A couple of months ago (April 2008) I was down at a colleague's doing some work with him and I took down my flywheel balancing system. After I lighten a flywheel I balance it to very fine standards to ensure smooth running of the engine. This means locating the flywheel very precisely about its central hole where it fits over the crankshaft spigot. Most balancing systems, much like the wheel and tyre balancers you see at your local tyre shop locate the item on cones which screw together. However if the flange on the flywheel, or your car wheel, has a burr on it the location will be off centre. Even if there is no burr there is a margin for error when two cones get screwed together as to how they grip the item between them. My system uses a custom made mandrel for each type of flywheel which is a press fit into the central hole. Yes it's a considerable degree of buggeration factor rather than relying on a universal mount but it means you get precise and repeatable results.
My colleague lightens and balances a lot of flywheels for performance customers but has no balancing system himself so he farms that out. I took my system down there to show him how to make one himself so he could save the £2000 to £3000 a year he spends on this third party service. The first thing we did was find a couple of standard flywheels and check how well they were balanced at the factory. As expected they were spot on because OE car makers use very expensive equipment tailored exactly for the engines they build. My system measures in terms of grammes at the flywheel rim and in both cases there was less than 1 gramme error at about a 5 inch radius. Basically nothing measureable.
Then we looked at 2 flywheels he'd lightened but not yet sent away for balancing and 4 which had come back from the balancers but not yet been sent out to customers.
The 2 which had been machined but not yet balanced had errors of about 2 grammes at the rim which is pretty good. It shows that when machining the flywheels on the lathe he'd clocked them up concentric and removed metal evenly so they didn't go out of balance much. They'd actually have been fine to just put back on the engine.
The 4 which had been balanced by this supposed specialist he farmed this work out to were a completely different story. The best was 3 grammes out and the worst was 8 grammes, enough to seriously upset a high rpm engine. About ten times as bad as OE factory balancing. In other words the balancing was actually making the flywheels worse than after he'd machined them but not balanced them. As we checked each one his face fell further and further. It became apparent he'd been spending a lot of money for year after year to make his product worse rather than better. How a specialist in balancing could make flywheels so much worse than standard is debatable. Either a faulty machine or a faulty mounting system probably.
There's an old saying. If you want a job done properly do it yourself but of course if you could do that you wouldn't need people like me. But what sort of standard of work are you getting when you entrust your engine to reputed engine builders in this country? By my measurements not a very good one.
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