straight cut drive gears

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cbn70
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straight cut drive gears

#1 Post by cbn70 » Wed Feb 21, 2007 7:29 pm

Hi,
I have seen some straight cut drive gears for sale, for a banshee, and I am pretty sure they will fit my rz as well. My question is will I get any noticable difference in HP with these? Also what is involved in installing them?? How do they get installed on the back of the clutch basket? If not what is the point of getting them, as the only difference is the straight gears as opposed to the angled gears? thanks

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beebe
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#2 Post by beebe » Wed Feb 21, 2007 9:56 pm

Yamaha put the angled gear in there to make it run quieter.

You may gain 1-2 more percent out of it since there are less losses, but I think angled gears still are 98% efficient? Something like that.

You re-rivet the new gear onto the back of your clutch basket.

The straight cut gears do not put axial loads on the crank bearings. Do you need it? Probably not, unless you have a mono-block or something pushing out frightening amounts of HP.

cbn70
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#3 Post by cbn70 » Thu Feb 22, 2007 12:57 am

where do you get the rivets from? Can you get them from Yamaha ???

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beebe
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#4 Post by beebe » Thu Feb 22, 2007 1:32 am

Make 'em, or from a hardware store, or from an online industrial supply place like McMaster-Carr.

I don't think you can get them from Yamaha.

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#5 Post by smurph » Thu Feb 22, 2007 1:42 am

Yep. McMaster-Carr has them. I just ordered some the other day. You can get the flat sided rivets. 1/4" is about the same as 6mm. To rivet, you can use the hammer method to flatten the other side or use a press (my favorite way).

I sure do wish I could find a set of straight cut gears but the price has been prohibitive for me. Also, keep in mind that you may loose your oil pump, as I don't think the set comes with the oil pump drive gear. But you may be able to source one separately or have one made.

Steve
Fuel Injected RZ350

cbn70
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#6 Post by cbn70 » Thu Feb 22, 2007 9:42 am

isnn't the oil pump drive gear mounted on top of the clutch drive gear??

T.RexRacing

#7 Post by T.RexRacing » Thu Feb 22, 2007 11:32 am

1.)Noise will increase
2.)Measured power will increase-a little-and I mean little
3.)Crank life will decrease
4.)Premix mandantory
5.)The contents wallet will decrease

Not really worth the effort and expense.But if you want it to whine install a gear driven blower.Now there's some cool noise.With a considerable increase in power.

dirtball
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#8 Post by dirtball » Thu Feb 22, 2007 2:05 pm

one plus is that you can change the crank to trans driven ratio from stock - again, not worth it unless you have the power to back it up.

But I agree with Rex on the prognosis.

Anyone ever seen the supercharger impeller attached to the flywheel? I believe the ATC250Rs were used for this setup, dunno how it worked but it looks cool -
Do it right or do it over.

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#9 Post by Saving4Parts » Thu Sep 27, 2007 11:23 pm

T.RexRacing wrote:1.)Noise will increase
2.)Measured power will increase-a little-and I mean little
3.)Crank life will decrease
4.)Premix mandantory
5.)The contents wallet will decrease

Not really worth the effort and expense.But if you want it to whine install a gear driven blower.Now there's some cool noise.With a considerable increase in power.
I'm looking at buying a set of straight cut primaries, but not for the power increase. I'm putting my engine in a RS250 frame and there is sprocket size limitations (can't use any bigger than 17T on the front or smaller than 38T on the rear). So i'm looking at changing the primary ratios so it's a bit taller. I have found RDZ do a set of straight cut gears with 2.68 ratio.

Could someone explain to me why the straight cut gears would decrease the crank life? Is it to do with backlash? I would of thought that the helical gears would of been worse for the crank as they would give a side force.

What other options are there for changing the primary and secondary gearing?
"My biggest problem is that I have absolutely no fear whatsoever, and that scares me"

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#10 Post by xen-uno » Fri Sep 28, 2007 12:32 am

The helicals are as close to pure constant mesh as you can get, but I don't see that prolonging crank life. The helicals also have thrust loads that straight cuts don't. Any advantage given by the former (smoother transmission of power) is offset by the latter (thrust loads leading to reduced bearing life) ... IMO. Agree with all other points except 4 providing 5 is no problem.

Physical limitations on sprocket min-max tooth counts ... or that they're just not available?

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#11 Post by Saving4Parts » Fri Sep 28, 2007 12:50 am

Well... 5 is alway a problem, it's just the extent of the problem that varies. At least i won't get a crookered spine from sitting on a full wallet. That was my understanding, helical would be smoother, but i couldn't see them as being better for the crank. Yeah, its physical limitations (fouling).
"My biggest problem is that I have absolutely no fear whatsoever, and that scares me"

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hellmanns
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#12 Post by hellmanns » Wed Jul 16, 2008 12:55 am

Sorry to dig that deep on this topic... I read it several times but I still don't got the item numb 5... can someone explain to me?


I still want that race noise and this 2% of power...

:smt017
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Davidj
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#13 Post by Davidj » Wed Jul 16, 2008 1:44 am

hellmanns wrote:Sorry to dig that deep on this topic... I read it several times but I still don't got the item numb 5... can someone explain to me?


I still want that race noise and this 2% of power...

:smt017
"The contents wallet will decrease"

Its a joke, meaning that the money in your wallet will go away.
It should read "The contents in your wallet will decrease"

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#14 Post by Saving4Parts » Wed Jul 16, 2008 1:54 am

Thanks for bringing this back up, it'll give me a chance to ask if anyone has tried the RDZ 2.36 straight cut primary. Does anyone have a photo of one fitted? I'd be interested to see the clutch case clearance.
"My biggest problem is that I have absolutely no fear whatsoever, and that scares me"

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Davidj
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#15 Post by Davidj » Wed Jul 16, 2008 1:57 am

hellmanns wrote: I still want that race noise and this 2% of power...

:smt017
Yeah, that "race noise" is a cool sound. You can hear that sound from in-car camera's in like GT racing cars.

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