TonyAus

1914-26 Water Pump Shafts

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For reasons too long to explain here I need to clarify one aspect of water pump shafts used on single electrical unit (starter/generator) DB engines.  Does anyone have an old shaft that they can check for me?

These shafts have (from the front) a woodruff key slot and cross drilled hole for the fan pulley, a key slot without drilling for the drive gear, a key slot and hole for the water pump impeller and a key slot and hole for the distributor/magneto drive yoke.

Clearly the positions of the drive gear and yoke are critical to ignition timing.  What I need to know is are the key slots for the drive gear and yoke in line along the shaft or are they offset from each other?

 

Thanks in anticipation

 

Tony

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Can you ask a friend with a suitable machine to set it up and measure, if no-one comes up with a definitive answer.

 

I expect there is a way to set it up on a milling machine table, for instance, so the ends of the shaft centre under the mill bit centre, and use a drill stem the width of the key way to see if it goes into all the keyways. If not, then a lathe with a dividing head might be the job to measure the offset?

 

 

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It really has nothing to do with correct ignition timing. You can move the distributor a tooth at a time and the way to set the timing is to loosen the points cam screw and turn the points cam where ever you need it.

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The question is whether the slots are aligned or not.  If not I can make suitable arrangements.

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1 minute ago, dwollam said:

It really has nothing to do with correct ignition timing. You can move the distributor a tooth at a time and the way to set the timing is to loosen the points cam screw and turn the points cam where ever you need it.

Yes - but I have a magneto which doesn't have this luxury.

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Ahhh! I have a mag on my '22 Screenside too, it has a coupler that pinches down regardless of where it is on the shaft.

Edited by dwollam (see edit history)

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Hi Tony,

The shaft I purchased from Romar had them all in line.  Sorry I don't have a photo of the new one here is a (poor) photo of the old one.  This is from my '25 which has the combined starter/generator and it appears to show 3 woodruff key slots in-line.  The drive gear slot had wallowed out a bit.  Hope this helps.

P4100885.JPG

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Thanks for that Mike.  Looks like it's time to come clean with the full story.  Since getting the car back on the road I've been plagued with variable overheating - mainly associated with hot weather and higher speeds.  Most of the usual suspects, blocked radiator, lean mixture, loose fan belt etc have been addressed.  I've now turned to the possibility of not enough spark advance or that the water pump impeller has somehow come loose.  Both these could be associated with the stainless steel water pump shaft I had made up nearly forty years ago.  In any event I was not happy with the fit of the impeller on the shaft and raised the surface with a series of centre punch marks (a bodge dictated by not knowing better).  Being slightly under size the new shaft also has a habit of chewing up and spitting out the packing - another source of annoyance.  I also didn't check that the key slots were in the same places as the old shaft which had been cut in half to release the water pump (another bodge on my part).   Before pulling the whole mess apart to check I decided to order a new shaft from Myers but noticed that theirs has all the key slots in line.  The remains (front) of mine has the impeller key slot offset to the others which, of course, has no significance to the ignition timing. As the magneto end is missing I started to worry  that the problem may be the relationship between the drive gear and magneto yoke slots - and without a way of checking.  I also thought that having all the slots in line was an easier way to make the reproductions and may have relied on the use of a distributor, timed by the method dwollom suggests.

 

Mike, I take it that the  fan pulley end of the shaft is at the right side of your photo.  If so, I can't see a key slot at the left hand end, which is the one  in question.  There should be four slots rather than three.  Have my eyes failed?  If the left hand end slot is further around the shaft  than the drive gear one you may have answered my original question.  I'd be grateful for clarification.

 

Regards

 

Tony

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We learn from our mistakes and confession is good for the soul...  I did look around the shop to see if I still had the old shaft lying around but I think I machined some rivets from it.  I  think we can take some educated guesses though.  The picture here shows the water pump before I touched it.  The clean, un-corroded portion of the shaft must be where it was exposed to oil in the gear drive.  The heavily corroded portion must be inside the water pump (rust from water and galvanic action from contact with bronze impeller).  If correct, this would mean the right end of the shaft in my original photo was the aft end (I flipped it and re-pasted it here).  This suggests that the gear drive slot and the end slot (where rubber coupler goes) should be aligned, although when I look closely there does appear to be some offset between the two... maybe 20 degrees?  It's a shame I didn't have that photo in focus.  I can't explain why they would have bothered to put the slot in for the fan drive out of alignment with the gear drive though.  The moral of the story?  You can never take enough photos of tear downs.

