Tillerman6

Feetupfun, Glad to get your help! I think the DT250 B/C is exactly what I have. You would not think that KYB would make so many different forks for bikes that are more or less the same thing. Tell me about the Race Tech Valves. I'll send you a pic of my brake drum, but I'm guessing it is also DT250 B/C since the forks are. No problem with having enough weight I'm 180 lbs. Shocks will go on with body on top. (no mystery now) Will stick with the DT forks for now unless there is a windfall of TY parts coming my way. They sell sleeves for the fork sliders ready made. They would need a special jig made to hold them concentric if you were going to make your own on the lathe because they are so thin walled. You could not put them in a 3 jaw or 4 jaw chuck because they would distort from the squeeze of the chuck. When I get the new Dunlop D 803 GP installed I will weigh the front wheel without the brake backing plate and let you know what it weighs. I'm sure the rim is wider than a TY rim, but it might not weigh that much more. Made my own handle bar risers to get my standing riding position to be more upright. Tomorrw is my 70'th birthday, so I can't be riding all hunched over for too long Thanks for all your help! Wish you were in North Idaho- you could see my pile of parts! Or we could go fishing!

The only difference I can see is that at the bottom of the right hand slider, there are two studs sticking out of the bottom of the fork leg to hold the axle clamp. If you look at the parts manual online: https://www.yamahapartshouse.com/oemparts/a/yam/5004177af8700209bc784bdc/front-fork There are no visible studs showing on either fork leg. \ Could be another "artist" problem as you mentioned before about the springs. There are also possibly some differences in the internal parts between the diagram and what is on my work bench but I would have to line everything up and take another look. However, I am more than willing to try the TY springs if I can find some later on. Spacers are no problem. I have a good ol South Bend 10K metal lathe. What would the Race Tech Gold Valves do for this situation? You are indeed the Yamaha Guru! Don't know if the YZ setup is any heavier? I think the front rim is wider than the one on the TY. Had another look at the Falcon rear shocks today. I do indeed have the 50 pound springs on there. And the shock body should be on top to get the shock action working both ways 100% if that is the desired result.?? I might adjust the spring clip all the way down (up) and see if I can get the 50% sag situation to happen. I can get a used TY front wheel and hub for about $100.00 US, but the condition could be a problem. Worth it? Also I can get some Very used looking TY forks (pitted and worn chrome on the tubes) Seals shot for 170 Us, but there again, condition looks like a problem.

Yes, tried to cancel the order for the 15 wt and swap it for some 5wt oil. Hope that sounds better? As far as the source of the forks- Close as I can figure out it looks very similar to the 1974 Yamaha YZ 250 setup.Not 100% identical, but close enough. The axle is positioned on the centerline of the fork legs and anything newer than about 75 has the axle in front of the centerline. As soon as the seals and the new 10mm Allen bolt comes in I can at least put the forks back together (less springs and oil) and check for clearances around the new TY style front fender. From looking at the parts breakdown of the TY it looks like they use two sets of springs instead of just one big long one in each fork leg. Don't know if it would be possible to change out the MX springs for some TY springs? I hope so because the wheel hub I have now is also from a YZ and it does not fit a TY fork leg like it is with it's tennon and notch situation on the brake backing plate I have now. Buy a trials bike? Sure send me some $$$. As long as it is taking for the engine overhaul, paint, new seat, fenders, fork modifications, it would be nice to have another bike to ride !!!

