June 2007

Saturday, June 16, 2007

DynoTech : Discussion w/ Kevin Cameron on torsional vibration

I emailed to Kevin Cameron today:

Kevin

Last week I if you saw my blog I had an awful vibrating solid-mounted 1710cc crankshop triple asphalt sled brought here because of fuel flow issues (shutting off at half-track). From 6500-8000 the carbs were a blur, 90 lb/hr fuel flow was all we could muster couldnt support 300hp for more than 4 seconds. I bought a piece of aluminum strap and bolted it to the tops of all 3 flatslide carbs to tie them together hoping to settle them down. That actually made fuel flow worse. After maybe fifteen seconds of run time, the surface of the smooth aluminum bar and carb tops were fretted where they contacted each other.

Is that fretting localized melting/ transferring of metal from bar to carb? That would mean the small contact surfaces are reaching 1200 deg F from friction.

We switched to a brand new smoother running 1710 engine (turns out the first engine's crank was out of phase), added some rubber to the motor mounts, and fuel flow was good with just the right fuel pressure

Also Ive had a question posed to me by a guy on the internet about changes in torsional vibrations in the wicked turbo boosted big bore F1000 twin with about triple the stock torque output (and 414hp instead of 165 stock that I just posted on DTR), but operating at stock RPM. This guy has a boosted Yamaha RX1 or apex, and he's galling clutch parts, so he's suspecting that the same would happen to the Arctic Cat big twin. The twins are a little buzzy stock, and 280 lb/ft is maybe not constant, probably rising and falling twice/ revolution? could it be 400 lb/ft relaxing to 100 lb/ft twice/ rev (somehow averaging out to 280)? If I use a solid non rubber shaft from the engine to the absorber, there's a way of using an oscilloscope to observe/ measure the torque spikes each revolution. I did that once after I built the dyno 20 years ago to ensure that my lord soft rubber couplers were doing their job, and the oscilloscope was nearly a flat line.I should do that again with a solid shaft with stock, turbo, and N2O added to see what the crankshaft is putting up with. I could also do that with a Yamaha 4 cyl, which has some rubber in the output shaft gear I think, which probably gets wound very tightly under boost.

Just looking to clarify these things.

Thanks
Jim C.

also here's the Hardcore Sledder internet post I was referring to:

Super Advanced Member Current Sled: 2005 135.8 MPH Mach-Z Previous or Other Sleds you Own: 03.5 blair morgan, Location: Eastern Ontario Favorite Riding Area: eastern Ontario Mileage so far this winter: 00000000 Mileage last winter: 607 Your Age: 41 Riding Since: 75 Group: Members Posts: 157 Joined: 6-February 04 Member No.: 9,778	QUOTE(DynoTechJim @ Jun 14 2007, 05:20 PM) < motorsport17 is teasing because he knows I have bulletproof glass in front of my face looking out into the dyno room, but 5/8" drywall in front of my testicles. That's why Glenn, Jason and Dale were fighting to get that seat right behind me in the control room to use my body for a shrapnel shield. Also galling clutch parts are in my opinion due to torsional vibes not pure torque. Jim Just a question fo you I would have thought that a 2 stroke 1000 would have more torsional vibration then a 4 stroke yamaha. Please correct me if i'm wrong Thanks Cliff -------------------- making them fast one sled at a time!
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DynoTechJim

Yesterday, 03:04 PM

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Cliff that is more of a Q for Kevin Cameron than me. Surely the stock F1000 crank is smooth enough at operating speed from say 6500 to 7800, but they surely have some evil vibrations between idle and clutch engagement where you dont spend much time at. Glenn has nearly triple the stock torque of the engine, so I bet there are worse torsional vibrations with his monster turbo than stock due to the increased torque peaks two times per revolution, winding up and unloading the crank, maybe 50% harder, twice each revolution even though he's operating at stock RPM.

