After more thought and review of manufacturers presentations, a few industry white papers, and some wiki articles I'd like to offer a bit more on Pat's Sportsman 200, and vibration, at whatever level may exist.
I like the look of 'board track' styled bikes very much, and Sportscarpat has shown himself to be an excellent craftsman.
That being said, for me, a boardtracker would be just about un-rideable for anything longer than a few minutes! I take short hops on my cruiser styled mab, and that's about all my lower back will take. lol
Perhaps I should complete fabrication of my 'bent' bike and see how that works out...
Never-the-less, I feel that if I failed to comment on any presentation here at MotorBicycling.com, a most valuable aspect of the forum would be squandered.
As there is no perfection in design or construction, IMO, every artist or mechanic can hopefully benefit from constructive criticism.
If one sole aspect of my commentary is beneficial to any builder, I would be pleased, and sleep well! lol
Suggestion of isolators is valuable and certainly worthy of consideration. The pictures of the mab with an isolator mounted power unit are very nice. It must be smooth as a BMW!
The Barry elastomer isolator info is from the aircraft industry where catastrophic failure of aluminum becomes problematic after a finite number of cycles which, apparently, can be calculated.
Best information I have reviewed indicates there is some engineering point where this phenomena does not exist in fabrication with steel.
Here's the Barry Control pdf for their Double Stud series isolators:
http://www.barrycontrols.com/UserFi...ud/bcdi_prod_cylindrical_stud_double_stud.pdf
They manufacture a number of other configurations.
Perhaps the number of vibration cycles acrued would be reached in this MAB application, causing failure of the motor mount attachment points on the engine casing itself. If that were the case, employment of isolators could be in order, from that viewpoint.
Otherwise, IMO, improvement to a number of Pat's design aspects would be of great benefit.
...rolling the engine forward about 10 degrees, effectively lowering the crankshaft center, positioning it better for improved mounting.
The existing front motor mount angles downward. It seems to me it would function better if that angle was effectively upward, in the same degree. (flipped, to bring point of attachment higher on the frame loop.
Increase the diameter of the main frame loop by 20-25%, retaining the same wall thickness.
Polyurethane foam, injected into the frame tube following fabrication could possibly substantially dampen or subdue vibration??? (This might be a real nightmare if subsequent repair welding was to be done!)
In the present configuration, the motor mount anchor to the top frame tube is too far to the rear. Seems it would more effectively subdue vibration, and be stronger, if it were on the front of the cylinder head.
IMO...
Perceived engine vibration of a racing machine is key to optimal performance and a valuable tool which may be employed by the rider, to win.
If vibration is excessive, causing failure of mechanical components or inducing rider fatigue, improved engine balancing and construction design are in order.
Isolation of mechanical phenomena from the operator is certainly adviseable for comfort oriented machines.
Best
rc
