pmk

For whatever reason, the InMotion website no longer loads or directs to the site from my laptop or IPad. Anyone know what is going on with them?

As for the Curnutts being overdamped, the recommended oil was Type A transmission fluid. Seems Curnutt even recommended a mixture of Type A tranmission fluid and Diesel fuel. With so many fluids and weights available today, and the pretty basic design, I think they will respond well to different viscosities. The metering rods appear to engage well into the shock stroke, basically the great grandfather of the KTM White Power No linkage PDS. Regardless it will be fun.

Do you happen to know who has seals? The one pair of my MAR have badly pitted shafts, but good everything else. The pair my friend has were hammered and the pot metal sealheads are shattered. His shafts are not perfect, but should polish up ok I hope since that will be a display bike. My friends second MAR will be his rider. Like mine it will not have stock rear shocks or a stock carb. Ultimately, we should have two fun MAR riders.

The budget on cost was perfect, so no loss in trying the Curnutts. No doubt, The spring rates may be a big factor unless the oem Betor springs could be salvaged and made to work. As for Curnutt damping, I have rebuilt many shocks but these will be my first Curnutts. I also got a set of probably first generation Works Performance shocks. Those would need springs in order to work and the cooling fins will probably be a concern unless I cut a good portion of them off. Time will tell how it comes together.

Still moving forward. Guess I am doing a restomod as they call it with cars. Got a Clarke plastic tank in white. Broke the budget and ordered a Smartcarb. Got a box today with vintage shocks, probably going to install Curnutts. The rest will hopefully be ordered soon and seems available. Any thoughts on the Curnutt shocks? I also got a pair of very early Works Performance shocks, those would need softer springs and not so sure the finned bodies would fit well. Need to add, some of the items off my bike are headed towards my friends MAR he is making original. IZD single needle carb, 4 shocks hoping to make two originals, original headlight and wire harness, etc.

Local ACE Hardware had 7mm hex head bolts in stock. Not ideal, but fine for getting the skidplate back on and being able to safely keep it on the stand to work on it. Thanks everyone.

Good info on Menards. Those stores are not in this area, but we do have one local hardware chain that may carry them. I have been checking Fastenal also. These skid plate bolts are oddballs. Before I get too crazy, I think checking with some of the OSSA parts guys here in the USA may be best. I will post how it is sorted out.

Thanks Woody and others for the reply. I have been looking at EBay, Fastenal and several other online sources with minimal luck. Since I am doing this bike kind of restomod, rather than restoring it, it may be easiest to do as you suggest and convert to 8mm at all mount locations.

Here in the US, 7mm fasteners are not common. Not that I need many, but is there a reasonably priced source for this size fastener. The real oddballs I need, since I had to drill them to remove the skidplate, are the 7mm flush head slotted screws.

In regards to the Pirelli MT43, no doubt there are mixed comments about the history and different variations over the years. So, I recently acqired a 73 OSSA MAR. It still has the square block MT43 tires on it but they need replacing. Seeing as this machine is kind of porky with a claimed weight about 50 pounds more than a modern bike, anyone have opinions on if these older machines should use the older style tires with a more rigid casing or go with the more modern lighter tires? At the moment, if the bike is used for any competition, it will be fun based, primary plan is fun riding with a friend who also has a 72 MAR.

Guys, thanks for the replies. The machine I have is a vintage OSSA MAR, so the rear travel is pretty short travel. As original it has a springloaded tensioner with rubber type material slide block. Seems the slider style is still viable as they are used on modern machines also.

Kind of as the title mentions, newbie question. I notice it seems the chain tensioners, whether on a modern bike or vintage machine use a non roller style wear block. Is there a valid reason for the slide to be preferred over rollers?

Good option.

My 73 MAR 250 has an IZD carb installed on it. This was what came stock on these machines. I am compiling a list of items needed, all cables are needed. Problem is, no where do I see the cable to go from the Amal throttle to an IZD carb. Would it be the same cable ad for an Amal carb or Bing?

After getting it running today, it is appaarent that the exhaust note is a bit harsh. Without doubt the spark arrester / silencer needs repacking. As for the mid pipe, I plan to rework that and repack it also.

Spent some time today doing the common clean the carb, lube cables and assemble it enough to see if it runs. After a bit of verifing spark, ensuring fuel she would give that poof like it wanted to run. Accidentally, I overlooked a paper towel in the head pipe, and that poof just sound like a plugged exhaust, some since the slincer had not been cleaned or verified clear, I pulled it thinking it was plugged up. So my care while washing and that paper towel had moved into the mid pipe stinger. Next kick it blew the paper towel out and fired up. Ran it several times on the stand. Engine sounded good with no bad sounds. Next, I will give it a couple easy runs to ensure the gearbox feels good under a load. After that, it comes appart for some cosmetic refinishing, and I plan to split the cases, replacing seals and bearings, with hopefully no issues on internal stuff. So at this point, it looks like she will be a nice machine, not restored but for riding while keeping the vintage theme.

