Tillerman6

Well this old bike is still giving me surprises and while I'm waiting on the cylinder re-bore and new piston, I thought I should look at how much crud was hiding in the tail pipe. Not to be disappointed, the tail pipe decided to cough up a couple of peanut sized chunks of pure carbon. So I know there is more in there somewhere. took off the expansion chamber too of course and it was not as bad ( I think) but the engine (when it was together) would belch 2 stroke smoke from all angles when it first started up. Could be that this carbon was what was causing the detonation during deceleration? Something was definitely going on in the cylinder. (see pictures below) And now the packing that resides in the tail pipe is completely soaked with dirty goo. So I think the engine was not breathing properly when i ran it last. I did not get a heads up from the previous owner or understand that this tail pipe cleanup was even needed. Never had a TY before. I'm running Amsoil Saber at about 40 to 1 which is probably too much oil. So is this packing material really just fiberglass?

I wish I had gotten a chance to ride a recently overhauled TY to get an idea of what sort of power they should have. I think mine was way down on the beans available, but I didn't have anything to compare it to. It ran OK for put putting around the yard, but this year it refused to start. See new topics Clean out the tail pipe and what oil ratio to use.

Tony, Small potatoes, but Wossener does not include the bearing- Just heard from Wossener customer service this morning. I will order one from Partzilla.

Tony 27 ! That was a GREAT lead on the Wossener pistons! I can read the part number off the box and I did eventually get with Wossener USA customer service. They are very helpful and there are dealers in the states that may have stock if you look around. Some of the rebuild shops are also dealers and all you need are the part numbers. Millenium Technologies is one of these. FYI if any other TY ers are looking for the part numbers available from Wosserman for the TY250 A here they are: 8179DA 8179D050 8179D100 8179D150 8179DD200 (4th oversize) At this time, there may only be stock available from Germany, but customer service said that they have it coming over to the states weekly. I think I will go that route. They are the only ones that say specifically that the kit they sell WILL FIT and the prices are about the same. The other alternatives are not really clear to me. The Wiseco brand does not say that their DT 250 piston is a direct replacement (234M07000 series) and their web site does not mention the TY 250 A at all. Likewise the OEM stuff is only available piecemeal so that you take your chances with Ebay and buy all the parts from different suppliers and pay thru the nose for what you get. Even then there are about Zero oversize OEM pistons coming up on Ebay that are new.

Just about to send off my cylinder to Millenium Technologies for re-work. Trying to source a new upper end con rod bearing for the 74 TY 250 A. I have sources for everything else. The part number listed in the factory documentation says it is 93310-21854 But the one I found at Yamaha Partshouse (Babbits) was listed as 93310-218A6-00 . Don't know if this is the same part or if someone has a cross reference list somewhere? Or if there is a NOS part still in the wrapper that someone is willing to part with? Just trying to avoid a SNAFU at the time when everything goes back together. The old bearing was missing a roller when I took it out of the engine.

Feetup fun , It was good to see that your post from way back in 2010 mentioned the DT 250 pistons from Wiseco. They are still available according to their website today 8/14/2018! Do you remember if you were able to just install them AS IS? or did they need any modifications? Thanks in advance!

you can be sure I tried that. I even turned the bike upside down on the handlebars, but nothing fell out. (wish it did)

Don't know if you are using ethanot in your fuel, but you might not know that ethanol eats rubber fuel lines from the inside out and deposits tiny bits of rubber into the carb where it clogs up everything. Some gas stations sell non- ethanol premium fuel and that is what I make all my 2 stroke mix out of. Also good to replace all rubber fuel lines with Tygon lines instead. also run a fuel filter just before the carb just for insurance. However, all that being said, a carb has more tiny holes in it than a piece of swiss cheeze. and they all have to be clean for it to work.

