out and compete successfuJly witbout the lISual bassle. Remember, there is no substitute for good workmanship. Tbe more effort you put in your bike at home, the less time you'll spend working. and more fun you'll have at the track. Like that old adage sa,ys - A stitch in time saves nine. Cut a standard YDS3 throttle sprlne In half and use one hall In eacll carburetor In place of the sWIdard TD1B sprlnes. Speed Secrets stay away from hopping UP the en- gine. I've tried a lot of things to extract more horsepower but I always go hack to the basic engine as it comes from the factory. True, yOU can get mOre power, but this narrows UP the power band considerably and puts an additional lead on the engine and drive line. Unless you're a super fast rider I wouldn't worry about getting more power. If yOU want an increase in power try a larger carburetor. A 29 or 30 mm will give yOU more beans, but yOU may find y.ou'll need the close ratio box that comes standard on the new bikes. I personally wouldn't recommend it as it really ruins the mid-range. If you're a real bot sboe 'OU may wa nt to try it. l! you'te not, forset it. By making the improvements outlined here you'll be considerably faster than someone racing an out-of-the-box bike. Tbe transmissionls extremely strong and the possibility of your doing any damage to the gear boxis pretty remote. It will take a terrible flogging and come back for more. I use 10:30 Shell oil in the gear box. You'll probably find that #190 main jets and BLOEN plugs are a good combination for the SOuthern California area. If it's an unusuaJly hot day yOU may want to use B10EN plugs. For timing purposes I set the ignition at 2.10 BTDC. Since every bike is diffe... ent it is impossible to prescribe the exact plug and jet requirements, hut tbese should be pretty close. If you warm the engine up on a set of old plugs and then install a fresh set just before you race you'll find the engine will fire instantly. One little tip that will help you start quicker is to screw 2'h or 3 turns instead of the prescribed 1'h turns. Also, on the TOl B it isn't necessary to hit the tank with your shoulder as the port timing is fairly radical and there isn't a great deal of compression when pushing off in low gear. Just push off, release the clutch and you'll find the engine turns over easily.· No fuss, no muss. • • •

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