Author Topic: Mk series generator drive  (Read 13463 times)

0 Members and 1 Guest are viewing this topic.

Offline alwyn

  • 1928 - 2009
  • Co-Founder
  • ****
  • Join Date: Mar 2004
  • Posts: 1759
  • Location: Late of Encounter Bay, South Coast, South Australia
Mk series generator drive
« on: 03 Jul 2008 at 04:22 »
Hi all,
To start at the beginning, it was during the Centenary Rally last year that the dynamo on the '48 T35 spat the dummy throwing solder and a segment of the commutator into the innards. Within a short while after returning from the ADCR, I was able to purchase a matching dynamo albeit one not in the best of condition outwardly, but the armature at least was in good order so I took that armature and incorporated it into the existing dynamo after carefully checking all other components, refitting the brushes, checking the field and so on. It was declared servicable.

The dynamo was just recently installed on the bike and initially all seemed ok but soon the ammeter needle was seen to swing and vibrate rather wildly and the output slowed to just 1 - 2 amps - finally no output at all was registered.

The dynamo and regulator were removed from the bike and set up on a 'test-bed' (on the mill) where a voltage meter/ammeter showed adequate output which was tailored by adjusting the regulator to desired values for voltage and output - when all was working ideally, the dynamo, apparently in first class working order, was reinstalled on the bike but alas it failed to produce even the dimmest of sparks - the process of removal, testing and reinstalling was repeated twice more before someone questioned whether the dynamo was indeed rotating when installed to the bike.  :o  Eureka :!:

You guessed it - the dynamo was found not to be rotating! The reason? - well, this I think - when it was re-installed to the bike a modicum of grease was applied to the dry dynamo pinion. Apparently this has been enough lubrication to rob all semblance of friction from the friction drive (or spider gear) located within the magneto housing which has allowed the drive pinion to rotate freely without turning the dynamo pinion.

The question is, can someone advise whether or not the friction drive is intended to run dry or does it require to be lubricated? (at present there appears to be a coating of dried grease within the housing in the magneto and perhaps a very small amount of fresh grease is discernible too.) Also, how is the pressure of the friction drive adjusted? - and how much pressure is required for it to operate as intended, i.e., presumably it is intended to have sufficient friction to drive the dynamo under normal operating conditions yet allow it to 'free-wheel' if for some reason there should be some unexpected resistance from within the dynamo, whatever the cause?

BTW, it may be important to note the dynamo ID data. It's Lucas of course - the data reduced to a single string reads, "Mn 2.6 - 460210 - XX1 - 1147" - (the hyphens do not appear on the stamp and the point between the 2 and the 6 is superscripted).

Alwyn

The magneto/dynamo drive sprocket...

Quotable Quote - "640 k should be enough for anybody"! - Bill Gates - 1981.

Offline Doug

  • Administrator
  • ****
  • Join Date: Mar 2004
  • Posts: 4335
  • Location: Glen Mills, PA, USA
Re: Mk series generator drive
« Reply #1 on: 04 Jul 2008 at 18:23 »
Alwyn,

Yes the gear case should be packed with grease; stiff wheel bearing grease was recommended. Nor was there any adjustment for the spring pre-load, it was fixed by the design at the factory. It is there to prevent inertial overload of the drive to the dyno, due to a rapid acceleration of the engine (which would be multiplied by the gear ratio.)

The finger spring should bear on a large steel washer, which in turn bears on the face of the fiber gear. Omission of the washer would reduce the spring pressure slightly and probably cut grooves in the face of the fiber gear. Also any washers behind the center of the spring that would stop it from fully seating on the hub would reduce the spring pressure. The hub that the fiber washer can slip on, is itself keyed to the magneto armature shaft (two small woodruff keys if I remember correctly.) If these were omitted, it may not be the clutch that is prematurely slipping, but the entire hub spinning on the armature.

Finally the dyno pinion itself should be keyed securely to the dyno armature.

-Doug

Offline alwyn

  • 1928 - 2009
  • Co-Founder
  • ****
  • Join Date: Mar 2004
  • Posts: 1759
  • Location: Late of Encounter Bay, South Coast, South Australia
Re: Mk series generator drive
« Reply #2 on: 06 Jul 2008 at 04:05 »
Thanks Doug,
The dried grease in the housing certainly suggests it was once lubricated by packing in the manner you mention.

Do you have Lucas literature that confirms this? - I ask because I have been referred to an elderly guy in a neighbouring township who it was said by the referent has been servicing these particular things and similar for many years so I had a chat with him - certainly he seemed very familiar with the subject part and was able to give me a pointer or two about disassembly - contrarily, he told me they're meant to run dry!? He also told me he has a supply of new parts including pressure springs so before I start trying to engineer more pressure via the existing spring I think I'll pay him a visit to see exactly what he has to offer!

I haven't cleaned up the clutch for closer inspection of the fibre gear yet but through the mire, it looks OK - there is a source of these gears on e-bay I believe and the old boy over yonder may also have one in stock?

