- piston weights, balancing, machining, whether to use R65 conrod and pushrods or longer R100 etc)Actually, the easiest way is to go with longer connecting rods. That way, everything else IS bolt together. Making it work well after bolting it all together...there's the fun!Rob Frankham wrote:It can be done...
It has been done (many times)...
But it ain't as easy as that.
If you lay out the parts (either in actuality or in your mind), you will see that you can't just bolt up stock parts from various machines to make a different engine.
The biggest problem is that, if you use the 1000cc barrels and the conrods from either the 1000cc or the 650cc engine, the engine will turn no problem. You may even get it to run after a fashion (though I doubt it) but the compression ratio will be so low that it will not produce any useable power.
There are actually two ways to approach it:-
The first solution is favourite as (or at least so I'm told) there is precious little cylinder wall thickness left if you bore the barrel out that much.
- Reduce the length of the barrels by machining so that the compression ratio is restored or
- Bore the R65 Barrel big enough to take the bigger piston.
Of course, machining the bigger barrels down is still no walk in the park because the pushrod tubes will now not meet cleanly with the machinings in the crankcase so that will need to be adjusted.
As I say, it can be done but I would question if the end result is worth it. Much easier to get a set of 800cc barrels & etc. (or a 800cc engine) and get a smoother engine without the hassle.
Rob
Yeah, but then you lose one of the advantages of building a short-stroke: reduced engine width.the quinner wrote: Actually, the easiest way is to go with longer connecting rods. That way, everything else IS bolt together. Making it work well after bolting it all together...there's the fun!
More than outweighed by the advantages of the longer rod ratio. I have literally scraped a valve cover on the tarmac once...and that was on a race track. Quite often I have wished for more power, though. IOW, (for me) a narrower engine is a non-advantage...more power is a definite advantage.Major Softie wrote:Yeah, but then you lose one of the advantages of building a short-stroke: reduced engine width.the quinner wrote: Actually, the easiest way is to go with longer connecting rods. That way, everything else IS bolt together. Making it work well after bolting it all together...there's the fun!
Don't get me started on mass-centralization....the quinner wrote: More than outweighed by the advantages of the longer rod ratio. I have literally scraped a valve cover on the tarmac once...and that was on a race track. Quite often I have wished for more power, though. IOW, (for me) a narrower engine is a non-advantage...more power is a definite advantage.
I've been drawing up various layouts, short rods, long rods etc. To get minimum width short rods and Mahle pistons (if they're still available), but width isn't my real concern. I'm after smoooooooth with nice midrange and lowdown torque, and I suspect the longer rods with the lesser angularity changes will help with smoothness.Major Softie wrote:Yeah, but then you lose one of the advantages of building a short-stroke: reduced engine width.the quinner wrote: Actually, the easiest way is to go with longer connecting rods. That way, everything else IS bolt together. Making it work well after bolting it all together...there's the fun!
Certainly that's an opinion I'd trust. I would still like one of his frames.chasbmw wrote:Worth talking to Richard Difazio from Frome Somerset, he made more than one 850cc airhead engine, one was written up in classic bike, he is semi retired now, but I think there is still a website and if could get him on the phone I'm sure he would talk. Charles
Yes, over the last twenty five or so years, I have made several short stroke special R65's, mostly 94m/m bore 850cc, and they are all in regular use with their current owners and I hardly ever see them, so perhaps they are trouble free ? currently I use a monolever chassis with an R65 bottom end, and 88m/m bore which makes a very useful short stroke 750cc.
I have always gone down the road of using an all R65 (or 45) bottom end with rods, with appropriate bigger bore and 1981 on R65 heads, it is probably the most economical and simple route.
In the beginning I always bought Venolia pistons, they are forged, lightweight, slipper type three ring pistons and very strong, and I have never had any trouble with them.
When I thought I was going to do so some sprinting/hillclimbing with a special BMW, I had some R65 cylinders sleeved and bored to suit a pair of 95m/m Guzzi pistons, fitted with a pair of R100RS heads this would probably have been an outrageous machine, however, common sense prevailed.
The popularist theory of 'machining down' R100 cylnders and using R100 pistons and heads, is a bit too simplistic........the R45/65 shorter stroke is achieved by a different crank throw dimension, with shorter rods, and, pistons with the gudgeon pin hole nearer the crown.......so those three things are critical.
You could conceivably fit an R45/65 crank into other 'long stroke' crankcases, fit R45/65 rods, and then shorten 'long stroke' cylinders...but why..!
Whatever pistons you use must be dimensionally the same as R45/65.
