pmk

Agree on not quite following the modified rim idea. According to the Tubliss website, the 18' fits both 1.85" and 2.15" rims.

I did a search and some reading. There were some posts discussing using modern tubeless tires on vintage bikes / rims and how some owners have had issues with the tire dropping off the bead at the low pressures normal run. My 73 OSSA has an Akront rear rim. Unfortunately, probably on account of the slight ding in the rim from the previous owner, my Dunlop D803GP tire is dropping off the rims bead area. The oem Akront rear is a 1.85 width. Dunlop is suggesting a 2.15 width. I purchased a used OSSA wheel assembly from a different model than the MAR and unknowingly, it had the 2.15 wide rim. So, looking for opinions. Stay with the 1.85 wide rim and install the Tubliss setup. Install the 2.15 wide rim, and hope the spoke lengths are acceptable. The wheel was rebuilt recently with new spokes so it should disassemble easy. Then remain running a tube setup. Or go all in with the 2.15 wide rim and Tubliss setup. Consider, the Tubliss setup is specific to each rim width and does not interchage according to part numbers. Although, possibly it is only the width of the special Tubliss rim lock. It seems some have converted to Tubliss, so any info there would be good also.

Not sure which tank you purchased or from what vendor. Simply a FWIW, my buddy purchased an aluminum tank for his MAR. While it looked great, with use he found the tank had a couple of small leaks along the welded edges. The guy we use for welding is aerospace certified. He spent some time welding the tank and would smooth the edge back as it was with no bead of weld showing. Try as he might, the seam would open slighly in another spot. Point being, it appears the edge is a very thin joint after being sanded smooth. Ultimately, I asked our welder to do a nice functional but pleasing to the eye bead around every seam. Once polished the tank looks fine.

In regards to OSSA parts, I have been buying from Alex Snoop in New York. Alex has been great to get stuff from. He recently rebuilt my friends MAR crankshaft, that engine will be going together this fall.

In regards to the Preston Petty fenders, I have been talking with the current owner of Preston Petty Products for a long while now about various topics. Currently, the fenders are not available, but are on the list of things to be offered in the near future. Currently they are selling the MX Front fender which is the old Tony D, the mx rear, the enduro rear fender with light and without light, the headlight, and I believe the front fender with integral bracket to mount to the underside of the lower triple clamp. The modern day Preston Petty Products are molded by Polisport for PPP. The molds and tooling are expensive, but the quality is supposed to be very top level. If I remember, I will share when the fenders are released and ready to ship.

Typically, the resin used is Vinylester. Here in Florida, where boats are common, this resin is easily obtained locally and the cost is not expensive. Currently, I am helping my buddy repair two oem MAR tanks. He has been doing the sanding, and I have been doing and teaching him the glass work. When he returns to Florida this Fall we will finish them. No plans to coat them, but one maybe both were coated previously. To find the leaks, I used a bicycle pump on the tanks vent and sealed the cap with a section of flat rubber. Submerged in a bucket of water, I added a couple PSI slowly with the bike tire pump. As for the aluminum tanks, my buddies MAR currently has one of the Spanish aluminum tanks on it. He bought it new, and from day one it had a leak. Not bad, but it was on the upper seam. He rode it this way a while and just recently had it repaired. Our welder guy is a certified aerospace welder. Even when super cleaned, he commented that the aluminum is a bitch to weld as the original welding was kind of dirty. Ultimately, this aluminum tank was welded with the beads left and not sanded. Plan is to mirror polish it and hopefully not dent it.

Interesting, but are you certain retarded timing causes backwards running. I was always led to understand if the timing is too advanced, the engine kick back and provided the kickstart is not engaged, this is the initial engine firing that sets in motion the backwards direction. After that, the timing is firing after top center, and look out when you let the clutch out.

Photo did not post. Was this the orange bike in Missouri, USA.

Until filled to the top, then the excess will purge out the radiator cap.

Try the Fowlers website for the TYZ, that's your best bet. I assume you are referring to the letter code. Most times, if it is the first piston swap use a B, but they may go as high as D.

Thought you were selling the bike. Seemed like it was sorted out, what happened.

