Tillerman6

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?

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!

Bultobi Well noted ! And I soon realized that this was way over my head, so I sent the crank out for an overhaul along with the piston, rings and pin and circlips. In case they want to weigh them or if there is any question about the small end of the con rod. The specs are in the DT250/DT360 1974 shop manual, and that was enough information to find out that the crank was spun. To me this means that the two ends of the crank are not concentric. But the manual was a little ambiguous. They show the specs for each end as .0012" max runout and a - line for the runout (reference ?) on the weight circumferences. So you could theoretically zero your DTI on the weight circumference and take the reading off each bearing journal. But that would not neccessarily make any sense because like you said, the weights could be non-concentric with their own respective weights and that still would not give you a reading that would be useful. So I just Zeroed the clutch end in my 4 jaw and took the reading on the other end. I got .005" total runout which is a bit too much. There was also a tiny bit of squeeze to the weights. I.E. the gap between the weights near the bottom end was different than the gap at the other side by about /004". Hopefully that will all get sorted out. I don't know exactly when the damage occured either. I am probably the 3rd owner, so no telling. but I do know that this engine of mine likes to backfire on occasion. I'm thinking of adding a diode into the wiring harness like the 75 models have.. That might make a difference. I will be making or purchasing some tools to pull the crank back into the cases. I can see now that the crank is not bullet proof, so it needs some TLC like everything else. There is now a set of pusher and puller tools on the internet that seem to be nearly an exact copy of the Yamaha tooling that is shown in the shop manual. These are made by TUSK and there are even demos on You tube where you can watch them being used. I think the install tool is about 65.00 US and same for the puller. But I have a nice lathe, so I'll be doing it the hard way of course! Tillerman6

Bultobill, That seems doable,but I don't have any confidence that it will stay in position unless the pins are welded or pinned in place, so I sent it off to be rebuilt. The pins are just a press fit and the bike has a tendency to backfire when starting, so there is considerable strain on the pin to flyweight junction. When I checked the runout, the specifications are very tight IMHO, so there was no wobble you could see just by looking, it was only when you put a dial test indicator against the flyweight circumference that you could see a .002" runout on one side and a .003" runout on the other side. And the spec is .0012 left or right. But I do want to ask you- what has been your experience with this sort of fix? It's a lot of trouble to tear down the bike again if something slips. Special tools, new gaskets, and possible bearing damage plus too much down time and expense. The case halves are also sealed up with a sealant after a repair like this, so there is that sealant to deal with as well

So now it looks like the crankshaft is out of tolerance for "Deflection Tolerance". Basically the crank is "spun" as the engine rebuilders like to say.. So in simpler terms, the left end of the crank is not lined up with the right end. The tolerance in the shop manual is only 0.0012" per side and I've got .005" of runout total. Does anyone have any experiance with "tapping" the crank halves back into alignment?

So today I mounted the crank in my lathe between centers to get an idea of any problems before I start ordering parts (mostly new seals). i didn't get very far and the wife wanted to put up a dog fence, so off we went. After we installed the fence I was pretty tired and just putzed with the front fender mounts. This bike has the forks off a DT or an YZ, so there are no mounting points for the bolts that hold the front fender on. So I made up some new split ring clamp on ones from scratch. But they were too tight and I spent all afternoon fitting them to the fork legs. So that's done, but I still have to mount the aftermarket fender. This type of fender is traditional on the TY's but I don't have one to copy. Do you know about how much room there is between the front tire and the inside of the front fender? It will be tricky to get the spacing right with that slippery plastic fender so I've got the bike on the corner of my table top work bench with the front forks hanging off the edge. If I put the front wheel on, it should be possible to figure out where to drill the holes (I hope) Tools- for the crank installation tool - The manual has no dimensions for the Yamaha tool, But it looks like the tube tool sits over the left end of the crank and rests on the inner race of the main bearing? That way there is minimum strain on the bearing. but you need a threaded rod with a female nut on the business end to attach to the magneto end of the crank and another nut to take up the slack. I have not had a chance to unpack all the little paper packages of engine parts I got back from B & j engineering. I'm hoping everything is there. Some of the shop manuals show a shim that goes on the right end of the crank, but some others don't. Did your 250 have a shim on the right end of the crank? it would be right against the right hand flyweight if it is there at all. But don't bother looking if your engine is not torn down of course!! Tillerman6

Majesty- That was still a big help! The TY manual You sent said on page34 that the engine overhaul information is actually in the DT250A/DT360A 1974 manual. I found a digital download on Ebay for $7.00 Apparently the DT series is pretty close to the TY series in the 1974 model year.

