06-4791/B High Power
Starter Motor
1975 Norton Commando MKIII
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The much misunderstood and challenged electric start of the Norton Commando is riddled with little deficiencies that have earned it a reputation for problematic starting. The lack of good original cores has prompted this effort to supply to Norton enthusiasts a functional starter with improved capability.
Addressing the following areas help to define both it's original capability and limitations, and highlights potential improvements.
Battery
The original battery was the Norton Villers 06-6515 or
Yasua YB.14.L or B.64.12
13AH at 10 hr rating, this battery capability claims
190-200 cold cranking amps and can in fact supply well over 300amps
It is in fact, quite capable of cranking and
starting a correctly equipped Electric Start Commando quite handily.
However, defining what a "correctly equipped" Electric Start Commando
will remain the focus of controversy.
Other Batteries
Both stock sized hi capacity sealed Gel Cell and larger
wet lead acid batteries will undeniably help cranking of any of
these starters. The larger battery method
unfortunately requires the removal of the original air box which is arguably the
best all weather air cleaner the commando ever had. This is an
unnecessary and undesirable modification in the opinion of some owners, yet it
seemed to be a way to upgrade, considering the previously available
options. The selection of gel cell batteries that
will fit in the original space are limited in selection and are a little pricey,
but certainly lighter then a big wet cell. A worthwhile upgrade.
Charging System
The importance of a charging system that will bring the
battery back up to a adequate state of charge in time for reuse can not be
understated. The external drain from the system,
while running, reduces the ability to recover to an adequate charge. Examples
are electronic ignitions that use excessive amounts of electricity, and high
current headlight. The MKIII came with an RM23 180W alternator. It has been
often reported that the battery does not always keep charged up in all
electrical load configurations of the MKIII. The
Lucas Power Base 180W alternator is an upgrade that makes more power at lower
RPMs. The SPARX 220W alternator provides even more
charging capacity.
Ignitions
The Boyer analog, while being popular, and often used on
MKIII's , must be woken up before it is functioning, and during cranking
is subjected to BELOW it's minimum reliable running voltage. The risk for
kickback is real, and has been known to be disastrous and cause expensive damage
to the sprag clutch and other starter drive components.
The Lucas Rita is now out of production, but should still be sought out as an
ignition that has been shown to reliably fire the plugs down to under 6.5v
thus minimizing the chance of damaging backfiring.
Cables
Higher resistance wires reduce the current available to the starter,
reducing the ability of the starter to spin-up the engine.
See Upgraded Cables 06-5909/A,
0605910/A & 06-5911/A.
Starter
The following measurements/observations were made while
using 6G heavy duty starter cables, and a new, fully charged stock
sized battery.
Norton 06-4791/Prestolite MGD4111 Starter- stock 2 brush
21 segment single wrap armature-about 3.5 gauss/amp in series with 2 - 6
turn series fields
*Long out of productions. Some NOS units are reported to
still be available for around for $600
**Draws about 300 amps stall, 200-266 normal starting
current, 120 amps once engine is turning.
Voltage depression at battery during current surge,
9.41-9.77v typical.
***Impression- Functionally adequate if all factory stock
systems are up to snuff.
****10 tooth armature gear
*****6-1/2" installed length
Norton starter-modified to 4 brush
21 segment single wrap armature-3.5 gauss/amp in series
with 4 - 6 turn field coils
*Rebuilt units available from suppliers for over $600,
Yours rebuilt or modified For typically $300-$400
**Draws about 344 amps stall, 207-220 normal starting
current, 125 amps once engine is turning.
Voltage depressed at battery during current surge,
6.32 - 9.45v typical.
*** Minimally better than stock.
****10 tooth armature gear
06-4791/B Starter - based
on a modified hi volume production japanese starter
4 brush 21 segment double wrap armature, about
7.5-9 gauss/amp in series with 4 - 10 turn field.
**Draws up to 372 amps at stall. 280-312 amps normal
startup current, 170 amps once engine is turning.
Voltage depressed at battery during current surge,
7.40-7.92v typical
***Spins the engine with VIGOR, very
noticeable/significant increase in cranking speed
****9 tooth armature gear
*****4-1/2" installed length
Gear reduction and starter mechanism
Norton/Prestolite
*One huge, but largely unknown defect condition is the worn end of the starter
armature shaft and it's mating support bore in the back of the primary
chaincase. Many starters are rebuilt without even addressing this issue.
*Unless sealed, the starter suffers when gas infiltration from carb
tickling gets inside and washes out lube from the bronze bush bearings.
Accelerated bearing wear and harder cranking will occur. The internal gasoline
cleaned surfaces will be prone to rusting since rain water is not
effectively kept out. Rusting on the armature thrust surface prevents quality
rebuilds and is a permanent degrading of the core.
06-4791/B Starter
*4 Brush-high driving torque
*Ball bearings for efficient/easy spinning
*O-ring sealed motor for gas and water exclusion
*9 tooth pinion provides a 15.78 gear reduction ratio for an 11% improvement in
torque over the 10 tooth presolite with 14.2 gear reduction ratio.
*2 Lbs lighter than stock unit.
*Completely bolt in interchange...NO MODS REQUIRED ON
STOCK MACHINES
Caveat
The manufacturer strongly recommends Lucas mechanical points/AA or a RITA over
the analog Boyer for any electric start... and especially for this starter.
Pre-existing problems or defects with the existing starter mechanism may be made
apparent by, and will not be rectified by, use of this starter.