pmk

Like the idea of larger footpegs. Does anyone have photos of the KX footpegs installed on a MAR, or know the details of how to modify them?

I have never rebuilt an MAR, but do have one of my friends I will be going through very soon. I did notice they bearings are supposed to be a C3 category for tolerance. Consider that when purchasing bearings. If I can find where I read that I will copy and post it. That spec may only be for the crankshaft main bearings.

The work continues. I had no major issues to get the MAR running and have ridden it around the yard. Most if not all of the parts needed are now in hand. The frame is currently being blasted and epoxy primed. In an effort to save some cost, I will paint, rather than powdercoat the frame, swingarm and kickstand. One expense not anticipated was the spokes having aluminum nipples that would not release even after soaking in Kroil penetrating oil. Needing new spokes front and rear had me also replace the hugely flat spotted front rim also. The front rim had also been welded long ago and showed a lot of cracks. Wheels are rebuilt, need to be tensioned and trued. Forks have been rebuilt, totally disassembled, then built up with new seals and dust seals. Silencer / Spark Arrester has been straightened, blasted and repainted. Then reassembled with new packing material and USFS approval highlighted for easy reading. The new replacement parts have been test fitted and are ready to install as the bike builds up. Fuel tank, seat, cables, throttle assembly, tires, tubes, rimlocks and more. Much of the recent effort is removing corrosion and refinishing various parts. Again, not restoring it, making it into a resto mod rider. Keeping the overall look of the original machine while overcoming things like the fiberglass tank and alloy fenders. I think it will be a worthwhile project once completed.

Woody, the OSSA is coming along. Regarding the exhaust center section, I am going to repack it. I have a section of stainless automotive exhaust tubing that matches the OSSA center pipe diameter. Planning to make an access cover that is removable, allowing repacking without any welding required. This will also allow repacking over time if needed and will be an easier task. In regards to the oem OSSA packing material, do you know if it was a stainless steel wool or fibreglass material? I have access to both. Thanks

Excellent humor. I agree the parts will wind up matt finished in time. The Spanish aluminum needed some love to remove light corrosion, and you are correct about the doloop of muck helping the finish from polished to patina. The aluminum mudguards do rank in the same catagory as polishing the skidplate. Not too worried about polishing the skidplates outer surface, just need to polish the inner surface to allow easier cleanup from the leaking oil out of the dumb right side shift shaft stub.

Not restoring. Building a resto mod rider. Trying to keep the 73 theme though. In regards to the aluminum parts, I am not 100% certain on what parts get polished. The fenders /mudguards are plastic, so those will not be polished. Currently I have polished the front and rear rims, front and rear hub ignition side cover, lower fork legs. Next will be the brake backing plates, and clutch cover. These items I am not sure about if they need polishing or a brushed type finish. Triple Clamps? Clutch and front brake levers? Lever perches? Sheet metal aluminum chain mud guard? Skidplate? Rear Sprocket? Anything I forgot?

That sounds how mine is. Clip, washer, spring washer.

Thanks for the lead. Google search worked well. Searched Fantics. Appears this machine is modified with the front forks and wheel, plus the rear wheel off a drum brake Fantic. There are other mods, but that pins down the wheels.

I was sent this photo, pretty certain we know the guy in the photo. What I am curious about is what hubs / brakes are those. The forks do not look stock either. Compared to stock brakes, those seem much larger diameter.

I suspected humor, and accepted it as that. However, I am sure someone here somewhere has done exactly what you posted. Over thars at slow speed. Agree that super powerful brakes may not be vintagey, if that is a word. But seeing the efforts some have taken appears to be a problem needing something. Case in point, this 73 OSSA MAR I have...the rear brake is small with kind of narrow shoes. Add to it the craziest cable setup ever designed. No doubt good enough for some stuff, but as mentioned in another post, it may require steel soles followed by a sparking light show. I suppose modern brakes on both moto and mountain bike are pretty evolved. Seems I am comparing an older drum brake passenger car to modern sport sub compact. New is smaller, lighter and better brakes. But we did survive the older drum brakes and talk about it.

I tend to disagree with the over the bars concept, while possible, that would seem more technique or a brake system with no feel or progression. My asking about brakes being too powerful, is, as I see modern riders hopping about, wedged between rocks, those brakes must be very powerful. For the drum brake vintage machine, is this simply not needed, or is it too powerful of a brake system. As I mentioned, this is new to me. I read mixed comments. What is the truth in all of it?

New to trials stuff, but longtime rider. Silly question, can the drum brakes be too powerful on a vintage machine?

The modern Ohlins like many modern rear shocks often does require special tools to work on. I may be wrong about your specific shock, but most modern shocks operate best and last longer between rebuilds when vacuum bled. As a person with 40 years experience rebuilding suspension, yes almost any rear shock can be rebuilt without vacuum, but vacuum bled if the design supports it, is far superior. The KTM WP, PDS series is a good example of a rear shock that does best being vacuum bled. I designed and built my vacuum bleed equipment about two years prior to the trend of folks selling DIY vacuum bleed setups. Having done vacuum bleeds for about 12 years now, trust, it does do a better service if accomplished correctly. If the damper is not provisioned with a bleed port, a good shop can hand bleed the damper.

Yes there were bug nests inside the silencer, but none in the pipe. Those did fly out once it fired up and I slid the silencer back on.

