Crankshaft grinding

This was good a good article for me on crank scope of single cylinder 360' engines and locomotives, maybe you too. Basically says make sure special attention given to strength and binding torque on all the engine and body work fasteners, unless its a righteous isolastic Commando : )

http://modelenginenews.org/etw/etw_bal/p2.html

As a general rule, it may be said that engines which are required to run at widely varying speeds require a greater portion of reciprocating weight to be balanced out than those which can be kept running at well above critical speed. In some small high-speed engines it is possible to "get away with murder", by using very sketchy balance weights, or even none at all. This is because the reciprocating parts of these engines can be made extremely light, and their structure resilient enough to absorb vibration; but it should be remembered that the unbalanced forces are still there, and are registered in the mechanical stresses and bearing loads, also that these forces have to be generated by the engine itself, thereby detracting from the power available for useful work.

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Does someone have a ph# for Mile High Crankshaft in Denver. Motor's in a non isolastic frame, shooting for a balance factor of 74%

Don't have their number but have collected BF numbers from Brit factories and racers over USA and over seas. You will be hard pressed to find any 360' crank in solid mounting that is below 80's BF. Only solid mount I've hear of going to mid 70's is Kenny Cummings new crank after installing Jim's Schimidt's light piston rod kit. I don't think they have run it yet but Kenny said was smooth with 80's BF they decided to lower BF. I don't know the reason the lower BF is desirable except to shave a few oz off total crank mass. My orbital tracing and then Schimdt's both lead us to believe mid 70's BF would give most circular motion. Whether that is desirable or not - don't know. Kenny has broken his Seeley frame using 80's BF a couple-3 yr ago, so beware experimenting beyond what is proven to survive using the parts available at the time. You should have a reason to try 70's BF, can I ask what it is? Do it and get back on how it feels.

Mile High Crankshaft

http://milehighcranks.com/

hobot said:

Don't have their number but have collected BF numbers from Brit factories and racers over USA and over seas. You will be hard pressed to find any 360' crank in solid mounting that is below 80's BF.

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Not really, Steve Although a lot of experts do recommend BF in the 80s for Commando engines in rigid mount frames, there are others who disagree. Steve Maney recommends 75% for 750 and 850 engines in ridgid mount frames. Quite a few flat track Nortons in the '70s were running the 62% BF recommended by Bob Milliken, the local balancing guru in SoCal back then. I've run my long stroke 750 engines in my featherbed racer at 62% for years with good results. It makes a lot of difference what sort of frame you're using, and whether the engine is mounted vertically, Atlas style, or tilted forward, Commando style. As Jim Comstock has pointed out, it's all about finding the BF where the engine forces don't excite the bike parts at their resonant frequencies at the rpm you want to mostly run at. You can't get rid of the primary imbalance forces. All you can do is move them around in direction. The only way to reduce the imbalance forces without a balance shaft is to reduce the reciprocating mass (or shorten the stroke). Jim Schmidt's lightweight/long rod kit does that. I think the reason 62% works well in my bike is that the engine is tilted forward. The 920 I built for my friend's Atlas framed racer is mounted vertically, and works well for him with a BF of 80%. On the other hand, I once put the 920 out of my Commando racer, balanced at 62%, into a Caffrey Seeley frame to see how it worked, and it vibrated so bad on the track at Riverside that you couldn't ride it more than a couple laps without loosing feeling in your hands. The normal 872 cc engine in it worked fine at 80+%. In Jim Schmidt's monoshock frame I ran an 850 at 70% and a 920 at 80%, and both worked fine, without excessive vibration. There's not just one size that fits all.

Ken

I generally keep the balance factor somewhere between 50 and 80%. The higher you go the more stress is placed on the cases and crank. Jim

For the record, my first race motor ran a stock MK3 crank that was balanced to 84% for rigid mount in my Featherbed. After a year I went to a Maney crank with the same factor, ran it for a year, then changed to Maney's recommendation of 78% the following year when it went into the Seeley for the next 3 years. With the advent of JS Motorsports rods/pistons, we went with 75% for most of 2010. Then, at Jim Schmidt's recommendation we went to ~70% and I raced it at Barber this past October, and it felt wonderful.

I will be running ~70% for 2011.

