meshing of kicker gears

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nifty
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meshing of kicker gears

#1

Post by nifty »

As is well known, badly worn Kicker Shaft bushes and loose Starter Gear bush together, effectively widens the installed centerlines of mainshaft & kickshaft, which allows the kicker gear teeth to move out of mesh with starter clutch gear teeth, which then allows the Starter Gear to ride up on OD edge of cam of 24T kick gear, which jams KG & lever in approx mid-kick-stroke. At this point many riders throw all their body weight, plus inertia, onto the jammed lever, which when jumped on, brutally further widens both gear centres, causing further destruction to both gears, cover fracture and of course poor kickstart action. (and also causes kick lever to not fully return to vertical) This has been known for a long time and the evidence clear in the destroyed parts. Can also destroy riders knee if/when unmeshed gears do unlock and slip.
ramp damage jock cropped.jpg
ramp damage jock cropped.jpg (52.67 KiB) Viewed 1264 times
Note: To the right of above 2 bad ramp gouges, there is a 3rd witness mark on periphery of camplate, apparently where Starter Gear “climbed” to completely un-meshed condition. Note: Also teeth tip damage at left where tips of Starter Gear appear to have run completely un-meshed on tooth tips of above Kicker Gear.
kick arm upright cam on SG .095 clutch teeth separation rsz.JPG
kick arm upright cam on SG .095 clutch teeth separation rsz.JPG (197.11 KiB) Viewed 1264 times
I wanted to know more, so I cut up a kicker cover and made a new for me discovery. IMO the reason that so often the gears become un-meshed with worn bushes, is because at least some gears are only approx 50% meshed when everything is new. This light bulb moment was a bit of a shock.
good meshing.jpg
good meshing.jpg (14.08 KiB) Viewed 1264 times

Example of normal/good gear meshing, the sliding contact at flanks occurs over almost full depth to tooth root, at least 2 teeth of each gear share load.
teeth meshing KG to SG rsz.JPG
teeth meshing KG to SG rsz.JPG (163.27 KiB) Viewed 1264 times
As can be seen with cutaway cover, only approx 50% teeth meshing depth occurs with all new AM 24T & 16T gears, new kick shaft & bushes, new mainshaft, new bearing, minimal bush clearances. In above condition these gears share load at only the outer 50% of 1 tooth of each gear. Yet these same gears have only 0.006” backlash, which is completely normal for teeth of this size*. So it’s not like my cutaway cover is poorly made with shaft centers too wide. *must have some backlash.
Above KG tooth height = approx 0.242”
Above SG tooth height = approx 0.226”
Using drill bits as gauges:
Above SG root to tip of KG = approx 0.080”
Above KG root to tip of SG = approx 0.100”
With above as a “new parts starting point”, by the time the bushes are worn sloppy, during each kick, as the normal meshing process pushes the gears apart, the gears are hardly meshing at all.
OD of above AM Kicker Gear = 3.155”; another AM KG OD = 3.184”; Baker KG = 3.180”. (changing gear could improve above meshing by approx 0.030”)
Root ø of above AM Kicker Gear = 2.670”; another AM KG root = 2.675”; Baker KG = 2.693”. (changing gear could improve above meshing by approx 0.020”)
OD of above AM Starter Gear = 2.138”; another AM SG OD = 2.140”
Root ø of above AM Starter Gear = 1.685”; another AM SG root = 1.690”
Additional gear data courtesy of Mongrel505558

Backlash 0.006”
.006 backlash rsz.JPG
.006 backlash rsz.JPG (200.23 KiB) Viewed 1264 times
Short of obtaining deeper meshing gears, nothing can be done to improve this situation. Bottom line is, minimum, replace worn kick shaft bushes as soon as they are noticed, or you risk trashing every part of kickstarter mechanism, possibly including your knee. To maximize life of bushes, upgrading to a quality, full-width kick-shaft bush and external oil seal, also a good idea.
Above poor meshing also explains how some folk can break teeth off 24T kicker gears.
76up KG tooth broken.jpg
76up KG tooth broken.jpg (20.83 KiB) Viewed 1264 times

Tooth broken off at root, classic overload failure, exacerbated by only partial flank contact, load only at tip subjected tooth to bending, pulled out at root. Worst case is engine with high static compression.

