"Pete C." wrote in message
er.com...

Karl Townsend wrote:

"Pete C." wrote in message
ster.com...

Karl Townsend wrote:

What happens when you change the tension on the fan drive belts? If
they
are
implicated at all, that'll change the resonant frequency. It's a bit
far
to
drive over to Blighty so we can instrument it up and workout where
the
resonance is :-(

Mark Rand (Did similar work on power station foundations once)
ETFM

I've never tried that. I keep the eight belts pretty tight, 1/2"
deflection
in the three foot between pulley spacing. can't go tighter, I'd take
out
bearings. What do you think running loose would do? Not much margin
here,
I
smoked all the belts once, pretty spendy to rebelt this unit.

Karl

I recommend you closely inspect the spray pump as noted in my other
post. If it is a triplex pump like the one on the other unit you posted
a link for it could very well produce a "lumpy" torque load if one of
the pistons was not functioning like from a stuck inlet valve.

The other thought, is that if this lumpiness occurs once per PTO shaft
revolution i.e. 9 times a second, something may be bent, such as the
shaft the pulleys are on, causing the belt tension to cycle every
revolution.

Thanks for the thoughts. This unit has a centrifical pump, no bumps there
plus it only uses a couple horse. You have a thought on bent, I know its
not
in the shafts, but possibly the fan itself is bent. The entire fan could
be
removed and put on some sort of unit to check balance and vibration.
Anyone
know where I might find equipment to do this?

Karl

If the "bump" is indeed at the rotational frequency of the PTO, I'd be
looking at the drive sections that rotate at that RPM. Presumably the
fan is overdriven from the 540 RPM PTO to a higher RPM so an issue there
wouldn't manifest once per PTO rev.

If the drive pulleys from the PTO shaft aren't concentric, there would
be a cyclic variation in belt tension on each revolution, and since the
belt will tend to move in and out in the groove with tension, it would
also translate into a cyclic change in the drive ratio. It could be
subtle, but with that much HP and mass involved, it could become
significant at that resonant frequency.

Since you report that the problem keeps coming back, it may be that an
issue like pulley concentricity has always been there, but becomes more
apparent over time as everything loosens up and the vibration can have
more effect. Perhaps get out the dial indicator and mag base and check
the run out on the drive pulleys?

Thanks Pete, more good suggestions.

Julie hit a home run on the PTO rebuild. The fleet farm store was stocked
out. So, she found a specialty drive line shop and had everything rebuilt
with top-of-the-line parts. She's not only a great go-fer, she's a good
looker too. (That means she can find stuff)

I'm puttin' the machine back in the field tomorrow but a complete rebuild on
this unit is job 1 at end of season.

Karl