HTH

Ok a bunch of exceptions to the rule then, especially with engine tilt thrown into the equation. Harmonics and resonance into chassis, pilot and tires are my top mysteries to explore on Ms Peel, thank goodness the isolastics nullified my sense of a motorcycle under me. In searching world wide some years ago I came across a reference to a Texas shop the owner had died but on contact his associates/family would not release his data sheets but it covered crank balancing for a wide range BSA, Triumph and Norton plus others, some vertical some tipped and in various type frames. They told me about range of BF that you covered but not which applied to what. So only real answer on each case is pure trial and error from some known ball park till best compromise shows up in that particular engine/chassis/use combo. My P!! internals were a mystery to me, its tach was marked 9000 but I didn't need or use that range very much as way too fast in public but also hurt to hold on to bars and bare pegs. Its motor was solid mount 90* to frame rails but the whole chassis/fork made 2" low in front so engine was Commando cocked froward. How you'd pick a BF in that to stand long in road race use I sure don't know.

As too hi'r BF being more stress on cases, I can understand that some d/t extra counterbalance mass but have my doubts as Norton cases I've been shown all fracture more horizontal from vertical stresses. Hi BF would tend to shove on cases more horizonal, so why the hi BF concern on them? I'm not talking about a rod cap rolled up to punch out cases, just the cases letting go before other things, it that's possible. In Capt. Norton notes there is long dragster discussion on crank mass and BF vs crank and case and bearing flex tolerance. The highest rpm examples tended to be roller bearings and thin cases to allow more flex before popping and they liked the Combat cases over 850's ???

I don't think iso Peel will transmit detectable vibration differences in BF but do expect to feel BF differences in how much throttle/rpm can be tolerated by rear tire > upright to max lean. I did find more mass in rear tire gave less skip out on THE Gravel 110-19" vs 120-18" both aired to same 28 PSI for similar foot print, so I assume dampened the power hits better? Best traction on THE Gravel gotten by heavier cast wheels with160-170 bald 17" race only tires after hwy heat softened at 28 PSI on my SV650 but its rigid chassis rings back into tire so much it could not hill climb hook up or lean as good on Gravel as either my Combats. As speed climbed the advantage goes to my isolastic skinny tire Commandos. Transition speed from similar to different occurs about 30-35 mph depending on how loose, humid-dry or sloped surface is. SVtwin hooked better than the inline 4's on tarmac or loose climbs. I sense power pulses on tire are the main factor between moderns - plus to me V2's tend to fight comming back up yet inline4s tend to fight staying down. By fight I mean a scary tank slap-chassis juddering on forced lean changes going fast under power. I learned to ride this out but its lots of work and no fun at all, so done with that but for hazard saves, when possible.

Both Schimdt and me traced orbits with 50's BF and both figured 70's BF would give more circular orbital. Kenny seems to like it so that is what i'd like to try frist on Peel variable BF crude crank. Jim's pistons in Peel too. Next experiment would be 90s BF.

I once posted a test I made by placing a needle sharp tool against a metal plate temporarily attached to the cases that recorded the motion of the motor. Ran various RPMs.

This was in an Atlas frame that many have suggested works best with an 80% balance factor. With a 72% balance factor the orbital motion was round up to abut 4000RPM then it stretched elliptical towards the front and rear at 6000RPM and above indicating that the BF was too high at 72%.

I think that the BFs that have been passed around are accepted just because they have been passed around. I have seen resonant frequencies affect the way a frame vibrates but that has been limited to such a narrow RPM band that I don't think its very important.

I think it should be established when the motor is BEST IN BALANCE WITH ITSELF, especially at high RPM where things break. And you need a tool for this.

The bottom line is the heavier the pistons the worse the vibration. I remember Rob Tuluie racing his heavy piston&pin 920 Commando at Laguna Seca with very firm substitute bushings in the isolastics. His arms actually puffed up from cramping trying to hang on to the handlebars.

I haven't found the low end of BFs where too little is worse (although I did race at 49% and thought it terrible), but I'm convinced that anything above 70% is too high. Andy Molnars manxes are balanced at 68% and modern speedway singles are about the same - and the Nort twin is just a side by side single. Since Norts are balanced anywhere from 52% to 84% it should be a clue to us all that the sweetspot should be in the middle at around 68%. Lower might work but I would have to see another scratch test to be convinced.

