[s-cars] Harmonic Vibration?

[CyberPoet]

Sorry, Todd,

I haven't had to do a clutch on an S-car yet (knock on
wood), but I am not familiar with the whole "heavy spot"
concept on the flywheel, which normally would be
virtually ideally balanced in all cases. I mean, think
about it, if the flywheel weren't ideally balanced, then
the crank would constantly be subjected to lateral
stresses and sheer forces (induced by the flywheel),
which would tear up crank (main) bearings quite quickly
at higher speeds. I could see the flywheel being
slightly off-center to compensate for a counter-matched
imbalance in the design of the crank (so the imbalances
balance out), but not in the clutch plate (and
especially not in such a way that the 'heavy spot' would
match to the 'heavy spot').

I suspect it sounds very much like the PO was playing
around under there and didn't pay close attention during
a clutch change (?) or other tinkering, if he has a
notion that this is the reason...

Still, try disconnecting the various Serpentine-driven
accessories and see if the vibration disappears -- it's
not uncommon for an alternator or A/C compressor, etc.
to develop such a problem in that RPM range.

=-= Marc

TM wrote:
>
> Thanks.  Timing and Serp belts and tensioners, engine and
> tranny mounts, oil and filter.  All were very recently
> replaced by 2Bennett.  Vibration occured before and after.
>
> One interesting thought is this (transmission was removed
> and repaired by previous owner in December):
>
> "I'd suspect that the clutch pressure plate is out of
> balance.  Usually, it has to be installed on the flywheel
> in a certain way, with the heavy spot opposite the heavy
> spot on the flywheel.  If they are both in the same place,
> you will have a vibration such as you describe.  Heavy
> spots on these parts are usually marked with either a punch
> mark or a paint spot.  Check the Bentley manual to see what
> it says."
>
> This thought comes from a fellow s-car enthusiast.  Do you
> have any direct experience with the clutch assembly?  Do
> the pressure plate and flywheel really have these markings?
>
> Thanks.
> Todd
> ======================================
> Subject: Re: [s-cars] Harmonic Vibration?
> ======================================
> That harmonic vibration at 3200 - 3800 and reappearing at double that
> (6500 RPM) is not necessarily from the engine unless you have isolated
> it down to the engine. Any part connected to the engine area can be
> induced to vibrate when it hits the right harmonic frequency (every
> item has an inherent frequency; when the engine hits a specific RPM, it
> causes whatever else to vibrate with it).
>
> The first things to check are (in order, based on the KISS principle):
> 1. Engine Mounts -- if you're lucky, this is it.
> 2. Tranny mount(s).
> 3. Timing Belt/timing/tensioner.
> 4. Disconnect A/C, hydraulic pump, alternator and recheck for
> vibration. Reattach if not basis.
> 5. Remove the oil filter and cut it open -- check for metal particles
> (indicating a bearing has failed and metal is grinding - if yes, go
> straight to step 9).
> 6. Have someone else run engine at 3500 RPM and work around it
> with a stethoscope.
> 7. Front, rear cam, crank bearings from the outside.
> 8. Drop the oil pan, look for signs in the galley, slop in rod
> bearings, etc. Remember the idea here is to find the problem with
> minimum effort.
> 9. Yank the whole engine and tear down (goody, fun for the weekend...
> do it in the living room just for shits and giggles).
>
> Good Luck!
> =-= Marc Glasgow
> www.cyberpoet.net
>
>
> TM Wrote:
>
> Has anyone experienced vibrations coming from the 2.2T
> engine in specific RPM ranges? My engine seems to vibrate
> b/t 3200 -3800 RPM (significantly) then again after 6500
> RPM (very slightly).  Runs really smoothly when it is out
> of those ranges.    Happens in all the gears and in neutral
> (even happe ns when the car is stopped and in gear with the
> clutch engaged.  I have che cked all of the heat shields
> and the exhaust system - everything is tight. If it is a
> harmonic vibration, can it be fixed by tearing down the
> bottom end of the engine and re-balancing everything
> (harmonic balancer, crankshaf t, rods/pistons, and
> flywheel)?  i.e. leaving the top-end un-touched?
>
> Any input would be much appreciated.  Thanks.