Oh, so it could have been an ex-race engine, with fully modified bottom-end, balanced, lighthened and optimised -;) - it all makes sense now :eek:

You'd never spot a crank that has been balanced tbh. It's nothing more than "perfecting" the spec'. Blueprinting if you like. No different to taking a pot of pistons and picking 2 that are the same weight, if you like.
Lightening is a different ball game and not cheap. If you were going to the expense of lightening a crank, you'd move some metal which would be obvious. A balance could be no more than taking another mm out of the holes that the factory drill in the first place.
There's very little, if any, performance advantage to be had. Reliabilty is main/only benefit. You'd get more by shimming the crank a little on the light side to get less drag on the mains.....

Only added after reading the first page, but now read it all :)
Frank brings up an interesting point....
If the big ends failed, would a crank regrind and oversize shells be illegal?? The rules, if followed to the letter, would indicate so. Surely common sense would prevail??
There's a distinct line between balancing and lightening.
I think the point made about "good practice" in building a good motor is well made. There's no performance benefit and policing it is nigh impossible.

That sort of talk won't be tolerated here !

:rolleye:

Woohoo, if that was the case I've been breaking the rules for 2 years then, except when I was on the ex-Geoff Spencer bike.;)

I'll hand back all the trophies I won as a result :lol:

Anyone else bored of this thread yet?

Tut tut Paul ;)

With regard to possibly regrinding a crank after a blow up (how much would this cost against sourcing another crank) then surely the course of action would be to email the RC and seek permission to get it done.
Not unlike Paynep emailing and asking about using a different frame.

I agree that balancing a engine is good practice and to some extent this is carried out at the factory, but as the Desmo Due rules not only state no Modifications to the crankshaft but also that it should remain as it left the factory there are quite a few entrants out there that have followed the rules.

For example Senna3 had his engine rebuilt at Baines Racing last year including the fitting of two new pistons, Now I wouldn't dare suggest Geoff or John don't know how to assemble a Ducati engine be it air-cooled or water-cooled but they did not adjust/alter/modify the crank as they were asked to make sure it complied with the rules.

Surely it is one rule for all

Nelly I'm not sure how many Desmo Due engines you have built from the crankcases upwards, maybe none. But if you have, have you always applied best practice or have you left the crank well alone inline with the rules

A regrind and shells would most likely work out cheaper than sourcing another crank. You'd re-shell it anyway as a matter of course.

I've built several motors from the cases upwards, and yes, i always apply "best practices" so as to build a good, reliable motor.
If i was asked about balancing as part of a DD build, then i wouldn't have a problem having it done. I don't interpret it as being outside the rules.
The cranks are balanced at the factory. Further checking/balancing is merely checking that it's as close to optimium as possible. No different to setting the squish, filing the piston rings to make sure the gap is spot on, setting valve clearances, setting the air gaps on the pick ups........ There's more benefit to be had adjusting those than checking/having the crank balanced.
Who's to say that nog's crank went away, was checked and nothing needed doing? More than possible.
If i was asked to have the crank webs machined away and knife edged, then i'd suggest they take it somewhere else, if i was asked about balancing then i don't see the problem.

May well get asked a lot more now than in the last few years after this rivetting read :)

But the thread wasn't meant to be just about Nogs crank, although the thread where it was mentioned was the catalyst for the initial question "No Modifications - what does it mean"

To me and many others No modification means leave well alone, if it doesn't and relates to meeting factory specifications I'm wondering if I can afford this little lot


one of my con rods is slightly heavier than the other and both are heavier than the minimum weight quoted by the factory, I know what I will do I will balance them so that the meet the factory minimum weight. After all the engine will be smoother and less likely to shake apart

Same as above goes for the new pistons

Also my rear cylinder head has a lower flow rate than the front cylinder head and I know someone elses flows more than that, so I think I'll get someone to alter them so they both match the higher flow rate of somebody elses engine, so long as I don't exceed the class bhp limit

Just been comparing camshafts and found mine have a fraction less lift than my mates and are even different to each other, I'll have to get them ground to the factory tolerance that will give the best performance. I'm not modifyong them as thats probably how some left the factory.

After checking the combustion chambers one is marginally smaller than the other so what I will do is match the other one to it, a quick skim will sufice after all its not really removing material as thats how it should have left the factory it just good practice to balance them out.

Just found out so and sos flywheel weighs a tad less than mine but is still within factory tolerance, I'll have to adjust mine to suit.

Crikey how much :o
be better off racing in CB5s