To big bore or not to big bore, that is the question

ksoholm

ksoholm

Senior member
Location
Bellingham, WA, USA
As I'm having the RGS's heads done, I've been thinking about doing this too, with Carillo rods and a larger oil cooler.

But then I got thinking about the fact that Laverda didn't make the RGS/SFC as so-called 1200s. Perhaps there were technical reasons why they didn't, having had experience with the factory 1200s. Were the liners too thin? Inadequate heat management/dissipation?

What are your experiences with big bores? Worthwhile?

Thanks -
 
Making the bike a 1200 is a very good thing! There are no issues or problems that will happen doing this other than more speeding tickets from the police. And no the liners are not too thin. Why Laverda did not make a 1200cc 120 triple, only Piero can answer.

You will need to have the crankcases bored to fit the bigger liners.
 
You need to bore the block and the top crankcase for new liners.
They are not 1200 ccs because the 1200 used the same bore size as the 750s, the 1000, the same as the 650s.
Paul
 
With - I think - 78mm Pistons, you can re-bore and hone the original liners and use them. Less issues with Oil-lines beeing touched, but thinner liners... Did that on the 1000 SFC, works.

But then... if you do not race the bike or are for the very last horse-power and torque, it is a quite costy experience... 3 new pistons, 3 new rods, taking the crank appart, cleaning, potentially lightening the crank, new bearings, re-balancing, the work, getting the right head gasket, adjusting the carbs etc. - It's a years (at least) project... And to get the most out of the engine, you will then have to open the inlet ports, get bigger valves etc.... Then the exhaust does even more not match the engine and restricts power than it already does... so you invest into a new exhaust, too. Once you have the engine right, you will - if you haven't done so - see a need for better suspension, better road-holding etc. etc. => GSX-R-Rims or similar with more modern and wider tires are a must then... means new sproket, chain and chainwheel... And then the question is: how is the gear-box? RGS are prone to break the main shaft bearing (the one in the engine housing on the right side where it exits to the sproket). The more load you put on one side, the more it needs to transport to the other side... And then you want the bike to be lighter to better turn, handle easier... oh - did I mention brakes? Soon you'll need 4-pot calipers etc.

Can of worms really...

Results can be VERY impressive (gains of 30 HP and more and equal torque improvements are not uncommon). Cost will be between 6.000 and 8.000 € at least for all of this, not mentioning that you will want perfect paint everywhere once you have gone this far...

Been there 3 times, was fun, cost me a fortune, still nothing half way modern... Ride a well prepared Zane. Costs the same, handles dramatically better, performs better in ANY regards and costs the same. Or buy a modern bike like the Triumph Trident (nice little Triple!) or any modern Japs bike, BMW, what ever... Lesson learned. And learned a lot along the way! Wouldn't do it again though. But if you have the patience, the time and - much more important - the money, the lust for the experience - go for it. But don't tell me I did not tell you... :oops::ROFLMAO:
 
Laverdalothar said:
With - I think - 78mm Pistons, you can re-bore and hone the original liners and use them. Less issues with Oil-lines beeing touched, but thinner liners... Did that on the 1000 SFC, works.

But then... if you do not race the bike or are for the very last horse-power and torque, it is a quite costy experience... 3 new pistons, 3 new rods, taking the crank appart, cleaning, potentially lightening the crank, new bearings, re-balancing, the work, getting the right head gasket, adjusting the carbs etc. - It's a years (at least) project... And to get the most out of the engine, you will then have to open the inlet ports, get bigger valves etc.... Then the exhaust does even more not match the engine and restricts power than it already does... so you invest into a new exhaust, too. Once you have the engine right, you will - if you haven't done so - see a need for better suspension, better road-holding etc. etc. => GSX-R-Rims or similar with more modern and wider tires are a must then... means new sproket, chain and chainwheel... And then the question is: how is the gear-box? RGS are prone to break the main shaft bearing (the one in the engine housing on the right side where it exits to the sproket). The more load you put on one side, the more it needs to transport to the other side... And then you want the bike to be lighter to better turn, handle easier... oh - did I mention brakes? Soon you'll need 4-pot calipers etc.

Can of worms really...

Results can be VERY impressive (gains of 30 HP and more and equal torque improvements are not uncommon). Cost will be between 6.000 and 8.000 € at least for all of this, not mentioning that you will want perfect paint everywhere once you have gone this far...

