5 replies to this topic

[hundred]

Hi, please can someone tell me what are straight cut and straight cut drop gears, and also what is the difference between them and standard gears.

Thanks 100

[Asphalt]

Drop gears are the gears that transfere the power from the crank to the gearbox (which is below the engine ('transverse gearbox') on a Mini, not on the side as with normal cars ).
Consistent of: primary gear (crank), idler gear ('transfere/drop gear'), gearbox input gear.

See this: http://www.minimania.....rop gears.jpg

Usualy, the gears are cut in a helical pattern: http://www.woodcarbs... GEARS 013a.jpg

Straight cut gars are - straight cut: http://www.7ent.com/images2/FOR100.jpg

Straight cut gears are in theory a bit weaker, but way cheaper to produce, that's why they are used for close ratio gearboxes (which are only produced in very smal numbers, compared to the millions of gearboxes BMC/Rover/Leyland did produce).

For the drop gears there's another reason for straight cut teeth: helical gears tend to be pushed to the side (caused by the helical cut). That's why high performance engine 'need' straight cut drop gears - to prevent the idler eating through the clutch cover. Which is only alloy - the gear & it's shims are made of steel... Hard eats soft... For 'low' power engines (generaly said to be 'below 100hp') helical gears are said to be ok. But with high torque/power outputs - it's neccesary to use noisy straight cut gears.

Edited by Asphalt, 21 August 2009 - 07:48 PM.

[Pauly]

Standard helical cut gears have a slight curve in the teeth, straight cut is self explanetry really, the teeth are straight.

If you look on minispares or minisport at helical and staight cut gears you will see what im trying to explain.

Paul.

Edited by Pauly, 21 August 2009 - 07:46 PM.

[bmcecosse]

Great answer from Asphalt ^^^^^^^^ !! They 'supposedly' don't absorb as much power -although in truth it's only marginal. They also make a shrieking noise - which is great at first - but soon gets on your nerves if you do many miles in the car!

Edited by bmcecosse, 21 August 2009 - 07:49 PM.

[hundred]

Drop gears are the gears that transfere the power from the crank to the gearbox (which is below the engine ('transverse gearbox') on a Mini, not on the side as with normal cars ).
Consistent of: primary gear (crank), idler gear ('transfere/drop gear'), gearbox input gear.

See this: http://www.minimania.....rop gears.jpg

Usualy, the gears are cut in a helical pattern: http://www.woodcarbs... GEARS 013a.jpg

Straight cut gars are - straight cut: http://www.7ent.com/images2/FOR100.jpg

Straight cut gears are in theory a bit weaker, but way cheaper to produce, that's why they are used for close ratio gearboxes (which are only produced in very smal numbers, compared to the millions of gearboxes BMC/Rover/Leyland did produce).

For the drop gears there's another reason for straight cut teeth: helical gears tend to be pushed to the side (caused by the helical cut). That's why high performance engine 'need' straight cut drop gears - to prevent the idler eating through the clutch cover. Which is only alloy - the gear & it's shims are made of steel... Hard eats soft... For 'low' power engines (generaly said to be 'below 100hp') helical gears are said to be ok. But with high torque/power outputs - it's neccesary to use noisy straight cut gears.

Great thanks thant answers my question. Thanks again

[mini7boy]

Hi, please can someone tell me what are straight cut and straight cut drop gears, and also what is the difference between them and standard gears.

Thanks 100

straightcut gears, either drop gears or internal transmission gears, differ from normal(helical) gears in that the teeth run parallel to the bore of the gear, rather than at an angle to it.

maybe if you think of watch gears you will visualize it.

Pro: straightcuts reduce side movement under loading

Con: straightcut drops are very noisy. If you want any proof of this, witness a Mini7 or Mini Miglia race.

straightcut idler gear: http://www.minimania...A/InvDetail.cfm

"normal(helical)" idler gear: http://www.minimania...4/InvDetail.cfm