My only first hand experience with aggravating torsional vibes in a 4 cyl 4stroke was my old Suzuki GS1100 that I big blocked to 1394cc plus larger cams. once modded this thing was loaded with torsional vibrations. Though I couldnt feel anything while riding, the vibes were evil enough to continually snap the socket head cap screws that attached the inner race of starter sprag clutch to the flywheel on the left side of the crank. The inner sprag race is a light thing, probably incapable if having enough inertia to snap bolts regardless of the severety of the vibration. So what I think was happening was at some RPM, dont know where, the flywheel was actually going backwards for an instant, driving the starter ring gear into the starter drive gear like an impact gun, eventually shearing the bolts. I think this happened twice, then someone sold me a set of grade 10 bolts or something like that that all big bore modded Suzukis required. Problem solved, but surely the life of the sprag clutch/ gears would have been short had I put many miles on it.

But I had done four things to create the evilness in the crank--heavier pistons, way more torque, higher revs, and straight cut gears between crank and countershaft plus a clutch basket nearly devoid of the soft springs that normally soak up vibrations from the right side of the crank (the starter drive and flywheel are of the left). I don't know which aggravated that Suzuki crank the most, maybe it was a combo of all four. But you have to appreciate how bad the vibrations were when you think about the crank end actually going backwards for an instant one or more times per revolution at some RPM between 1000 and 10,000 (maybe at several different RPM).

Kevin Cameron has addressed this in the archives on my website, and he may be able to elaborate on pure torque increase and effects on torsional vibrations. That's another issue I will raise the next time I talk to him. But if Glenn eats up his 6-weight clutches I suspect it will be from mostly from increased torsional vibration, not just the added twisting force.

Kevin replied:

Early computer-controlled engines had cam position sensors to tell the computer which cycle they are on. Now they do without - they just use the speed difference in the crank to tell them (I guess the engine sparks at every TDC during start-up). So, yes, there are very large speed variations, especially with singles and twins - enough that they give the two cylinders different fuel and ignition maps. Enough, for example, to toss the valves prematurely because the instantaneous cam speed is high. One speed variation comes from the actual cylinder firing, and others come from the steady exchange of kinetic energy between the pistons and the crankshaft (which is twice per revolution).

Nearly every race engine in history has had to have special attention given to the cam drive during development, because crank/cam interactions, through the flexibility of the drive (or lack of it, just as often) create problems. Cosworth make a trick torsion spring that goes in their gear cam drives, and has with it a stack of tiny clutch plates compressed by a diaphragm spring, to absorb the oscillatory energy at the speeds where it tends to get out of hand. Ducati found they had 32nd-order torsionals in their camshafts. They made a big improvement when they changed from ball bearings to plain - every plain bearing is also a hydraulic shock absorber. The oil pump refills it and the thumps of valve acceleration squeeze the oil out of the bearing.

Torsionals were a HUGE issue in the development of the large radial aircraft engines. Generally they had a 4.5-order (firing frequency) and a 2nd-order (secondary vibes coming from the asymmetry of the master-and-links con-rod system) dynamic counterweight on the crank - really massive things that swung back and forth, alternately storing the excess energy from a cylinder firing, then giving it back as the firing impulse died away. When this wasn't right, pieces would vibrate off the tips of hollow steel propellers - chunks about 18" long, going about 500-ft/sec. Or the prop reduction gears would crumble, or the shaft crack, &c. It was a major part of development - hours and hours of running tests to get the crankshaft system stable.

A few years back the NASCAR guys were floating the valves in the back of their engines. This looked like cam twist so they bored some blocks for bigger bearings, increased the cam base circle, and made some experimental cams on bigger tubes. Imagine their surprise when they got LESS power. After a while they figured out that enough valve float to increase time-area, but not enough to wreck the parts, was what was happening. SO next they designed cams to float intentionally, and gradually learned how to design the ski jump so the skier didn't lose his balance when he landed after the jump. At first, these were used just for qualifying. Now they use such "lofting" cams for 500 miles, and the Europeans are calling them "Ballistic valve trains". I think it can work only because NASCAR engines don't run across a wide range of RPM. The guys at Spintron have books and books of development records of this kind.

then Kevin added six minutes later:

The old 1100 Suzuki GSX-R (like the one we did the cam rolls with [at your dyno for Cycle Magazine]) had serious torsional problems down at 6500 - endurance teams that ran them that low broke cranks. So they went to the US Cosworth importer, who made them up a replacement crank out of trick 4340 material. Broke in the same place.