If anyone can provide additional OD & tooth root dimensions of gears I would appreciate it
Nifty
Raytag
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Re: meshing of kicker gears

#2

Post by Raytag »

This is why I was asking here if cs and ks are inline ?
After pulling the kicker shaft bushings I miked the bore in the kicker cover just to find it wallowed.
Yes, the bore in the cover is wallowed.
To make it a lil more difficult the ID of this bore next to the kicker gear is wallowed more than the ID of the same bore, next to the kicker arm.

Still busy with other stuff but occasionally mulling about it

Ray
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Re: meshing of kicker gears

#3

Post by Mongrel505558 »

Interesting. The gears I measured were aftermarket. Were factory H-D any better in terms of mesh area? That could help account for the Big Twin kickstart mechanism being sketchy and the fast wear rate of parts. Perhaps the contact area here was reduced to help disengagement of the ratchet action - same idea as the bushing in this gear being a loose (almost sloppy) fit on the mainshaft. I don't think close tolerances here would last too long. Look at what happens to the kicker shaft and bushings, or how many cracked covers you see.

Jim
nifty
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Re: meshing of kicker gears

#4

Post by nifty »

If anyone reading this has an 80up trans case and a ditto countershaft (.749") and a kicker cover with good bushes, they might easily answer Raytag's question.
And I'd like to know too.
I'm thinking ...
If the kick shaft is actually in-line with countershaft, the late countershaft should pass right through the 1980 case bush and into the bushes in kicker cover.
Or a factory blueprint of trans would also tell us.
And Jim,
Yes, it may well be that MoCo had to loosen everything up in order to get the Starter Gear to slide easily in real world.
Its also scary that dimensions of my set of AM gears, are so different to yours.
Nifty
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Re: meshing of kicker gears

#5

Post by Mongrel505558 »

nifty wrote: Thu Dec 09, 2021 12:06 pm If anyone reading this has an 80up trans case and a ditto countershaft (.749") and a kicker cover with good bushes, they might easily answer Raytag's question.
And I'd like to know too.
I'm thinking ...
If the kick shaft is actually in-line with countershaft, the late countershaft should pass right through the 1980 case bush and into the bushes in kicker cover.
Or a factory blueprint of trans would also tell us.
And Jim,
Yes, it may well be that MoCo had to loosen everything up in order to get the Starter Gear to slide easily in real world.
Its also scary that dimensions of my set of AM gears, are so different to yours.
Nifty
Like I said regarding my measurements - they were not taken under ideal conditions. Also, I didn't use measuring pins. I might have some more gears around that aren't mounted to anything and therefore will be easier to get a caliper on.
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Re: meshing of kicker gears

#6

Post by RooDog »

For whatever it's worth:
I installed a new one piece kicker arm and pig snout kicker cover from Tedd's V-Twin on my Panny project. These appeared to be very well made and looked great. Installed in concert with OEM kicker gear, and the original ratcheting clutch. I didn't touch the clutch as it appeared to be in good working order. I had to replace the bumper & screws, more V-2 parts. But in the end the mixture of new AM and vintage OEM pieces made for a sweet, no slipping, kick start experience. And after it aged a bit it assumed patina matching the natural aluminum of the OE tranny case.....
DSC01899.JPG
DSC01899.JPG (176.97 KiB) Viewed 1207 times
Nifty....
Your cut away kicker cover is genius, revealing, to say the least. Surely as handy as a cut away E-start primary cover.....
nifty
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Re: meshing of kicker gears

#7

Post by nifty »

Thanks RooDog
IMO the biggest single problem with the BT kicker is not being able to see the mechanism working and thus accurately diagnose faults. Fully half of the mechanism is in cover, while other half is in end of transmission. As needed over the years I had measured and generally dicked around diagnosing problems. For my intended accurate analysis I needed a foolproof, repeatable methodology.

On my TIG welding table I had a near new AM kicker cover with a broken-out lower release bush (never actually run on a bike). I had fully intended to repair the cover, instead I put it through the bandsaw, Voila: instant crystal clear view of the kick mechanism working, or not. No guessing, or potential measuring errors, wish I’d done it decades ago. Now I want another scrap cover to cut, but keep the clutch release intact for eyeballing finger function.

The poor meshing was a spin-off surprise. But thinking about it later I concluded that if the gears meshed properly, the bushes would have to be completely gone before the teeth un-meshed. More gear data will paint a clearer picture.

