Ossa Mar Airbox Wearholes And Dust Infiltration

[worntorn]

I'm in the process of restoring 2 1972 MARs. One hadn't run in 22 years, the other last ran a couple of years ago. That bike had been sitting for a year or so then was started but only ran for a few minutes before dying. After the bike died, the previous owner could not restart the bike even though he tried many times and many methods. He eventually gave up and sold it to me. It had almost no compression. On removal of the cylinder I found the cause. The rings were worn down to almost nothing and both the bore and the piston were quite scuffed. I've sent the cylinder to Alex Snoop for a rebore and fitment of a 2nd over NOS Tarabusi piston. This bike came to me more or less together but not running, of course. At present I have it stripped right down, having sandblasted the frame which will be powder coated this week, along with the frame for the other 72 MAR.

The bike that had been sitting for 22 years was in pieces, so before the resto I put the engine back together and installed it in the frame to make sure it would run. It started up easily and runs great, although the clutch is stuck (as is the clutch on the other bike).

Today while cleaning the airbox of the bike with the worn out bore I found duct tape on the outside of the airbox. Under the duct tape were two approximately 1/8" wide x 3/4" long holes cut right thru the airbox, one right where the sharp bottom edge of the inside filter screen had been sitting and wearing, the other was right where the back edge of the same screen had been wearing on the airbox. Ahaa! The previous owner said he had been riding the bike in very dusty conditions, so the dust would have been going directly into the motor, entering on the wrong side of the air filter. The duct tape looked new, so the bike likely ran for quite awhile with these open holes in the airbox.

On inspection of the airbox for the other MAR, which appears to have done far less miles, I found the same wear marks and one spot where the screen had worn right throught, although the hole is small, it is there.

So if you have a 72 MAR best check for this problem before you do damage to your motor. I think the later bikes also use the same or a very similar airbox setup with the sharp edged metal screens sandwiching the filter, so it would be good to check this out on your later model bikes as well.

I will repair the damage to the airbox with a fibreglass repair kit and see if I can do something to the edges of the screens so that the problem is not repeated. At the moment I'm thinking of applying a very small bead of silicone around the edge of the screen and allowing it to set before installing the screens.

Glen

[b40rt]

What did we do before silicon & zipties ? Now this is/was progress.