Thanks Jim S. for BF numbers and feedback findings with philosophy on them. My best guessimate prior was 77%. Peel w/o mass plugs > ~57%, so will ask Ken to make some up for 68% and 77% and maybe 96%.

All very interesting reading. The bike in question has a solid mount motor tilted like a commando. The balance factor in the bike now is 74%, and the frame developed a crack near the right peg mount, probably not because of the b/f, mabey an age thing. So may I shoot for 68% for longevity. Bike does short sprints, revving from 3-7000 in 1 gear. Bike doesn't seem to vibrate while racing, but near idle it shakes like hell. It has 11:1 comp. Thanks for the link. I'll also weigh my next pistons.

My meager understanding is when solid mount frames with then available pistons, fractured frames they bumped BF into 80's to tolerate it better. You suspect age over engine vibration. Is this an area that carries engine loads or just strut for foot?

Its the over all mass that is being reciprocated as the fundamental booger boo in 360 cranks. Ms Peel project got more tedious when her balance factor for a pair of forged Lightened Cosworth race pistons and Norton rods shot from 77 to 96 on fitting JIm's even lighter pistons and steel rods. That's how Kenny gets away with lower BF in solid Seeley. Can you w/o comparable piston/rod mass? I encourage any experiment of course, even if I take opposite view point at times, lets learn something eh. This post may be one of the few times a wide range of testers has discussed BF scope as prior its was valuable race formula.

I still ponder that so many shun the isolastic solution to BF on frame and pilot.

I have to wonder why you would consider a 93% balance factor. An engine with a 93% balance will shake forward and rear with the same ferocity that an engine with a 7% balance factor would shake up and down. And that would be pretty severe. Jim

Commoz I don't know why I'd want mid 90's BF either, yet i've some hints and reasons to believe it may help traction. It may just as likely shake my teeth out and fracture frame as 90's BF would engage both front and rear isolastics way more the just the front one taking up almost all the bouncing. We know Norton had to reduce rubber area to tame vibes by 2000ish. Additional isolastic mounts like head steady all report can't tune out the buzz. I don't have feed back on Dreeer style under slung extra iso mount but bet they buzzed too. I only came across one report over a decade of a Cdo racer with 94% but w/o feedback on how it worked/felt. I've different reasons to experiment on Peel than vibration or frame tolerance. I can almost ride THE Gravel as fast as tarmac curves on Peel but boy howdy not my regular Combat of SV. There is something different going on with Peel and I want to exploit it to the max. Peel isolates all sources of resonance - not mix and clash them as other bikes i've pressed. The rear tire patch on road texture gets through clear as can be.
My ponder is what if most the engine vibes were directed in line with the drive thrust - would the isolastics also take up more tire hysteria to plant more power?

A Harley Shovehead devote told me the smoothest he'd experienced was upper 90's BF. Does his V twin sense apply to Norton, who knows yet. I've been recently educated here that 'heavy' cranks seem to help Nortons and other go better. So maybe I can detect benefit with heavy plugs to rise BF. Who knows maybe 110% would be even better. With light pistons wouldn't take that much extra.

hobot said:

My meager understanding is when solid mount frames with then available pistons, fractured frames they bumped BF into 80's to tolerate it better. You suspect age over engine vibration. Is this an area that carries engine loads or just strut for foot?

.

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Bike in question is my Baker framed dirttracker. Could be vibration that caused the fracture. Back in the day (70's) this bike was raced 3 times a week and I had no frame problems. I also do not know what the balance factor was back then as I didn't build the engine. A place called Digitron in LA did the crank.
when sending out the crank, should I send out all the reciprocating parts with it?

Hobot, I am glad you are doing this experiment and not me! Are you really wanting high balance factor or more mass? It seems to me a good argument has been made to increase the mass but to keep the balance factor closer to factory on an isolastic frame. But then I have been lost and found a couple of times in these crankshaft threads and might not be where I think I am.

