SUBJECT: WHAT STROKE?
FROM: Gary Taylor
SUBMITTED: 31/7/01

Here's my take on the subject.

The short stroke {70mm} models were;
V7 - 80 by 70mm for 703.3cc
V7 Special - 83 by 70 for 757cc

then for eligibility in 750cc racing came the
V7 Sport - 82.5 by 70mm for 748cc - also for 750S and 750S3

All 850s {844cc} and 1000s {948.8cc} had a 78mm stroke.

Conrods are uniform dimensionally throughout so are the cylinders except for bore. The different stroke is achieved with a longer throw crank and a shorter piston. To stroke a 750 you would replace the 70mm crank with the 78mm crank. You would then need new pistons with a shorter deck height. These are available in 83mm bore as in 850T-series. You could also use 850 Lemans pistons but cylinder head modifications would be required.

You could go further and instead use 88mm pistons from say, an SP1000. Or even {with boring of the crankcase mouths} to 90mm bore for 998cc, or to 92mm bore for 1040cc. In preparation for the planned bore increases from 83 to 88mm Moto Guzzi introduced new rocker arms with the 850T in 1975. I believe that one can go to 88mm bore without them but no higher. It is not so easy to convert your long stroke motor to short stroke unless you are happy with 748cc and a high domed piston. The problem is the availability of pistons/cylinders. One would have to adapt a piston from some other application and then use an iron linered cylinder appropriately bored.

I hope that I've got it right as it won't be long before I'll be putting it to the test. I've got a V7 Sport fitted with 78mm crank and pistons/cylinders from an 850T-series soon to be running again after a re-build that incorporated the stroking. I did all this pre-Guzziology {I wish I had a copy 15 years ago}, but having read all the relevant sections I feel sure that all is well.

Why did I stroke it? I found the V7S to be a very difficult bike to ride in the Adelaide Hills. Sure, it was well worn and had a bent frame but the combination of very high gearing, heavy flywheel, slow gearchange and poor mid-range torque made things so much more of a chore than I was used to when I had an 850T3. The V7S was more rev-happy but it sure needed to be as well to provide adequate punch. I figured that by stroking the V7S I might be able to improve that mid-range which would suit my modest riding style better. Of course, I've still got the V7S cam fitted to hopefully provide a bit more sparkle at the top end compared to an 850T-series bike. To get it going and run it in, I plan to use the standard 30mm VHB carbs but, waiting in the wings I have a pair of 32mm PHF carbs and custom manifolds. I'll keep you informed.

GRT