The Motoplat, even after the abuse of sitting and corroding, cleaned up and fired the spark plug allowing it to run.

Found it. As mentioned, the case breathes via a small passageway at the center case screwhead above the countershaft.

Mine has the single needle IZD carb. Original owner mentioned it ran well with it for many years.

Mark, I had plans to do a case leakage test, but held off for the moment. When I removed the flywheel and stator, I noticed the crank seal sitting a bit proud. I did not mess with it at the time, simply went about cleaning the yuck from that area before placing the stator and flywheel back on. Curious, beyond the simply mark the stator to reinstall it, and wanting to read how the timing is set I browsed through the manuals, both my Clymer and the online version. As I read, I payed close attention to the photos that showed the seal and the text read the seal should be flush with the case. Not sure if the original owner installed a thicker seal or what, I did not want to set it flush. Rather I grabbed the seal with my super short finger nails and it pulled right out. Basically, the stator backing plate retained the seal from completely coming out. I cleaned the seal and for the initial test run, reinstalled it flush. I am not sure why the seal was sitting proud. Possibly the bike was sunk and water filled the bottom end, popping the seal out. Maybe, since the flywheel and stator had been removed previously, the seal was replaced and never seated. I honestly don't know. My friend I got the bike from told me as we loaded it up, she probably needs rings or a top end since it was down on power last time he rode it. Maybe the seal was leaking and it was one of those lean enough to need jetting but not lean enough to quit running. Again I don't know. At this point, once I know the ignition is good, carb is ok, and it at least fires up, It will come back apart, changing those seals and others at a minimum but probably split the cases and do more. Simply time will tell, it all adds up. Tires, cables, shocks, fork seals, paint work, fuel tank(?), chain tensioner stuff and maybe more. Best part is the parts are out there. Still have not gotten my 81 KTM 495 back together yet. Some of it on parts availability, some on simply refusing to pay far more than fair market value from dealers and private sellers.

Yes, it does have matching numbers and I agree parts are available. The possible wrench in the works is how much it will cost to make good vs what it is worth. I am not really into making it a perfect restoration, rather a nice rider that retains the look and ambiance of a vintage trials bike, I think...

I first will say I appreciate the experience and knowledge here. I grew up riding when these machines were being made, but never considered them as I was a kid growing up racing MX when the Japanese bikes arrived and became dominant. Fast forward to 2016, I wanted a trials bike. Many reasons why. My good friend and riding buddy purchased a 72 MAR about a year ago that was supposedly very nice. He learned it was good but lacking in the fine details and he does not have or own junk. A few weeks ago, knowing he needed some original parts, I noticed another MAR on a Facebook group that was for sale reasonably inexpensive. He acquired it. So he had plans to build a very original machine with original parts, and a second rider. His words were that of we could ride together. During the time while his second bike was in transit, the wife and I travelled for both family stuff and vacation. The wife and I ride tandem bicycles, both on road and tandem mountain bike. During an event, I spent time with a friend and his wife. With a combined age of my friends at 160 years, it is always fun to see them and ride with them. They still to this day ride a tandem mountain bike off road. During one of the meal gathering, I was talking with my tandem mtb riding friend, and long time dirt bike rider, about trials bikes. He knew I wanted one, and we discussed my local friends two MARs. He informed me he had one that he had purchased new in 1972. He had ridden it a bunch, but his wife also told me it was her favorite dirt bike of all those she rode. The following morning, they insisted I pick up the MAR and if possible bring new life into it, or if beyond reasonable effort and expense to get going, use parts as needed to build one of the other two into a more original machine. So we drove to their home on our return trip to Florida, and picked up the MAR. It had been sitting for a while, stored outside, but had been run randomly but not in a while. The owner said the last time he rode it the clutch was stuck and would not release. She is rough cosmetically, but viable still at the moment. Ironically the engine is free and smooth.

I have studied the parts diagram and notice there is a plastic tube inside the gearbox with slotted ends that serves as a gearbox breather. In my cleaning up of this old machine, removing concrete like mud, I have yet to find where this breather vents to ambient outside air. Could someone please explain where the gearbox breather vents externally? Thanks

Agree, the taper must not be abrasive blasted or cad plated. I considered this before removing corrosion. It will be possible to install a bolt through a washer, then through a rubber washer, through the flywheel taper, then a rubber washer followed by a washer and nut. This once tightened will seal the taper from abrasive grit blasting and the liquid cadmium bath. Previously I worked in an aircraft propeller repair shop. I will use them to replate the items needed and should be minimal cost if any. So I think plating it should be done, especially since where I live, here in Florida the humidity is high any everything rusts. As for the added vent, I had read about people doing this. Since the previous owner had some type of failure that cracked / broke the side cover top to bottom just aft of the clutch actuator, the case will be repaired and is a viable candidate to be modified after welding.

Photo before corrosion was removed and after removed.