>  > From listening to the motor, I try to always keep it under 3k if I can,
>>  but when fully loaded and on a trip (going uphills/etc) I find myself
>  > often pushing the 4k mark.

I would think that the redline constraints on these engines is
exactly the same as the aircooed engine it's based on... due to
having 2 paired/staggered big-ends without main bearings in-between
(ie effectively a 3-main-bearing crank where any other design would
be a 5-bearing) means serious flexing & whiplash in the crankshaft,
which is exacerbated by high rpm and will chew-out the main bearings.
A FULLY-counterweighted crank can alleviate most of this flex,
thereby allowing the engine to rev much higher... whereupon conrod
tensile strength & piston integrity become the mechanical limiting
factors (not taking oiling & cooling into account).

Of course, having said that, I used to wind my 57 Split (single-port
1600 & stock 57 trans) up to 60mph in 3rd and attain 80mph without
any difficulty...
--
Andrew Grebneff
Dunedin
New Zealand
Fossil preparator
<andrew.grebneff@stonebow.otago.ac.nz>
Seashell, Macintosh, VW/Toyota van nut