Hi Bob:
Most of the modern hi-po motorcycle engines have bearings galore. The
earlier ones used balls and the later ones use plain bearings. The secret
is size. The bikes use multiple cylinders with very short strokes, DOHC,
multiple carburetion, 4 to 6 valves and high compression. Most four
cylinder bikes have 5 mains.
The early Hondas made incredible power using multiple cylinder, multi-valve
engines. Famous examples are the 50cc twin which revved to 22,500 rpm; the
125cc five cylinder and the 250cc six cylinder. All of these engine
produced well over 150 horsepower per litre.
Two-stroke Yamaha and Suzuki engines made even more power by the early '70s
and used multi-cylinder V-engines of different sorts.
Bearing failure in any of these engines was rare.
John
>Bill Eastman wrote:
>>
>> Last week I received more ammunition for my continuing "MGA's are God's
>> gift to the sports car world" campaign.
>>
>> On this list we have had a wonderful debate over the advantages of the
>> three bearing engine.
>
>Uh-huh. The 'A' and early 'B' motors are great revvers because they have
>three bearing cranks. And the S*itfire motor in RB Midgets have weak
>lower ends because they have three bearing cranks.
>
>I recently read that the biggest contributor to frictional losses are
>piston rings, specifically the oil control ring, and the length of the
>piston stroke -- both of which, alas, the 'C' motor has in abundance.
>
>Hey, John McEwen, who appreciates them murdercycles, what allows a 12K
>rpm redline on them mid-size street bikes? How many main bearings in a
>4-banger Jap motor?
>
>The late 60's Z28 (5 liter) and Boss Mustang (5 liter) could rev to 7
>grand (occasionally) and have a long life. What was the secret there? I
>understood it to be a combination of high compression, lumpy cams, and
>big carb throats. The trick is to have the motor breath at rpm to
>overcome frictional losses. You can only make so much power under 3,000
>rpm for a given displacement.
>
>My 'C' with three Webers, a mild cam, and dual exhaust starts to fade at
>6K rpm. I'm assuming not enough compression and too much valve float but
>I haven't checked it out fully.
>
>The TR6 is out of breath at 5 grand but the poor old girl is shackled
>with 7.5 to 1 compression that model year.
>
>Bob Allen, Kansas City, 69CGT, 75TR6, 60Elva
>"The President has kept all of the promises he intended to keep." --
>George Stephanopolous, 1994
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