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GS674 Dose anyone "back-cut" their dogs?

  • Thread starter Thread starter ashdricky
  • Start date Start date
A

ashdricky

Guest
So i am waiting to assemble the motor and seriously considering having my transmission dogs "back-cut" (i think this is correct), as i have the ignition setup to kill during upshifts and if i understand correctly back-cut dogs will help with gear engagement?
 
I really think you are over thinking alot of things . You already have straight cut gears which should be plently strong. As far as I've read over the years you have nothing to worry about strength wise in the case. Only times I've read about backcutting has been high HP drag racers.

The whole point of the iginition kill is to aid in gear engagement. You theoretically could do the same thing without the ignition kill with some risk of grenading parts. What's going on is when the ignition cuts as you shift the engine and trans should have no load for that short period, thus easily popping to the next one.
 
yes i may be confusing the term "back-cutting" with something else as i meant actually having the dogs themselves machined with a 5-7 degree angle so when slightly engaged the gears actually pull together under load, not cutting the actual meshing teeth. ill upload pics in the morning to try to clarify things,
 
if you want send it off to be back cut.
makes for a better shifting bike all around.
i have a guy that does back cuts pretty cheap.
p/m me if your seriously interested as he runs a business and doesn't have a lot of time for questions.
 
here is an example of what i meant
undercut.jpg
 
The dogs are already backcut or undercut or whatever you want to call them from the factory..over the years they get beaten flat, mis-shifts and false neutrals can result, especially on the one/two and four/five upshift. Worse when hot or when your bike says it needs an oil change, or if you're lazy on the shift, or if your linkage is sloppy. If you're gonna go hog wild you can usually get it up and down cut (both sides of the dogs) for not much more.

As far as straight cut gears...the only place youd want straight cut is the clutch mesh gears, and really with the relatively low HP this will produce even with your upgrade in displacement I wouldn't really worry about it. The only GS that came with straight cut gears in that area were the 8v 750s. They whine, which I don't mind. You may look into bolstering your clutch backing plate however, as helical gears such as these came with side load the basket and if you're going to be banging through the gear box with vigor, it may be some insurance the basket doesnt go boom.
 
There will likely be someone here with specific knowledge regarding GS gears, however as a general principle removing material from gears requires consideration.

Obviously one large consideration is that the gear dogs must still engage and index accurately or there will be side/radial loads resulting. Such loads can contribute to gear failure/wear or encourage jumping out of gear.

I have seen cases where someone was too "enthusiastic" in terms of the engagement angle which made it difficult to disengage for the next shift. Not to mention any names...
Oh, the things we thought we could improve when we were young.:o

Another consideration is as to whether the gear material is uniformly conditioned and composed to a sufficient depth to accomodate the machining. Some gears have a very hard/tough surface treatment with a less conditioned material composition below the surface layer. One can see this when grinding gear material in an attempt to correct chipped teeth, jumping out of gear due wear to dogs, etc.

It sounds as though this area is well represented by those who have experienced this work in drag racing and performance so it would be interesting to hear of the long term (if that can apply to racing) effects and all other quantitative observations.
 
he means primary gears, from crank to clutch basket. the gearbox is straight cut-and good and strong!.:dancing:
 
I see. I'll have to take some more time checking that out. Learning stuff everyday. Thanks

Here's a Picture I was able to google of a 77 550 transmission for reference:

gs550transmission.jpg
 
Last edited:
I was digging around ebay and found that ALL 1977-78 had a clutch basket straight cut gear:

1977gs550straightcutgearclutch.jpg


ALL 1979 and up had the Heli cut:

1979gs550helicutclutchgear.jpg


Now I know ebay isn't 100% reliable but there were multiple parts listed for each year that all matched up with no crossovers between the years.

My case is a 77-78 from what I recall so next time I'm working on it I'll try and get and see if I can verify any of this.
 
wow I finally had time to check this thread, ive been really busy setting up other things for this project. Blowerbike thank you for the offer i should have checked this sooner I dropped my gears off at Fast by Gast days ago and they asked 300.00 for the job. which is a little less than the other shop i checked. there are not any downsides to doing this correct?
thanks
 
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