Bill Eastman wrote:
> Were the crank and flywheel balanced separately or as an assembly
> when the car was built?
I don't know ... but, IMHO its doubtful that they balanced them
together.
Here is a snipet from one of Barney's posts on balancing and MGA
engine ...
"When balancing an engine, you may hear that you have to supply
all the moving parts to the shop doing the work, crankshaft,
harmonic balancer(front pulley), flywheel, clutch cover, clutch
disk, bearings, connecting rods, pistons, wrist pins, piston rings.
This may lead you to believe that they balance all the parts
together. This is usually not so, and for an MG engine in
particular this is not necessary.
The key factor here is that the MG crankshaft is symmetrical when
viewed from the front, so can be balanced alone with no other
parts attached. To state that differently, #1 and #4 rod journals
are symmetrically opposed by #2 and #3 rod journals, and everything
else on the crankshaft is round and concentric to the main axis of
rotation. All other parts are either also concentric to the main
axis, or come in pairs offset by 180 degrees on the crankshaft to
counterbalance each other.
All that means that the rotating parts can be balanced individually,
and the reciprocating parts can be balanced as sets. In this case
it is also best to do it that way. If you balanced the whole
assembly but ignored the individual parts, then changing any one
part
later could unbalance the whole system."
> A friend has a used flywheel with a decent ring gear that he may
> be willing to part with but I don't want to have to pull the
> crank and rebalance just so that I can save the money for a new
> ring gear. I would not mind saving the money if there was no down
> side, however.
Another snipet from Barney's post ...
"The flywheel is by far the most massive moving part of your engine,
so the most critical to balancing. Even if you use a light flywheel
that weighs less than the crankshaft, the bulk of the mass of the
flywheel is much farther from the center of rotation and will affect
the balance proportionately. Spin balancing is the preferred method
here as well, with material being removed from the non-contact face
at the rim. The factory always balances flywheels (within reason),
so you will generally find some drill holes in the front face of the
outer rim just inside of the ring gear.
The factory balancing of the flywheel may not be close enough to
satisfy some people (especially for a race engine). With
considerable
age, warping by thermal stress or wear on the friction surface may
require refacing of the flywheel. It is a good time to have it
rebalanced if any machining is done. Also, while changing a ring
gear should not significantly affect the balance of a flywheel, if
you're superstitious or critical or if it's a race engine, this is
also cause for rechecking the balance.
The clutch cover (pressure plate assembly) and clutch disk are
usually well balanced as shipped from the factory, and can generally
be ignored. However, if you're concerned, or if it's a race engine,
the clutch cover can be mounted to the flywheel and balanced after
the flywheel has been balanced alone. The MGB diaphragm type
pressure
plate assembly is not likely to loose the balance over time. The
MGA
three-arm pressure plate assembly is more likely to get out of
balance
if somehow misadjusted, especially if it is disassembled for
reconditioning. After reconditioning and reassembly the MGA
pressure
plate should always be re-balanced."
... so, it would seem that you could fit the used flywheel without concern,
however I would consider having it refaced and balanced.
> The ring gear is worn in a couple of spots only (typical of four
> cylinder engines). I know this is crazy, but can anyone think of
> a down side to just re-indexing the flywheel to put fresh teeth
> where the wear has occurred.
I've never tried this, but have heard of folks that have.
> I am thinking about having the flywheel lightened. Anyone have any
> recommendations about area and amount to cut? I would have this done if
> I choose to have a new ring gear professionally installed.
Sorry ... don't have a recommendation, but the 1800 3-main flywheel is
lighter ... perhaps that would be a good weight to shoot for.
> Has anyone installed a starter ring gear at home? Any pointers that you
> are willing to share?
To my knowledge this it not a DYI item ... best to leave it to a machine
shop.
> Thanks for any help you can give.
As per Joe Joe Ratigan's post ... the "trick" thing to do is to fit the
superior
'B' clutch bits. The 'B' 3-main flywheel is lighter that than the 'A'
flywheel
and will bolt-up to the 'A' crank without modification. You will also need
the
front tranny cover and release bearing arm from a 'B' 3-synchro tranny ...
this
will allow you to fit the 'A' clutch disc, 'B' pressure plate, and the 'B'
relase
bearing. The 'B' pressure plate is a bit thinner than the 'A' ... the 'B'
tranny
cover and release bearing arm corrects the geometry so that the 'B' pressure
plate
can be fitted.
If you replace the 'A' 10 spline input shaft with the 23 spline input shaft
(from
a late 'A' tranny or a 'B' 3-synchro tranny), then you can fit the 'B'
clutch disc.
You can use the 'A' flywheel, in lieu of the 'B' 3-main flywheel, however
the
'B' pressure plate will not bolt up without modification ... the locating
pins on
for the 'B' pressure plate differ from the 'A'.
I have a spare front tranny cover and release bearing arm from a 'B'
3-synchro
tranny that I can sell ya if your interested.
Safety Fast! ... larry.g.unger@lmco.com
'61 MGA 1600 MkII
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