Raytag, I have found an AM cover with tapered bore, but it wasn't wallowed, the taper was the "draft" for die/mold release, then the sneaky bastards pressed sintered/oilite bushes into the tapered bore. Presumably they then "sized" the bushes with a press mandrel. Looked good and worked for a short time until the bushes crumbled away. Honed out the taper, oversize full width bush & outside seal, far as I know still good. Other AM covers have machined bores for bushes.

Nifty
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Re: meshing of kicker gears

#8

Post by Robert Luland »

No manufacture presses a bushing into casting before running a mill end though it. No way is it tapered. Where do you come up with this shit?
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Re: meshing of kicker gears

#9

Post by panhead »

Where do you come up with this shit?
Please stick to the board rules:
3. Members have an absolute right to free speech with these restrictions: personal attacks on others will not be tolerated. Challenge others' points of view and opinions, but do so respectfully and thoughtfully.
4. Treat others like you want to be treated yourself. In other words: show respect
nifty
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Re: meshing of kicker gears

#10

Post by nifty »

Raytag
For clarification:
It was a 1980's unknown make kicker kit, with late style pressure-die-cast cover, cover had no cracks, I punched out what was left of the crumbled bushes, I saw the hole was not machined, I measured the hole and found the "draft" taper (I can't remember the dimensions), I honed the hole until taper was gone, progress of honing showed that taper was consistent for full depth (again I forget the finished bore size, but new stock bushes were slightly too loose), I completed the repair.

Nifty
1950Panhead
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Re: meshing of kicker gears

#11

Post by 1950Panhead »

Interesting. The gears I measured were aftermarket. Were factory H-D any better in terms of mesh area?
The factory gears are better then after market parts with the exception of Baker which are great.
No manufacture presses a bushing into casting before running a mill end though it. No way is it tapered. Where do you come up with this shit?
Bob is correct
It was a 1980's unknown make kicker kit, with late style pressure-die-cast cover, cover had no cracks, I punched out what was left of the crumbled bushes, I saw the hole was not machined, I measured the hole and found the "draft" taper (I can't remember the dimensions), I honed the hole until taper was gone, progress of honing showed that taper was consistent for full depth (again I forget the finished bore size, but new stock bushes were slightly too loose), I completed the repair.
The factory cover was precision reamed for the bushing.
If your cover was not reamed it is worse then most after market parts.
nifty
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Re: meshing of kicker gears

#12

Post by nifty »

1950Panhead wrote: Fri Dec 10, 2021 2:39 pm
The factory cover was precision reamed for the bushing.
If your cover was not reamed it is worse then most after market parts.
That was the original point I was making to Raytag

Nifty
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Re: meshing of kicker gears

#13

Post by RooDog »

Forty years ago we all did things we wouldn't do again today.
....RooDog....
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Re: meshing of kicker gears

#14

Post by Andygears »

“ I have found an AM cover with tapered bore, but it wasn't wallowed, the taper was the "draft" for die/mold release, then the sneaky bastards pressed sintered/oilite bushes into the tapered bore. Presumably they then "sized" the bushes with a press mandrel. Looked good and worked for a short time until the bushes crumbled away. Honed out the taper, oversize full width bush & outside seal, far as I know still good. Other AM covers have machined bores for bushes.“

I could picture the bushings getting smushed into tapered bores in a factory far away making parts by people who care not and know not. Simple, the reaming operation was skipped, accident or rushing, and minimal material for reaming would allow bushings to start. Back when kickers were popular, there were a lot of people making covers.

Andygears
nifty
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Re: meshing of kicker gears

#15

Post by nifty »

nifty wrote: Thu Dec 09, 2021 12:06 pm If anyone reading this has an 80up trans case and a ditto countershaft (.749") and a kicker cover with good bushes, they might easily answer Raytag's question.
And I'd like to know too.
I'm thinking ...
If the kick shaft is actually in-line with countershaft, the late countershaft should pass right through the 1980 case bush and into the bushes in kicker cover.
Well no-one responded, but recently a late 1980 trans came in for a rebuild, so I checked.
OE trans case & OE kicker cover
So Raytag, and anyone else who may care
Categorically
Mainshaft C/L to kick shaft C/L is different to M/S to C/S C/Ls
I don't have time or reason to set up and measure accurately, but difference is approx .090"
Nifty
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