Similar story with the Honda twins that have staggered crankpins. When they run at higher revs, the two flywheels clapper back and forth like a lo-frequency tuning-fork, straining the shit out of the crankpin fillets, which crack. First thing the rider knows, the crank "feels funny". Then BLAMMO, it becomes two-piece, and the bike slows right down.

I think there is a driveline resonance in my Cobalt, which is just building up as the engine is pulled own to about 1350 in top-gear lock-up. Then the shift program clicks in 3rd, before it gets too noticeable. It's like "fan growl" that you feel more than hear, in airliners - maybe 80 cycles or so.

Back in the 1930s engine researchers had their choice of two different types of torsiometer for measuring the action. Lots of engines had trouble with magneto, supercharger, or other accessory drives failing because they were getting so much chatter from the crank. Gears broke, shafts spiral-fractured, stuff fretted to death.

Yes, friction is caused by welds that occur at the very tiny points of actual contact, and must be broken in order for sliding to take place. Temperature is high, but in such tiny places. The wear particles oxidize - when they are iron-based, it makes the familiar red powder.

Then Kevin added again five minutes later:

Yosh used to try to get away with no spring drive between the engine and gearbox. Sometimes it worked. Other times it just broke parts. The spring drive is very old. When Napier offered the first in-line six for sale about 1903, the vibes caused the cam drive to chatter audibly. Master salesman and early racing driver S.F. Edge called this "power rattle".

When Rolls brought out their six, they weren't having this problem so after having a wood friction damper catch fire, they came up with the idea of the spring drive. On their wartime Merlin V-12s they effectively cut the crank's free torsional vibration length in half by making the center a node. This they did by connecting the front of the crank to the prop via a springy quill-shaft, and the back of the crank to the accessories by a spring drive just like what's in every motorcycle clutch.

There were all kinds of failures when Diesels with long lightweight cranks were put into subs, driving the props directly. There had to be lists of forbidden rpm at which the crank could not operate for more than a couple of seconds. To solve this, the US Navy adopted Diesel-electric drive (same reason it's used in rail locos) so the Diesel would run at a constant safe speed and the props could be controlled separately.

A stewardess was killed on a commercial flight NY-Miami in 1948 by a piece of prop tip, coming through the fuselage like it wasn't there. Metal remembers every insult - cumulatively.

Your instincts [regarding high combustion chamber pressure] are correct - Diesel engines, with their very high compression and high combustion pressures, need much "deeper" spring drives. ZF Transmission gives their trannies a double spring drive for Diesel applications. They say it improves fuel consumption by about 6% (a lot) because the driving torque converter element rotates more smoothly, and does not advance in a series of eddy-producing jerks, which are wasteful.

This is why I have missed you these past years - we've had so many good conversations in which we try to think of explanations for observed phenomena.

June 16, 2:33pm email from KC:

Steve Weinzierl had that case of the prototype triples that Fuji had built for Polaris a number of years ago. They all broke cranks in testing (20 of them, and not cheap either!) and the Polaris people were just throwing up their hands. Steve, in his methodical way, got out the thick books on crankshaft math simulation and plowed through it all - approximating the flywheel discs as separate masses and working up all the shafts as torsion springs. And the math showed about what they had - a bad maximum at 8500. He added 2-mm to one or two shafts, parts were made, and on test everything was sweet and calm.

Kevin

I remember that the word on the street was to avoid 8500 on 600 or 650 triples, something bad was supposed to happen there (even if they strengthened parts no sense pressing luck). Its good now to know how that info came about. So triple pipe makers all stayed at 9000-9200 except for Aaen who had peak hp at 9800 as I recall.