Been there 3 times, was fun, cost me a fortune, still nothing half way modern... Ride a well prepared Zane. Costs the same, handles dramatically better, performs better in ANY regards and costs the same. Or buy a modern bike like the Triumph Trident (nice little Triple!) or any modern Japs bike, BMW, what ever... Lesson learned. And learned a lot along the way! Wouldn't do it again though. But if you have the patience, the time and - much more important - the money, the lust for the experience - go for it. But don't tell me I did not tell you... :oops::ROFLMAO:
Click to expand...
Yeah, I'm well aware of all these things; it's why I'm carefully considering it.
 
GregT said:
If they're Ross pistons, it would not surprise me if they're lighter than OE 1000 ones.

Red will know.
Click to expand...
correct, 1200 Ross pistons I order are internally profiled and have a few other piston features so the 1200 pistons are indeed lighter than the original 1000 Mondial tractor pistons

But now people will ask about the 1000 Ross pistons being lighter again and the affect on the crank balance

Well the Ross pistons in 1000 form are also significantly lighter than original 1000 pistons and the engines turn out to be far smoother than original without touching the crankshaft balance factor
Which is due to the lower mass of the pistons at TDC/BDC lowering the inertia of the pistons at that point in not having to stop/start such a heavy piston
I believe this is why the engines are smoother, may be talking shit but in real life, that is what I have found when building engines and is how I build my engines be they street, hot rod or race engines, using the lightest pistons that meet the engine demand possible

My race pistons for example are even way lighter than what I use in street engines that is for sure and they last unless I do something dumb in their tune up
Which I have done in the past, burnt up a few sets, only way to learn
 
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ksoholm said:
As I'm having the RGS's heads done, I've been thinking about doing this too, with Carillo rods and a larger oil cooler.

But then I got thinking about the fact that Laverda didn't make the RGS/SFC as so-called 1200s. Perhaps there were technical reasons why they didn't, having had experience with the factory 1200s. Were the liners too thin? Inadequate heat management/dissipation?

What are your experiences with big bores? Worthwhile?

Thanks -
Click to expand...
have built a number of 1200 x 120 degree engines, there are no valid reasons why you cannot do that

maybe concern around the use of needle roller bearings on the middle crank bearings, was cautioned years ago by a certain Laverda individual about using that set up on race engines
Is one of the reasons why I stay with 180 degree race engines as I can install far stronger Roller bearings on the middle mains on a 180 engine but is not the main reason
Main reason and it is personal is that I do not like and have never liked the 120 engines in general, Laverda lost their "Soul" when they ditched the 180 engines
My life was over :cool:
 
redax5 said:
have built a number of 1200 x 120 degree engines, there are no valid reasons why you cannot do that

maybe concern around the use of needle roller bearings on the middle crank bearings, was cautioned years ago by a certain Laverda individual about using that set up on race engines
Is one of the reasons why I stay with 180 degree race engines as I can install far stronger Roller bearings on the middle mains on a 180 engine but is not the main reason
Main reason and it is personal is that I do not like and have never liked the 120 engines in general, Laverda lost their "Soul" when they ditched the 180 engines
My life was over :cool:
Click to expand...
My Jota has had a significant amount of work by Keith ..I had already bought the RGS head from the Slaters show engine, valve seats recut, some porting work by Keith. It sports78mm pistons new Arrow rods, rebuilt crank, drilled cam wheels, lightened , drilled balanced clutch drum, and...Mikuni carbs. And apart from a hitch with a dodgy head gasket, btw Keith now has those specially made sans crappy o rings , it is simply bloody lovely. So much more torque, power fuel economy too. Some baulk at fitting Mikunis , but a chap with a truly mint Jota went for a spin on mine at Baskerville, and came back wanting that engine🙂 True to say its a lot of money though...and waiting time for the work. All I can say is, if you tried it, yiu'd have to have it😁
 
Try going larger inlet valves, this removes an edge in the intake that eats up some power... (you can feel it when the valves are removed; just grap into the valve seat hole towards the inlet and feel the edge...). If you have someone that can shape the inlet from 32 to 36mm and can taper your manifolds from 36 (head side) to 32 (carb side), this gives some extra gas flow improvements...
 
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Paul Marx said:
You need to bore the block and the top crankcase for new liners.
They are not 1200 ccs because the 1200 used the same bore size as the 750s, the 1000, the same as the 650s.
Paul
Click to expand...
Yeah, no thanks.
Laverdalothar said:
Try going larger inlet valves, this removes an edge in the intake that eats up some power... (you can feel it when the valves are removed; just grap into the valve seat hole towards the inlet and feel the edge...). If you have someone that can shape the inlet from 32 to 36mm and can taper your manifolds from 36 (head side) to 32 (carb side), this gives some extra gas flow improvements...
Click to expand...

Yes, 41.5mm intakes, no harm in that - I have Mikuni RS's, so will have my intake manifolds shaped etc.
 
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