I agree with FeetUpFun, make certain the carb is clean. These bikes do not like any debris in the carb or jets. Next, ensure the throttle and cable are rigged correctly with a small bit of freeplay in the grip with throttle closed. I will add, my own SY recently had some weird stuff happening. Turned out to be the rubber disc in the choke plunger had fallen out of the brass plunger. Not lost, but would randomly reposition itself, the bike ran pretty good, but would die on any descent.

Reading posts here on TC, I was under the impression that one of the mods done to these bikes was replacing the cylinder studs that secure the head with bolts. This was done so the cylinder head could be removed with the engine in the chassis.

I have been looking for it, just no luck yet.

Somewhere on the internet, there is a set of photos about accomplishing this. I thought they were linked on the laptop but apparently not. I searched quickly with no luck. I think the guy is from Italy that did the repack.

Always liked the looks of those bikes. Never seen one in person and not even sure if many made it to the USA. How do they compare to the production bikes of the same ERA, such as the TY and MAR, plus more.

Agree, the OSSA requires the cable be cleaned and lubed constantly, and typically. Most times this is done the day before an event.

If it matters, my friend uses these on his 72 OSSA MAR. Forget his setup, but thought he used the hot start to activate his compression release, with it on the clutch side. Pretty certain, after he stalled and could not refire the motor on a downhill, I think he listened and moved the compression release to the brake side. None the less, he runs these levers. My OSSA uses the oem Amal levers, not endorsing them, just saying. https://msracing.com/hard-parts/controls/levers-and-perches/aof-clutch-lever-assembly.html

No changes made yet. Thought this was interesting. Was asked to inspect cylinders of a friends RD Yamaha. Cylinders inspected good, but has a drilled hole above the exhaust port. Photo later after I resize it.

Your photos are accurate. Yes, it appears the split lockwasher has failed and broken into two halves. You should take the extra effort to replace the seal. My MAR had the original seals in it, and they slid out with little more than finger pressure. On these OSSA engines, what is confusing is that what appears to be a washer is not. The entire spline comes off the crankshaft. Most modern bikes have the spline machined as part of the crankshaft. The puller is reasonably priced and must be used to remove the short spline adapter shaft. From the washer as you call it to the top of the spline will come off.

Pretty much the same type tool we bought from Alex Snoop in New York

Agree, you must have the puller to even consider reusing the part. Even with the correct puller, the cush drive spline on my 73 MAR still broke during removal. The shaft and cush drive spline are a tapered fit with no keys or driving locks. Simply tne tapers press fit, by tensioning the bolt secures it on the crankshaft. As you go back together with it, proper torque is a must for not only the cush drive spline but also the flywheel, and clutch basket. My buddies MAR with a previous owner homebuilt engine overhaul died and would not run, after a bit of troubleshooting, I sorted out the flywheel had sheared the key. Essentially, the flywheel was not properly tightened. I explained to my friend, after seeing the flywheel issue, and several other issues, we needed to check the torque on other stuff. Sure enough, the cush drive was not tight, and tne chutch nut was finger tight.

Don’t like the bike or just trying to flip it? Recently, an SY250r was advertised for $3800 USD. Not sure if it sold, or what it sold for, but the price seemed agressively optimistic for the bike in the condition it was in. Mine is pretty well sorted out now and actually, as posts here and on other sites mention, these are a grat bike for new riders and most riders up into intermediate levels. While I enjoy wishing I had a new bike, reality is, this bike is far more capable than I am. Plus, they seem to be a good value. Currently, mine is getting new brake and clutch hoses, new throttle cable, had to replace a recently failed thermostat switch, so the new style is installed now. Planning to install a new super flexy rear mudguard, while sealing the airbox better against water, plus adding a quick drain incase I suspect water entered the airbox. It does run very good now that I dialed in the jetting, I want to measure the ignition timing setting. This is a USA SY250R and it seems the manuals timing spec is possibly for the UK bikes. Time will tell where the numbers come in at. Likely I may slight adjust the timing to retard it. Just to get less flameout that randomly happens while riding. As is though, super smooth, and very tractable with electric motor type power.

Looks very nice. Want to ask, did you tie wrap the rear mudguard at the bolt holes? Curious if you drilled the airbox as that lets in unfiltered air.

When are you planning to share photos of this masterpiece?????????