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About Tillerman6

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    Advanced Member

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  • Bike
    Yamaha TY 250 A

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  • Location
    North Idaho (Sagle to be exact)

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  1. So with this teardown and inspection- looks like there are cracks in the clutch basket. And looking at the examples on Ebay, this is a very common problem. Every example on ebay has at least one crack visible, and there are about 5 examples for sale on there right now. Mine looks exactly like most of them, and I'm not sure how to post pictures on here, so if you want to check out what I'm talking about, just go to Ebay and look for ty250 clutch baskets. The crack I noticed first goes directly thru the "9" that is moulded into the part number. Mine is exactly cracked in the identical same place! There is also a crack in the flat steel smooth ring on the other side near the thru hole. None of the ebay examples even show the back side, so I can't show you pics of that, but do you think I need a different clutch basket, or is this a non-issue? I don't think the basket will explode due to high revs, and it has 3 strong rivets that hold it together, but I'm not sure what to do about the "problem" if anything can be done. The clutch was acting a bit strange before the teardown, but that was not the most serious problem (vibration) so I figured that I would check it out later. Well later is now. What is your experiance with this problem and how did you deal with it? I would almost bet anyone that if they have a TY 250 and they take all the clutch plates out of it they will see cracks in the aluminum housing (basket). There seems to be no easy source of new parts for this eitherr.?
  2. Is there any chance that you are missing the ball bearing out of the assembly? I think it rides on the inside end of the pushrod. Also the pushrod is rounded on one end and flat on the other end (at least mine is) and those details are not visible in the diagrams. So it would be possible to get the pushrod in backwards and or forget the ball bearing that rides on the inside end of the pushrod. There is also a spring outside the cases that returns the "cam" rod back to the starting position. If that spring was missing or broken, it would keep the whole mechanism from working.
  3. The rod length for the 74 250A is 125 mm and using the calculator above, the angle you seek is 22.74 degrees on the wheel. That is the starting point anyway. So is your kit from electrex? how do you like it?
  4. I found a piston position/degrees calculator online but you need to know the length of the rod to use it. That should be doable http://www.torqsoft.net/piston-position.html#ex2
  5. the flywheel nut (magneto) gets 4.0- to 4.5 kg-m or 28.9-32.5foot pounds of torque, but you need a special tool to hold on to the flywheel. there are 25.4 mm to an inch. the timing is set with a dial indicator riding on top of the piston with the head removed. the spec is 3.1 +/- 0.15mm BTDC and the engine rotates CCW as viewed from the left side. Who made your electronic ignition kit and how do you like it?
  6. I hear what you are saying about kickback, but it doesn't make sense to me. Let's say the piston is on the way up and it's half an inch from the top dead center and the plug fires. What's it going to do at low rpm? it wants to reverse course because of all that pressure when the gas ignites. Your foot is now indirectly fighting with the piston because you have the starter gear engaged and you are forcing the piston UP. But most likely the explosion will be more powerful than your leg, so you get a little bite from the kickstart lever. So timing is everything and if I am not mistaken, moving the timing so that the spark happens at or just slightly after TDC will reduce the chances of a kickback. Especially if the piston is already on it's way back down the cylinder and the flywheels are moving in the same direction that the kickstarter would spin them. Anyway that has been my experience with engine timing. Last time I did that I think I was at 3.5mm BTDC and it was kicking back about every 10th kick. It had lots of power, but you were always wondering if this was going to be the next episosode or not. Then I decided to try to set it for 2.5mm Btdc and that reduced the kickback tendency by about 50%. it also reduced the available power maybe 20%. in my estimation. So I put it back to 3.5mm BTDC, but on that very crude points system this is only a best guess. I'm probably going to retrofit an electronic ignition as soon as I get the hot setup from you guys. That way you get a system that has automatic timing advance and you are now rid of the fiddling with points and condenser. But just so that i don't offend anyone I want to explain my definition of "advance". To my way of thinking, more advance to the spark timing means that it happens earlier in relation to Top Dead Center. I think this is a universal idea as far as I know. Maybe somebody has another viewpoint, and I am not saying that they are wrong, but just that's what advance means to me. I've never had my engine run backwards under any circumstances except for the times it kicked back and that would only amount to maybe a half revolution in the wrong direction. So does anyone have any good or bad things to say about the elelectrex brand electronic ignition systems from Speed and Sport? or is there another brand that is better in some way? And please forgive me for not sticking to the stock points and condenser. I think I'm all done fighting with that. Let's move on. There is a good video (if old one) about the electrex system being installed onto a TY 250 with a blue painted frame on You Tube. They did not finish the install, but got the major components mounted. It would be nice to hear about the reliability of that system if anyone knows about that system from personal experiance?
  7. So what are the options? It seems pretty iffy to get the timing perfect trying to set the points with a feeler gauge and just a tiny access hole in the magneto wheel, and I am not that strong to give it a mighty kick thru. My chainsaw does the same thing. Thanks very much for the reply!
  8. I watched those and I was amazed. If I can even get my engine back together properly and it runs, I will be very happy. Thanks for the "link"!