I'll give you a report later about what I find upon disassembly.

Thanks again for your response.

Alwyn
Quotable Quote - "640 k should be enough for anybody"! - Bill Gates - 1981.

Offline trevorp

  • Master Member
  • ****
  • Join Date: May 2005
  • Posts: 502
  • Location: Australia
Re: Mk series generator drive
« Reply #3 on: 06 Jul 2008 at 07:03 »
try a phone call to this gentleman he has been servicing them for 40 years
see www.dropbears.com/p/peterscott/index.html





URL repaired by Dave 6th July
« Last Edit: 06 Jul 2008 at 07:51 by Dave »

Offline Doug

  • Administrator
  • ****
  • Join Date: Mar 2004
  • Posts: 4335
  • Location: Glen Mills, PA, USA
Re: Mk series generator drive
« Reply #4 on: 06 Jul 2008 at 14:55 »
Quote from: Alwyn
Do you have Lucas literature that confirms this?

Well, not quite. The instructions to pack the gear case with grease came from Modern Motorcycle Mechanics; J.B. Nicholson. fourth edition (1953). The chapter on electrics and dynos is plagiarized from Lucas material. For example the chapter on Douglas is an abridged version of the factory handbook, including illustrations. (I believe Nicholson Brothers is still, or were up until quite recently, publishing this book.)

I dug a little more and I found some Lucas publications for the magdynos. There, any mention of lubrication in the gear case is conspicuous by its absence! It does helpfully give a torque range for the clutch to slip between 4-12 lb*ft.

Having a fiber gear does not on its own mean that it is self-lubricating. It is probably more to provide silent running and avoid a steel on steel clutch surface. But fiber would also be more tolerant to running dry. Probably the best solution if the grease is degrading the torque capacity of the clutch (and it is not a weak spring) would be to wipe just a smaller amount of grease in the gear teeth. What is slung off is less likely to find its way back into the clutch.

There are apocrathal stories of Mark series with failed magdyno oil seals and blocked engine breathers the vented oil through the magneto; they must have had well a lubricated clutch, and armature!

-Doug
« Last Edit: 14 Jul 2008 at 12:33 by Doug »

Offline alwyn

  • 1928 - 2009
  • Co-Founder
  • ****
  • Join Date: Mar 2004
  • Posts: 1759
  • Location: Late of Encounter Bay, South Coast, South Australia
Re: Mk series generator drive
« Reply #5 on: 07 Jul 2008 at 00:43 »
try a phone call to this gentleman he has been servicing them for 40 years

Thanks Trevor, I did and he was most helpful! - he practically anticipated my questions and volunteered the information I needed.

Alwyn
Quotable Quote - "640 k should be enough for anybody"! - Bill Gates - 1981.

Offline eddie

  • Master Member
  • ****
  • Join Date: Mar 2006
  • Posts: 1726
  • Location: Hampshire, UK
Re: Mk series generator drive
« Reply #6 on: 07 Jul 2008 at 15:22 »
Hi Alwyn,
               The problem of the exploding cummutator happened on a mate's Mk 5 some years ago, and just riding it a few miles with the dynamo locked up resulted in the inner flange on the fibre gear becoming burnt to a cinder! On removal, the flange fell to pieces (like granulated coal!). The heat generated also cooked the star spring, leaving it devoid of any pressure - so at least a new spring, facing plate and fibre gear will be needed to restore the drive. This would also be a good time to fit a new magneto oil seal, but remember to fit the seal closed side to the mag - the seal should stop engine oil getting into the mag, not keep the grease in!
                         Regards,
                                       Eddie.
                                         

Offline alwyn

  • 1928 - 2009
  • Co-Founder
  • ****
  • Join Date: Mar 2004
  • Posts: 1759
  • Location: Late of Encounter Bay, South Coast, South Australia
Re: Mk series generator drive
« Reply #7 on: 08 Jul 2008 at 00:29 »
Hi Eddie,
I suspect my experience mirrors that of your mate's.

I dismantled the magdyno drive 'clutch' yesterday. Similarly to your mate's experience, I found that the contact face (flange) of the fibre gear that bears (under pressure of the tension spring) upon the the 'Gear Centre', is worn (or more appropriately described, burnt!) to the extent that just a thin layer, maybe a millimetre thick, of compressed but crumbly grease impregnated carbon residue remained of it beneath the 'Pressure Ring". The latter is scored too, a significant channel of a width consistent with the tips of the 'fingers' of the 'Tension Spring', is quite visible and I suspect too that there has been sufficient heat generated to anneal the spring.

I have secured the replacement parts and expect delivery from Sydney within a day or two. But I still have a significant problem to resolve! That is to grease or not to grease the mechanism by packing the case? I note your comment about the seal - I'm intent on renewing it and had noted the direction of it upon dismantling - but more to my point, you say in respect of the seal that it's not meant to "...keep the grease in". By this I think you intimate that the case should be packed with grease upon assembly.  Contrary to this, I have been advised by two magneto repairers (both of whom claim 40 years of experience in their trade) that the drive is/was designed to run dry and any oil or grease introduced within the case will cause the drive to fail!

