Topic: back cutting trans gears

[Metalhead]

we're getting ready to assemble the 836 motor and we need to know which gears to back cut and at what angle.

[MRieck]

3rd was the big one. The angle...I'm not sure.... 4 degrees maybe eyeballing Gast stuff. Why not send it to Gast for a full work up?

[sparty]

I second Gast.  My tranny is awesome.

Sparty

[fuzzybutt]

i work for metalhead and i'm doing the build.........he owns/runs a machine shop and has all the equipment for me to do this. I'm building an 836 with wiseco pistons and a new unmounted 30+ year old r/c head, megacycle cam and 31mm cr's.

[paulages]

I second Gast.  My tranny is awesome.

Sparty

how much did they charge you? PM me if you don't want to post it...

[Sam Green Racing]

About £150.00

Sam.

[754]

I talked to a  buddy that does his own.. not super hard.
 
I would have thought grinding stone (or cup wheel) but he says he used carbide insert endmill.. not too tough if you use a dividing head or even a rotary table with a shim..

 I will try to find out a bit more.. re angle etc..

[sparty]

I second Gast.  My tranny is awesome.

Sparty

how much did they charge you? PM me if you don't want to post it...

Let me look at my records, but somewhere around $300.

[HondaMan]

What is this "back cutting" technique?   

[754]

slight undercut on the pressure side of the dog tooth. and or mating gear.
 promotes gear staying in rather than popping out when it gets slightly rounded off.

[MRieck]

What is this "back cutting" technique?   

Art has a pic or 2 in his engine build file. It's a little fuzzy but you can see the cut on the dogs. (it's the 2nd pic of the tranny)

[HondaMan]

Ah, thanks, guys.
We used to call it "pull cutting". 

[MRieck]

Ah, thanks, guys.
We used to call it "pull cutting". 

I've never heard that term but it describes it perfectly.

[HondaMan]

Ah, thanks, guys.
We used to call it "pull cutting". 

I've never heard that term but it describes it perfectly.

Well...it's from the mid-60s....
We first did it with Puch motorcycles when I was a kid, 'cuz they had terrible stay-in-gear performance. We trimmed the dogs with a Dremel tool and cutoff wheel so it would pull the gears tighter together under the load of 3 kids hanging onto the little 106cc Sears-Puch at full throttle in 2nd gear...so, we called it "pull cutting" after that! It caught on when I was building the 750s and 500 for RR work at Western Wheels in IL, so at least that local group knew it that way!

[Quail "Owner of the comfortable k8"]

I did it on the old johnson outboards also.

[HondaMan]

I did it on the old johnson outboards also.

They had a gearbox?    Mine didn't. 

[Quail "Owner of the comfortable k8"]

Use to back cut ( we called it taper cut) the drive dogs for forward on the 40hp.  They worn badly, and would jump in and out of gear when you juiced it.  if you did it when new they never wore

[GammaFlat]

Use to back cut ( we called it taper cut) the drive dogs for forward on the 40hp.  They worn badly, and would jump in and out of gear when you juiced it.  if you did it when new they never wore

I have a "way old" Johnson 20 / Johnson 18 / Evinrude 18.  I think they're all the same and mine is a mix of at least 2 of those.  I have heard that "once they start jumping out of gear, the problem just gets worse" - the fun part was they always did it at full power of course.  Are they the same as the 40 you speak of?  Can they be salvaged after the problem starts occurring? 

[Quail "Owner of the comfortable k8"]

I don't know, we only did it when we were replaceing worn dogs or if we had a unit open for another problem.