Also remember I was having Ron Chastine map the EFI on my Bender 3 cyl Exciter (an extra throw and rod pressed onto the original 2 cyl), Dyno mapping 55 gallons of gas thru the engine, steady state at all throttle positions, all RPM we surely found the RPM where resonant frequency (?) was the worst and spent enough time there to hurt parts. The flywheel taper and crank taper were welded together in a small spot, instead of a nice pop removing the flywheel with a puller, it sort of gooed off, like pulling apart a piece of licorice. About 3mm diameter chunk was pulled from crank taper, welded solid into the flywheel taper. Jim

email from KC June 17, 12:25

I have many times in crank rebuilding seen such welded regions. Once I took apart a crank from an early-model 500 Kaw H1 streetbike with 50,000-miles on it. Both mainshaft press-fits tore extensively on the way apart and the pieces had to be scrapped.

In the early days of British motorcycling the common 500 single had two cast-iron flywheels, a tapers-and-nuts crankpin, and a pair of mainshafts. As rpm got up near 5000, all the shaft started to work loose - the iron was no longer strong enough to maintain the tightenss of fit against the rising stress. So they began to use steel wheels, and then later, alloy steel.

It's interesting to see that the US lagged behind Europe (notably, France) in adoption of alloy steels. Schneider-Creusot began to offer nickel-alloyed steel in the 1880s, and Winchester adopted it for gun barrels after 1895. But top brands of US cars had their cylinders cast in nickel-iron and their nickel-steel crank forgings sourced from France before WW I. All US artillery designs traced back to French originals, right through WW II. The French were the first with the quick-firing 75-mm gun, which thanks to its hydraulic recoil gear was still aimed at the target after recoil - the whole gun no longer "retreated" at every shot. So all the gun crew had to do was keep slapping shells into its breach.

I think it was the Triborough Bridge near NYC, that was made of 3 1/2% nickel steel. Everyone was so horrified at the cost that they adopted the much cheaper low-silicon steel, which is what the Titanic was made of. That stuff was very poor in corrosion resistance, so as US manufacturers made more and more requests for better materials, suppliers did the necessary research and little by little the alloyed materials we know came into being. Now that the US is rapidly de-industrializing, I hear it's not so easy to get even basic stuff like 8620 or 4340 steel stock - "Sorry, special order only - there's no call for that stuff any more".

Suzuki 2-stroke flywheels were always almost file-hard, but Yamaha stuff was a lot softer - if you put a dial gage on the OD of a flywheel you could "see" the bulge caused by the pressed-in crankpin.

Tuesday, June 05, 2007

DynoTech : Month of June 07 schedule

5/7 Jim Cooper's PS1000 triple Skidoo asphalt racer, dialing in new MSD ignition last Friday had a bad timing pickup so were waiting for a new one. Before the pickup went bad, we had Megatron fuel flow inconsistencies (solid mount twins are usually the worst, solid mount stroker triples are almost as bad). Jim had trouble at the racetrack with this, usually dropping 500 revs from half track on regardles of clutching. I'm betting the carbs were foaming like they are doing on the dyno. Along with new MSD pickup, Jim's getting larger, viton N&S's to try. Looks like Thursday AM/ PM. Got the MSD working again, turned out to be a missing crankcase bolt allowed A/F mixture to escape into the flywheel area and foul the MSD crank trigger. But those carbs are still giving us fits, fuel flow is 86 lb/hr at HP peak must be milkshake in the float bowls. Will try agian Saturday, mess with adding weight to carbs, fuel pressure etc.

Thurs AM sliding Jim Cooper's sled off the dyno, cameras off, private tuning session for another pro racer, Jim Cooper will be back on to finalize his tuning late thursday. Private session was Glenn Hall's first crack at dyno tuning a Boondocker turbo system/ D&D F1200/ Firecat (he was concerned that we might fumble this and he didn't want to goof on camera). Off the trailer it was effortless 325ish at 10 psi boost. So we spent the day cautiously tweaking boost/ fuel/ timing/ exhaust components, gradually working up to 286 lb/ft torque and 414 CHP at 15psi boost!!! This pretty good HP for a Firecat chassis. This AM I'm going to put that HP screen up on the dyno computer, set it up to contuously replay the 400 plus HP tuneup dyno run.

