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sam christie
United Kingdom
3101 Posts |
 Posted - 18/03/2008 : 12:35:01
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Is it possible to improve the performance of the early 6 volt dynamo used on M-types and early OHC Minors without simply changing to the later fatter type ?
Can worthwhile improvements be achieved within the existing casing with minimum alteration of the external appearance?
What options exist ?
Sam |
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Nick Feakes
USA
3372 Posts |
Posted - 18/03/2008 : 12:47:45
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Sam
simple answer is, I doubt it. I believe the armature is the same as the 12volt dynamo and therefore you will be limited to about 8 amps else you risk melting the solder that holds the coils onto the commutator. I am not familiar with the 6 volt machine but it would seem very possible to change to a 12 volt dynamo (if it will fit?) and change your system over to 12 volts which will give you much better headlamps etc. Your starter motor will most likely be fine provided you are careful to allow plenty of cooling time between attempts should the engine be difficult to start.
Nick |
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Bob L
Sweden
50 Posts |
Posted - 21/03/2008 : 17:00:29
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The best you can do, if you have a lathe, is to obtain a 6V Bosch generator as used on the early air cooled Volkswagens. You then use the Bosch rotor, the Bosch brush holder end cover, the Bosch stator (shortened slightly) and the original Lucas end cover which mates with the engine. The result has the same external diameter as the Lucas generator and the only difference in looks are the terminal which end up around the front of the generator.
I have rebuilt a 6V generator for an M type and a 12V generator for my PA. The conversion is a bit tricky but well worth it as you can then pull all the Amps you want.
Bob |
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sam christie
United Kingdom
3101 Posts |
Posted - 21/03/2008 : 20:33:06
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Bob,I seem to recall reading an illustrated article on this theme (though I cannot recall where).The idea sounds really interesting. Is the the Bosch dynamo as slim as the smaller M-type/OHC Minor dynamo ?
Sam |
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talbot
United Kingdom
718 Posts |
Posted - 22/03/2008 : 09:05:50
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Sam,
I bought a VW dynamo to see if I could do a conversion. The problem I found was the length of the armature. To fit between the cam fork and the bevel box I would have had to use the outer face of the dynamo fork boss as the top bearing. In the end I just got Wood Auto to rebuild me a 12V new dynamo. I still have the dismantled VW unit and can take measurements for you if you want. An alternative is to fit an alternator from Kawasaki motorbike inside the MG case but I was informed that cooling could be a problem.
Cheers
Jan T |
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sam christie
United Kingdom
3101 Posts |
Posted - 22/03/2008 : 11:12:31
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Has anyone on the Forum experience of using an alternator from a Kawasaki motorbike in this way ?
Both the Bosch and Kawasaki options sound very good but rather complex and advanced for my limited skills.
Perhaps the simplest option is to settle for a modest improvement and look out for a later front housing - though I am not sure if I can tell the difference. I understand from a previous posting that a larger dynamo can be fitted to an early engine block if a later front housing is used - is this correct ?
Sam |
Edited by - sam christie on 22/03/2008 20:21:07 |
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Bob L
Sweden
50 Posts |
Posted - 22/03/2008 : 13:57:18
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Sam. The outerdiameter of the Bosch generator is the same as the diameter of the later Lucas generators used on our mmm cars i.e larger than the earlier Morris Minor generators.
To get the height down so it will fit I modified the top bearing (used SKF61902-2RZ) and machined 7.5mm off the length of the stator. You have to remove the field poles to do this.
The bigest problem is the fact that the diameter of the driving end of the Bosch generator is 15mm and the MG bevel gear needs 5/8 inch (15.875mm) Here I machined a sleeve and pressed it well up towards the rotor laminations, pinned it onto the shaft and used Locktite. Then machined it down to 5/8 inch.
When finished, the length of the generator from mounting face at the bottom to top of the generator fork is 193mm (compared to 192.8mm for my original Lucas generator).
I must admit you need some machining experience to do the job however the results have been very good (Amps in abundance).
Bob |
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talbot
United Kingdom
718 Posts |
Posted - 22/03/2008 : 19:40:43
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Bob,
I am really interested in how you converted the VW dynamo. I bought a 12V one but decided there were too many problems so got my original one rebuilt. I have measured the length of the VW armature and from end of field windings to end of comultator it is 160 m/m. The length between the inner faces of the bearings in the original case is 150 m/m. You say you machined the stator - do you mean you reduced the length of the comultator? This would be possible since the brushes on the VW unit are qite long. The real problem was as you suggest the diameter of the VW shaft at the input end. I had considered a sleeve but was worried about this opening out when I milled the keyway for the gear. The central case for the VW unit is 174 m/m long by 105 m/m diameter. The Lucas one is 150 m/m x 110 m/m diameter. Please give us more details.
Cheers
Jan T |
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sam christie
United Kingdom
3101 Posts |
Posted - 23/03/2008 : 11:49:56
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Perhaps this might form another thread but -
Would it be possible to make better use of the reputedly meagre output from the original six volt dynamo ?
The need for more Amps arises from the safety driven demand for more and brighter lights while still charging the battery.
Could better lighting be achieved without changing the performance of the original dynamo ? Could Light Emitting Diodes help ?
Sam |
Edited by - sam christie on 23/03/2008 14:15:54 |
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talbot
United Kingdom
718 Posts |
Posted - 23/03/2008 : 15:37:33
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Sam,
The same question arose some time ago on the TD/TF site. One of the contributors from the States (they delight in knocking anything Lucas) suggested burning the candle at both ends to double the light output.
Cheers
Jan T |
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Bob L
Sweden
50 Posts |
Posted - 23/03/2008 : 19:08:20
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It is difficult to get any more Amps out of the old Lucas generators. In my Uni days in Sytdney during the 50s I drove (thrashed) a 1929 Morris Minor (=Mtype MG). After a lot of fiddling I managed to get a few more Amps out of the generator but then the solder melted on the comutator and the winding ends flew out radially. After that experience I decided that something more radical was needed when the generator in my P type gave out a few years ago and hence I rebuilt the generator using a VW Bosch generator.
I have a set of frehand drawings showing the conversion if anybody is interested.
Bob |
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sam christie
United Kingdom
3101 Posts |
Posted - 24/03/2008 : 00:13:46
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Yes please Bob - I was just about to ask if it was possible to see pictures of the conversion.
Sam |
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Nick Feakes
USA
3372 Posts |
Posted - 24/03/2008 : 02:16:03
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Hi Bob
if you would me a set of drawings I will add them to the site for everyone to use.
Nick
Specialties: P-types & Electrics |
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Bob L
Sweden
50 Posts |
Posted - 25/03/2008 : 18:24:31
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I have cleaned up my free hand drawings and I am making a short description for the generator conversion. I'll send it to Nick when finished so he can put it in the site.
Bob |
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sam christie
United Kingdom
3101 Posts |
Posted - 12/04/2008 : 08:28:27
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Thanks for all the above.
If a VW/Bosch dynamo proved too large to fit in front of an early block is there any reason not to grind back the dynamo casing (within reason) to help make it fit ? Could this provide enough clearance ?
Sam |
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Nick Feakes
USA
3372 Posts |
Posted - 23/05/2008 : 12:35:39
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I have (at last!) put Bob's diagram of the Bosch dynamo modifications on the Document Downloads page
Nick |
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