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knife edge crank 202

Started by basicgreen , Jun 26 2015 03:53 PM

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91 replies to this topic

#76 _STRAIGHTLINEMICK_

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Posted 12 July 2015 - 09:39 PM

I dont see the difference except the one in Jonnos pic looks lighter and cleaner .

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#77 _STRAIGHTLINEMICK_

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Posted 12 July 2015 - 10:04 PM

Come on Mick, it doesn't matter how many cranks they've done the laws of physics are the laws of physics. It's not rocket science either; you have a beam (engine block) with forces at each end going in one direction being cancelled out by forces near the middle of the beam in the opposite direction. Sure the beam/block won't shake but the forces are trying to flex the block repeatedly, and eventually it breaks. Besides, every modern straight six is designed with counterweights. Or does some old bloke that was taught by Bert Jones know more than the OEM crank designers?

Like you said, we'll have to agree to disagree on this one, and I'm sticking with the laws that have been known for hundreds of years, not some grub on a pedestal drill...

I never doubted there are forces at play here and you can read your theory out of your book but this is the way it is done in practice and we just live with it .If you have a better way then do the testing and see if the result is any better . This setup has worked for many years on many engines without one failure so how can you knock that.

And i resent the disrespect you show to others who have a wealth of experience and diferent opinions to you ,there is no place on this forum for those comments especially when you are hiding behind your computer . We'll agree to disagree .

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#78 _oldjohnno_

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Posted 12 July 2015 - 10:36 PM

Sorry to offend Mick it wasn't intended, even though I have encountered some unbelievably ignorant professional builders. But I'm not spouting book theories or even my own opinions, they're nothing more than facts, the same facts of physics that keep aeroplanes in the air and take rovers to Mars and make a bazillion cars and trucks do their stuff every day. You can no more argue against them than against the earth circling the sun for example. People build things to these same basic principles every day and it's not even complex stuff, just plain old schoolboy physics. I believe the old blokes always did what they did because they had no other options, but those days are long gone and if the old fellas don't upgrade their skills they'll be left behind. We're way past the point where the big-time racing teams can win from behind their flowbench and in the workshop, they also have to be competent with computer modeling and have a little more understanding than what was previously sufficient.

Here's something else to think about: sketch the block, looking from the side and pencil in the force vectors with 1 and 6 at TDC, then again with 2&5 and 3&4 at TDC. See how the bending moments on the block change as the (identical) forces move from pair to pair? All of a sudden the oversize counterweights on the very ends of the factory cranks start to make sense. As usual, the factory engineers knew what they were doing all along...

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#79 _STRAIGHTLINEMICK_

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Posted 13 July 2015 - 01:28 AM

I've never doubted the theory johno. The cranks are lightened because they accelerate quicker without any noticeable effect on reliability.
I think we are going around in circles here and I'm over it , you do it your way and I'll do it mine.

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#80 _oldjohnno_

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Posted 13 July 2015 - 06:01 AM

I've never doubted the theory johno. The cranks are lightened because they accelerate quicker without any noticeable effect on reliability.
I think we are going around in circles here and I'm over it , you do it your way and I'll do it mine.

:iagree:

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#81 _duggan208_

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Posted 14 July 2015 - 12:57 AM

Plenty to think about and consider while i muck around with my crankshaft.

regards

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#82 _rich243_

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Posted 14 July 2015 - 12:08 PM

So Mick, with the blue full counterweighted crank are you taking the same amount of meat of each weight when you knife edge it, effectively making it lighter of course but each weight still weighs the same as the next one beside it, like the factory blokes designed it just lighter for each weight?

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#83 _Bomber Watson_

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Posted 14 July 2015 - 03:49 PM

Stock ones have bigger counterweights at the front and back ^

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#84 _STRAIGHTLINEMICK_

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Posted 14 July 2015 - 06:17 PM

So Mick, with the blue full counterweighted crank are you taking the same amount of meat of each weight when you knife edge it, effectively making it lighter of course but each weight still weighs the same as the next one beside it, like the factory blokes designed it just lighter for each weight?

Yep a certain amount is taken off each counterweight and as bomber said the front and rear weights are larger than the rest . They are not really uniform as cast anyway and the final amount comes off during balancing . Some cranks are worse than others and are full of balancing holes before machining. Some cranks are also harder to machine than others but as far as i know they are cast from the same grade of iron .

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#85 N/A-PWR

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Posted 16 February 2016 - 08:53 AM

Does the quality of machining the knife edge crank make a difference in the oil mist?

Found these pictures:-

VS

http://www.vwwaterco...ging-38291.html

Never heard of RAG Engineering before lol.

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#86 S pack

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Posted 16 February 2016 - 09:34 AM

I've heard of Dodgy Bros. :spoton:

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#87 _cupboard_

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Posted 27 March 2016 - 08:40 PM

In the motorbike world say talking 2 stroke motocross bike like a yz250 these are very snappy bikes meant to shoot from corner to corner but some people will use these as enduro bikes so they need to be tamed a little fitting a flywheel weight is very effective way of slowing the way they build revs thus controlling wheel spin which is better suited to enduro riding,the bike will still rev the same rpm just take a bit longer to get there. (think bultaco johno a pursang motor will have lighter clutch/flywheel than say alpina ) this I feel sums up what lightening the crank would do.

what about crank scrappers are these not effective in controlling windage

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#88 _STRAIGHTLINEMICK_

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Posted 29 March 2016 - 09:28 PM

At high revs the crank will pick up oil and spin it around in one large mass , the oil is no good to you there so a scraper setup is used to guide the oil to the sump where the oil pump can get to it .

Power losses will vary with different engines and how much oil is carried by the crank .

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#89 _Dansthemanow_

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Posted 08 August 2016 - 12:43 PM

I thought I might contribute my thoughts on the issue of crankshaft weight.I would agree with old johnno that minimizing rod/piston weight as far as practical is the way to go.However I think the benefits of lightening the crank are very marginal at best.When you consider that all the mass in the crank is within 3 or 4 inches of the axis of rotation,you realize it has only modest influence on the overall moment of inertia,as compared to the flywheel/torque converter.Firstly lightening the crank will have zero effect on horsepower or torque.Secondly,the responsiveness of the engine in an unloaded state is a greatly overrated asset.Once the weight of the entire driveline/wheels and car are attatched to the crank,its weight becomes relatively insignificant.Yes the responsiveness helps with fast gear changes and rev matching,however you would find the improvement in lap times on a circuit car would be miniscule or more likely unmeasureable as a result of a lightened crank.In fact,I just increased my flywheel weight by over 100%, and quite frankly the responsiveness is virtually identical to what it was before.So how much difference does a kilo or 2 off the crank make?

Edited by Dansthemanow, 08 August 2016 - 12:45 PM.

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#90 _Dansthemanow_

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Posted 08 August 2016 - 02:20 PM

Actually you would lighten the weights to maintain the balance rate after lightening your reciprocating assembly.But I think shaving them to a sliver probably doesnt help the overall cause greatly.Perhaps reduced windage.Thats about it.My crank is heavy as buggery,and so is my flywheel,but it takes about .3 of a second to go from 800 to 6000rpm in first gear.I dont think response is an issue if the rest of the package is sorted.

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#91 _Dansthemanow_

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Posted 09 August 2016 - 12:56 AM

I guess you would gain 1 or 2 percent horsepower from reduced windage,and maybe a very slight improvement in responsiveness.Overall,doing this to a crank might see a tenth come off your 1/4 mile time.I suppose if it doesnt cause the motor to shake apart,its o.k to do it.Every bit counts n all.