Feetupfun! Great info and good news. I was afraid the triple clamps were not TY in which case it would throw off the rake and trail. The lower fork legs have a TYB sticker on them. I guess they still could be from an MX or YZ Yamaha as the TYB rep said that TYB sells to OEM source makers. I was able to steer and manouver fairly well with the old high fender setup and with the fork tubes sticking up out of the top triple clamp about an inch and a half before I took the bike apart for the engine overhaul. The new fender is a TY replica from DC plastics and it looks pretty authentic, so I'm hoping I can get it to work with the new brackets I made. Lots of things to do before I can mount the new fender it though, as I need some dry weather so I can paint the frame and swing arm. Should happen next week I hope. I ordered the new front tire, some fork oil, and some new fork seals in the last couple of days. I guess I will wait for the seals and get the forks back together before I try and mount the new fender. It might be easier to have the bike on it's wheels and just leave the fork springs out until I can see how far the wheel moves up with no springs installed.? The rear shocks are Falcon brand and 13 5/16" center to center or 338mm. Is that longer than stock? How much ground clearance do I need for novice trials? Had to drill out one of the bottom allen screws to get one of the fork legs off. The threads were stuck to the innards of the fork metering rod and would just spin and not let the allen head screw back out. Somebody had put some yellow goop on the threads of the allen screw and it grabbed the metering rod threads permantly!. I ordered some 15 weight oil. don't know if that was a good choice or not, but gotta start somewhere. There is a small captive steel "washer" at the bottom??? end of the main springs( same OD as the spring OD) -looks like a small top hat with a hole in the middle. Is that supposed to be at the bottom of the spring or the top end? Thanks for all your help!

You have raised a good point about the clearances behind and above the new fender that I had not thought of. . Fortunately, the new brackets are somewhat adjustable up and down the lower fork legs so the fender can be adjusted up or down about an inch or so, and also the fork tubes themselves are about an inch and a half longer than they need to be. These are TYB forks and the last 2 inches at the top of the tubes looks to be a separate piece, although they have resisted my best efforts to unscrew them. I can't tell if the triple clamps are Yamaha, or they have also been swapped out for the TYB. I will include some pictures here and maybe you can tell if they are Yamaha triple clamps? I had to replace the lower balls and races inside the center post, and I ordered Yamaha parts for that and they fit the frame and the center post perfectly, so i think it's just the fork legs and front wheel assembly that was swapped out. ?

Apparently there are two models of Dunlop 803 series tires. there is the straight D803 and the D803GP for about $20.00 more. So due to my size limitations and the advice on here, I went ahead and ordered the 803GP tube type model. This will help me finalize the position of the new fender so I can drill the new holes in the exact spot they need to go and also make sure there is enough room for the expansion chamber and some mud on the tire. What would be a good height above the tire front and rear?Thanks for all the good advice!

Not looking for a crossover tire, just for trials use, but thanks for the input.

Lineaway, I don't know if the new metric sized tires will fit the english 2.75x 21 front rim. The Dunlop 803 GP seems to only be available in metric sizes ? Lineaway, I'm in the states and it's good to know that the metric marked tires are the same thing. Your link is showing a fairly low price too, so I will check out the shipping prices and see if that still makes sense. The michelins here in the states are only showing the metric numbers for some reason. Kind of confusing. Will do some calling around tomorrow. Good info and my "brackets" are special to the forks on this bike. They mount right to the fork legs to accomodate the TY style fender, but the fork legs on this bike have no mounting boss for the bolts from the fender, so it's off to the mill and the lathe making lots of aluminum chips to make something that will do the job. Not the easiest trick I've ever done either! But it beats buying more forks!

By the way, I'm making my own front fender brackets (long story), and I have a brand new TY style front fender to mount. How much space should I have between the tire and the inside of the fender?

I have a TY 250 which had knobbies and a fat seat on it. The front fender was mounted high up under the triple clamps. All this is being changed out in favor of trials riding. wish me luck!

From just a little research I did just now, the only 2.75 x 21" tires made for trials are made by IRC. If you know of any Dunlop 803 GP's or Michelin competition tires that are sized in inches, that would be good to know.

