Speedometer drives and confusion.

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Re: Speedometer drives and confusion.

Postby Don G » Tue Jun 11, 2019 2:52 pm

I am with Fatboyfreddy I get overwhelmed with the brain power that comes to the table on these issues. It's all but backwards engineering to find the solution.
Thanks guys for all the input.....
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Re: Speedometer drives and confusion.

Postby bobscogin » Tue Jun 11, 2019 4:25 pm

There won't be any progress on the speedo drive investigation today. Perfect weather here for painting so I'm squirting some blue on the '63 Scat.

Bob
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Re: Speedometer drives and confusion.

Postby bobscogin » Tue Jun 11, 2019 6:26 pm

I wasn't going to pursue the speedo issue today since I was painting. However, while I was waiting for my base coat to cure, I decided to use the time to get back on the speedometer drive investigation. I used the 23 tooth drive gear on the 18" wheel, It's diameter is actually .027 smaller than the 21 tooth 16 wheel drive gear. Since it was the smaller of the two, the driven gear teeth should have .0135 less engagement depth. I put modeling clay between a few of the drive gear teeth, installed the driven gear and rolled the wheel around a couple of revs. The photo shows what seems to be adequate engagement since it squished the modeling clay out to about 3/4 the depth of the teeth. I did not pattern the larger gear since the engagement depth will be deeper on it. Drawing on my auto experience, I know that it is not uncommon for car speedometers to use a range of teeth on a specific driven gear without changing the drive gear. Is that what Harley intended? Maybe not based on part numbers, but it appears that it would work and both my Pacer and my Scat had the same driven gear. I'd like some input before I install on my bikes. What say y'all?

Bob
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Re: Speedometer drives and confusion.

Postby DCHRISTEN » Wed Jun 12, 2019 12:48 pm

FOLLOWING THE SPEEDOMETER DRIVE/DRIVEN GEAR COMMENTS.
IT IS GIVEN THAT: THERE ARE TWO DIFFERENT PART NUMBERS FOR THE BOTH THE DRIVE GEARS AND DRIVEN GEARS. THE ONLY OBVIOUS MEASUREMENT THAT IS DIFFERENT IS IN THE ( HUB)DRIVE GEARS FOR THE 16/18 IN WHEELS.

THESE GEAR SETS ARE THE HELICAL TYPE AND CRITICAL MEASUREMENTS FOR THOSE SETS IS MORE THAN A LITTLE DIFFICULT WITHOUT CORRECT INSTRUMENTS.
IF YOU LOOK AT TECHNICAL DATA/MEASUREMENTS IN MACHINERY'S HANDBOOK FOR HELICAL GEARS I THINK YOU WILL AGREE THAT A HELICAL GEAR SET IS CONSIDERABLY MORE "FUN" TO ASSESS THAN A SPUR GEAR SET.
THAT SAID, THE ONLY DIFFERENCE I FIND IN THE TWO 9 TOOTH DRIVEN GEARS IS THE HELIX ANGLE WHICH IS ABOUT 6 DEGREES. WHILE I HAVE THE TWO DIFFERENT DRIVEN GEARS TO MEASURE AND COMPARE, IT WOULD BE MUCH EASIER TO CONFIRM THAT IF I HAD THE TWO DIFFERENT DRIVE GEARS TO COMPARE BUT THEY ARE NOT IN MY INVENTORY.

ALL THAT SAID, I APPEARS THAT THE DIFFERENCE BETWEEN THESE GEAR SETS IS THE "HELIX ANGLE" OF THE GEAR TEETH PLUS THE KNOWN OD OF OF THE DRIVE GEARS.


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Re: Speedometer drives and confusion.

Postby Don G » Wed Jun 12, 2019 4:28 pm

Thanks Duane for your follow up and insight
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Re: Speedometer drives and confusion.

Postby bobscogin » Wed Jun 12, 2019 6:44 pm

Yes, thanks Duane! You're right about the instruments required for measuring the helix angle and I certainly don't have them. Just micrometers. I had to resort to the more primitive method of checking using the modeling clay to verify engagement and pattern. So there are two different 9 tooth driven gears varying only in helix angle? I'm more confused than ever.

Bob
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