Russ

More mass equates to a less cammy engine, good for traction.

mkane77g you make darn good points to question what fractured the frame, rough race use &/or engine vibes. If it was me I'd weight the reciprocating mass and if in ballpark of past examples I'd use the higher BF they gather around. If closer to Jim's kit then I'd be restless to reduce BF towards upper 60's. My Ms Peel will primarily be a stripped down desert type racer, then other stuff stuck on to make more practical for daily - legal use. I just know my ole P!! gave pleasant thumper vibes in putt putt to city traffic up to ~50-60 mph then it made me hurt then go numb above that. You need to determine what its prior BF was to judge which way to go too.

Hobot, I am glad you are doing this experiment and not me! Are you really wanting high balance factor or more mass? It seems to me a good argument has been made to increase the mass but to keep the balance factor closer to factory on an isolastic frame. But then I have been lost and found a couple of times in these crankshaft threads and might not be where I think I am.

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Russ

I did not intend this experiment any more than I intended to learn stunt riding getting to pavement : ( I know that Ms Peel could hook up better on skinny tire for loose hill climbs and more impressive to me hook up in hook shaped tights more power than heated fat tire hi hp sports bike. I could not corner sports bikes as fast nor others I contested with, so pretty firm in my opinion.
How can that be????
Besides Peel's fame taming to articulate to take out tire angle/traction conflicts I sense the isolastics act like power pulse dampers to the tire chirp-grip resonance. Hi BF seems to work fine for racers edge grip and they increase BF to have smoother loads on frame and pilot - so why wouldn't Peel like hi'r BF too? Experiment is if the more fro-aft oscillation of ~1/8-1/4" would - help - hinder - or do nothing for traction. Skipping around on THE Gravel paths is almost the same as on pavement, rear or front go out at similar angles or momentum by lean or power or steering, similar pilot efforts to recover on THE G. as ii is from low or flat tires. Pavement has more grip so its easier to control or stop slides and of course to AVOID them. The more rear hooks up the faster/safer to go around on pavement before new phases of looseness or air borne handling occurs. This would up Peel's corner advantage against bikes with more limited lean and traction and chassis load tolerance, maybe even with their traction control that lets pilot peg throttle w/o fear of spin out or wheelie.

There is another factor I'm fascinated with on Cdo's over sports bikes. Where and what the vertical CoG is and what it allows or prevents in a max leaned motorcycle accelerating. I've seen perfect skilled pilots hugging a turn close to others and starting to inch past on inside, carefully keeping the oscillations of forks/chassis under control to take a bit more power with pilot hanging way off - suddenly the whole bike-pilot-tires as a unit tip completely sideways, lifting both tires at once off surface to fly out horizontal taking other folks out with him. That Does Not Happen on Peel. Un-linked Cdo flop around before those states can be worked up to. Crank mass and location seem vital in this regard.
Best I can tell Commando got it pretty darn right. Is heavier crank better here too?

When Ken reported how hi Peel's BF was with JIm's kit - 96+% and before knowing what could be done, I rationalized the extra mass would help tame Peel's fast throttle-torque response on wet grass creeping to hard over chicane cornering. There is close threshold of tire merely grinding slightly loose ~10% max slip grip to sudden complete let go into snap downs or fly ups. i do not think of flat track crossed up slides as fastest way around but an easy relieving fun method when luxury of wide open spaces to pull it off. If I over do a Gravel turn I too have to freak out and spin out rear to cross up and slide till back under control away from ditch-fence-trees. I do everything I can to AVOID this long slide state. Some resistance to small throtte increases would be nice as Peel should have power enough to easy spin out, so not spinning out till then is my inner desire to live and ride again. Breaking loose on purpose is whole other state than breaking loose in surprise!

Its unknown territory to explore, to gain a tad more advantage and pilot ease.
So Peel's BF is all about tire-power reaction not vibration to frame or pilot.

rvich said:

Hobot, I am glad you are doing this experiment and not me! Are you really wanting high balance factor or more mass?

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As it is Hobot I'm actually surprised that he's not going for - say - 110% ..... :mrgreen:

SCNR


Tim

Tintin said:

rvich said:

Hobot, I am glad you are doing this experiment and not me! Are you really wanting high balance factor or more mass?

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As it is Hobot I'm actually surprised that he's not going for - say - 110% ..... :mrgreen:

SCNR


Tim

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I think that was mentioned a few posts back. Jim