Feetup Fun and Majesty, Great advice and nice book! Majesty- looks like I need the DT250A/360A Service Manual after all. Feetup fun- I will take a closer look and see if my tubing stock is about right for that tooling.

Don't know where you live, but in the states they sell a product for preserving the gas in fuel tanks. It's called "STABIL". It works fine for all gas engines. 4 stroke or 2 stroke- your gas should last at least 6 months or more if you slosh it around a bit when you mix it into the tank. One ounce of Stabil will treat about gallon of gas.

So with all this unwanted "time off" I decided to try and put my old TY 250A back together. I don't have a shop manual for the A, just the B model, and the B model shop manual calls for 3 special tools to re-install the crankshaft. Spacer (looks like a very large washer) P/N 90890-01016 Crank Shaft Setting Pot P/N 90890-01012 - Looks like a tube about 6" long and 1.5" diameter with a large flange at one end. Crank Shaft Setting Tool P/N 90890-01017 Looks like a special threaded rod about 6" long. All this can be seen on page 110 of the TY250B shop manual from Cycleserv publications, but I don't know if these tools will work on the A model or not? Also- I have a lathe and a mill- If somebody has the time- can you please measure your tools and let me know the dimensions? I could make my own most likely. Much thanks for any advice or tips that you may have! Tillerman6 po

So to answer my own question about the TY250A ignition- years later, but better late than never. It's relatively simple. There are only two coils that matter for the ignition. One is the large left hand single winding inside the magneto, and the other is the High voltage coil which is tapped with one side to a short number of turns leading to ground. Above the tap, there are a large number of turns that develop the high voltage for the spark. Both coils are in parallel, and one end of each one is grounded to the frame, so the resistance to ground is VERY low. When the tapped side of the HV coil is hooked to the source coil, the total resistance to ground is about 0.75 Ohms. That is measured with the points open and the kill switch set to run (also open). The magneto (source coil) provides the inductive kick at a very low voltage, and lives inside the flywheel. Physically the ignition wiring is fairly simple, and since I am not running any lights, I am only going to mention the ignition wires specifically. Over the years it looks like my wiring harness has seen some changes. In that regard there is one area that I had to remedy to get the bike to run. That was the area between the Magneto output and the input to the wiring harness. Unfortunately both of these wires have a female connector on the end. So I took a small male-to male jumper I had left over from the headlight installation and jumpered the Magneto output to the female black wire leading to the HV coil primary tap. The other leg of the Y comes in from the kill switch. There is another black ground wire in the harness with a male on the bottom end nearest the magneto. The top end of it leads to a ground lug which is thru-bolted to the frame. I just taped it off near the magneto end, as I am not using it. If anyone has any questions- fire away!

Junglejeff, thanks for the reply. One major problem with piston replacements is weight change. The yz piston is 30 grams heavier than the TY so unless you do some major magic, it’s gonna vibrate like hell. I’m about half affraid to open the box from B&J as he has it apart and says he cant’ figure out what to do If I can make the special tools to put the cases back together I will try that. If not, it’s going to get sold for parts. Nobody is gonna hold my engine for ransom any more

Duly noted and I ended up spraying it myself with automotive paint. Glad I didn't powder coat after all! Thinking of following that with a clear coat before re- assembly if I ever get the engine back and back together. Arrrrgggghhh!

Tony- Thanks for that input, but I found that just by warming up the rubber coupling with a hair dryer it comes back to life and you can still use it. - Don't get it too hot, but even warm water should be enough to soften the material and it becomes stretchy and not prone to crack again. Good luck!

I went ahead and used the automotive paint on most of the frame. Should have sanded it more. A little rough to the touch now. But that's the least of my problems with this bike. The engine has been in limbo at B&J racing since April, so I'm having him send it back to me AS IS. I don't think I will worry about the paint if the engine is toast.

