Broken kicker gear

That looks to me like an engineering design flaw. The broach that Baker used to create the square hole has sharp corners instead of radii, which creates stress risers that will lead to cracking exactly like what you have there. In my experience Baker's stuff has always been top notch, but this looks like an oversight to me. It really doesn't even make sense from a manufacturing perspective, since extremely sharp corners on a broach are much more prone to wear and higher maintenance/replacement costs over time. I looked on Baker's website and it appears they are still making them this way.

The Sifton gear definitely does not have the same sharp corners in the broached hole.

WhizzbangK.C. said:

The broach that Baker used to create the square hole has sharp corners instead of radii, which creates stress risers that will lead to cracking exactly like what you have there.

Click to expand...

Thanks for chiming in.

I had similar thoughts based on seeing the cracks radiate out directly from shaft boss corners. Your point about keeping broach tooling sharp in a production shop is also a good one.

One thing that has bothered me a bunch over the years is how poorly starter gears fit in the kickstart shafts with anything other than the oem parts. I've used JIMS, Drag, VT shafts and every variety of gear and the fit always kind of sucks. Too much play. Too many bevels reliefs around the boss on the gear limiting contact (more force per area . . . higher stress).

Since this bike is for me only and I'm firmly in the DGAF phase of life I may weld the new gear on this time.

Jason

p.s. - This is the bike with the issue. I built it when I was a . . . let's say younger and crazier man. Hoping I continue riding it into my 70s. Will have to eat my wheaties and keep up the exercise ;-0

While I agree about the piss poor fitment, I can tell you from experience that welding it isn't the answer. I've seen it done twice, and both times the weld failed quickly. There's just no way to get enough penetration into the gear and shaft to make the weld hold up without completely annealing the gear and shaft. The slop between the gear and shaft are just more motion than the weld can stand up to. I've had better results shimming the square with good quality stainless feeler gauges. Just find the one that you can barely wedge in on one side of the shaft, and cut pieces for both sides of the shaft from one half that thickness. Do this for both axis of the square and then install the washer and nut. You want a fit that you need to use a small hammer to tap in, but that will go. I do this with every kicker gear I install now, and haven't had a failure from it yet. I have taken them apart on down the line and found the shims flattened and a bit loose, but still better than without.
BTW, I find it a good idea to keep extra sets of feeler gauges in my box specifically for shim stock. They're cheap and very useful.
Very nice bike. I like a lot!

Good point about the welding. Talking out my ass from frustration I suppose.

I'm with you on the shimming (and especially equally to keep gear centered to prevent binding). I shim most loose things in the shop.

I made a good find a few years back . . . box of stainless shim stock in a broad variety of thicknesses. Inexpensive. $25 for what will likely be a lifetime supply on Amazon.

Jason

never seen baker gears do that, hummm.
what I do see makes me wonder and remember.
I put baker gears in mine when they first came on the market... 12-13 years ago?
at the time there was a heat treatment problem with the starter clutch.... the part on the mainshaft.
I was told they split at the keyway.
I notice yours split but they don't show the normal wear that many others do...


and...


it may prove interesting to know just how hard the baker gears are heat treated to.
too hard = brittle = $$$ replacement...

@WhizzbangK.C. inspired me today with this:
"Well, I'm sure it's been figured out by many folks over the years, and it's probably written down in shop note books all over the world, but I've never seen it called out specifically on a public forum. To me the real value of the internet is sharing information, so I did. I get a lot of use from info that others have posted here and elsewhere, and I think it's only right to repay at least some of that if I can."

So I'm gonna turn this post into what I hope will be helpful to others for later reference.

Will cover all the steps and checks I've gone through to get the kickstarter on the 93" mongrel bike back in service and hopefully durable. You can also call it "jeezus christ, this guy does all that just for two gears. i did that shit drunk on a dirt road in thirty minutes one time and mine works just fine".

Disclaimer: I do things how I do them. I'm always open to suggestions and feedback. If they make sense to me, I'll probably file in my brain for later reference. You may have other ways. Here is mine.

Enjoy.

So we left off with cracked/bent starter gear, salvageable starter clutch set, deformed starter shaft, chewed up kicker cover, intact but untrusted late-style throwout bearing and rod. I bought a new "Sifton" (V-Twin copy) starter gear, a repop early throwout bearing (Eastern) and clutch rod.

Issue: I run an old JIMS extra lengthy heavy duty I-beam kick arm. Bike is kick-only with stroke, big-bore, and over 9:1 compression. This kick arm is necessary and I've been running it for twenty years. The boss where arm attaches to the starter shaft is much larger than stock. No one makes starter shafts for this arm any more except me. The last one I made from two donor shafts in 2012 is still intact (my welding doesn't totally suck I guess) but it got got chewed up by the cracked kicker gear so I'll need to make a new one.

Bottom is the last one I made. Note size of arm boss compared to stock dims one above. Also note gear bosses torn up from cracked starter gear. Top is an extra JIMS shaft (new) from the 4-speed drawer. Will make a new one from these donors.



I cut them up and prepared the ends to be welded on the lathe, which turns out is also my welding fixture. Ground clamp directly on the parts to be welded so I don't send current through the lathe bearings ;-0



After many passes with my trusty MIG (I have a TIG, but I have more experience on this machine and it's fast for fill work) it's done. I polished up the shaft with some oily emory while i was there. Yes, I see the small voids and don't care.



Issue: The kicker gears bound up when they broke and deformed the woodruff key and mainshaft where the starter clutch mounts. I cleaned up the mainshaft with jewelers files and made a new key out of a larger piece of keystock to ensure full contact with the shaft and gear. Lots of test fits with dye (Sharpie) and filing. Advice: key fits are often overlooked and are worth spending some time on. Typical problems are: too tall preventing full contact on tapers between parts, wrong shape or too small allowing movement.

The old one:


The new full contact one. Note: made key short enough to allow the lock tab washer to engage the starter clutch. Otherwise risk of nut tab washer being useless and nut coming loose. Note: depth of gear with and without key must be checked to ensure key is not preventing full engagement on taper.



Checking depth of gear on shaft with and without key in place. Not shown: checked gear runout with a dial after final install to confirm it runs true. Out of true could lead to failure of starter gear set again.



Issue: Old cover got majorly gouged up by the cracked kicker gear, needed new bushings, and did not fit with early style throwout bearings. I've gotten 24 years of service out of it and it was a repop anyway. Decided to replace with S&S pig nose style.

Clutch release parts test fit and new clutch rod polished up for easy operation.


Advice: with old machines and mixes of aftermarket parts, check the fit of EVERY THING, EVERY TIME. This cover was designed to allow use with early throwout bearing. Well I don't have one, I have a COPY of one.

I test assembled the throwout finger parts, starter clutch set, rod and throwout bearing to ensure full range of operation. Guess what? Travel was limited by bearing hitting the cover. Marked up the cover and bearing after taking off some material with a die grinder. Repeated until full range proven.

Contact near finger boss. Thowout finger (early style with offset/rotated finger boss) good.


Contact shown on bearing:



Will get into more next post . . .