Ok I decided to go ahead and tear down the top end of my TY 250 A and get a better idea of what sort of condition it is in, I never did get a compression reading before the teardown, but looks like the wear on the piston , rings and cylinder would have dictated something less than a perfect 99 psig. As you can see, the piston pin did not want to come out of the piston without some encouragement. The threaded rod and two sockets provided the persuasion, but there was a surprise involved. The surprise is that one of the needles in the upper end con rod bearing was missing out of the cage. I don't know how long it has been missing or if it just flew off when the cage was released from the piston pin during dis assembly today. I noticed it was missing when the cage came half way out the end of the con rod, but I have no idea where it went or how long it has been AWOL. As far as the piston itself goes - looks like it is a stock diameter 69.96 mm. It has the reduced diameter above the top ring and there is a ring expander ring under the bottom ring.Does that make it a 311 part number? There was some scuffing on the piston just to the left side of the intake port, and this by itself does not seem to be a big deal, but the rings are grooved in this same position on the piston for a short span of about .25" or 6mm wide. I took the measurements below without honing the cylinder, so the cylinder measurements after honing to break the glaze will add another .001" at least to the already marginal service limits that exist for this standard piston. So here are the measurements before the hone ( in inches) Piston diameter 2.7535 to 2.754" ( Taken 1/2" from bottom edge of skirt and at right angles to the piston pin) Bore diameter 2.7566 Taken just above the exhaust port. Delta of 0.0026 to 0.0031 The max tolerance is .004" Rings - I was surprised to see the "L shaped " top ring on my 74, because the previous owner did not say anything about having changed pistons and furthermore, the L shaped top ring came along later on the 75 model. Right? So I am wondering if this piston is really off of a 75 or later machine? Maybe someone can tell me for sure. And inside the piston skirt it says YAMAHA, so it could be a 311 part off of a DT 250 or IT 250? The top end of the piston is definitely a smaller diameter than the rest of the side walls. There are some numerical markings on the crown of the piston, but I am not sure what they mean. You can see these in the pictures. Rings- this piston has two rings and a ring expander inside the bottom ring. There was 1/4 inch of damage of both rings near one end of the top and bottom rings. looked to be vertical scratches about .005" deep The free gap measurement on the top ring was 6.68 mm, free gap on the bottom ring was 7.22,, These are roughly in the ballpark. The installed end gaps - top ring .019" with .020 being max. (ring is pushed down into the empty bore and end gap measured) bottom ring .015 with .016" being max The last test is with the rings re-installed on the piston. The gap from the inside of the groove in the piston to the adjacent surface of the ring in the same groove. Top ring .003" Max .0031" Bottom ring:.002 Max .0031" There does not seem to be any wear ring or lip around the upper circumference of the cylinder. It looks like I could almost use another stock piston and rings and a new needle bearing and piston pin and call it good, but the scratches in the bore may not come out with just a hone. As far as the missing needle bearing out of the cage - what do you guys think? I think there was some cyclic vibration with this bike as it warmed up. The vibration seemed to go away after it was warm - So the bearing could have been missing for years I don;t know. I've only had this bike for one year. The other needles look good with no flat spots and the cage is not cracked that I can tell.

Wow that 311 is built much heavier than the original 438. I would imagine that it would not run very smooth because of that. If I do actually need a piston after the inspection, I will go with the Wiseco first try because of the wait time and extra shipping costs. If that does not work then the Wossner. The last option is the Ebay 311's because most of them are the original size and that will not be big enough I don't think.

Thanks SS I will check them out! Does this reply constitute a recommendation as to the quality of the product?