The Lucas literature kindly provided to me by Doug is silent upon the matter of lubrication. Can you advise further on this question please Eddie?
 
Regards,
Alwyn

PS.
It may assist those interested and who are unfamiliar with the mechanism as I was before this incident, if I attach a cut away illustration of the drive taken from the Lucas instruction book, so here it is....

Quotable Quote - "640 k should be enough for anybody"! - Bill Gates - 1981.

Offline eddie

  • Master Member
  • ****
  • Join Date: Mar 2006
  • Posts: 1726
  • Location: Hampshire, UK
Re: Mk series generator drive
« Reply #8 on: 08 Jul 2008 at 06:26 »
Hi Alwyn,
              I can't find any official reference to lubrication either. In the past, when rebuilding magdynos, I have applied a smear of grease to the teeth without any unforeseen problems. Also, slippage of the drive 'clutch' does not seem to occur when the seal fails and floods the compartment with oil - so the drive seems to be very 'oil tolerant'. One little snippit of information from the Lucas technical sheets is that with the fibre gear 'locked' to the body of the magdyno, the torque needed to turn the armature should be at least 4 ft lbs and no more than 10 ft lbs - a factor of 2 times - so it is quite possible that a dry or lubricated clutch could still come within these limits.
           Hope this is of some help,
                                   Regards,
                                                  Eddie.

Offline alwyn

  • 1928 - 2009
  • Co-Founder
  • ****
  • Join Date: Mar 2004
  • Posts: 1759
  • Location: Late of Encounter Bay, South Coast, South Australia
Re: Mk series generator drive
« Reply #9 on: 11 Jul 2008 at 04:37 »
....... This would also be a good time to fit a new magneto oil seal, .......

Hi Eddie,
The seal looks to be pretty good Eddie - nevertheless, I'd replace it if I could buy a new one - I haven't been able to locate one here - do you know where I may be able to buy one? Has the LDMCC spares department got them?

Alwyn

PS 11/07/2008 - Have replaced all parts of the 'clutch' - all new parts except the gear centre which is used but in better order than the existing one.  A.

PPS 15/07/2008 - Eddie confirmed by PM that the LDMCC spares dept. do have stocks of the subject seal.  A.
« Last Edit: 15 Jul 2008 at 00:39 by alwyn »
Quotable Quote - "640 k should be enough for anybody"! - Bill Gates - 1981.

Offline David H

  • Full Member
  • **
  • Join Date: Mar 2007
  • Posts: 47
  • Location: Melbourne Australia
Re: Mk series generator drive
« Reply #10 on: 14 Jul 2008 at 08:44 »
Hi Alwyn
Been looking at my old workshop manuals as to the use of grease in the fiber drive of the magdyno units I can only find two references one in a matchless book that suggests a small amount of white zinc grease to the teeth of the gear only and one of my old army apprenticeship training manuals says similar a small amount of ZKN-39-xxxx grease (I have no idea what that is) applied to the teeth only.
I replaced the seal in my magdyon with one from CBC with the correct od and id it was slightly thinner than the original but I am 100% confident it will work OK and cost only a couple of dollars.

All the best
David H

Offline alwyn

  • 1928 - 2009
  • Co-Founder
  • ****
  • Join Date: Mar 2004
  • Posts: 1759
  • Location: Late of Encounter Bay, South Coast, South Australia
Re: Mk series generator drive
« Reply #11 on: 15 Jul 2008 at 00:35 »
Hi David,
I'm still in a bit of a quandry about the lubrication - limiting it to just the gear may be the safest option and should remain effective over a long time given the limited mileage covered by the bike.

I have been able to track down a suitable seal - started my search in an old Repco catalogue and found a couple of near perfect matches to the required 17.3 mm id x 30.15 mm od x 6 mm thick - the imperial one was numbered PR3338 and the metric one PR8031. These numbers were quoted to a local stockist and he matched it with a seal of another make unknown but numbered TC12418 - I thought I'd put that on record here - it may be useful for someone down the track!

Thanks for your interest.

Alwyn
Quotable Quote - "640 k should be enough for anybody"! - Bill Gates - 1981.

Offline David H

  • Full Member
  • **
  • Join Date: Mar 2007
  • Posts: 47
  • Location: Melbourne Australia
Re: Mk series generator drive
« Reply #12 on: 15 Jul 2008 at 08:04 »
Hi Alwyn

Good to see you got a seal OK, Thouse old Repco seal books can be invaluable when chasing old imperial seals.
I would not get to concerned about the lubrication on the fiber gear set. it would run dry for years and a little grease will help bed in any small irregularities or misalignment. just make sure the teeth are not binding or rubbing on the housing and it will be fine. I bought an after market fiber gear from Modac in Melbourne it was about .025inch wider than the original and rubbed quite heavily on the front cover. Thinned it out on garnet paper and a piece of glass worked just fine.

Best of luck
David H