750 crank balance factors

As an aside to the desaxe amusement. When the FIM observer measured the Britten after they'd set World records, he found different strokes on each cylinder....Not intentional, the case decks had been machined so that the bore centerlines didn't line up with the crank center....
John would never spend the money to get a CNC mill so things like that happened.
 
bob said:
I wonder if re-phasing a Zane engine might cure some of the fragility problems that seem to plague them. A fuel injected ,twin cam. 8 valve ,90 degree 750 might be an interesting concoction.
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I hear you Bob, but how about a fuel injected, single cam, four valve, 270 degree 880?  I used to have time for crazy things like this!
 

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Wow Nick, that's interesting, please elaborate! And have you still got it..?
 
Cam,

Offset pins have been used by many bike manufacturers, BMW being probably the most noted for their almost silent running boxers (back in the day when the cranks had balls and rollers).  Still have them to my knowledge, at least the 2-valve post 69 airheads did.

The offset is usually in the 1-1.5mm range and its main purpose is to control piston slap to a degree.  A nice by-product is the easier time it gives the conrod and big-end bearing at TDC which in turns helps smoother low-speed running, not that many Lav riders seem to be interested in that anyway.

Personally, I like a nice even tick-over on my engines and I like them mechanically quiet, wouldn't even consider using a piston without offset.

Reckon offsetting the pin in the piston is easier cheaper in production than offsetting the cylinders which may lead to later misunderstandings on the part of owner/mechanics.

piet
 
sfcpiet said:
Reckon offsetting the pin in the piston is easier cheaper in production than offsetting the cylinders which may lead to later misunderstandings on the part of owner/mechanics.
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Probably true, but they're not alternative methods of achieving the same outcome. The recriprocal motion maths is the same but the forces involved are quite different.

Cheers,
Cam
 
Haven't been able to spend much time in the Lavertory the last couple of years but there are still some bikes in there, I hope.  The twin needs the wiring tidied, a bit of paint, oxygen sensor connecting and some screening of injector cables to get rid of some glitches.  Had lots of fun with the processor code, ran several different versions before it decided to play ball.  Also had oil pouring out of the head and base joints with local gaskets, went back to gold/platinum laminate German ones and it is no longer incontinent.

May not be riding this season, need to get house fixed and workshop rebuilt, did about 150 miles last year and I reckon $5 per mile is a bit steep!  Would like to get some miles on the twin if I can, though.  The engine is pretty well proven apart from the ported big-valve head I just put on it.  Should go ok when it gets wound on, I'd say.

The Accralites in my motor have offset pins.  And back to the topic - 65% is quite nice.
 
and a shot of a collection of 750 crank webs fresh from the CNC
just need to get them sorted now

Webcollection.jpg


 
as well as finishing machining the crank webs we finished the press dies for the oil slingers
this set of dies for triple cranks and modified twin cranks
works great, very happy with end result

Slingerdies.jpg


Slingerdies1.jpg


Slingerdies2.jpg


 
GregT said:
Looks good - got a price for two sets for triples yet ?

thanks

Greg
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no, not yet, I ordered 100 discs last week once we sorted out what diameter we needed, I have to wait and see what they will cost
and as Mark says, overheads on press work are huge  :D
let you know Thursday/Friday

 
I made turned aluminium slingers for my 270 crank because the originals had been butchered, and I wanted to be able to lose some diameter off the crank webs.  Would be easy enough to make them splittable, but could just unbolt them and get enough movement to clean them out in one piece, maybe.
 
here you go Chris, one of these is indeed your crank, be the one with the corroded ends

2 x 0/270's and 1 x 0/284 cranks, +/- 10 mins
be heading in to get balanced Monday, then back to get conrods installed, be glad to see the end of them, burnt some serious time doing these cranks
not a 5 minute job by any means

Barecranks1.jpg


 
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