After some searching on Ebay and my local Yamaha bike shop (no help there) I am wondering about my next top end overhaul. I don't ride it much, but I noticed last time out that it was dinging a bit louder than I would like going down hill with the throttle closed. From what I am seeing, the time between overhauls on these 2 strokes is on the order of 30-40 hours! So I'm going to do a compression test as soon as I can fabricate a right angle adapter for my compression gauge hose. The hose I have with the compression gauge is too stiff to allow it to thread into the spark plug hole without risking damage because the frame is centered right above the spark plug hole. When I do run the compresion test, I expect that I will find the compression to be something less than ideal at 99PSI. So the next question is what parts to buy and from where?. The original piston part numbers here are the range of what Yamaha used to provide, but they are all long gone. Yamaha itself was not much help either. 438- 116331-00-96 or 98 (original size) 69.96 mm to 69.98mm 438-11635-00 ist os 70.25mm 438-11636-00 2nd os 70.5mm 438-11637-00 3rd os 70.75mm 438-11638-00 4th os 71mm alternate p/n' from the manual : 434-11630-10, -20, -30,-40 The Wiseco pistons also do not seem to be a direct replacement for the original 438 or 434 part numbers although the rings and ring groove spacing looks about right. Anyway the pictures do not show the holes in the skirt for the exhaust side of the piston. I do have a means of machining the holes if that is something that would be required. The Ebay items are substitutions using the 311 part numbers?, I think these are from the older DT250's or IT 250's?? So what has to be done to a 311 piston to make it work with the TY 250 A? and there are lots of STD (not oversize) pistons on there right now for cheap, but I don't think the standard size would do me any good unless the cylinder could be brought back to standard dimensions by some means?. Nikasil? And since some of you guys have been there done that, I wanted to humbly ask your opinion as to what the best course of action would be?. I know it will be costly, but a new bike is a lot more costly than that, so any ideas and or advice would be much appreciated!. Looking for a smooth running engine that is easy to start and lasts a long time. I have some precision tools that I can measure the bore and piston with, and now the shop manual to read (thanks Jazzyman!) so the next thing will be parts and a good shop to mail my cylinder to for the re-work if that is even possible. I tried to contact B & J racing but it was after hours and I can't tell if they are still doing engine work? Most of their comments about their activities are several years old, so it's hard to tell what is going on there right this minute.

feetup fun, Thanks for all your help and patience! I think my knowledge of this ignition circuit is about 3 times more accurate and easier to work on now as compared to the shop manual. So do you have this same flywheel? If not I could extrapolate from the 21mm and your outside diameter onto this outside diameter and come up with an equivalent number. It would be so much easier than doing the factory style setup.

Feetupfun, Thanks for the clarification! I was wondering because all the comments just said to hook a light across the points with a battery. They didn't say to disconnect anything. Sorry if I got confused. As far as the 21mm measurement on the circumference of the flywheel- I will look for the top dead center tool or make something myself. That sure beats removing the head and then I can put some permanent marks on the flywheel for the next time I need to service the points. Do you know if there were different versions of the outer flywheel ring weight? I am including a picture of my flywheel for your inspection. I am sorry for the inconvenience and my ignorance of the situation. My electronics training kept telling me that the light bulb was not going to see a .8 ohm difference when it was already at full brightness when the points were opening. But if the points wire is disconnected first and another wire is hooked externally to the lamp circuit then you really have got something that is either on or off. No guess work then.

