one for those good with maths
Turbo Mini Forums

Im trying to spec up my bearings up for my gearbox build, but I can't work out how to convert the loads they are capable of withstanding to actually figures I have.

The figures given for the bearings I have been looking at are:

Dynamic load 22900Kn
Static load 38000Kn
Fatigue load limit 4900 Pu

I want this box to be bullet proof, so im working on the figures of 250lbft torque being put through it. How do I convert this to work out the loading put on the bearings?

Cheers
Matt

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1/4mile in 13.2sec @ 111 terminal on 15psi

id make that 350lb/ft matt?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Matt, don't forget a good factor of safety, ie X 2!

Jk

If Carling made Mini engines
it would probably be like this one!

Whats your workings Robert? Remember always show your workings.

John - Is that an exaggeration, or really what is needed?

Im looking into needle rollers, due to being compact in size. On simplybearings they seem to be one on the best for load carrying.

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1/4mile in 13.2sec @ 111 terminal on 15psi

Think of it like this Matt. The standard mini gearbox was designed for 35bhp. It'll take 4x that!

I would say x2 is a minimum. Can't help with the maths though.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Ah point taken Wil. It makes you wonder if they designed it knowing that there was going to be 1275 cooper engines running the same the box.

Ive found another bearing, that is absolutely the maximum size 'i can fit in, the figures are as follows.

Dynamic load 31900Kn
Static load 43000Kn
Fatigue load limit 5500 Pu

All always thought taper rollers were the best for load carrying, but looking at the fibures of a few there not all that great.

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1/4mile in 13.2sec @ 111 terminal on 15psi

Ive got a feeling the power, not just rpm knocked through that box is going to have an effect. put as power is a product of rpm and torque.....what sort of rpm to you expect peak torque to be?

im sure ive got something in a txt book about this somewhere....

Edited by Sam on 7th Feb, 2012.

I have been thinking about this. If maximum torque is at a higher RPM surely this would put less radial load on a bearing?

If you had say 200lbft at 2000rpm, that force has to be 'absorbed' somewhere, so rather than it being 'absorbed' as rotational force its absorbed as a radial force. If you had say 200lbft at 8000rpm, as the gears are turning faster wouldn't the force be more in the rotaional direction, as the load is divided between more teeth per sec...If that makes sense?

Looking at Matt w, JohnK and Jims torque figures, Matt goes through more boxes than anyone, so to me that would say torque has more effect on bearing/gear life than actual BHP?

I think my peak torque is at 6800rpm. We estimate the power to be around 200bhp on 15psi looking at a comparison on 1/4 mile and terminal speeds reach compared to others with similar weight cars. Im now running 25/30 psi so no idea what its actually putting out, but seeing as Johnk and Jims torque figure are around 200lbft I won't be any more than that.

Im going to look at some standard mini layshaft bearings to see what they are spec'd at as a comparison. Which has lead me onto thoughts that maybe it would be beneficial to run longer needle rollers on the layshaft to spread the loading and maybe illiminate the groove that wears on the layshaft?

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1/4mile in 13.2sec @ 111 terminal on 15psi

run mutiple bearings like they do on the A+ layshaft?

I was thinking along the lines of a longer single bearing and one directly inline with 2nd/3rd gear. Everytime ive had a shaft wear, the groove is always biased the outer edge, which makes me think that under load there is flex in the shaft causing the bearing to be loaded up more on the outer edge. If you fitted a support bearing in the centre of the layshaft wouldn't that act as a support for the whole shaft? Could be waaaaaaayyyyyy off mind.

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1/4mile in 13.2sec @ 111 terminal on 15psi

Bearing size will play a part no doubt also.

Ill go ask one my tutors about it tomorrow.

Wheres TurboDave hiding? im sure this stuff is right up his street? I have been too long out of the books so wouldn't dare to speculate, but you do need a comfortable FofS to take into account shock loads, as its shock loads that have killed all the drive-train components i have ruined.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Send me an email with the numbers, loadings, approx PCD of the gears, and I'll see what I can work out for you.

