Gregory Bender

Displacement - ways to increase it

Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models

Updated:

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Alright, I'm just learning about this, so the information presented here is certainly not expert and does not come from direct experience. That being said, I believe it to be accurate and - of course - useful.

Upgrading a 700 cc or 750 cc to 850 cc

There are at least two ways to do this...one utilizing a long stroke crankshaft and one using a short stroke crankshaft.

Long stroke 850 method

This is simplest of the two methods in that it involves direct replacement of parts. Here is what is involved:

  • Replace the short stroke crankshaft (70 mm stroke) that is stock in the V700 and Ambassador models with an long stroke crankshaft (78 mm stroke) that is stock on the Eldorado models.
  • Replace the existing pistons and cylinders (80 mm bore on V700 or 83 mm bore on Ambassador) with pistons and cylinders from an Eldorado (83 mm bore). Ambassador pistons cannot simply be reused as the wrist pin is in a different location from the Eldorado pistons. However, Ambassador cylinders can be reused.
  • Connecting rods can be reused across models.

Short stroke 850 method

This is method can be more complicated as machining of parts may be necessary. Much of this information was gleaned from Mike Tiberio off of the Yahoo! Loopframe_Guzzi news group. Here is what is involved:

  • Method 1
    • Bore the case to accept the 950 cc cylinders
    • Keep the existing short stroke crankshaft (70 mm stroke)
    • Install pistons and cylinders from a 1000 cc engine (88 mm bore)
    • Keep the same connecting rods and shorten the cylinders, studs, and pushrods
  • Method 2
    • Bore the case to accept the 950 cc cylinders
    • Keep the existing short stroke crankshaft (70 mm stroke)
    • Install pistons and cylinders from a 1000 cc engine (88 mm bore)
    • Run longer connecting rods and do not modify the cylinders, studs, or pushrods
  • Method 3
    • Bore the case to accept the 950 cc cylinders
    • Keep the existing short stroke crankshaft (70 mm stroke)
    • Install pistons and cylinders from a 1000 cc engine (88 mm bore)
    • Use special extra tall pistons and keep the same connecting rods and do not modify the cylinders, studs, or pushrods
  • Notes from Mike Tiberio
    • Of course there are compression ratio factors to take into account as well, Convert etc pistons are already low compression, and this would lower it further (good for mexico). A lot of work, but if you have a 950 cc case, Pete Roper can get the long rods, and then it ends up quite manageable. On my old short stroke 850 race motor, I went the stock rod route. I went with what I had at hand, in retrospect, I'd get a set of long carrillos...
    • One real benefit of a short stroke motor is an improved rod length to stroke ratio. Little known fact that the longer the rod relative to the stroke the more power. Less power wasting piston slapping.