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1975 Norton Commando MKIII - Electric Start
06-4791B 1.4hp Replacement Starter click for pix

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 Villers066515 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. This battery is available at NAPA for about $40
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 argueably 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  (single phase) 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 RM24 180W (3 phase) 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  kickback/backfiring.
You can review igniton issues in more detail elsewhere on this website.

Cables
Higher resistance wires reduce the current available to the starter, reducing the ability of the starter to spin-up the engine.
Follow this link for a few additional details on this subject

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 $600.
**Draws about 300amps stall, 200-266amps normal starting current, 120amps 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 06-4791/Prestolite MGD4111 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 some norton suppliers for $656, Your old core rebuilt or modified for typically up to $300-$400.
**Draws about 344amps stall, 207-220amps normal starting current, 125amps once engine is turning.
Voltage depressed at battery during current surge,  6.32 - 9.45v typical.
*** Minimally better than stock.
****10 tooth armature gear

06-4791B  starter-based on a hi volume production japanese starter-modified for the norton application,
4 brush 21 segment double wrap armature, about 7.5-9 gauss/amp  in series with  4 - 10 turn field.
*$375 outright, +s&h
**Draws up to 372amps at stall. 280-312amps normal startup current, 170amps 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.

06-4791B 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.
*Net weight 2.16kg,  Approx 2 Lbs lighter than stock unit.
*Completely bolt-in interchange...NO MODS REQUIRED.

Caveat
I recommend  Lucas mechanical points/AA  or a RITA over the analog boyer for any electric start...and especially for this starter.
Preexisting problems or defects with the existing starter mechanism may be made apparent by , and will not be rectified by, use of this starter.