Tapers are not the best for radial loads - cylindrical rollers win every day. They are also the simplest, and most robust.

One piece of advice though; a hangnang or whothef**k ever bearing of idential load size and rating (on paper) as an SKF bearing will fail long before an SKF bearing ever will.

Second and final piece of advice - engine oil is dirty and full of crap that rolling element bearings do not approve of. For the best bearing life, look at different filters, perhaps a depth media filter to soak up the stuff that walks stright through a 20 micron pleated filter...

Cheers,

On 7th Feb, 2012 matty said:
I have been thinking about this. If maximum torque is at a higher RPM surely this would put less radial load on a bearing?

If you had say 200lbft at 2000rpm, that force has to be 'absorbed' somewhere, so rather than it being 'absorbed' as rotational force its absorbed as a radial force. If you had say 200lbft at 8000rpm, as the gears are turning faster wouldn't the force be more in the rotaional direction, as the load is divided between more teeth per sec...If that makes sense?

Looking at Matt w, JohnK and Jims torque figures, Matt goes through more boxes than anyone, so to me that would say torque has more effect on bearing/gear life than actual BHP?

I think my peak torque is at 6800rpm. We estimate the power to be around 200bhp on 15psi looking at a comparison on 1/4 mile and terminal speeds reach compared to others with similar weight cars. Im now running 25/30 psi so no idea what its actually putting out, but seeing as Johnk and Jims torque figure are around 200lbft I won't be any more than that.

Im going to look at some standard mini layshaft bearings to see what they are spec'd at as a comparison. Which has lead me onto thoughts that maybe it would be beneficial to run longer needle rollers on the layshaft to spread the loading and maybe illiminate the groove that wears on the layshaft?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Ok quick maths.

1lbft = 1.35582Nm
1Nm = 0.001Kn

So working on 250lbft we get,

250 x 1.35582 = 338.955Nm
338.955 x 0.001 = 0.338995Kn

So from these calculations you will need a bearing that will withstand a minimum of 0.338995Kn. This ofcourse is not taking into account the additional loads put on the bearing through rotation, friction etc.
Does that look right to everyone? That numbers seems a bit low.

The turbo build has finally started

You can't just convert torque to radial load.

You need to draw up some force vector diagrams, but you will need the gear PCDs, contact angles etc etc.

See what TD can do, it is his specialism.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

This may be of some use:

http://174.122.7.157/~turbo91/Newsletters/6-2.pdf

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Dave - That would be great if you could! Whats your email address?

The dimensions I have to hand are:

centre distances of shafts, approx torque figure im working with, distance between bearings, and the size and ratings of the bearing I want to use. Anything else I need to get?

Ive been looking into the SKF range as ive heard from many people that they are one of the best bearings.

Cheers guys that gives me some food for thought.

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1/4mile in 13.2sec @ 111 terminal on 15psi

possibly the rotating mass weight ,to calculate poosible shock loads ?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Do you think the bearings are the weakest link in the gearbox ?

I'd have thought the casings, then layshaft, then gears were the weak links.

Not the main bearings ?

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Steve, im basically trying to get to the point where i know the bearings up are to the job, as i don't want the box to munch itself to pieces because i haven't spec'd them right, and have all my hard work go to pieces. the gearset and shafts are the only non variables i have, and there is not much i can to increase there strength. so if they break first i kbow the limits of the box and know whether or not i should gox back to a normal box.

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1/4mile in 13.2sec @ 111 terminal on 15psi

I've seen more collapsed first and third motion shaft roller bearings than any other broken component in a gearbox

On 9th Feb, 2012 matty said:
Steve, im basically trying to get to the point where i know the bearings up are to the job, as i don't want the box to munch itself to pieces because i haven't spec'd them right, and have all my hard work go to pieces. the gearset and shafts are the only non variables i have, and there is not much i can to increase there strength. so if they break first i kbow the limits of the box and know whether or not i should gox back to a normal box.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

This is for my sequential box im building, so evrything is a complete unknown. Ive never had a bearing failures in a standard box, only worn layshafts.

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1/4mile in 13.2sec @ 111 terminal on 15psi