What do you think: balancing crank needed or not?

jakepeewee

I am doing a little tuning on my 851SP3 and have amongs others machined my 95 mm JE pistons (compresion thing). They are now weighing 467 grams each including pin etc. The weight of the original 888 piston is 529 grams, so the new pistons will be 12% lighter.

The project started with just installing a set of 'new' ported 748R heads, but you know how it goes 😱
So also bought the 748R cams and machined the JE pistons en the cilinder base to gain some compression.

And now I am asking myself do I need to rebalance the crank or not. I am a little worried for the crankcases since the motor with the 748R cams wil like higher revs.

Opinions appreciated!

stafford

Re-balance your crank

jakepeewee

stafford wroteRe-balance your crank

Thanks Stafford.
If I am going to re balance the crank I think I will also let them (probably Ducati Kaemna) reduce the weight of the crank .

Love your blog BTW.

jakepeewee

Any tips on where to go to balance and enlighten the crank?

I live in the north of Holland. I know of Ducati Kaemna, but there probably are good alternatives.

stafford

jakepeewee wroteThanks Stafford. If I am going to re balance the crank I think I will also let them (probably Ducati Kaemna) reduce the weight of the crank . Love your blog BTW.

I don't think you can reduce the crank weight as it were, it will still need to be balanced as a unit with pistons, con rods, and if possible alternator and flywheel. I think that's how mine are done down at Louigi Moto. The weight reduction comes from lighter flywheels and race alternators.

hauge

http://www.foxperformanceengines.com/crankshaft.html

jakepeewee

stafford wroteI don't think you can reduce the crank weight as it were, it will still need to be balanced as a unit with pistons, con rods, and if possible alternator and flywheel. I think that's how mine are done down at Louigi Moto. The weight reduction comes from lighter flywheels and race alternators.

I know it is done with the pistons con rods etc but was hoping they could also shave some weight of the crank as well. The motor allready has a lighter flywheel.

jakepeewee

hauge wrotehttp://www.foxperformanceengines.com/crankshaft.html

Thomas,
I read about fox performance but I understand they are located in the US (so not witin the EU). Or is Peyton in the UK?

nine16

stafford wroteI don't think you can reduce the crank weight as it were, it will still need to be balanced as a unit with pistons, con rods, and if possible alternator and flywheel. I think that's how mine are done down at Louigi Moto. The weight reduction comes from lighter flywheels and race alternators.

Balancing is the most important part, of course, but you can absolutely lighten the crank. You can go further too--knife edging, polishing...

Don't know the European sources, but Ben Fox did the 996RS crank in my 851. Beautiful work--its a shame you don't get to look at it once it's all bolted up.

griff851

The whole crank thing is about what you want the engine to do. If you lighten all the rotating and reciprocating mass. It will spin up faster, but at a price. Things can get very responsive, to the point of being down right touchy.
When you balance the piston assembly to the crank, your moveing the inherent vibration from one place to another, not removing it. The trick is to get it in harmony with the frame, then the bike feels smooth.
If you lighten the crank flyweights, it will spin up and be more responsive, but you might find if it not done really well, you'll have a really fast accelerating thing that you can't hang onto for long because your feet and hands have gone numb.
In twins this is that 50%/51%/52% business you hear about. Somewhere, depending on who doing the job, it's sweet with the frame. I've ran the same single engine from 56% to 64% to 73%. And it moves the buzz by about 2000 rpm all up. Which was handy in mating the frame to to optimum rev range for the race bike. (Being on the 250 getting absolutely no feeling in your hands at 11-12k, makes getting the brake thing happening a new experience.)
If your engine is too responsive, throttling on or off mid corner while seriously into it, can give you those extra adrenaline hits you could probably live without.

I've found the best place to start is where the rev range the bike is going to spend most of its time in. And you have to be honest about it. Then talk to a couple of guys that have done a few twins and see what they say. When you get consensus go for it.
There is a lot stuff said on the subject and a lot bikes badly balanced because egos got in the way of common sense. A mate has got a 916 sps crank as a door stop, thanks to a balancer who knew what he was doing, or so he said.

Have a read of Phil Irving's Tuning for speed. That will help get a bead on what's going on.

Changing the crank weight is relatively cheap when removing, and bloody expensive when adding, the metal they add is hexy stuff.

As for balancing after piston change of mass, at 12% I'd be looking into it. Can't remember the threshold exactly but. 8% rings a bell but I wouldn't put money on it.

jakepeewee

Thanks, I´ve just send Ben Fox an email. He seems a true expert at this.

nine16 wroteBalancing is the most important part, of course, but you can absolutely lighten the crank. You can go further too--knife edging, polishing... Don't know the European sources, but Ben Fox did the 996RS crank in my 851. Beautiful work--its a shame you don't get to look at it once it's all bolted up.

griff851

Oh boy, more verbal runaway I'm afraid.
Knife edge: came to ducati world via Steve Wynne and his merry bunch of men. The job was done by a bloke called Rob M. whom I spoke to quite a bit a few years ago. We have a guy over here who is not my favourite bloke, but a talented balancer, Ron Young. Specialises in dynamic balancing. There is another guy Pete S. as well. Following the adage if you want to go fast ask those that are fast, I queried the knife edge. They all said the same thing. Great idea at the time, but it does sod all. Old mate Ron did before and after dyno work to form his opinion.
Then theres the final argument, if it's so good, why don't factory cranks have it.