 

798674140_WPcloseup1.thumb.jpg.a4e2d78852b5aa6943dcc9a2d7e1b839.jpgP3180854.thumb.JPG.566a051a7e1c7f9415cc6929409f2cd2.JPG998062069_FlipP4100885.thumb.jpg.f8f77810876380289c650d14b43db1ec.jpg

 

 

 

Edited by MikeC5 (see edit history)

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2 hours ago, MikeC5 said:

Watching this video closely, It also appears the distributor drive end slot and drive gear slot are more/less aligned.  

https://www.youtube.com/watch?v=A8y0gjGofwU

Thanks again Mike

This video was interesting but unfortunately it doesn't show the old shaft coming out (he lost charge on his phone)  - bugger!  The new shaft he used is from Myers and has the key slots in line - the arrangement I have questioned.  Perhaps I worry too much.  At least it confirms my conclusion to another problem that the impeller pins were drilled for individual fit.  Regarding your photo , I think that the apparent offset may be an optical illusion  caused by the camera angle.

 

Has anyone else got an old shaft which might kill my doubts?  Please!

 

Tony

 

 

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I will talk to the fella that actually makes the shafts for Myers. I know him well. I'll try tomorrow. I also know he makes more than 1 shaft as at least the 6 volt cars are different and as I recall maybe two different ones for 6 volt. (I know yours is 12 volt) I will also try to find some of my old shafts.

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For all you hanging on this topic I've been able to determine from a local source that, viewed from the front, the drive gear keyways on original shafts were cut approximately 28 degrees behind the others - which were in line.  This means that the use of a shaft as supplied by Myers would give me a retard position of 20 degrees before TDC and an advance position  of 40 degrees  before TDC.  Probably not good given the correct figures of 8 degrees after TDC and 12 degrees before TDC  respectively.  Moving the drive gear  from the timing marks would give a 16.36 degree correction per tooth.  Two teeth would therefore give a 3.28 degree ATDC retard and 16.72 degree BTDC advance -  possibly not ideal.  Looks like I'll have to get a shaft made locally.   

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I've tried to call him but just get an answering machine. He must be traveling. Will keep checking.

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Problem now solved.  The drive gear keyway  on the shaft I had made nearly forty years ago was cut approximately 15 degrees out.  Not enough spark advance and therefore overheating.  It should go like a bomb after I get a new shaft made! 

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Hi Tony and all. Might it make sense to consider the difference in octane between 40 something in the mid '20s, and the 80 something we suffer today in our 4.X:1 compression ratio engines ? Critical to performance timing. Perhaps Meyers is on to something. I am eager to see what Dave will have to tell us after having a very interesting talk with his friend who makes the shafts. I am very curious regarding timing to compensate for the extreme octane change.   -   Carl 

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I have mentioned before about advancing the internal gears in the magneto. I read about it somewhere about 20 years ago. I cannot remember the number of teeth I advanced it but it made a hell of a difference in performance. A couple of years ago my magneto siezed so I sent it down to a bloke in Melbourne to be rebuilt and told him over the phone I wanted the advanced timing noted and put together the same way. I even attached a note to remind him. Well, I get it back and old mate put it back together with standard timing and the difference in performance is depressing. I think it was 5 or 8 teeth advanced so I suppose I will have to experiment. If only he had done as requested. Of course he didn't take note of the number of the teeth. Never again for him.

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I can only quote from the Book of Information.  "Since the primary current must be broken while at its maximum to give the hottest spark, the gears driving the distributor rotor must never be disturbed".  Sound like your extra performance came from additional advance but a weaker spark.  The rebuilder was only following sound practice.  I understand that Cled Davies in Bendigo sells an adjustable magneto coupling to achieve additional advance without compromising the spark - could be your answer.

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