Pushing Pistons Up & Down

[Kato]

I started a little sub project a few months back, probably very unwise as I have so many things to get finished the last thing I need is more distraction.
Anyway the idea came about following a conversation with a mate, we were talking in general about club racing using Ducati based bikes and how it was actually quite tricky as there are not that many classes (other than SBK) that Duc’s can be competitive, an M600/600SS however highly tuned is going to get nowhere near an R6, this lead on to the one or two classes where we could be competitive power wise but cannot make the capacity limits, or we could make the limit but a Monster or SS with clip-ons is just not going to cut it the class rules do not allow massive mods, but you can change bore and stroke, exhaust as long as the basic bike is what it started life as!

More about the class in mind bike/engine combination if and when it happens

After a bit of messing about with crank/rod/piston combination it was quickly obvious that Ducati don’t make the right combination of parts, rods being the main problem, Pankl, Carrillo etc will all sell me rods but only in the std lengths, Arrow will make anything I want but at a stupid cost and that’s where I should have left it, however…….I have now been working with a very well known (in racing) UK firm to overcome the problem and as a result now have prototype H-beam billet rod, initial modelling results show equal or better numbers than of the shelf Carrillo rods, and the cost to me is much less, so if all goes to plan early next year I should be able to offer Steel billet rods to you lot at very favourable prices…….

[utopia]

'scuse my ignorance, but what is the coloured picture ?
Some sort of computer modelled stress analysis ?

I dunno what the rules and regs are, and Kawasakis seem to have the class sewn up, but I've always wondered why nobody is campaigning a Ducati in the Supertwin class.

[Kato]

Originally Posted by utopia

'scuse my ignorance, but what is the coloured picture ?
Some sort of computer modelled stress analysis ?

I dunno what the rules and regs are, and Kawasakis seem to have the class sewn up, but I've always wondered why nobody is campaigning a Ducati in the Supertwin class.

Correct Jeff stress model

As for supertwin, the answer to that is a certain F***WIT called Ryan Farquhar

That and there is no lightweight-ish Ducati 600 putting out 100 rwhp

[jerry]

will that stress model work on me ,, i really stressed out and breaking to easily ???????

[Bitza]

Bit of an asside, but I had Carrillo make me a rod for a Matchless G80cs short stroke scambles engine that I used in a road/clubmans style bike. The rod was basically a G50 (the GP cammy engine of the late 50's early 60's) being slightly shorter than the G80 one but with the same big bearing, however I wanted the small end to take a different piston. When I enquired they said no problem or extra charge as they made rods to order anyway, it cost about £120 as I remember, but of course this was about twenty years ago and things do seem to be changing?! Quite interesting how changing the length of the rod alters the nature of the engine, via the relationship between the position of the piston, the cranked angle of rod to big end, and of course what the valves are doing at the time? I maybe no Sir Harry Riccardo but its just the kind of thing I find interesting, sad or what, Bitza.

[Kato]

Indeed the geometric relationship between the rods, crankshaft and pistons. so your 900ie has a rod ratio of 1.911 I'm looking at achieving 2.3ish. In general the lower the rod ratio, the greater the side forces exerted by the pistons against the cylinder walls, in turn this increases wear on the piston skirts and cylinder walls, and creates a higher level of vibration inside the engine. these increases in friction can also elevate coolant and oil temperatures.

However lower rod ratios do have some advantages. Shorter rods mean the overall height of the barrel can be shorter, which means the overall weight of the barrel is lighter. The engine will typically pull more vacuum at low RPM, which means better throttle response and low end torque (good for street performance and everyday use). Spark timing can be advanced a few degrees for some additional low speed torque, and the engine is less prone to detonation, which can be a plus in turbo, supercharged or where you might want nitrous.

But then longer connecting rods with the same stroke will reduce the side loading on the pistons, which reduces friction. It also increases the piston dwell time at TDC, holding compression for maybe half a degree of crankshaft rotation longer at TDC improves combustion efficiency and squeezes a little more power out of the air / fuel mixture. Typically, an engine with a higher rod ratio will produce a little more power from mid-range to peak RPM.

Longer rods would require the gudgeon pin to be located higher in the piston, or the engine has to have a taller barrel. Longer rods also mean shorter and lighter pistons can be used, so the additional weight of the rods is more or less offset by the reduced weight of the pistons.

Having said that the disadvantages of longer rods and a higher rod ratio is that low RPM intake vacuum is reduced somewhat. Reduced air velocity into the engine hurts low speed throttle response and torque, not good for everyday performance, but works well on a high-revving race engine.

[Mr Gazza]

I must admit to wondering why you would want to play with the rod length, because it cannot possibly effect the stroke. I simply thought that as short as possible would best as far as reciprocating mass was concerned.
Thanks for explaining why my assumptions are wrong.

I should have know better about the geometric relationship having a profound effect.
I had an AJS 250 lightweight, not the prettiest bike but a lovely motor (it was a late CSR)

It produced far more power than it deserved, and I think this was down to it's "De-Saxe" arrangement.
That is to say that the centreline of the bore did not intercept the centreline of the crank.
It was slightly ahead of it..... I can't really get my head round exactly how that worked, but I think it has something to do with the piston being able to exert more force on the crank on the downward stroke?
I also had a Moto Morini three and a half... I can't remember if that also used De-Saxe geometry... Another lovely little motor with far more power than it should have.

[Kato]

Arrived about 10 mins ago, the first two sets of Kato Racing forged steel conrods, lighter and stronger than std,
I'm very pleased with the final production version, and can now offer them at a very good price
If I get enough interest I will place an order roughly 4 weeks turnaround

Both of these sets are spoken for

looks like a simple design and yet soo beautiful

[Nickj]

Didn't the morini's use heron heads which ought to give a bit more power.

Those rods look rather tasty and elegant

[Kato]

Originally Posted by Nickj

Didn't the morini's use heron heads which ought to give a bit more power.

A british invention Samuel D Heron an Aero enginge designer invented the head to use on aircraft just after WW1, still used today on many vehicles

[Mr Gazza]

Originally Posted by Nickj

Didn't the morini's use heron heads.

Morinis did use Heron heads, but the heads were flat with the combustion chamber in the piston... Should have been called Heron pistons really... Didn't realise they were invented by a Brit.
I thought there was something quirky about the Morini crank too, but maybe I was just thinking about the sideways offset of the cylinders.

If you want to see a really awful piston design, just look at a 650 AJS/Matchless twin.

Your Conrods look really good Kato.

[jerry]

works of art Kato

Originally Posted by Kato

Arrived about 10 mins ago, the first two sets of Kato Racing forged steel conrods, lighter and stronger than std,
I'm very pleased with the final production version, and can now offer them at a very good price
If I get enough interest I will place an order roughly 4 weeks turnaround

Both of these sets are spoken for

Are they a direct replacement of stock conrods for 1000 2V ?
Weight?
BR
Henrik