CRANKSHAFT balancing Australia

If it were a 360 crank and in a Commando you should stick with the factory 53% dry balance factor. The isolastics allow you to take advantage of that BF. If it is a solid mount engine then use the BF recommended for the frame. Seeley Mk2 is best at around 78%, a Featherbed I am told is 68% to 83%.

As for cutting down cast iron flywheels - you would be courting disaster. Been there, done that.

Good to see you are looking at a steel flywheel. There's others on this list who have direct first hand experience with an offset crank that you are contemplating - I would listen to them on the matter of what BF to select.

My personal opinion is stay with a 360 degree crank and simplify your life. Changing crank phase is a solution hunting for a problem.

i will keep on doing this project, just want to try something new for me.. cams and ignition ready just need balancing the crankshaft..

@hobot where can i read that Jim Schmidt race manual?

Martin, you can buy it off JS motorsport online, quite cheap and plenty of info that will suit your requirements
Regards Mike

from JS
Example: 750cc with 65% balance factor
Lightweight Carrillo rod - small end 105

Big end of one rod including cap, nuts, bolts and shell bearings =371
Example: Carrillo rod big end = 371 grams X 2 cylinders = 742 big end weight plus 50 grams for oil in crank = 792
Rotating weight X 100% = 792


how to weight the small end and the big end on a conrod it's in one ?

Ah so now we know where your 1st shrapnel came from Dances. I'm not talking about racing competitive use on a trimmed down cast iron flywheel, only novice ignorant or desperate people would do that, one time, unless other faults wrong with them.

Here's JSM site - don't see the Race Tech Manual offered so just ping JIm on it. JIms been able to use essentially factory items and not grenade.
http://www.jsmotorsport.com/

Steve/Martin 3rd item from the bottom on his product page $25 (once the page fully loads)

http://www.jsmotorsport.com/products.asp
Regards Mike

MARTIN.K said:

how to weight the small end and the big end on a conrod it's in one ?

Click to expand...

Good explanation and pictures here.

http://www.eatonbalancing.com/blog/2007 ... ng-part-4/

Ken

Ok JSM site.. anyone got info on stock oem norton com conrod big end and small end weight?

i have uncle who lived in sydney , got info anyone can do this in sydney?

MARTIN.K said:

how to weight the small end and the big end on a conrod it's in one ?

Click to expand...

Take a look at the Eaton Balancing reference that Ken provided a link to. There they show a set up where the rod is horizontal with one end on the scale and the other end on a pivot. I have seen knife edges used to support one end. What also works is using a thin long string to support one end while the other rests on a scale. Keep the sting vertical. Repeat measurements until you have shown repeatable numbers.

Keep in mind the big end weight of the rod must include the rod, cap, bolts, nuts and bearing shells. The small end must include any bushing (if used).

If you are just into academic practice on figuring BF then you can use the mass given by people here or found online. If you are actually balancing for its benefits to run then must weight them your self then equalize the 2 rods then plug in figures for the BF for the static type balancing. Crank shops have the device to weight each end or can make one up yourself. Again Jim Schimdts Race Manual has this covered. Dynamic balancing requires spinning so can't be done with simple DIY devices.


Btw here's a blip that TC of Hogslayer fame could stand behind on Al vs steel rods.
http://www.rrconnectingrods.com/aluminu ... -rods.html

hobot said:

Ah so now we know where your 1st shrapnel came from Dances. I'm not talking about racing competitive use on a trimmed down cast iron flywheel, only novice ignorant or desperate people would do that, one time, unless other faults wrong with them.

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Incorrect assumptions and statements ..........again.

Plenty of other knowledgeable people can speak to the perils and problems of a cast iron flywheel. So recommending that someone cut down a cast iron flywheel is, as you would say in other words........bad advice.

A moot point on this thread as the OP is wisely going with steel.

AAll steel cranks are better of course.

As to cutting down a cast iron flywheel - if you know what you are doing you can make them stronger. Cast iron flywheels can explode from Centrifugal force. Reducing the diameter of the cast iron flywheel reduces the centrifugal force and so there is less chance of explosion. So you get a stronger flywheel. The next thing thats going to break is the PTO shaft. So you have to cut a .090" radius at the base to spread out the stresses. If you want to know how its done - its in the JS race manual.

I revved beyond valve float with racing valve springs and broke racing cranks until I performed these operations and haven't broken a crank since. Of course lightening the pistons made a big difference. After these modifications (& lighter pistons) - valve float & crank flex became the limitations (before I was using beehive valve springs & lightweight lifters).

Also - there is to much guess work out there about balance factors. The only way to know for sure is to measure if the bike is shaking more up & down or more front to back. Lower balance factors shake up & down more and higher balance factors shake front to back more. I had a thread on how to measure that if anyone can find it - using a scratch test tool at various RPMS.
I raced the hell out the the cut down & radiused 850 crank in the photo, then someone else raced it, now I'm riding it on the street. I've pushed it to 8000 or 8500 on the street testing my rods & pistons. Try doing that with a stock motor & see what happens.




the early days of lightweight 850 pistons below (mid 1980s)
See groove in cylinder for thin copper wire head gasket.