Lefebvre, I use my TY 250A for trial riding like you mentioned you are thinking of doing. The main things to consider for any trail riding (for me anyway) are: #1 Can you stand flat footed on the ground when you are straddling the bike without your body touching the seat? In other words you need at least 1" of clearance for the bike to move under you when you are stopped. If you ride a lot of rough trails and stop a lot then you will need more clearance than 1" Also the TY 175 and TY 250's are built low to the ground. Your Beta 200 says the seat height is 26". Most new motocross and enduro bikes are way too tall for me, so that is why I chose the TY 250. It looks like a baby when parked next to one of those, but as far as control you need the weight to be down low as possible. Recently most manufacturers have been building bikes that you need a step ladder to get on. Not for me at any price! Weight- the Beta you mentioned is super light weight and that is a plus. There is an optional trails bike tank for it, so gas should not be an issue. My TY 250 sips gas at a very low rate of consumption, so I would assume that you only need about 1.5 gallons to get you maybe 60 miles or so? That would be another item to consider. Since gas stations do not sell 2 stroke mix that I know of, your intended riding area needs to include some way of filling up the smallish tank if you want to go farther than 50-60 miles in one direction. #3 High speeds - Power available For most of my life I have had bikes under 450CC's (that was too big) and the ones that I have been injured on were around that size or slightly less. the 450 liked to kick back and needed a compression release which would have fixed that problem, but then I got a 360 CZ which was a screamer and handled like a dream, but I put it into a barbed wire fence and that was where I lost my love of that dual ignition system. Another bike that was too big was the old Honda 360 dual sport. Most of the weight was too high and if you dropped it you needed a buddy to help you pick it back up. sounded great, but too heavy for trails. Then there is the other extreme and that would be anything in the 100-175 cc class. Something under 200 pounds wet. The Hodaka bikes are around 100cc and even though they are small, they are super nimble. If you get in a tight spot you simply pick the whole thing off the ground and turn it around to the direction you want to go! And it was a steel frame! And I think we are talking something less than $6-800 dollars US. None of my buddies with larger bikes could catch me on the Hodaka Ace 100 and they had 250's and 360's while we were running thru the jungles of North Florida. At some point I bought a Husquavarna 250 moto crosser and immediately regretted the close ratio gearbox. The Husky dealer helped me change it to a WR and it became my favorite bike as far as over all. You could do enduros in the desert or you could go thru the woods. I modified the piston and put reed valves in it and then it had a lot more grunt. But while I had the Husky I used to run into a guy with a Penton 125 and he could always run off and leave me in the dust. It was the light weight and low CG that was the difference. Unless he missed a gear shifting that thing, there was no way I could get close to him in the tight stuff. Another question for me was always cost. I am retired now and every dollar counts, so I ended up trading a guitar for this TY250 A which I was happy to do. I think in the states these go for between 750 and 1500 dollars in this vintage and if you find one that runs good, you can't go too far wrong. The 74's are much more plentiful and easy to get parts for, so the 74 model is the one to look for if you go that way. The 75's and later are easier to get, but harder to find some parts for. The production numbers dropped off sharply after 74. The 175's are becoming much more in demand for trials use because of the shorter wheel base and lighter weight. I don't know about parts for these, as I have only been looking at the 250 model A, but If I was going for another bike, I would try and find a 175 to test ride and see if it was something that would be fun. You just have to ride it and see if it feels right to you. My TY is set up for trails not trials, so it has knobbies on it from the previous owner. It also has a cushy seat and lights. (another consideration if you are wanting to be street legal with a title in hand!) This is a BIG question because without a title, there is no way to get street legal and drive to your riding spot on the street. But then again, with around 1.5 gallons in the tank, you may not WANT to drive the bike to the riding area?? However, I don't think there is such a thing as THE PERFECT Bike, so you have to make some compromises and choices. Do you have a pickup truck or a trailer to get the bike to the riding area? Then you don't need to be street legal on the bike itself. This will save you a lot of money if that is a consideration, and I think most cars and trucks can't see motorcycles very well anyway, so I stay off the streets with mine as a mater of safety. Then there is the engine size and speed you are looking for. If you need to go highway speeds, then look more at a 350cc bike. A 250 will do for short stretches, but not every day. The trials bikes get squirrley to ride much above 40 MPH so that might make another difference to you. (Steering geometry is not right for higher speeds.) The knobby tires are great in the mud or loose ground, but are squirrley on the highway especially when stopping fast. Trials tires do better on the pavement than knobbies, and if you are "dual sporting" then go with the trials tires. It all depends on how good you are with the wrenches and your pocket book. If you can try it before you buy it then that is always a good thing to think about it first. Good luck and happy riding!

So is your clutch arm seal installed OK with no leaks now? I had to do mine day before yesterday. Mine is working fine now.

Sorry that is a little confusing. On this engine the points gap translates directly to the "timing". they are one in the same thing, so I agree with you when you say the timing is critical but I have to disagree about the points gap not being critical. There is a direct relationship between the two. If you change the points gap you are also changing the timing. All that being said, the engine will probably run anywhere between .2 and .5 mm gap of the Points? and if my math is working properly this translates to .0078" to .0196" which is in the ballpark of what has been suggested locally at .0016". Too bad that the factory manual has you taking the head off to get .122" of BTDC piston position. This is not easy to do and it is even harder to get the points to actually open at this point because you are forced to work thru a tiny hole in the flywheel. But if you could be so kind as to suggest a way to get a buzzer or a light to work in this scenario, I would be most interested to hear how it is done on this engine. Since the primary ignition coil is almost a dead short to ground and the other end of the winding is hooked directly to the insulated side of the points, then both sides of the points are already almost at ground unless you do something to change that?

