9 replies to this topic

[adammini]

Hi all,

I was just pondering whether there would be any benefit of making helical drop gears with the idler gear with a roller bearing inside, just like they do for s/c drops.

Would having the bearing in the centre, help prevent the the twisting motion that can destroy gearbox and transfer gear cases in and high powered a series engines?
As far as I understand both helical and straight cut gears themselves are as strong as each other, its just the twisting motion of helicals (under lots of torque) that can damage other things like bearings and cases.
I heard somewhere (dont know if its true) that F1 cars use helical gears.

I was just wondering because I want to supercharge my 1380 soon but, I want the gearbox to be as stong as it can be. S/c drops are a nice sound in a car not used everyday, but I think it could be a bit much when used regualry!


Thanks

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[danwebster]

I personally wouldn't consider helical gears on a supercharged 1380 unless you intend to drive like my grandma.

It is indeed the side loadings that cause problems in torquey mini's. The strength of the teeth is not an issue although a lot of people have picked up on it lately and got into pointlessly long discussions about how helicals are stronger than straight cut.....nobody who knows anything actually cares about that as it misses the point of straight cuts somewhat.

Roller bearing straight cut drops are a fit and forget item, I personally wouldn't consider anything less.

[The Matt]

Some straight cut drops are less noisy than others! You can get ones that have had the teeth 'topped' so they are quieter.

[adammini]

I personally wouldn't consider helical gears on a supercharged 1380 unless you intend to drive like my grandma.

It is indeed the side loadings that cause problems in torquey mini's. The strength of the teeth is not an issue although a lot of people have picked up on it lately and got into pointlessly long discussions about how helicals are stronger than straight cut.....nobody who knows anything actually cares about that as it misses the point of straight cuts somewhat.

Roller bearing straight cut drops are a fit and forget item, I personally wouldn't consider anything less.

Thanks Dan, its sounds like s/c is the way to go.
I was thinking about having helical gears in the box, s/c drops and a x-pin diff. Do you think that would be wise or go all out s/c?

Am I right in thinking that the roller bearing drops replace the bearings in the transfer and gearbox case? I do like the sound of reliable drop gears, having had a mini where the idler gear tried to cut its way out of the case!

Thanks

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[adammini]

Some straight cut drops are less noisy than others! You can get ones that have had the teeth 'topped' so they are quieter.

Oh right, I didnt know that. What do you mean by 'topped'? Are they more like a series gears rather than a+?

[dklawson]

I won't restart the straight/helical argument here. It appears you've researched this already.

In response to your question though, a roller bearing in the center of a helical idler won't improve the situation. Helicals generate a side load by virtue of their tooth design and they will still require thrust bearings/pads because of that.

[Guess-Works.com]

As above... and "topped" gears are ones which the curved profile of the tooth has been machine off at the top, so there is actually room for the oil to escape when the gears mesh... Oil sheer is the term and is the majority of the noise generated by SC drops, and gears for that matter.

[adammini]

As above... and "topped" gears are ones which the curved profile of the tooth has been machine off at the top, so there is actually room for the oil to escape when the gears mesh... Oil sheer is the term and is the majority of the noise generated by SC drops, and gears for that matter.

Oh I see, very interesting, cheers John.

I will have to have a look to see which drops are topped or not.

Thanks dklawson, answers my question, the things I think about when im supposed to be working!

Edited by adammini, 29 March 2007 - 12:43 PM.

[Guess-Works.com]

Topped Drops...

[adammini]

Great pic, thanks John.