Clearly one takes their chances on the cast iron. Not sure how you can make the Norton cast iron flywheel stronger. Not sure if there's any reliable NDT for cast iron either. Cast iron is one big notch waiting for a crack to propogate from. Certainly understand the desireable results of lower rotational mass.

I did not go about lightening the flywheel blindly.

I had my flywheel lightened based on instructions by a respected racer/builder and looked near identical to the flywheel in the picture above. So it's like a box of chocolate, you never know what you are going to get (without lightening); so why would I or anyone recommed this today?

I still have clear visions of a fist sized piece flying ahead of me real fast when mine let go coming onto the paddock straight at Mid Ohio. Felt a pronounced slap in the pants and then silence. There was virtually nothing left of the center of the crankcase and the bob weight landed on the gear box. The crank cheeks and crank through bolts remained intact. Bolt holes in the trans cradle were stretched and torn like taffy.

Also have vivid memories of Jimmy Comstock's flywheel letting go at Gratton, MI at the start line. It was almost like seeing a WW2 vintage film of a bomber coming apart in slow motion. At first I thought it was something blowing out of his exhaust as I blew past him at the start but after the red flag I saw the carnage. Pretty sure it was cast iron and certain it was not steel.

As for balance factor, vibration comfort is the compromise. If you are looking for easiest on the motor, 53% dry is the way to go but it does not help much if it is unrideable due to vibration discomfort and/or frame breakage, thus higher BF if not an isolastic.

Given the energy released when one of these frags I'll never build a racer with cast iron flywheel - ever. Street applications - maybe.

It also makes one think about what can happen if there's no steel spine tube (similar to those on the Commando) between the rider and the flywheel. A good example is a Seeley Mk2 where the only thing between the rider and the business end of a flywheel is a flimsy cast crankcase, a couple of carbs and an alloy gas tank.

Everyone agrees that cast iron flywheels can explode.

Not much else to do but use steel. But reducing the cast diameter worked for me. If you could reduce the diameter enough - the Centrifugal forces would drop to a safe level - but there probably wouldn't be much weight left.

Some blew and some didn't - I saw lots of them break at the PTO shaft but never saw one explode.

One goal in life is to experience as much as possible.

Another goal in life is to survive those experiences.

Been a pretty wild ride so far.

Just called Blissett W A Engineering Services, they workshop in sydney and they can do it... anymore info in sydney?

i try to look for more info in singapore malaysia, and couldn't find one that can do balance factor adjustment

One goal in life is to experience as much as possible.

Another goal in life is to survive those experiences.

Been a pretty wild ride so far.

Click to expand...

Boy Howdy I second this wisdom in face of all life styles being fatal. Who knows what lurks in a run of cast iron flywheels. One of the worse I heard was just warm up idle in drive way 850's that left the scene out the down tubes and ended up inside bedroom across the street after first passing through living room sheet rock and window from the glancing blow off their car outside. While considering which steel alloy, might also consider narrowing the flywheel OD like Peels deal. Responsive as it is happy to rev. I don't know how hi Peel's nitrided crank is good for over 72-7300 like Maney uses, otherwise Bee hives would be in order. Btw I Jim goofed a bit, O BF gives most vertical vector while 100% give most horizontal vector but one can exceed 100%. 50's factor BF gives like 2/3's vertical motion at front iso, 1/3rd horizontal, so trace looks a bit bent football shaped, bend coming from the arc on rear iso pivot. This BF gives best load averaging on crank ends. Mid-upper 70's should be pretty circular orbital but with more loads on crank.

On 3 point hydroplanes I've had the sense of being a WWI or II fighter pilot flying through victims debris almost like slow motion, 1st explosive blinding white sun glare, then large pieces emerging in various vectors twisting as they blasted through the wind then glittering sparkles of various colors of shattered paint and gel coat chips spinning in a clouds as ya pass through the plume... Not good when 1/8" door veneer and doped fabric and balsa sticks hit nose down in wave trough over 60 mph. Sometimes pilot ejected pulling out dead man cut off cord with him.

blow or not , curiosity is common to human beings at all ages... someone like to discover it themselves learn in the hard way, some just like to read a scared story and will not do it.. so if you guys want to find out it will blow or not try it yourselves and you will know.. cheers

Sydney people, anyone tried this guy
http://www.startlocal.com.au/industrial ... 16584.html

i found this site gives some list of people that can do Crankshaft Grinding
http://www.startlocal.com.au/industrial ... Marys.html

More like those who fail to learn from history are destined to repeat it or the definition of insanity is doing the same thing again and again and expecting a different outcome.

@MARTIN.K - As for the rephased crankshaft, what firing arrangement have you designed into your cam; 45 degrees (nearly a twingle) or 405 degrees?