Friday 24th, Philippe Tusler wrote, in response to my earlier mail:
>You mention the dismal balancing of clutch assemblies and recommend
>balancing them with the rest. However, the clutch assembly does require
>changing ever so often.
Yes, I quite agree!
That is the reason why we, at first, only balance the crankshaft itself,
then assemble the flywheel to the crankshaft and drill away any unbalances
that may still be present in the flywheel.
Then we assemble the clutch assembly to the flywheel. Any unbalances there
will be rectified on the clutch assembly itself, then.
BTW at that time we also check for mechanical errors. If there are any, we
notify the owner.
Frequently we come across main journals that are not (enough) in line.
Sometimes fixing a flywheel to a crankshaft is not possible accurately enough.
(Notably with VW Beetle and similar Porsche 356 engines where the design is
a bit weak in this area). Such errors should be rectified first, of course.
Only last week we had an interesting problem with a MGA crankshaft.
Our customer, the repair workshop that brought the crankshaft in, told us that
this particular car had a high vibration level over a large speed range.
We found that the bore in the spigot bush in the flywheel (that is, where the
input shaft of the gearbox goes) was eccentric. Probably unobtainable once,
somewhere in the past,
a DPO or DPW had made one, though not very accurately.
After balancing in the way described here, a clutch assembly or a flywheel
(provided they have been balanced, of course) can be changed without
disturbing the mass distribution (=balance) of the assembly.
>Can the new clutch assembly be checked for
>balance before installation? How would one do that? With a modified
>bubble-level wheel balancer, maybe?
Forget it. The problem is that you should have the actual clutch centerline
to coincide with the desired centerline (as determined by the three (?) dowels
on a B-flywheel). You can never do this accurately enough, i.e. within 0,02 mm
(.001 in) without quite a lot of tooling.
A trick of the trade is, that you can check the accuracy obtained with a
balancing
machine / device by rotating the clutch under test over 180 degrees with respect
to the tooling. You should get the same (zero) result as before.
Checking can be done more accurately by a balancing workshop. You should, if
possible,
also supply the matching flywheel, to keep tooling costs (if any) minimal.
BTW, an unbalance in the crankshaft assembly will cause vibrations to exist.
Damage may not immediately be imminent.
Mostly these vibes will be felt over a certain speed range only.
What range that is, is different from car to car (design), e.g. 1500 ...
2000 rpm or 3000...5000 rpm.
I've test driven several cars with vibration problems (mostly new ones,
including some VERY
expensive and desirable ones), sometimes both before and after balancing.
Important is to pinpoint where vibrations come from:
Is it the drive train (i.e. only at, say, xx mph, put the tranny in neutral,
switch the engine off,
is it still there?) or is it the engine (only at xx rpm, even with the
tranny in neutral?)
Not all vibrations are caused by unbalance, however. Sometimes exhausts
cause trouble,
sometimes camshafts are not symmetrical enough.
Hope this has been of some interest to you.
Bert Palte
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Bert Palte Alumnivereniging 'Elysium'
Roggeveld 25 Universiteit Twente
3764 ZB Soest Faculteit Elektrotechniek
kamer EL/TN 8238
tel. 035- 602 39 49 (huis) Postbus 217
tel. 035 - 601 38 16 (werk) 7500 AE Enschede
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