Gear repair?

Dirt Bike Technical discussion. This is for a little more in depth discussions :-)
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60something
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Location: Midwest USA

Gear repair?

Post by 60something » Tue Mar 06, 2018 7:29 pm

I am rebuilding a 1987 KX500 and found one of the transmission gears; 4th input, has some damage to one of the teeth. As this gear is discontinued, I was wondering if anyone has tried (successfully) to repair a gear by brazing and re-finishing the damaged tooth area? I am aware of a couple of these on Ebay, but I have already spent way more on this project than I should have...it has seemed to snowball lol. I will post a photo of the gear if I can figure out how, as I'm new to this forum. Also, the same goes for the power valve rack gear; it is probably useable, but has an area of damage, and these apparently are like hen's teeth. Thanks guys for any input!
I don't know half of you half as well as I should like, and I like less than half of you half as well as you deserve.

2006 KDX200 qty-2
1987 KX500
1991 CB750 Nighthawk
1973 H2 750 Triple - gone but not forgotten

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60something
Posts: 54
Joined: Sat Mar 03, 2018 6:45 pm
Location: Midwest USA

Re: Gear repair?

Post by 60something » Tue Mar 06, 2018 7:31 pm

P.S. I'm not going to be doing any racing, just putting around the trails.
I don't know half of you half as well as I should like, and I like less than half of you half as well as you deserve.

2006 KDX200 qty-2
1987 KX500
1991 CB750 Nighthawk
1973 H2 750 Triple - gone but not forgotten

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Sandblaster
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Re: Gear repair?

Post by Sandblaster » Tue Mar 06, 2018 11:30 pm

Yes, you can repair them by hand.
It takes a bit of work but we have done it several times with good results.
Take a look at this gear.
See the circle?
You drill a hole through the gear right next to the damage.
Then you get a small square file and go to town.
Since the material is hardened it takes a while but it is doable..


gear repair.jpg
gear repair.jpg (369.26 KiB) Viewed 432 times
Any questions?
Post them up 8-)
If bikes are for kids I'll never grow up.

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60something
Posts: 54
Joined: Sat Mar 03, 2018 6:45 pm
Location: Midwest USA

Re: Gear repair?

Post by 60something » Wed Mar 07, 2018 3:29 pm

So how do you ensure that each dog is making contact, sort of seat-of-pants, or is there some procedure? I watched a couple videos showing back-cutting the dogs on a milling machine, but that defeats my goal of trying to get by as cheaply as possible. I like your idea of drilling the hole to give the file room to work. :)
I don't know half of you half as well as I should like, and I like less than half of you half as well as you deserve.

2006 KDX200 qty-2
1987 KX500
1991 CB750 Nighthawk
1973 H2 750 Triple - gone but not forgotten

User avatar
60something
Posts: 54
Joined: Sat Mar 03, 2018 6:45 pm
Location: Midwest USA

Re: Gear repair?

Post by 60something » Wed Mar 07, 2018 3:45 pm

Sort of on the same topic, the power valve rack gear (or rod) on the same bike (‘87) has a tooth that’s chipped. I haven’t found a replacement anywhere yet. I was wondered if that could be repaired somehow by brazing and reshaping the tooth with a Dremel or something. The metal looks kinda cheap; not sure brazing would even work. Loctite makes a metal repair epoxy, I wonder if that would work?
I don't know half of you half as well as I should like, and I like less than half of you half as well as you deserve.

2006 KDX200 qty-2
1987 KX500
1991 CB750 Nighthawk
1973 H2 750 Triple - gone but not forgotten

User avatar
Sandblaster
Posts: 5610
Joined: Thu Jun 07, 2012 3:50 pm
Location: Eugene, OR
Contact:

Re: Gear repair?

Post by Sandblaster » Wed Mar 07, 2018 4:27 pm

60something wrote:
Wed Mar 07, 2018 3:29 pm
So how do you ensure that each dog is making contact, sort of seat-of-pants, or is there some procedure? I watched a couple videos showing back-cutting the dogs on a milling machine, but that defeats my goal of trying to get by as cheaply as possible. I like your idea of drilling the hole to give the file room to work. :)

If your doing it by hand... and on the cheap... You can use some contact paper which will leave a mark if it makes contact... Or other products such as some plasitgauge. Whittle a little at a time...
I liked the diamond files the best for the hardened gear surface.
If bikes are for kids I'll never grow up.

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Sandblaster
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Joined: Thu Jun 07, 2012 3:50 pm
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Re: Gear repair?

Post by Sandblaster » Wed Mar 07, 2018 4:35 pm

60something wrote:
Wed Mar 07, 2018 3:45 pm
Sort of on the same topic, the power valve rack gear (or rod) on the same bike (‘87) has a tooth that’s chipped. I haven’t found a replacement anywhere yet. I was wondered if that could be repaired somehow by brazing and reshaping the tooth with a Dremel or something. The metal looks kinda cheap; not sure brazing would even work. Loctite makes a metal repair epoxy, I wonder if that would work?
Get me the part number you need..
I'll see what I can find for you.
If bikes are for kids I'll never grow up.

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60something
Posts: 54
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Location: Midwest USA

Re: Gear repair?

Post by 60something » Wed Mar 07, 2018 4:37 pm

Makes sense.
KX500 power valve rod.JPG
KX500 power valve rod.JPG (978.85 KiB) Viewed 422 times
Regarding the power valve rod, I've posted a pic...a few of the teeth are chipped. Any ideas on repair? I haven't located one just yet. Kinda hard to conceive of how they get chipped like that, as the power valves themselves are aluminum, and it doesn't seem like there'd be that much force applied with the governor arrangement :?:

Thanks Sandblaster for the simple directions on posting a photo!
I don't know half of you half as well as I should like, and I like less than half of you half as well as you deserve.

2006 KDX200 qty-2
1987 KX500
1991 CB750 Nighthawk
1973 H2 750 Triple - gone but not forgotten

User avatar
60something
Posts: 54
Joined: Sat Mar 03, 2018 6:45 pm
Location: Midwest USA

Re: Gear repair?

Post by 60something » Wed Mar 07, 2018 4:39 pm

Oh, as a follow-up, the power valves themselves are in great shape with no damage to the gears.
I don't know half of you half as well as I should like, and I like less than half of you half as well as you deserve.

2006 KDX200 qty-2
1987 KX500
1991 CB750 Nighthawk
1973 H2 750 Triple - gone but not forgotten

User avatar
60something
Posts: 54
Joined: Sat Mar 03, 2018 6:45 pm
Location: Midwest USA

Re: Gear repair?

Post by 60something » Wed Mar 07, 2018 4:45 pm

The part number for the 1987 power valve rod is: 49046-1057 ROD-GOVERNOR
I don't know half of you half as well as I should like, and I like less than half of you half as well as you deserve.

2006 KDX200 qty-2
1987 KX500
1991 CB750 Nighthawk
1973 H2 750 Triple - gone but not forgotten

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