25 replies to this topic

[happydude2012]

Chaps

 

Ive been offered a set of nearly new straight cut gears for my 1275 A Series - i believe they are from mini sport and have done about 300 miles.

The chap who bought them realized he cant take his Mrs or kids out in it because they all hate the noise - also he motorway commutes from worcester to near bristol every day and he reckons its making him mental and is having to wear ear defenders, which given the fact hes a suit and boot type guy makes the image of this lawyer bombing down the motorway in a snappy suit with his bright orange STHIL gardening ear defenders on even more hilarious....for me anyway.

 

They are compatible with my gearbox and at present i have helical gears which are just fine - for anyone asking why oh why would i want to change if its already fine? well i like the sound. its that simple and only do about 10 miles a day in it.

 

Ive touched on this in previous posts and was put off the idea because of the racket the drops make, but hes sold the drops to his brother and has offered me the gear set in exchange for a bit of DIY so i reckon its a good deal.

 

1st gear - 29 teeth, Ratio - 2.54:1

2nd gear - 25 teeth, Ratio - 1.73:1

3rd gear - 22 teeth, Ratio - 1.25:1

1st motion shaft (4th gear) - 19 teeth

Laygear - 25, 23, 19, 15, teeth

Reverse idler - 17 teeth, Ratio - 2.69:1

 

My question is this, can i change the gear kit, whilst keeping the drops standard to minimize the whining but keep the whining.....if that makes sense?

I know alot of people dont like straight cut especially with drops too and i know that by leaving the drops, im making them the weak point in the gearbox -  but can this be done?

 

thanks

 

 

 

[mini13]

Yep. With the std drops 4th will be quiet as the box drives straight through.

[Swift_General]

Yes you can change the gear set without changing the drops. Are the ratios suitable for your engine though? To be fair a straight cut gear set is quieter then straight cut drops as they are bathed in oil. Also helical gears are inherently stronger than straight cut, not weaker.

[happydude2012]

Yes you can change the gear set without changing the drops. Are the ratios suitable for your engine though? To be fair a straight cut gear set is quieter then straight cut drops as they are bathed in oil. Also helical gears are inherently stronger than straight cut, not weaker.

ah! well thats a new bit of info, all the people so far ive heard from about straight cut are adamant that the straight cut are stronger......what makes you say the  helical are stronger Swift, genuine curiosity on this one. - thanks

[Icey]

Yes you can change the gear set without changing the drops. Are the ratios suitable for your engine though? To be fair a straight cut gear set is quieter then straight cut drops as they are bathed in oil. Also helical gears are inherently stronger than straight cut, not weaker.

ah! well thats a new bit of info, all the people so far ive heard from about straight cut are adamant that the straight cut are stronger......what makes you say the  helical are stronger Swift, genuine curiosity on this one. - thanks

There are some more complex answers around how torque is transmitted but the simplest reason helical is stronger is because each tooth is effectively larger than on a straight/spur type gear.

The main reason spur gears are used is because the are cheaper/easier to manufacture.

[happydude2012]

 

 

Yes you can change the gear set without changing the drops. Are the ratios suitable for your engine though? To be fair a straight cut gear set is quieter then straight cut drops as they are bathed in oil. Also helical gears are inherently stronger than straight cut, not weaker.

ah! well thats a new bit of info, all the people so far ive heard from about straight cut are adamant that the straight cut are stronger......what makes you say the  helical are stronger Swift, genuine curiosity on this one. - thanks

There are some more complex answers around how torque is transmitted but the simplest reason helical is stronger is because each tooth is effectively larger than on a straight/spur type gear.

The main reason spur gears are used is because the are cheaper/easier to manufacture.

 

Ill look into it, thanks for the knowledge though swift. So ill still get the lovely whine without drops, just not as intense as with drops?

[happydude2012]

 

 

Yes you can change the gear set without changing the drops. Are the ratios suitable for your engine though? To be fair a straight cut gear set is quieter then straight cut drops as they are bathed in oil. Also helical gears are inherently stronger than straight cut, not weaker.

ah! well thats a new bit of info, all the people so far ive heard from about straight cut are adamant that the straight cut are stronger......what makes you say the  helical are stronger Swift, genuine curiosity on this one. - thanks

There are some more complex answers around how torque is transmitted but the simplest reason helical is stronger is because each tooth is effectively larger than on a straight/spur type gear.

