For the next few weeks or so, all 400 plus HP tuneups are on hold. The following photos show what is left of my $1000 big driveshaft.
In my blog schedule I facetiously suggested that last weekend after the Shootout, “OSP Jim and crew [were coming here] trying to break my dyno….”. I won’t be making jokes like that anymore!
Saturday afternoon, OSP Jim and madman driver R. Dustin came to demo the power of Shawn Burke’s Adirondack Shootout record setting turbo Nytro (anyone who was at the Shootout knows it really didn’t need much dyno tuning), but we never got to make any big power with the Nytro before the steel molecules in my big driveshaft got tired of holding hands. While loading the engine at 8500 RPM in preparation for our first dyno test, we felt a 1/2 second shudder followed by a loud pop and the engine was against the rev limiter for a fraction of a second before being shut down. The driveshat had separated at both ends–from the rubber vibration dampener at the engine, and the automotive ujoint coupler at the absorber end.
Fortunately, the orange colored driveshaft loop did it’s job, and the roof of my building is dented by small parts but unpunctured. But there was a violent 360 degree spray of bolts, u-joint bearing caps and bearing needles that created many new holes in the ceiling tiles, walls, and light fixtures. And there are surely some IED-like steel shrapnel that I will find, rusted, in the parking lot next spring.
The taper end on Shawn’s nytro is bent, but that working end, splined to the end of the three cylinder crank is replaceable from the side of the engine.
But most importantly no one got hurt. I will keep what’s left of the driveshaft to explain to people that come come here why we never enter the dyno room with the engine under power.
Do I need a stronger driveshaft? Nope–it wasn’t fatigue from too many high power sled engines (the shaft is designed for 500 lb/ft continuously), but operator error that created this havoc. Trying to assess this mess, like a forensic detective, I think this is what happened…
Torsional vibrations–impact gun-like forces that create havoc with crankshafts/ crank tapers/ clutches appear to be extremely violent on three cylinder four-strokes when boosted to many times their designed torque levels. Monsterous torque levels can cause those engines’ cranks to wind up and unwind, creating torque spikes up to 10x higher than the engines’ average torque. This can cause premature wear on clutch parts, and slippage of crank tapers creating wedging of clutch tapers or even worse fretting enough to melt and weld the steel on the crank tapers! Recently FPP Justin was here with a high-boost 4tec that after maybe five 400+ HP tuning runs, and spot welded it’s crank to my SkiDoo dyno adaptor. I was able to remove the adaptor from Justin’s crank, but there were some small chunks of his crank taper melted and welded into the female taper on my steel dyno adaptor. But I have had very little trouble like that with the many high boost four cylinder Yamahas and two cylinder Z1s tested with big torque. There just seems to be more torsional vibes with the big triples.
I was hoping not to do unintended taper welding with the OSP Nytro. So when R. Dustin showed me a light coating of moly lube on the crank taper (they do that to prevent stuck clutches), I decided to not clean it off, and see how that might help prevent taper galling during dyno testing. I installed the grade 8 dyno adaptor bolt with all the torque my IR 1/2″ drive impact would put out, and attached the drive shaft. But when we began testing–loading the engine at 8500 there was some unhappiness with the dyno trying to control things. The SuperFlow dyno is completely automated–if you set the control to hold the engine at 8500 before beginning at test, it will try to do that regardless of whether it’ 50 or 500 HP there. In this case, the dyno seemed to obtain the desired 8500, but then it would misfire like tuning was poor but Jim saw on his laptop monitoring the stand alone that it was against the rev limiter. But the dyno measures dyno speed, and Jim was measuring engine speed so that difference was probably my coupler slipping on the crankshaft taper! But that didn’t register with me (never had that happen before), and it should have. Brain failure one is I should have removed my adaptor, cleaned the tapers and started over. But we tried again several more times befor the catostrophic failure, and this time I believe the torsional vibes/ slippage caused my tight crank bolt to begin backing out creating even worse slippage, and severe out of balance condition at the engine. And that perhaps created more strange, almost indescernable vibrations that were causing the four bolts on the dyno end to become loose, and eventually completely remove themselves from the adaptor and fly away. So my second brain failure was not going to check the condition of the driveshaft fasteners prior to each attempt to test. All four nuts flew, as did the lockwashers and bolts. Nothing broke, the fasters just loosened up and removed themselves in just a few seconds of operation, then flew in all directions like the square pieces of a pineapple hand grenade. I’ve done this so many 1000s of times without fastener issues, I ignored them at the worst possible time.
So OSP Jim will need to replace the Nytro crank end (hopefully only a few hundred bucks) and I will replace my big driveshaft. No need to redesign it, just build it again. But my cavalier assumption that what I tightened during setup will remain tight during the session is changed. And maybe now blue locktight on dyno shaft fasteners on these big engines will be part of the program for gonzo HP things.
And I must compliment the OSP guys on having the demeanor necessary for anyone who regularly races/ tests/ sells engines approaching 10hp/ cubic inch. Not everyone has that. Gaskets can squirm out, pistons can sieze, blocks can crack, rods can snap, and dyno drives can fail. I don’t know who coined the calmly spoken southern drawl phrase “parts is parts”, but it’s appropriate.
This innocent looking small engine coupler is about $600 worth of stuff- the eight hole Lord torsional vibration damper is a key component necessary to protect the engines from their own harmonics. And that center self aligning bearing (what’s left of it) is designed for the linkage of helicoptor rotor assemblies. The aluminum part is custom made on CNC machinery. New parts are on the way here.