5/9 Justin Fuller with turbocharged Yamaha 1000cc streetbike, maybe an R1 using the Cycledyn eddy current roller dyno to dial in boost/ A/F ratio. Justin's still not quite finished with kit, will reschedule.

5/10 Justin Fuller has the R1 turbo system done, will dyno tune this PM about 4:00 Easy to fine tune, same fuel management as Justin uses on Apex turbo kits, made 200 DJHP on pump gas at the rear tire at 5.7 psi boost. Everything is hidden under the fairing, stock mufflers are used.

5/12 Finishing Jim Coopers PS1000, then Steve Bennett from West Virginia with CS1710 asphalt sled with fueling issues once more. Short on time, pulled Jim's sled off the dyno to redo fuel system and add 5 lb of mass to Lectron carbs and will be back. Since Steve Bennett's last trip to dyno where we had bumped fuel pressure to 6.9psi to overcome foaming float bowls, then made 321hp, Steve was fine for most of the season. But then he added n2o and snapped a conrod, replaced crankshaft and vibration was worse and fuel flow became impossible once more. Back to Batavia. On the dyno carbs disappeared into a silver blur at 6500 and no juggling of fuel pressure could make carbs deliver usable fuel flow--either 140 lb of fuel flow and float bowls went dry or add 1/4 psi and fuel flow went to 250 lb/hr and drowned the engine. Frustration over a vibrating engine with solid motor mounts. Tomorrow AM Jim Cooper is dropping in a brand new CS1710 engine into the solid mount chassis, hoping this is smoother and if we can see the carbs, maybe we can get decent fuel flow for 8.5 seconds. We have difficulty with most solid mount long stroke engines.
5/13 Jim Cooper spent today dropping in the new 1710, after transferring carbs/ ignition from old engine. Tripod Dan brought some rubber mounts which we used to isolate the engine mounts from the chassis. After an hour of sputtering trying to start the engine (glad we have electric start) on the dyno we discovered the new engine's keyway was about 100 degrees off from the old one. Jim would come back tomorrow with his degree wheel/ dial indicator and figure this out.
5/14 while Jim was indicating the old engine, we discovered the crank was out of phase. Could this have been the source of excessive carb-foaming vibration? Jim rotated the MSD flywheel to align it properly with the trigger, and we were running. Now from 6500-8000 we could actually see the carbs, and even though the mechanical fuel pump was inadequate the Holley pump was tweaked up and down to where we got smooth fuel delivery without drowning the engine. Fine tuning timing and jetting netted us 229 /b/ft at 7400 and 328 CHP at 7700. Smoother due to better crank balance and/ or rubber isolation of engine from the rigid chassis.

5/15 AM Robert Murray with Bill DiFranco's D&D F9 engine that he bought from the guy in Canada who Bill sold it to. Robert bought the engine only just as when LT Bill had it, except a reed change, Robert added his own 03 ECU and it was way too fat on top end, way too lean in midrange. He brought another 03 ECU from his other Firecat, this one was 10 lb/hr fatter than the first one. We tuned it to add midrange HP by adding fuel there, but we couldnt get the top end perfect. Robert's Boondocker had the original program with not enough steps for a twin pipe engine (only 6700 and 7800). We got the fuel perfect at 7800, but fuel drops as revs climb to 7900 and beyond to deathly lean. He's sending the Boondocker back to have D&D's program installed (he pays D&D $75 but ships it direct to BD). Then he'll have a step at 8200, use his current settings for 3000-7800 then add a particlar number at 8200 that should flatten out his declining fuel flow as revs climb. The engine now makes the same torque and HP as when Bill dyno tuned here a two or three years ago.

Just sold my 90 Exciter with Bender Avalanche triple/ IRS EFI, but my pipes are still missing after I loaned them to Mark Forte in NJ for testing at New England dyno service 15 years ago. Need to buy another set if anyone has some hanging on their garage wall please email me. I found out that Mark Forte still has his Avalanche with MY pipes on it (he said that to the fellow who bought my sled from me--he also said that his were lost in shipping to Jaws for modification). I plan on getting my pipes back.

.5/21-5/28 cameras off intermittantly for private test session with engine on my motor plate.