The main reason spur gears are used is because the are cheaper/easier to manufacture.

 

sorry, i mean icey! lol thanks for the reply

[Cooperman]

Helical gears are stronger. The SC sets are a different ratio which is not ideal for normal road use. 1st, 2nd & 3rd gears are all higher than the standard box and that can make 1st a bit high for pulling away uphill as a lot more clutch slipping is needed.

SC gears are intended for competition. The reason they are SC is because the cost of cutting helical gears for a low-volume of sales is expensive.

There is something of a lack of understanding about SC CR gears. The reason the gears need to be closer ratio is because a full-on competition engine will have a narrow power band and the torque band will be at higher revs. Thus to keep the engine 'on the cam' when driving flat out it is vital that when the up-change is made the engine will still be near to peak power in the next gear. For example, a rally engine may give peak power at 6400 rpm with power strong from 5500 rpm to 6800 rpm. So you change up at 6800 rpm and the close ratio gears will mean that the revs in the next gear will still be over 5500 rpm. The problem with this is that 1st gear will be a high for when pulling away, so a very low ratio final drive is fitted which makes 1st low enough to pull away with good acceleration. The downside is that in 4th gear the revs will be high for cruising. But then, competition cars don't normally 'cruise', they just go flat out! I can give an example. My Cooper 'S' has SC CR gears and I use a 3.9:1 final drive ratio (FDR). This is fine and the engine stays on the cam through the gears. But the mph/1000 rpm in 4th is only 14, so 98 mph is 7000 rpm. Fortunately the engine can sustain these revs, but a normal road engine is entirely unsuited to a SC CR gear set.

As for SC drop gears, they are intended to enable easy adjustment of gear ratio to suit different circuits. It is easier to change the drop gears than the diff for different circuits. They are simply horrible on the road without a crash helmet or ear plugs. I have them in my 'S' and they are being replaced with helical drops very shortly.

The ideal gear set for a mildly tuned road engine is the original Cooper/Cooper 'S' ratios and these are available in helical form. They give good performance with a slightly better cam (MG Metro, Kent 266, etc) and head and 1st gear is not to high.

I hope this helps explain the gearing issue.

[happydude2012]

Helical gears are stronger. The SC sets are a different ratio which is not ideal for normal road use. 1st, 2nd & 3rd gears are all higher than the standard box and that can make 1st a bit high for pulling away uphill as a lot more clutch slipping is needed.

SC gears are intended for competition. The reason they are SC is because the cost of cutting helical gears for a low-volume of sales is expensive.

There is something of a lack of understanding about SC CR gears. The reason the gears need to be closer ratio is because a full-on competition engine will have a narrow power band and the torque band will be at higher revs. Thus to keep the engine 'on the cam' when driving flat out it is vital that when the up-change is made the engine will still be near to peak power in the next gear. For example, a rally engine may give peak power at 6400 rpm with power strong from 5500 rpm to 6800 rpm. So you change up at 6800 rpm and the close ratio gears will mean that the revs in the next gear will still be over 5500 rpm. The problem with this is that 1st gear will be a high for when pulling away, so a very low ratio final drive is fitted which makes 1st low enough to pull away with good acceleration. The downside is that in 4th gear the revs will be high for cruising. But then, competition cars don't normally 'cruise', they just go flat out! I can give an example. My Cooper 'S' has SC CR gears and I use a 3.9:1 final drive ratio (FDR). This is fine and the engine stays on the cam through the gears. But the mph/1000 rpm in 4th is only 14, so 98 mph is 7000 rpm. Fortunately the engine can sustain these revs, but a normal road engine is entirely unsuited to a SC CR gear set.

As for SC drop gears, they are intended to enable easy adjustment of gear ratio to suit different circuits. It is easier to change the drop gears than the diff for different circuits. They are simply horrible on the road without a crash helmet or ear plugs. I have them in my 'S' and they are being replaced with helical drops very shortly.

The ideal gear set for a mildly tuned road engine is the original Cooper/Cooper 'S' ratios and these are available in helical form. They give good performance with a slightly better cam (MG Metro, Kent 266, etc) and head and 1st gear is not to high.

I hope this helps explain the gearing issue.

Hi Cooperman

 

Thanks for the comprehensive reply!

Im 1275 with a stage 2 head and swiftune sw5 cam.

I admit that presently there is nothing "wrong" with my set up at all, i just love the sound of straight cut gears - in your experience, is this obtainable to some degree without the "horrible" aspect you discuss?

