Trials Australia Forums

The OSSA yokes probably did come out of the same mould, but the steering axle holes are in different places, to provide angular offset for the tubes
Montesa 348 yokes are even more economically made - they are cut from thick aluminium plate
The fork oil quantity is something like 180 or 185 ml. I'll have a look at my records tomorrow. I usually measure the depth from the top (125mm) rather than the quantity. Don't use heavy oil or it will have a dead action. The damping actually works in OSSA Betors. I think I used 10 or 15wt fork oil
re the brakes having excessive spring return, I took off the return spring that was on the brake camshaft (on the outside surface of the brake plate) and it lightened it up. Your idea had me thinking that maybe you could fit a spring to the chain tensioner that went to the swingarm rather than the brake shaft, and remove the spring that twists the brake shaft upwards
I've got a theory for why the OSSA fork action is so good too - but not tonight

I did some more work on the MAR today and thought that it might be fun to see if anyone can come up with logical (or not-so-logical) reasons for some of the the bizarre design features they used.

There are quite a few things that are a bit weird, but I thought I might start with the finning on the crankcase. I took this photo with the bashplate removed to show the fins better

Any ideas?

Surely that one is obvious David. By including those fins in the design they can use that much more alloy and thereby increase the mass of that part of the machine. It is very important for inertia and momentum, as well as balance to have significant ballast down low on the bike, so that it keeps the centre of gravity low and helps counteract the pendulous stomachs and bloated nether regions of certain riders.

Oh, and I almost forgot to add: It also makes an excellent place to trap vast amounts of grass, leaves, mud, dirt and the occasional stray wombat, all of which also adds to the total ballast and its effects as described above.

I think your engine mount is Bizzar and prone to breakage. if your engine mount is on the other side in the same position i would put in a long threaded bar with nuts and washers on both sides of each engine mount and frame mount to keep them aligned to prevent uneven wear of the engine mount & frame which in time would snap off from the engine. your wondering what the hell I am talking about I'll put it simple if you are joining a chain you would use a d shackle rather than bolting the two end links together with a bolt.

Having those fins there would keep the fuel cool prior to entering the combustion chamber thus when the fuel is ignited it would expand at a more rapid rate than if hotter. bit of acomparison would be driving at night compared with driving in the day at night the vehicle always goes faster and performs better.

Hey Kombivan, those strange front engine mounts are not my creation, they are yet another bizarre standard feature of the marque.

Mark K, you are obviously being kind to me by not mentioning that the spaces between the crankcase fins are also to catch the oily drool that comes out my exhaust pipe joint to the cylinder

David, those bashplate brackets are meant to be on the outside of the frame downtubes and are arse about face also, at least on a mk2. You can see what I mean from this pic hopefully.


http://www.twnclub.ch/classic_trial_fil ... a1973g.jpg

Thanks Rod, I guess those brackets must be reversible because the bashplate fits fine the way they are in my photo. I'll see if my brackets fit the bashplate just as well the "right" way round

Kombivan wrote:Having those fins there would keep the fuel cool prior to entering the combustion chamber thus when the fuel is ignited it would expand at a more rapid rate than if hotter. bit of acomparison would be driving at night compared with driving in the day at night the vehicle always goes faster and performs better.

I like your theory Kombivan. It makes sense. I wonder why no other manufacturers have picked up on it yet

OK here is another weird thing to consider:
The kickstart lever doesn't look too unusual, a bit long maybe, located on the less common side of the bike for kickstarters, but the thing that I think is really unusual is the gearing of the kickstart. While most two-stroke kickstarts rotate the motor somewhere between one and one-and-a-half revolutions per kick, the manages a bit over three revolutions in 90 degrees of rotation of the kickstart shaft
The first photo shows the point at which my kickstart engages, and the second photo shows where three revolutions is achieved. Yes it does feel pretty weird to use. Why is it made like that?