  9. I am assuming that since we are in the Yamaha section of the forum that there is some chance that you may have re-built a TY 250A? IF so, are there any tricks to getting everything re-assembled properly? I will have the Tusk puller and probably warm up the cases in my old barbbeque and freeze the crank with some dry ice before I try to put things together, but if there was anything unusual or noteworthy that you remember about your experience, I would love to hear about it.
  10. You might check your TY 250 A model if you still have it and see if the magneto wheel is wobbling with the cover off. I got about .010" of side to side wobble on mine and that ended up requiring a teardown to "parade rest" All the gears and guts are all in small piles on my workbench right now. - not fun. When the crank was out of the engine it turned out to be the culprit, although I can't say if I caused the problem or it was already "spun" when I got the bike. I will also try and test the trueness of the magneto wheel itself when I get the crank back from the rebuilder's shop. Right now there is still a problem with some of the parts suppliers because of the Covid-19 situation. For what it's worth, the stuff on Ebay is pretty much un-affected by any delays. It probably won't affect you if you are not in the States, but Partzilla is reporting delays. Question- Do you think it's possible to add a diode to the wiring harness on my 74 250A like the ones on the 75 and later models? I am still worried about the backfiring /kickback situation I had going on before the vibration problem showed up.
  11. There is an external spring under the engine cases that returns the control arm to the ready position. I had trouble with that once before and was able to remove the arm and replace it and the seal without splitting the cases. But you'll want to drain the transmission oil before you pull out the control arm if you want to work on it. Therre is also an adjuster bolt on the side of the case that sets the end play and that controls how much throw is transferred to the clutch plates when you squeeze the clutch lever. But don't take that adjuster bolt out. I'm not sure the internal parts (a ball bearing and a spring) would stay in place if that adjuster bolt was completely removed. You want to look over the repair manual real close before you do too much tinkering.
  12. I have been trial fitting the cylinder to the empty engine cases to see how the fit is working now that I have a new cylinder. And it went on over the studs but only just. If you put a few pounds of pressure towards the rear it will just slide down over the studs. I spent some time measuring everything and it turns out that the bolt pattern is not rectangular at all. The holes in the cylinder are oversized by .020" and the bolt pattern is actually out of square. None of the distances between the studs are the same. Anyway that's Ok because the holes in the cylinder are out of square the same way. I ordered all new parts for the engine except the piston. It will get all new seals and bearings, new rod and upper and lower needle bearings, washerrs and o ring. Also new pins top and bottom. I's only money and what else could i do to stimulate the economy? i also have been sanding off the rough outside burrs and flashing edges of the castings to improve the appearance slightly. There were several places with sharp edges that are now rounded down to a dull roar. I'm not too worried about the sanding dust getting into the castings now because it wiil get all new bearings later on. I noticed a little corrosion starting inside the front case ears where the front mouninting bolt passes thru. Fortunately this was cleaned out without much problem. The aluminum is stained pretty deep in several places. not sure if it's worth sanding it all out because intend to be riding it more than polishing it. There is quite a bit of cleanup to do to get all the old case sealer off the edges of the castings. I'm using Goof off and a rag for that. Acetone eats up the rubber gloves too fast. I still did not hear from you about how you knew that the weights of the con rods are different between the 74 and 75's? Is it riding weather over there now? Having any fun at all? Probably still no trials meets any time soon? Stay safe!
  13. That's very interesting! I had a similar problem with mine, but I found a couple of things that (on my bike) were bad. #1 was I had a twisted crank shaft, and #2 I had an engine mount broken loose from the frame. I fixed the frame, but I was told by an old timer that the mounting bolts could use beefing up on these bikes- like go to an english sized grade 8 bolt that is stronger. And the factory book has you torque the frame to engine mounting bolts - I doubt if mine were torqued to specs. Note that the front bolt is a different size than the two rear ones. so quoting from the DT250A/360A factory repair manual - the 8mm bolts get 217-251 inch pounds, and the 10mm bolts get 390.6 to 477.4 inch pounds. But how did you find out that the 311-11651-00 from the 74 was heavier than the 431-11651-00 from the 75 TY250B? Could be the pistons are also a different part number and weight- but now you're talking unobtanium.
  14. So the crank is out for an overhaul. I would assume that you use the tube type puller on both ends of the crank? Seems a bit tricky, but some folks are obviously doing it. And what is this about a "flat tool"? By the way have you done this yourself? I mean re-install a crankshaft on a 175?
  15. Lineaway, It might be wishful thinking. But if you are racing every weekend you probably have 3 or 4 bikes and at least one torn down to bare bones at all times. I'm not in that category. This is my first and hopefully last case splitting party, so I have to get it right this time. And I would respectfully disagree with your flat tracker friend about an engine "balancing itself out" if everything else is as straight as possible. What does that mean? As far as I know, a reciprocating engine is never perfectly balanced. And a single cylinder 2 stroke is probably one of the least smooth running engines out there. Of course you can optimize things and make improvements with some expert balancing techniques, but those are also out of my area of expertise. I'm just wanting this thing not to shake the handlebars so hard that it puts my hands to sleep or breaks another lug on the frame!
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