Some of you guys could help me out a bit if you will. I have decided to convert my trail bike to a trials bike, so I ordered new fenders and am fabricating my own front fork mounting brackets. The bike originally came with a 2.75 x 21 Bridgestone tube type tire on it, but that one is long gone. What I need to know is what is the overall width of some of the2.75 x 21" trials tires out there now.? The tire on my front right now is a 3.00 x 21 knobby, so it is almost touching the inside of the new fender .I think the trials tire will be a bit narrower, but different brands are different sizes even though they all say 2.75" x 21" or what ever. I need the measurement OVER the knobs, not the body of the tire and the brand/model number. There doesn't seem to be any actual dimensions available anywhere of actual mounted tires after they are inflated so that I can tell which one to order.

Feetupfun! Thanks for the coil spring info. This stuff is hard to figure out without some expert help!

feetupfun, noticed this old thread on the Falcons shocks. I have the same shocks, but the springs seem to be very stiff in relation to your 50 pound springs. These springs on mine are chrome plated. I don't know if the color/finish is the identification for the spring rate on these? Some companies do color code their springs to identify the spring rate, but don't know about Falcons. Is there some way to tell what the spring rate is for sure?

Tony, Just admiring that TY250A that you did the tricks to. Is that frame chrome plated? or painted silver? or Powder coated? Any thoughts now? Things you would do differently? I am sort of restoring my TY 250 A and haven't decided on what to do with the frame coating? paint? powder coat? Etc Your thoughts are most appreciated! Nice work by the way! Tillerman6

When I last rode my ailing TY 250A around the yard I noticed that the clutch does not engage at all until the last 1/4" of the lever throw.(All the way released) Then it sort of grabs. Is that a problem? or is it just out of adjustment?Something worn out?

Feetupfun, So with the pegs back about an inch and 3/8" and down about the same. will the 250 lift the front wheel off the ground much with a blip of the throttle? Or do you need to bounce it a bit first? Just wondering what a normal healthy TY 250 is like? And are you running a radial rear tire?

Do you know anything about paint? I am really tempted to use just a galvanizing paint in a spray can that I stumbled on while doing some welding work last year. This stuff is about 50% zink, but it goes on thin and evenly. dries in about 3 minutes. is fairly tough and fights rust to the bitter end. You can touch up any scratches with just an extra squirt of the stuff and it is a medium silver color. I painted my home made rear bumper on my old pickup with the same stuff and it is holding up thru the winter really well. The best thing is that if you do get some rust somewhere from a scratch or whatever, you just sand off or wire brush off the rust and spray again. Assuming that you can get to the area in question, you are done in about 30 minutes and dry to the touch in 3 minutes or less. This stuff also seems to stick and flow down onto the metal really well too. I went to a powder coating place today just to see what they could do and they wanted $150.00. Probably worth it, but the zink paint can be patched at home.

Thing is I need so much stuff for the bike and all at once. Tires, throttle, handlebars, foot peg work, paint, engine work, postage, a seat base and seat cover, a new front fender bracket and a new front fender. Probably a new rear fender too.

Lineaway, (or anyone?) did you notice the boot being too short on any of your TY's? What's exasperating is that they want an arm and a leg for that new boot and you might get one and it would be too short just like the old one! Arrgh! I might go back to the autoparts store and look thru what they have in the way of a radiator hose, there might be something that could be cut down or cut off one end. Most of their stuff is not so extravagant.! The other thing is that I might get a new carb soon and it would probably be different than the old JK that is on there now. I think that is the case with the carb I have been considering the OKI I think it is. Paint- Still working on cleaning off all the old paint. There was zero primer under that (what I think was the original paint) , so most of it comes off pretty easily. Today I used a You tube trick that one guy did by making a mini air blaster from a Harbor Freight air gun and some walnut shells inside a soda bottle. So did you break your old one, or why did you replace it? Was it too short and is the new one slightly longer?