Or am i being a tit replacing these gears for the sake of something which is impractical....as i said i do commute in this car.

 

In ernest, the clutch needs replacing so i figured why not combine both jobs whilst the fella was down that way, but im considering not bothering as my gear set up is ok, it just doesnt go "wwwweeeeeeeeeeee!" ha ha. 

 

A friend of mine got walloped by a landrover last year and rolled his mini and it went like a pancake against a wall which has made me a bit more safety concious. i was considering a bit more support in the way of a cage and a nice bucket and harness on the drivers side. do you think this would be a better investment? i cant help thinking this gear thing has got me excited but im just being a bit of a divvy.

[Icey]

Will you be wearing a crash helmet while driving? If not then a cage will make a crash hurt more.

If safety is a concern, to be blunt, buy a modern car.

[Cooperman]

If it were me I would not fit close ratio gears to a Mini with your engine specification.

I can also promise you that the straight-cut gear whine will not be something you will continue to enjoy. To most people it is a downside to having them. 

Where is peak power with the SW5 and where is maximum torque? That is the key to it all.

You will find 1st gear very high unless you fit a low final drive and acceleration 'off the line' will not be as good. Your 0 - 60 time may not be as good with SC CR gears as you will need to slip the clutch when pulling away up-hill.

You need to build the engine and gearbox so that it all matches.

 

If you are nervous about the strength of a classic car, then buy a modern one which overcomes all the disadvantages. Minis are just 60-year-old classics with all the retro advantages and disadvantages. 60 years is a long time in terms of engineering improvements.

Edited by Cooperman, 27 January 2018 - 02:30 PM.

[mini13]

as normal some disinformation regarding the strength of sc/helical boxes.....

 

yes gear for gear helicals are stronger, BUT generally speaking we are not comparing gears of the same material, after market gear kits will normally be made from a superior material and be stronger, also you have to consider side loadings etc.

 

fact of the matter is helical boxes start giving up the ghost around 150hp, where as a good SC kit will live  to over 200hp, this has been proven again and again on turbo'd motors.

 

of course thats all a bit arbitary with your engine spec.

[Northernpower]

 

 

Yes you can change the gear set without changing the drops. Are the ratios suitable for your engine though? To be fair a straight cut gear set is quieter then straight cut drops as they are bathed in oil. Also helical gears are inherently stronger than straight cut, not weaker.

ah! well thats a new bit of info, all the people so far ive heard from about straight cut are adamant that the straight cut are stronger......what makes you say the  helical are stronger Swift, genuine curiosity on this one. - thanks

There are some more complex answers around how torque is transmitted but the simplest reason helical is stronger is because each tooth is effectively larger than on a straight/spur type gear.

The main reason spur gears are used is because the are cheaper/easier to manufacture.
 

Ill look into it, thanks for the knowledge though swift. So ill still get the lovely whine without drops, just not as intense as with drops?

Trust me, the whine is not lovely after 20 minutes. You can't hear anything other than the straight cut drops, not even a passenger talking. Stick with straight cut for the box (if you must) and helicals for the drops. With your engine a properly built standard box will be fine.

[happydude2012]

 

 

 

 

Yes you can change the gear set without changing the drops. Are the ratios suitable for your engine though? To be fair a straight cut gear set is quieter then straight cut drops as they are bathed in oil. Also helical gears are inherently stronger than straight cut, not weaker.

ah! well thats a new bit of info, all the people so far ive heard from about straight cut are adamant that the straight cut are stronger......what makes you say the  helical are stronger Swift, genuine curiosity on this one. - thanks

There are some more complex answers around how torque is transmitted but the simplest reason helical is stronger is because each tooth is effectively larger than on a straight/spur type gear.

The main reason spur gears are used is because the are cheaper/easier to manufacture.
 

Ill look into it, thanks for the knowledge though swift. So ill still get the lovely whine without drops, just not as intense as with drops?

Trust me, the whine is not lovely after 20 minutes. You can't hear anything other than the straight cut drops, not even a passenger talking. Stick with straight cut for the box (if you must) and helicals for the drops. With your engine a properly built standard box will be fine.

 

ill take your expertise on this one guys - stick with the set up ive got, its perfectly tuned so why mess. I just like to ask "what if".

Thanks all for your input.

[panky]

Might be worth doing the DIY/gear set deal and sell them on. There's always someone who will want them.