Well it's been April 21 to July 11. My lower engine cases were sent to B&J racing in Tennessee for a look see. After all that time- no joy. The owner said he didn't have time to put the crank in his lathe and check it out completely and he doesn't know where the metal chips he found inside came from. Apparently it was not a good time to send my engine to him. He had some serious family child illness and several trials events occurred during that time, so I guess I can't be too unhappy about the delay, but not having any idea about when my engine would be fixed was too much for me. They are super busy. So I am having him send me back the engine as is. They also did not find any pin from the needle bearing inside, so at least it was not in there doing nasty things to the innards. I am going to withhold judgement on B& J until I see what's been done and what I can do to fix it myself. If there is not too much damage, I will be trying to fabricate or borrow the tooling needed to re-assemble the engine case halves. If anyone has done this operation with the factory tools or equivalent, I would very much like to hear about the process and the tools needed.

Sorry it took me so long to get back to the question of seal replacement- You guys are great for making these comments! I feel a lot better after reading that I am not the only one having difficulty putting in the All Balls Racing seals. - I am lucky to have some precision tools to scope things out. So after getting one seal stuck half way in and half way out, I decided to measure everything and see what was actually going on with the fit between the seals and the slider inside diameter.- As Feeetup fun said, the new seals from AllBalls racing have a moulded ridge near the bottom which protrudes out around the circumference .This protrusion seems to be mostly "flashing" from the plastic moulding process, and I managed to trim most of it off with sandpaper at first. I wanted to get a micrometer reading on the OD. Much to my surprise it was .008" oversize for the bore of the sliders! And the sliders were not out of round, but the seals are not concentric. So after much dissapointment and considering my options, I decided to grind down the plastic seal OD to a point where it would go into the slider tube without destroying itself or the slider tube. I have a Dremel hand piece with a flex shaft and I put a standard coarse sandpaper drum on the handpiece and then put the handpiece in the tool holder for my Southbend Lathe. This gave me a steady and controllable way to reduce the diameter of the seal( oh I forgot to mention I made a 34mm mandrel on the lathe and mounted the seals on it while grinding down the OD of the seals. I was pretty surprised to find that the seals were several thousandths out of concenticity as well as being oversized. So as the grinding progressed - very quickly I was down to just .0015" oversize and I decided to stop there. Good thing I did becase any more and the seals would have probably been too loose of a fit to withstand the oil and air pressure changes that they will see in use.

Well, more seal problems- the All Balls seals jammed half way into the seats on the fork tubes and had to be removed. I made a male plug the same size as the fork slider and plugged up the bottom end with a threaded thick aluminum washer. this lead out to another washer on the outside bottom end and another nut. this sealed up the bottom end and I poured the fork leg full of water. Then with the fork tube in special jaws on the vise I put the male plug thru the seal and it rested on the water inside the tube. the seal kept the water inside when I hit the top of the special plug with a hammer. After a few whacks with a 5 pound mallet, the seal was pushed out from the inside by the hydraulic pressure. There was still some damage to the outside of the seal, but the fork tube did not get any scratches from a wrench or screwdriver this way. Now I am wondering if I can grind down the seals to a more reasonable diameter. The fork sliders are 45.999mm on the ID or 1.810" but the seals are .012" oversize or 1.822". Any ideas? I know they are supposed to be tight, but the seals are not just rubber. Has any of you guys ever run into this problem before?

Well, more seal problems- the All Balls seals jammed half way into the seats on the fork tubes and had to be removed. I made a male plug the same size as the fork tube and plugged up the bottom end with a threaded thick aluminum washer. this lead out to another washer on the outside bottom end and another nut. this sealed up the bottom end and I poured the fork leg full of water. Then with the fork tube in special jaws on the vise I put the male plug thru the seal and it rested on the water inside the tube. the seal kept the water inside when I hit the top of the plug with a hammer. After a few whacks with a 5 pound mallet, the seal was pushed out from the inside by the hydraulic pressure. There was still some damage to the outside of the seal, but the fork tube did not get any scratches from a wrench or screwdriver this way. Now I am wondering if I can grind down the seals to a more reasonable diameter. The fork tubes are 45.999mm on the ID or 1.810" but the seals are .012" oversize or 1.822". Any ideas? I know they are supposed to be tight, but the seals are not just rubber. Has any of you guys ever run into this problem before?

