pmk

Agree, timing is probably a key to these bikes based on what I read. Based on what Benz wrote a while back, seems a few of these mods could be valid still and while may not increase performance per say, could make it more consistent to ride. I copied the words and info from Benz post a while back. Others may have additional small changes. Sadly, Benz may have been enjoying his bike so much, he never added any more info or sorted out how to post photos. Mods that have been carried out are as follows............. 1) sump guard trimmed on water pump side 2) frame modified so complete rear end,airbox and silencer come off by just removing 4 screws and undo carb rubber 3) thermostate repositioned into water pipe coming from cylinder head 4) beta throttle spring in carb to make throttle lighter 5) larger AJP clutch master cylinder,much lighter than standard 6) carb has been set up by Birkett but as yet i do not know jet sizes 7) reed bloke has been modified,again by Birkett,again i have yet to investigate Benz I did contact Birketts and await a reply Like this

My reading about the bikes here, seemed to indicate the UK machines came with the heavier flywheel and retarded timing. Everywhere else in the world supposedly got the lighter flywheel and advanced timing. The machine I get will be USA version. So I assume, but can check the timing.

Exactly, I had read through many of the Scorpa topics and posts. That one you linked to really caught my interest. Was hoping someone might have more details explaining a bit more in detail for tne less obvious changes. Also read, Birkett removed the studs from the cylinder and used capscrews. This allowed removing the top end without removing the entire engine apparently.

I will probably send an email, but was curious if anyone may know. Sounds as if they took the time and dialed in a few things to make a bike that was deemed very good, even better.

I have read many references to SY250Rs that were modified by Birketts. Unfortunately, nowhere have I seen it posted what all these mods were. Does anyone know what mods were done, and if they could still be viable today or just not cost effective?

eBay an original type.

You might consider carefully polishing the o ring area of the shaft using Scotchbrite or super fine sandpaper. Then, use tne original o ring to get a size for it, then try a firmer rubber compound such as a 90 duro type. Then again, if the case has corrosion pits in the o ring groove, it may be best to modify the case for a seal.

The bike is together, and now has a bit of ride time around the yard. No issues, and very pleased with it. When I went to buy spark plugs weeks ago, I thought I got the correct one. I searched the internet quickly and found recommendations from heat range 8 to 5. I read that BP6ES was correct, and it did cross reference to the ages old Champion N9YC I removed. I now suspect, having seen other references to BP7ES being correct. I have pretty much ruled out the heat range 5 and 8. So, for a 1973 MAR 250, is it a NGK BP6ES or BP7ES? Ready to get the jetting fully sorted out, and prefer to do it on the truly correct plug.

Had a look at how Trailtech does the sensor and magnet install. They glue the magnet to the hub and position the sensor on the brake cable. This is for cable operated drum brakes same as the OSSA MAR of mine. Downside, the Cateye computer I have would need the wires extended, or I need to find a long wire kit. Not really wanting to splice the harness. Done it before on bicycles and those wires are tiny. Need to get by Aldi and see the wireless one they offer.

I saw your photo in another section, I think the machined parts topic. This being a vintage machine, the front brake is cable operated and snakes around a bit. Also, how did you mount the sensor close enough to the magnet on the wheel. Do you have a photo of the fork and wheel setup.

Took a little bit of Google search effort, but no big deal. These computers you mentioned are known as Bikemate brand, and here in the USA are carried by Aldi stores. My thought is Lidl and Aldi may be the same company or related. While traveling a couple of years ago, we did pick up some items in Aldi while in Ireland. Locally, Aldi has a store very close to home. On a downside, Aldi built the warehouse and distribution facility very close to home, and in doing so, tore down a large wooded area I used as a riding area.

I had mounted the computer I dug out of my bicycle stuff. On the OSSA it needed to mount to the left of the left side bar mount. In regards to the magnet and pickup, normally the gap must be pretty close for it to operate. With the sensor nearer the top of the fork leg, how were you able to get the magnet close enough to work.

That method makes it simple, though more expensive. A very good option though. I had a look at GPS bicycle computers, yes there are some lesser brands for less money. Need to ask my bicycle friends if they have something no longer used.

Just went through some mtb stuff I have. Tried to install a wired Cateye. Looks as though the movement of the brake cable will be too much for the wires. Do you have any photos you could share, of how you installed it on the Beta.

Was the Beta a wired or wireless computer. Do you recall what brand?

Since the Department of Motor Vehicles allowed me to get a street legal tag for my Resto Mod 73 OSSA MAR, it just seems correct to have a speedometer. I do not have the wheel driven type that mounts to the fork leg. I do have on hand an ICO Checkmate enduro computer, but consider it may be a bit cumbersome and is overkill on functions. Considering using a bicycle computer. Curious what brands and models others may have used. Is it possible to use a wieless type, or will the ignition cause issues?

I need to replace the O rings on the fork caps of my 73 MAR with Betor forks. The measurements seem to be 3mm x 31mm. Here in the USA metric Orings are not locally common. Also, before I order them, I was hoping someone knew the proper size. Thanks

Not on my OSSA, but my riding buddies 72 250 MAR, he had issues with the clutch pushrod. As mentioned the single steel ball had fallen between the seal and shaft. The ball had been displaced by the previous owner that had rebuilt the engine himself. This placed a slight groove into the clutch pushrod. To resolve the problem, the right side cover was removed. The short rod was withdrawn from the countershaft and as you mentioned, a small magnet found the steel ball. Using a dab of grease, and the bike laid onto its side, the ball and rod were installed, followed by the side cover. Not sure if you are aware, but there is an adjuster on the clutch pressure plate if you find all the parts are properly installed. Possibly the adjuster is not set properly.

The link I posted does have your number on it. Shows it as a 76 350. Not sure why it is green and not red as the list photo shows.

Always solid advice. Thank you for correcting my mis statement about swapping cylinders and crank. As much as I learn about OSSAs, seems the learning curve continues. Thanks for being here, you are a true resource with great info.

I have not done this yet, but was considering it. Costly, though. Has anyone run ARC levers and perches on a vintage bike? These would be the folding style brake or clutch levers with the slipper style perch. Was also considering the hotstart type lever for the perch clamp to be for the compression release. I know, expensive, but seems kind of a sweet setup if it is known to work.

Looks as if the slot for the rear axle was modified as it seems very long. I did notice the wires for the ignition are possible very close to the exhaust by the tank / seat area. Again, neat bike.

I did not see where you posted the frame and engine number. Possibly this was sold as a 250 and later had a 350 crank and cylinder installed. This link is one of the more complete list to ID the OSSA. You need to scroll down through the entire list to see the various 250 and 350 models. http://ossa.2y.net/ossa/bilder/modelos/index.html What is the frame / engine number if you don't mind sharing. Nice looking OSSA. Appears very complete. I think if I were to offer one tip, from my short OSSA experience, immediately and continually lube the spoke nipples with a quality penetrating oil. If the aluminum nipples are seized onto the stainless spokes, they need every bit of help to prevent breaking the spokes.

Not the OSSA tank, aftermarket plastic tank.

Scot, thanks. The fuel tank, one detail not visible or apparent in the photos is to drain the fuel, to prevent the tank from yellowing, I made it so you simply disconnect the fuel line, and then one nut secures the tank. No removal of anything else, fuel can be drained in a minute. Plus, no issues with the fibreglass...