going big-bore on a 1000

beauchemin

beauchemin

Senior member
Location
Victoria, British Columbia
Are there any issues switching from a 1000 to 1200 barrel?  This is a 1977 1000.  Is the crank balance going to be a factor?  If I stay with the 1000 barrel, what is the largest bore that I can safely do?  Read some nasty stories about liners getting too thin...
 
sfcpiet said:
Might be a bit marginal, but when done correctly, 78mm works nicely.

Very happy with mine. :D

piet
Click to expand...

Did you change the crank balance to go with 78mm pistons?

This is a street motor, so I'm looking for more mid-range grunt, so I assume that the smaller inlet valves (as opposed to the RGS-size inlets) on that head won't be a detriment.
 
Built my own lightweight crank to go with the bigger slugs.  Head was already to 1000SFC spec, and a bit beyond.

Old worn 980cc engine(MkI 180?) was putting out 95hp, now feels like 20 more... still need to put it on a dyno though, just to see what it can do.  Done 2 Bikers Classics meetings in Spa in current spec, otherwise used on the road for a bit of tootling around. :D  Has turned out very reliable and ridable, no disadvantages to speak of.

piet
 
  We used to do a lot of 1200 conversions - we didn't rebalance the cranks as the 1st one we did was with a customer who insisted that his crank was dynamically balanced to suit the new pistons. we sent the crank and pistons to be balanced - only for the balancer to 'phone us up and ask why we wanted it balanced! - He reckoned that with the heavier pistons the balance was ideal. We must have done another 30 or 40 conversions since with none being rebalanced and no problems occurring. maybe others have had different experiences. - regards - Phil
 
Need to add that I used completely different balance factors in order to maximise weight reduction, ie, split the counterweight to the outer cylinders normally located at the centre webs to the outside webs, approximately halves required weight(I've got an extremely clever friend that does the numbers).

Vibes on a whole reduced by a long way, perhaps the smoothest revving 180 I've experienced, almost as smooth as a 120. :D  In any case a lot smoother than my track bike, using a re-phased to 180? 120 engine.

Never had much of an issue with heavier pistons in stock engines either, almost seems like the factory allowed for larger/heavier pistons in their original design.

piet
 
Others may confirm this (or otherwise), I'm under the impression that 1200 barrels are not a drop-in replacement for the 1000 barrels. The top crankcase openings need to  be enlarged to fit the larger diameter liners, which requires splitting the cases.

Apart from that it seems like a very smart upgrade.

bazzee
 
we get our high comp Ross big bore pistons (80.5mm through to 83.0mm) internally machined so they actually weigh 20 grams less than a standard 1000cc Mondial tractor piston (75.0mm)
never had an issue with crank balance, all it does is move the sweet spot either up or down the rev range slightly

biggest difference made to a standard Laverda crank in regard to balance is to get all 3 reciprocating masses equal, they are far from being equal when they left the factory

 
bazzee said:
Others may confirm this (or otherwise), I'm under the impression that 1200 barrels are not a drop-in replacement for the 1000 barrels. The top crankcase openings need to  be enlarged to fit the larger diameter liners, which requires splitting the cases.

Apart from that it seems like a very smart upgrade.

bazzee
Click to expand...

when I converted my RGS to accept 1200 barrels, I took the studs out to get the top engine case half both to fit on the milling machine and to make the space to get at the liner openings, then the openings in the top case half have to be enlarged to accept the larger 1200 liners. Not a big deal, it was pretty straightforward.

I used J & E pistons from Wolfgang, weighed the stock RGS 75 mm pistons, weighed the 80.4 mm J & E pistons, they were pretty close, and as I was taking weight out of the J & E pistons to match each other, I wound up fairly close to stock 75 mm piston weight.  The RGS 1200 motor is quite smooth, no issues.

Paul LeClair
 
The issue with the thin liners on a 1000 was probably my bike.as far as I know its a one off problem.the liner cracking and dropping down and hitting the crank.No idea if it was damaged earlier before dropping,anyway Red looked after me with the problem.As far as I know there are a few running the pistons I was without problems.Lucky old me.
 
You must log in or register to reply here.
Back
Top