Kind of a generic problem I think. the fork sliders are from a 75 DT 250 and the seals are aftermarket from "All Balls Racing". The online instructions say to use a fork seal driver. Or if you don't have one of those, use a piece of PVC pipe split in half and put back together with a hose clamp. It looks like the fork tube is also inserted into the slider at the time that the fork seals are driven home. Well, I did it another way with a male plug with a shoulder at the top just slightly smaller than the seal OD on the top end and just slightly smaller than the inner bushing on the inside of the slider.- Then hammered on the bushing I made which should have driven the seal in straight. It was well lubed and so was the fork tube, but the seal refuses to seat all the way. I'm hitting the driver I made pretty hard, but the seal is stuck about flush with the top edge of the slider. Any ideas? Are all seals this tight?

Had a frustrating morning this morning as the seals I bought on Amazon did not fit the fork tubes. The fitment list said they would work, but did not. And they want about 40.00 US for each seal if you buy OEM seals from Yamaha 584-23145-50-00 for the 75 DT250. So I am trying a set from All Balls. For 30 bucks you get 2 seals and 2 dust covers. Hope they fit. I almost wrecked one of my fork sliders trying to get the first ones installed. It had a steel outer ring and it was .006" too big for the fork slider GRRRRRRRRRRRRRRRR! So it's going back. Live and learn. The next ones do not have the steel ring on the OD, so if they don't fit at least it will not damage the inside of the tube.

Feetupfun, I think actually I like the MX/YZ backing plates better since I'm not running a speedo. They sure made a lot of different versions over the years! Those shoes of yours marked 401 are from a MX 125 originally and you could look for more shoes on Ebay or whatever from that bike and that's how I got my new shoes that are on my bike now. They were brand new and not all that expensive on Ebay. They were not 401 series but something close. I checked out the Racetech Gold fork valves and looks like they don't make a version that will fit the 75 DT 250 B/C forks. I think the do make something for the MX/YZ forks in some years. So are you machining down the new shoes to fit the drum housings better, or you have found a source of brake shoe material and scrape off the old ones and somehow attach the new ones yourself? If I get rich I could email Race Tech and see if they could send me a set of valves that had not been sized for another application. Possibly I could thread them and adapt them to my forks? Do they go inside the forks or sit on top?

While we are on the subject of tracing parts back to their parent machines, I remembered that I had a "Yamaha Cross reference Index file on my computer. I can't seem to get it to copy and send to the Trials Central website, but I'm working on that. I think everyone that has an old Yamaha should have that information available. It's really just a list of the first 3 digits of the Yamaha part numbers and a "Tag" name for each one. The first 3 digits are code for the original bike that the parts were built for. Other bikes use the same parts later on, but having the 3 digit code on a part tells you what other bike the parts were originally used on. That way you can look up that year and model on Ebay or whatever under the original year and model and possibly find your missing parts that way. For instance, the part numbers beginning with 434 were TY parts. My brake shoes off the front wheel were 322 which was from an RT2 MR ( maybe a street bike?) I used Windows Photo Viewer to open these. Hope this helps! I will keep trying.

Rim pic below. I's a DID rim. So are the "speedo drive lugs" right near the axle on the side away from the brake drum? 3 little tabs that stick out just a little? Did a little painting of the frame today. It's supposed to rain for 3 days starting tomorrow, so I had to get that going. Handlebar risers just need longer bolts to finish up.

Well the UPS truck brought the new front tire today and I put it on the rim today. (pics below) The rim itself is a 21 x 1.6 after all. Apparently they measure between the rim edges on the inside and not the outside. The brake drum diameter is 130mm if that helps any. The shoes are marked "322-00". I was surprised at the weight of the new trials Dunlop D803GP at around 7 pounds whereas the knobby I took off was only about 6 pounds! Anyway, the width of the rim is probably the same as a TY rim at 1.6", so the weight of the wheel should fall in close to the TY wheel overall. The brake backing plate is magnesium, so that will not be a factor. I think the OD of the shoes will be very close to the 130mm ID of the brake hub if that helps any..