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Morris 1100
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PostPosted: Wed Apr 25, 2007 6:01 pm 
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>Rude< wrote:
ive got straight cut gears in mine, does that change the strength of the gears?
Helical cut gears are designed to last till the end of the warranty period.
Straight cut gears are designed to last till the end of the race. 8)

A lot of people say that straight cut gears are stronger and that is why they use them in race cars. They are wrong! Straight cuts are weaker by design but they use less horsepower to run, that is why they use them in race cars. :wink:

When straight cut gears mesh they have one tooth in contact at a time.
Helical gears can have two or even three teeth in contact at a time.
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Spaceboy
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PostPosted: Wed Apr 25, 2007 6:03 pm 
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:roll:
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ss wanab
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PostPosted: Wed Apr 25, 2007 6:07 pm 
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tinymorris1969 wrote:
straight cuts are stronger


:roll: :roll: :roll:

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>Rude<
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PostPosted: Wed Apr 25, 2007 6:10 pm 
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wats wit all the eye rolling, so straight cut gears not stronger - not good for street daily driving use?

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ss wanab
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PostPosted: Wed Apr 25, 2007 6:11 pm 
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not if u want a quiet ride and long lastin box :wink:

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Morris 1100
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PostPosted: Wed Apr 25, 2007 6:13 pm 
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>Rude< wrote:
wats wit all the eye rolling, so straight cut gears not stronger - not good for street daily driving use?
I think your gearbox may have the answer to that question.
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slinkey inc
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PostPosted: Wed Apr 25, 2007 6:14 pm 
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Although these expensive as hell straight cuts are stronger than mini gears as they are made from better materials, but they as said are expensive as hell.

Helicals are fine.

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>Rude<
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PostPosted: Wed Apr 25, 2007 6:15 pm 
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Morris 1100 wrote:
I think your gearbox may have the answer to that question.

touche :(

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>Rude<
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PostPosted: Wed Apr 25, 2007 6:23 pm 
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Contrary to popular belief, they are not stronger than identically manufactured helical's at all (identically being the key word). The only s/c sets you can buy for minis have all the teeth made on the same rack, and have the pitch and height corrected to compensate for the different teeth numbers. Very crude, very agricultural, very poor – but usually made from reasonable quality steel and heat-treat, so are easily able to cope with the torque the little A-series puts out. The main difference however – is that the helical’s are simply designed to last 100k miles and be quiet – SC gears are designed to take a higher torque at the expense of life and noise.

Helical's have a minimum of two teeth in contact at any one point. With some high helix angles, even three can be in contact. More teeth in contact = reduced wear, quieter running, and less stress per tooth, hence increased strength. Straight cuts have one in contact, maybe shared over two, but only if the tip chamfers and tooth bending at the rated torque is correct. Going slightly over on this tip chamfer (too small a chamfer) generates huge contact stresses which will cause micro welding & pitting in a very short time. This is why the tip chamfer is mostly 'erred' on the side of caution, which again brings us back to single tooth contact – and noise!


from here: http://www.manchesterminis.co.uk/technical/helical_vs_sc_gears.htm

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Curly
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PostPosted: Wed Apr 25, 2007 6:24 pm 
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Morris 1100 wrote:
>Rude< wrote:
ive got straight cut gears in mine, does that change the strength of the gears?
Helical cut gears are designed to last till the end of the warranty period.
Straight cut gears are designed to last till the end of the race. 8)

A lot of people say that straight cut gears are stronger and that is why they use them in race cars. They are wrong! Straight cuts are weaker by design but they use less horsepower to run, that is why they use them in race cars. :wink:

When straight cut gears mesh they have one tooth in contact at a time.
Helical gears can have two or even three teeth in contact at a time.

I was just about to write the same thing .... so to expand a bit on the accurate analysis above:
Straight cut gears have a smaller gear tooth contact patch compared to helical gears and yes, they do place all the engine's torque on that single thrust face of the tooth. Helical ones by design spread the load more effectively, and are therefore stronger.
So why do we use straight cut gears ?
I'm sure to manufacturers they are simpler and therefore cheaper to produce, although more expensive for you and I to purchase because of the economies of scale. :cry:
They do use less power to drive. :D
And very simply, they are more readily available in the close ratios we want for competition cars. Helical close ratio sets are the ideal setup but very rare over here and quite expensive.
The close ratio sets available for Minis have a very tall first gear which makes them rather unsuitable for normal road use in metropolital areas.

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>Rude<
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PostPosted: Wed Apr 25, 2007 6:28 pm 
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was just told by mum's bf aka my mechanic that i dont have straight cut gears......i guess i just have to wait till tomoro to see what is truly wrong with my gearbox.......i hate waiting!!

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Spaceboy
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PostPosted: Wed Apr 25, 2007 6:54 pm 
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yeah a worn gearbox or diff will whine quite a bit

oh and 1st gear is straight cut
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>Rude<
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PostPosted: Wed Apr 25, 2007 6:59 pm 
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yer u can deffinately tell 1st gear is straight cut, i usually short shift first gear for that reason.

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Morris 1100
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PostPosted: Wed Apr 25, 2007 7:02 pm 
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>Rude< wrote:
yer u can deffinately tell 1st gear is straight cut, i usually short shift first gear for that reason.
:roll: :roll:
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>Rude<
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PostPosted: Wed Apr 25, 2007 7:04 pm 
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stop rolling ur eyes at me! :P :P

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