Dr.Ben
Elite Veteran
Location: Richmond, VA, USA
| When it comes to dial indicating, the closer you are to 0.000", the better off you are. You cannot use what shows on the mode as vibration as the criterion for excellence. Even if the fuel is calm, if the system isn't as good as you can make it, some part of the model, especially the clutch drive bearings WILL see the effects of the added runout. This can be decreased bearing longevity or far more insidious things like subtle grommet "dust" where the whole radio tray is sucking up the vibration. Especialy on plastic framed Evos which are highly tolerant of engine vibration, you really must go for the best alignment job you can to protect the model components that you can't see and which can't speak for themselves, so to speak.
The heart of a good dialing job has to be getting the fan on there as close to zero as possible. Since the fan is the base for the clutch mounting, any error in the fan gets magnified as you go further up the clutch. For this reason I won't run anything over 1/2 thou on the fan. The Evo and collet type EX fans are truly excellent. Every one I've had has easily dialed in to 1/2 thou or less. If your run out persists at about 0.001", you may be able to lightly tap the fan's face as you incrementally snug the nut down to decrease the run out. I used this method for years with the MA fan's, and I was always able to get the run out to under 1/2 thou provided the crankshaft was true. This crankshaft issue is a real sleeper WRT to dialing and is a reason why kit mfg's get a lot of bad press for their fan and clutch designs when it is the engine and not the fan or clutch that is the problem. The OS engines are typically quite excellent in providing a true crankshaft on which to mount the fan. If you're mounting an Evo or collet EX fan and it refuses to dial under a 0.001", immediately suspect the engine. Also , the YS engines can be more challenging in this area because of their cranks. The ST91 can be a royal pain; the SR's are much improved but I've still received email where the dialing issue was isolated to the crank on an SR 91. The crank was replaced under warranty.
The clutch..............There are several critical points here. First, that clutch MUST, MUST, MUST have some wiggle room where it fits down into the face of the fan. I've had two that were a very snug fit. This is no good and gives you no wiggle room. In these cases I chuck the clutch up into a good lathe a reduce the OD of the step in the base of the clutch enough so that the clutch has some wiggle room when mounted on the fan. I also take a drill index and open up the mounting holes in the clutch a few sizes, also for more room for adjustment. You need to understand that when this wiggle room is present, dialing comes down to just moving the clutch around to the right place. If the fan is well dialed, it's easy to get the base of the clutch to well under 0.001". I go for between 0 and 0.00025". Then I check the tip. If the tip is out more than a few thou, I don't tweak it. I understand that the tip can be tweaked. I also know for a fact that hardened steel has a good memory, and the tweaking doesn't hold after the engine has been run. Recheck the tip on an engine you've removed that had been in for a while; you'll see what I mean. If the tip is way off, then the clutch shaft isn't running true to the clutch base. In these cases I go back to the lathe and "dust" the clutch's base so it is square to the shaft. Honestly, I do this as a default now because it really makes the whole process a dead easy no brainer. I understand that not everyone has a lathe. For those guys who are at wits end, you can send me your clutch, and I'll face it for you if need be. Once the shaft and base are squared up, then you'll find the tip and the base of the clutch run very close to the same TIR. If you get the base to 0 and find a small amount at the tip, then check the direction of the runout at the tip and move the clutch such that you add just a little runout back to the base while reducing the run out at the tip to where you want it.
One last little philosophical point.If somewhere were to look at the price on an item in one store, and it was one given amount, and then another place that item cost twice as much, you'd thnk the latter place was likely way out of line. Twice as much is 100% more. Remember this when you measure 0.002" of runout and when a little more time could yield half that amount. Even in thousandths of an inch, twice as much is twice as much.
'nuff said.
Ben Minor
Representing
MRC Hirobo Helicopters and Team Futaba for Radios
Morgan Fuels
OS Engines |
Plus the fan on my stratus is about .003 and it runs fine.
