Can washing machine start capacitor test good - and still be bad?

About a year ago the motor in my kenmore washing machine was acting up - buzzing but not turning. I suspected the start capacitor and picked up a used one for $10 at a local repair shop. These are black, about the size of a D-cell battery.
The original was 270 - 324 mfd, 110 vac. Model 3348058.
The one I got as a replacement was 189 - 227 mfd, 357021.
Even though I had a capacitance meter at work, I just went out and picked up the used cap, installed it and bingo - the washing machine works. That was a year ago.
So more recently, over the past week or two, the motor was acting up again. It would buzz, I'd bump the machine, and it would start. But yesterday even bumping / rocking the machine didn't work.
So I took the capacitor out and measured the original and this replacement. The original measured 298 mdf (micro-farad) and the replacement was 211. Both numbers pretty much exactly what they should be according to their labels.
So maybe the problem wasn't / isin't the capacitor - but a centrifugal contact in the motor? Do these motors have such contacts (start winding) ?
Or can hand-held digital capacitance meters perform correct measurements on these big caps?
I'm cross-posting this to alt.hvac, because my question about this washing machine motor capacitor and how well or accurately a capacitance meter can measure them if they're bad might also apply to compressor or fan motors.
As far as I can tell, there is just this one capacitor connected to this motor, so I don't think there are separate start and run capacitors.
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Home Guy wrote:

Hi, Rule of thumb, you don't replace cap. with lesser value. If same one is not available, use one with larger value. Even tho meter shows it OK, under voltage in circuit it can go bad.
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Tony Hwang wrote:

But why could I get the motor to start by bumping the machine?
Are there centrifugal contacts in the motor?
Or was the bump enough to get the spindle turning?
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Home Guy wrote:

Hi, You're doing the job of the cap.(shifting(leading) current phase) Motor winding is inductive, with cap. you counter the inductance. That cap. is called PSC(Phase shift capacitor). Most new appliance, even garage door opener, vacuum cleaner, furnace blower, nowadays use smaller more powerful DC motors. DC motor's efficiency is higher than AC motor using PSC. Also Diesel electric locomotive propulsion is by DC motor. Diesel engine drives generator, which in turn it drives DC motor. That is why it is called Diesel electric locomotive.
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On 3/3/2014 5:42 PM, Home Guy wrote:

Probably that. Glad you got it running, though.
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I had the same symptoms on a Maytag.
There's a centrifugal switch on the shaft. Sometimes they get stuck in run, the little spring is supposed to pull them back to start but it doesn't always work.
I put a little high temp grease on it and it has worked fine another ten years.
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Are you sure it wasn't running all the time, but the belt was slipping. That can sound like a hum too iirc.
Before I tightened it, I would give the edge of the drum a shove and that would start it on the spin cycle. (I think it's a sub-cycle really. Why is it called a cycle?)
On my Whirlpool I have to tighten the belt every 30 years, but some belts might loosen more quickly.

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replying to Home Guy , SC wrote:

#1 A new capacitor cost approx, $10.00. The capacitor you got is to small for the motor. The capacitor must be within 10% of the orig. 270-324MFD at 10% would be 243-292MFD below orig and 297-356 above the orig. That is a start capacitor, however it sounds like you have a motor problem or to much load on the motor. Could be a pump problem also.
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