I had to disagree here, but I would think the bearings are only a very
minor contributor to an engine's willingness to rev.
I'd say that the main factor (90% or more!) would be the ability of
the engine to efficiently pump fuel/air mixture into the combustion
chamber. If the ports are small, poorly shaped, small valves, restrictive
inlet/exhaust, short cam duraction etc, then the engine will not get
enough stuff to bang as the revs increase.
On the other hand, good ports, big valves, good exhaust/inlet, suitable cam
etc. will ensure that the engine will get enough bang stuff without losing
it
all through pumping losses.
Mike
----------------------------------------------------------------------------
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Mike Gigante mikeg@vicnet.net.au
Watsons Creek Vineyard http://www.vicnet.net.au/~mikeg
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-----Original Message-----
From: John McEwen <mmcewen@gpu.srv.ualberta.ca>
To: Robert Allen <boballen@sky.net>
Cc: mgs@autox.team.net <mgs@autox.team.net>
Date: Tuesday, December 30, 1997 10:54 AM
Subject: Re: MGA superiority
>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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