I could not see the engine moving around in the frame while it was running, and all the bolts were still tight when I removed the engine, so it was still locked in on 5 of the 6 mounting points even though the top right ear was loose from the frame at it's base. And you are right, Any loose mounting point is one too many. But the wobble in the magneto housing was the kicker for me. I am betting that B&J will find something out of alignment with the crank itself. Also it will be nice to finally get closure on that missing needle bearing roller that I never could find. Today I stripped the old paint off the swing arm and painted it. Then I stripped most of the paint off the frame, but I ran out of energy before I could finish that one. There are a few places where I can't get my wire wheel into close enough to get 100% of the old paint off. I guess it's Naval Jelly time. The frame itself had no other cracks, but the bottom race in the headstock will have to be replaced as it was pitted from corrosion/rust. I did not notice that the head stock was binding or anything, but with the forks removed, you could feel a little roughness while rotating just the triple clamps by hand. It's great that so many of the parts are available on Ebay for this bike! Now I'm trying to get the dimensions for the bottom bearing race itself. The previous owner swapped out the forks for some made by another company. So I can't tell if the head stock tube bearings are still Yamaha or not. The center pivot tube in the triple tree is 30mm at it's baseOD where the bearing is bad, The bearing I have on this bike is a30mm ID and a 47.6mm OD. but of course there are no dimensions in the parts list, only part numbers. in this case it is 156-23411-00. I have this question in to a couple of dealers on Ebay, and maybe one of them will measure what they have and let me know. I also want to do something about changing out this stock air box and handle bars. The air box outlet pipe is too far away from the carb and the plastic hose is therefore pretty fiddly to gt it to make a good seal. I really don't like the air box itself- heavy , awkward and hard to get the air filter set in place just right. Thinking of going to a K& N sock, but still need some protection from water ingestion. Any ideas? I am also removing the old front fender and brackets. Going to a trials bike setup. The lights and brake light switch are coming off. The seat will also be replaced when and if I ever go trials riding. This is turning into a 2K play bike, but I'm enjoying the changes. It's only money and I don't chase women, so what else am I gonna do with my few remaining years! And- someone was on here talking about mounting some larger handle bars. I think that is also needed. Especially if the foot pegs are mounted to the rear position. But I have not seen any handlebars that have more rise than standard. Any ideas there?

I wanted to see what could be accomplished by just straightening out the crank first. If that makes an improvement with the vibrations, I can always send in the head and cylinder next winter after the riding season. I did not want to introduce too many variables all at once. Today while I was stripping down the empty frame I found a broken off tang that was bolted to the right hand side of the upper engine boss. I got it welded back on and am in the process of stripping off all the old paint and rust while I am waiting for the engine to come back from B&J Racing. The rust is not too bad and the grinder motor is making short work of the rust removal. The forks I have on the bike are not stock and they don't have anyplace to mount a front fender bracket like the original. I might be able to fabricate something that will work soon.

Sounds like it. I explained what was going on with the vibrations and first thing he said was "sounds like you spun the crank!" So he's been there, done that! The lower end is in th UPS system now. On it's way to Tennessee.

Yes the piston tops out exactly at the same spot on the cylinder. The skirt is a few MM shorter than the old one The extra weight of the new piston was another problem. I am back to the old piston, but today I sent in the whole engine less the cylinder, head and piston in to B& J racing.The vibration I'm getting isn't normal even with the old piston. I took off the mag and backing plate and both outer covers to save weight. They will have a look and tell me what it needs. Probably be a week or so before it shows up, then another few days before they have a chance to look at it. I took the time to put a dial indicator on the very outer edge of the magneto while it was still mounted to the end of the crankshaft. I was getting 0.010" of in-out wobble. so I think the crank shaft is pulled out of alignment. I sure hope B& J can fix it permanently !! If I had known B&J had the correct pistons, I would have let them do my cylinder work. That was a few months ago, and I was on here and could not find the correct one!

Will do. I was just waiting for Monday morning to roll around. After watching some videos on truing and balancing it looks like I am no where near equipped or skilled enough to tackle the crank straightening or balancing job. Hope it's not too expensive.