Prestolite Starters

There will be a lot of advice forthcoming on this subject but if you do a research on this site on starters there will be plenty to keep you going. The most important first step is to upgrade the starter earth and neutral wires. I ersonally wouldn't bother with the four brush conversion, its difficult to do and the general experience is that it doesn't make much difference.

Options are available but the original starter will work if everything is in good condition. 

The two pole prestolite starter, as originally fitted, has a few inbuilt faults that gradually degrades its performance till it won't start the engine. The rotor gradually wears itself into the drive end plate till the rotor windings touch the end plate, wear through the insulation and short out. The quality control was not good, i've seen commutators 13 thou out of true, causing the brushes to oscillate in the holder and wear out. They weren't sealed so the petrol got in (from the amals), washed the lubricant from the bearings and then the rain got there so they internally rust very well indeed!

The biggest improvement to the 2pole prestolite is to fit it with proper bearings, A 6203 2RS at the drive end, a needle roller at the brush end stops the rotor moving and 'frees up' the motors performance to the point that it will turn the engine over like a jap bike. When doing this modification the rotors commutator is trued up and the mica undercut.

The problems start when well meaning others have been in there before, Field coils damaged when the frame has been sand blasted and they have blasted away the insulation, (seen this twice) The field coil connection to the frame made with tiny 6 B.A. screws or pop rivets. (seen this 5 times) This is a high amperage connection and has to be spot welded or soldered. Drive end plates with a cracked flange caused by over tightening of the starter mounting screws (this usually occurs when people fit cap screws and use over long allen keys to tighten them)

Now we come to the common dodge of fitting the four pole frame from the 5780BN Harley starter (the modern prestolite copy) This frame will fit the two pole prestolite but it will need a thin spacer ring at the drive end because of the differing sizes. BUT and its a big but, it will not do anything to address the rotor wear (the original bush bearings allow the rotor to move and wear into the drive end plate) in fact it will make this wearing action worse as the magnetic field from the field coils is that bit stronger. 

The four brush conversion is a complete waste of time, effort and money. I have removed a few in the past from motors i have upgraded. 

The cheapest way to a four pole starter is a converted 5780BN. Before now I have installed four field coils into the two pole commando frame (this is for folks who want the four pole motor but still looks like the 2 pole original) but due to the alignment of the core irons to the 2 pole frames input connection this is a very cramped and awkward procedure and as the bearing modded 2 poles work so well i only do this work to order now  

PM me if you want to know more 

Regards

Peter           

The four pole conversion is a very good option for a standard 2 pole Prestolite but the armature, windings, large and small bronze bushes, all need to be in good condition.

I skimmed the commutator to true it up and replaced the small bush with a needle roller. The end cap and armature needs machining for this so not for everybody. Fill the cast in cavities around the needle roller with JB Weld to give added support.  

I still have the original large bush on the drive pinion end, armature spins freely with no obvious play when oiled. I fitted a steel thrust washer at the pinion bush to control end float,  no chance of contact with the windings.

I agree with Tim that the original Prestolite in good condition works well, running smooth and quiet, unlike some modded versions which have a loud screech.

I use 16mm2 flexible multi core cable readily available online. It'll start almost within one revolution with a Trispark, even down to my lowest recorded of -7°c with tickling and full choke.

Hi Neil,

I have taken a spare drive end cover, removed the bush and opened up the bore to fit a needle roller bearing.  A consequence is that the remaining wall thickness is much reduced and I am wary about it damaging the armature or vice versa.  A thin thrust washer would be ideal, but I have not found anything suitable yet.  What did you use as a thrust washer?

Andy

If the brushes, field coils and rotor are good and if you can use a lathe or know someone who can, the cheapest route (approx £25) to reliable and better performance in terms of materials and components is to fit rolling element bearings (6203 2RS at the drive end and either a HK 09-12 or a HK10-12 needle roller at the brush end) 

You will also need a disc of 8mm aluminium alloy shaped to fit and bonded into the recess at the drive end plate before it is opened out to fit the 6203.