Polishing: well, what are you thinking you are trying to achieve. Reduce drag or oil clearance. How much gain honestly do you reckon your going to get with some sodden great chunk of steel rotating at 10000 rpm. It has rather a large inertial mass. If you think in terms of how fluids behave on surfaces, remembering air behaves like oil in an intake port, the golf ball effect comes into play. I spent bloody hours shaping the leading edges of 2 of my cranks, bevel and 888. Just trying to get them to behave like a jets wing leading edge. Looked great, all shiny and everything. Then get told the reality. A little bit deflating in the ego department. 🙁

In the end it's your money.

jakepeewee

Griff,

Rest assured, I understand what you're saying about the knife edge and polishing and although I really understand the appeal, my money isn't going to be spend on the knife edge thing.

However, on Ben Fox' website they offer different stages of balancing and lighting, for example a SPS/R conversion that kind a sounds interesting (ok, including polishing).

Besides Ben Fox I also emailed Andrews Precision http://www.andrewsprecision.co.uk/ducati-cranks/. He is located in the UK and there for up till the Brexit in the EU 😁
I understand Andrew balances ducati cranks for Luigi Moto / Chris Steedman.

Also interesting is the GBP / EUR exchange which is 1.10 right now and keeps tumbling the coming months...

griff851

Your on to it.
Sorry for the long burst, just I found my journey into crank world really cool. I spent hours chatting with some pretty switched on helpful keen guys. Man I would loved to have sat down over a beverage with Mr Bordi or Dr Taglinoi

hauge

You can "buff" it up your self.
I grinded the edges of and then gave it i light polish before i sendt it for balancing.
this is my 999R crank.

Mr.R

It's a "Must Do" IMO.
However the secret to reliability when using 851/888 cases is to keep the revs bellow 10k.
IIRC? Stafford's 996cc motor runs 748R inlet cam and still makes it's peak power under 9.5k.
My 851/916cc motor peaks at 9.2-3K running retimed 9*6 SPS cams, this's is only 2 rwbhp short of Stafford's 996cc motor, despite being 80cc smaller and with smaller 35mm inlet valves

Andrewsprecision are very good, I've recently had him do my 916SP crank for my 955cc motor.
The old boy who owns the business (and carries out the work himself) has been doing this type of work since 1963.
He has some interesting things to say about Italian ideas of balancing on OEM motors.

You need to send him your con rods complete with shells fitted, pistons complete, rings, gudgeon/piston pins, circlips and your crank assembled up with everything it's going to be running with, like the alternator rotor, rotor nut, tab washer, flywheel complete with sprag clutch, spacers,primary pinion with it's lock washer and nut.

Steve R

dudlington

Mr R that is of course an interesting point keeping the revs below 10 grand for reliability. Maybe there could be a different thread concerning the benefits of a chassis mod connecting the swinging arm pivot point to the lower rear engine fixing point and moving the bearings from engine to swinging arm (As demonstrated by Spondon and copied on every Ducati model from the 916). Both my 1036 Testerstretta engined 888 and 1198 cc engine 851 have these modifications. Once that rev limit is lifted then there are any number of other tuning mods on the engine that could be performed in the quest for more speed and reliabilty. The crank lightening and balancing is a must because of this design flaw especially during racing to reduce stresses into the crankcases. Polishing of course brings performance gains but are very small in the big grand flawed scheme of things.

nine16

I didn't have mine knife edged, I just said it was an option. It is polished and it did need some of that expensive metal.

Even with the stronger 996 cases, mine makes peak power at 9400 rpm. I want this thing to last a long time.

jakepeewee

Steve,
I agree on the below 10 krpm part, that's why I am advancing the cams by 6 degrees. That will shift the power curve a little to lower rpm. But because of the 748R exhaust cams I am not sure if the peak power will shift enough to occur before 10 krpm.

My bike was fitted with G-inlet cams and the A exhaust cams. Peak power was at 10.5 krpm.

Mr.R wroteIt's a "Must Do" IMO. However the secret to reliability when using 851/888 cases is to keep the revs bellow 10k. IIRC? Stafford's 996cc motor runs 748R inlet cam and still makes it's peak power under 9.5k. My 851/916cc motor peaks at 9.2-3K running retimed 9*6 SPS cams, this's is only 2 rwbhp short of Stafford's 996cc motor, despite being 80cc smaller and with smaller 35mm inlet valves Andrewsprecision are very good, I've recently had him do my 916SP crank for my 955cc motor. The old boy who owns the business (and carries out the work himself) has been doing this type of work since 1963. He has some interesting things to say about Italian ideas of balancing on OEM motors. You need to send him your con rods complete with shells fitted, pistons complete, rings, gudgeon/piston pins, circlips and your crank assembled up with everything it's going to be running with, like the alternator rotor, rotor nut, tab washer, flywheel complete with sprag clutch, spacers,primary pinion with it's lock washer and nut. Steve R

jakepeewee

Now if they only made glass crank cases 😁

nine16 wroteI didn't have mine knife edged, I just said it was an option. It is polished and it did need some of that expensive metal. Even with the stronger 996 cases, mine makes peak power at 9400 rpm. I want this thing to last a long time.