If you are using an ohm meter the power for the reading is coming from a battery inside the ohm meter, however the magnetic field and the coils of the mag will be jacking with the ohm meter reading if the flywheel even twitches. This is especially true for a digital ohm meter. All that being said, nobody has yet explained how they hook up the light bulb and battery. I think I have figured out a way using a new wire, but the flywheel has to come off to hook it up and also disconnect the normal wire to the points. So the flywheel has to come off at least twice for all that.

Guys! Well I must have done something right with all the adjustments. The LH crank seal was definitely leaking and there was a few drops of mix under the magneto when the cover was removed, so I know it was leaking from the seal right there. And that leak could have affected the carb air bleed setting, And the old setting was pretty wide open loose, so it might have been compensating for the bad LH crank seal leak. I just screwed it in most all the way and it caused the engine to run at a normal two stroke type of idle. I also adjusted the slide stop screw out a bit and lubed the throttle cable and housing and the twist grip itself. Now the idle is what I would call normal and it does not die if left for a few minutes, so I am super happy about that. Also the engine will just about idle up a hill if you back off the throttle all the way. I love that "tractor" effect and the low end grunt. This bike has the Boysen reed kit on it and they do work well at low revs. Then last night I decided to take a small chance and take it out to my spot in the hills and ride it for a couple of hours to see how it performed. And the more I rode it the better it got, so now it starts w2hen warm on the first kick. It also stopped kicking back for some reason, so now I'm thinking that the carb float might have let too much gas down into the crank case and basically flooded the cases? Otherwise why would running it for a few minutes make any difference to the kickback situation? It does not smell like gas any more, so possibly the float was stuck open (dry) when it was sitting over the winter. I appreciate you guys helping with my lack of understanding about the points timing. I am on a steep learning curve in that respect because I can't forget my electronics training and the idea of the zero point eight ohms for closed and only 1.7 ohms for open. (if you are using an ohm meter to the black wire of the mag wiring harness to ground). That is because the primary coil to ground is already at like 0.8 ohms or less and it is hooked directly to the points!. But now I see how a different circuit could work. Nobody explained the light bulb circuit yet and with just my doodling on a piece of paper it looks like you would have to disconnect the points from the normal wire leading to the mag and hook a new wire from the points to the light bulb center contact, then the shell of the light bulb to the + side of the battery. and the - side of the battery to ground. Now this would work for the light bulb and points, but you would have to tuck a new wire under the flywheel to make it work for timing. Everything under the flywheel is already almost at ground to begin with if you leave it hooked up normally. And the flywheel has to be installed for any of these measurements because the inside of the flywheel has the cam built into it. This means removing the flywheel at least twice. That being said, however, This new wire idea does have the advantage that it isolates the points from the almost grounded mag coils, so you could use a lamp or a buzzer no problem. But that is still an awful lot of work just to get the points set. I like the comment from one of the guys "set the points gap for .015 - .016 at TDC" what could be easier than that? I might swap the points screw out for a metric Allen head bolt next time I change the points out. Much easier to hit the hole in an Allen bolt than the tiny buggered up slot of a 40 year old plain screw! Any body know what the size and pitch are?

Can't be sure from your description, but if the engine is blubbering instead of reving when you open the throttle you might have the air bleed screw out too far or have a bad main crank seal leaking which causes a two way vaccum/pressure leak which causes the mixture from the carb to be mixed with too much air which will misfire or just not make much power. That is assuming that the carb is all clean and good with new NON-Ethanol premium fuel and 50-1 synthetic oil mix or equivalent.

Had to change my left side crank seal because it was leaking fuel vapors from inside the cases. the leak was slow, but the points were fouling out and showing white residue after just 5 or 6 rides of 1 hour each. Not fun to do, but using the sheet metal screw trick on the seal (mine needed two screws) did the trick for removing the seal. RE- lube the crank and the inside of the new seal and tap gently back in with a metal tube of the correct diameter. I will know this year if the new seal holds, and so far no leaks. Wish me luck!