Ossa Engine Size

[bambam_n_chunx]

Any ossa fans out there know if theres an easy way to identify the engine size of a 70`s mar. Its been suggested mine may not be a 244 as originally thought but a 310. As the bike is running ok at the moment I dont want to take it apart to find out but I would be interested to know.

[woody]

Definitely an earlier (as in pre-green model) 250 barrel. The early 250 barrels had solid fins like yours, the 310 has slots machined into the fins, so visually they are different

From the green bikes the 250 also had the slots machined into the fins so look the same as the 310, therefore not distinguishable externally. You can tell from the stud pattern though, as the studs are spaced wider apart on the 310, although I can't remember the measurements of either

Because of the stud pattern it isn't possible to put a 310 top end onto 250 crankcases, so another way of checking is from the engine number. If that identifies it as 250 then it can't have a 310 top end, so it has to be 250 - and vice versa. Also, the 250 barrel can't be bored out to 310.

This doesn't apply to the Grippers though as both 250 and 310 have same stud pattern

Example of a 310 barrel in this ebay ad.

http://www.ebay.co.uk/itm/OSSA-350-310-Mick-Andrews-Replica-crankcases-barrel-and-head-/321579683442?pt=UK_Motorcycle_Parts&hash=item4adfa48e72

[dadof2]

If you take the exhaust off (quick job) you will be able to measure the bore and stroke accurately enough to tell if its a 310 or a 250.

Stroke is bottom of exhaust port (top of piston at BDC) to the cylinder head joint.

[goudrons]

Hmm, doesn't look much like Mar to me!

Who's cantilever frame is that?

Edited November 13, 2014 by goudrons

[bambam_n_chunx]

Thanks for the replies, I guess its a 244 then, the engine number is 7862** but I guess the frame number is of no importance as it has no B prefix and too many digits.

goudrons, I`m still not 100% on who made the frame, I did post it on here when I bought it but was only told it was a holden bike, I thought someone might have recognised it but i`m never that lucky.

Im hoping to ride it next year once ive given it a good checking over.

[woody]

From the factory, the engine and chassis numbers matched, so the engine number can be used to date it.

Are you sure about that number though as the MAR serial numbers were nowhere near that high

[bambam_n_chunx]

Thats the number stamped on the front right eng mount, theres no prefix on that either so cant be sure its right. It doesnt seem to have been tampered with though.

I had a look for its ID on the ossa world site before my last post but thought the same as you on the high number.

Frame number is 768**241 which seems wrong to me although i`ve nothing to compare it with.

If its an after market frame it could be the original number although if its a converted ossa frame will make it wrong and probably the engine too.

Wheres JR when you need him?

[woody]

Confusing with the frame number as the 76 range is for the 250 Gripper....

The frame itself I can't help you with. I'm not that familiar with the cantilever bikes but that to me, is definitely not a converted Ossa frame, there are too many differences. But the cantilever bikes that had their own frames built also didn't look like that and the swingarms were very different as well.

[goudrons]

The only thing that I've seen that resembles that frame was around 15 years ago when I bought a TY250 off a bloke near Milton Keynes.

He had quite a collection of trials oddities from around that period, one being a cantilever Kawasaki KT250 and the frame and swinging arm was the spit of that in your pics on this and your other thread.

He told me it was a Bob Gollner, how true that is I don't know, though Gollner did make a few Ossa frames around '73, though as far I am aware, without the cantilever.