Ohlins USA is in North Carolina, no shame in a factory rebuild

Schoolboy mistake I made on mine. While cleaning the entire machine of the previous owners last ride dirt in the 80s, I removed the carb and exhaust. I stuffed several paper towels into the intake spigot and exhaust port, then sealed them with duct tape. As i reinstalled the carb, I removed duct tape and paper towel. Installing the exhaust, not all of the paper towel came out. My prestart process had me visually inspect the cylinder wall via the exhaust port, and add two stroke oil, plus many turns of the engine by hand with the kick starter. When I tried to get it fired up, it always acted as if it wanted to run, but refused. Finally, i removed the silencer / spark arrester and gave it a kick. A paper towel flew out 10 feet. Next kick it came to life. No assurance this is the problem, simply a suggestion and means to laugh at myself.

Thank you Woody. That is what I was thinking, but not certain about it.

OK guys, I have read the Jubilee clamp comments a few days ago. Without sounding totally dumb, where is the Jubilee clamp actually located OR is this not an oem part inside the engine? As best I can tell, my own 73 MAR, does not have a Jubilee clamp installed, unless it is between the right side main engine case and the shifter claw that actuates the shift drum. I do recall, when I had the clutch side cover off, placed into a groove in the shift shaft was a snap ring / circlip external type, followed by a flat washer (which could be a hardened thrust washer), followed next by a spring washer, then the side cover. Does this sound correct? If so, where does the jubilee clamp reside? Thanks. I am making progress but have had some other requirements take time away from the OSSA.

Woody and others offered good info. I suspect that you may have forgotten to install the snap ring (I guess Jubilee clip is another name for it) and the thrust washer on the clutch end of the shaft. With those parts missing, the shaft is able to move left, and will see the same problem again. The others posting are well versed in these OSSA machines. I learned about the shift shaft end play when I removed the clutch cover. You mentioned. 1/2" of movement on the shaft. With my clutch side cover removed there is that much end play. With the snap ring and thrust washers fitted correcty, the shaft end play is zero. Try moving the shift shaft outboard, if it can be drawn out of the side case, you may want to remove the side cover and ensure all parts are installed.

Want to add, if you start plotting the leverage ratio curves at various points, you may find many twinshock machines have a very slight almost microscopic rising rate in regards the suspension geometry. If the machine utilized a dual spring or progressive wound spring, it artificially has a rising rate in regards to the spring force. As for gaining a progressive damping curve to artificially accomplish a rising rate of damping, you must look inside certain dampers. Researching the KTM PDS modern off road machine you will find internally they utilize a needle that alters the damping curve based on the dampers position of the shaft. This design not only adds progression but is position sensitive as well. This trials thing is new to me, however dirt bikes are not. My own twinshock I am working to finish as a rider is a 73 OSSA MAR. The original rear coilover shocks were Betors and on the machine when I got it. They had progressive wound springs. On account of corrosion on the shafts, the units have been replaced. The replacements are 10mm longer. Not concerned about that. The shocks are vintage Curnutts. These were a popular upgrade on dirt bikes back in the 70's. Internally these Curnutts use metering needles in some ways similar to the KTM WP PDS. So, my 73 vintage OSSA, with the slightest of slightest mechanical rising rate based on suspension geometry, will artificially produce rising rate on account of progressive wound springs and position sensitive damping within the damper itself. Will it be better or worse, time will tell. FWIW, trying to compare a race car chassis and suspension design to a motorcycle is often not a wise idea. The full chassis dynamics is considerably different in how the wheel movement arcs, the effects of drivetrain squat / anti-squat, and more. The RaceTech text book is a good read and reference book. While I do not agree with everything Paul Thede states, the book is well written and does a good job explainig moto suspension.

Not sure if your reference regarding shock mounting and the angles involves the upper or lower mount? If the lower mount is moved forward on the swingarm that was / is called forwarded mounted. When the upper mount is moved forward, typically that is called laydown. With the travel being not very long, the swingarm arcs are small and it takes a pretty serious excess forward mount to have bad falling rate. Linkage designs are more intricate, based on the location of the pull rod mount points and how much they position and rotate the relay link. The comments about spring rate and proper sag is true. Those factors can take any motorcycle, whether road or off road and make it stellar or a turd. Unless well versed and experienced in suspenion design, leave it stock or with proven link mods and focus more on proper springs and quality damping.

Woody, thanks so much for checking that. No doubt OSSA has a simple low cost method with the O ring, but it does become more complex if leaking. Back in the day, I guess the idea of pulling the engine, and splitting cases for a small leak or replacing a bent shift shaft was no big deal. Possibly I became spoiled by Japanese engines allowing an entire shift shaft to be removed by pulling the side cover and clutch. Regardless,, and with no leak on the right side shift shaft, this MAR is moving forward. Thanks again very much for checking that.

Good info guys. Thanks. The countershaft side seems to not be weeping, but clutch side is weeping slightly. For future planning, if the right side shift spline was cut off and deburred, would the shorter shaft then allow Oring replacement without splitting the cases?

I have a 73 MAR, but it appears many OSSA models are similar regarding the shifter shaft and the O rings that seal the shaft. My MAR has a splined stub on both sides of the engine, and could be run as left or right side shift. The O ring in the clutch cover is easily replaced by removing the clutch cover. With the clutch cover removed, can the shifter shaft be removed to replace the right side O ring or must the cases be split to replace the O ring. When I had the clutch cover removed previously, I noticed there was quite a bit of movement where possibly the shaft could be removed, but I did not attempt it.

In general, gas shock with a seperation device, either bladder or floating piston can be positioned at any angle if serviced correctly or has not lost any fluid. Emulsion gas shocks, that do not isolate the the fluid from gas need to be positioned in accordance with what the manufacturers recommends. As for inverting a shock after it has lost fluid can make the bike feel good during the initial part of suspension movement, but as the suspension compresses further, it is likely there will be no damping to slow the bottoming action, and the shocks themselves will be hammered into useless condition.