Srtaight Cut drops V Standard Helical ?
Turbo Mini Forums

my thoughts exactly?

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

Own the day

I thought the snag was that the side thrusts wore the thrust washers allowing the actual load to be unequally distributed on each bearing/shaft/teeth the whole thing then wearing and getting slack and noisy.

I've had some properly shagged helical drop gears, I imagine the efficiency was shocking, but they struggled on, despite their material inferiority.

I thought that ignoring the side thrusts, the only reason SC gears were better was the superior material. From a wear point of view, they are crap.

Bugger off, I'm getting there.

you could apply the MED idea in theory to the helical gears but you would still need some kind of thrust bearings as no matter what kind of bearing you have suporting the idle gear if it is helical then there will be a trust load, where as with S/C there's not.

For the helical side thrust issue, I've been thinking about this as I actually don't want the noise from straights

Two potential solutions,

1 - I found this a while ago on another forum/website, a simple modification to the gearbox casing and/or transfer housing to provide a pressurised oil feed to the thrust washer(s). I can't find the link at the moment but basically it involved a bit of alloy weld build up adjacent to the thrust washer(s). Then drill, tap, and insert a small tube with a conecting drilling from the back of the thrust washer to the tube. The tube then goes out through a hole in the casing (with something like a compression fitting to seal the casing) and is connected with a braided hose to a high pressure oil supply (just like the turbo feed).

2 - My own thoughts.... why not replace the thrust washers with a proper thrust bearing. Cylindrical thrust ball bearings or roller bearings are too thick to fit in but needle roller thrust bearings can be built up quite thin (I have the SKF catalogue open at the right page as I type...)
The idler gear already has two recesses in it (between the thrust face and the teeth). Widen that in towards the shaft and machine it flat and square and fit one, possibly two, needle roller thrusts in the recess.
I'm sure there must be a reason this won't work or someone would have done it already, probably the dynamic load rating isn't high enough, but I'm off to do some measurements and calculations....

Schrödinger's cat - so which one am I ???

Rod,

Whilst you have the Skefco catalogue open, have a look at the thrust capabilities of their deep groove ball bearings.

If they are up to it, you could probably fit one each side of the idler, if you machine most the idler centre out.

You will need to calculate the thrust loading.

Deep groove balls are used in a lot of rotating machines these days instead of the old taper or spherical rollers.

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."

paulH , i dont know if this helps , but its a bit data anyway ,
i dynoed my car at 144 bhp ,with a lean mix ,i assess it at 150 bhp running richer ,ran 14.3 quarters at 98mph ish .
i then ran 13.9 @ 104 mph .. i estimate this to be 185 to 190 bhp ..
this was all running standard a plus drops ,so far v little increase in noise etc .
im using a high zddp oil ,which i think is pivotal in making the thrust sides last .. but this is theory and i have no proof its affecting it one way or another .

regards robert

Edited by robert on 8th Oct, 2008.

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

Robert,

I'm sure that the gears are up to it, particularly with good lubrication.

How many miles have your drop gears done.

I think that the theory goes that the side thrust will wear, allow the idler to tilt and put greater load on the journal bearings which will then fail.

If the side thrust bearings can be improved then there may be a solution.

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."

Sorry to hijack this thread. but my drop rattle? on tickover. Had it in gear, they just rattle a little, they are brand new and all the bearings were fine. Is this normal.

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

Paul (S), (and anyone else who's bored...)

From the catalogue technical bit...
"Axial load carrying capacity - If deep groove ball bearings are subjected to a purely axial load, this axial load should generally not exceed the value of 0.5 C(o). Small bearings and light series bearings (diameter series 8,9,0 and 1) should not be subjected to a load greater than 0.25 C(o). Excessive axial loads can lead to an appreciable reduction in bearing life"

C(o) is static load rating, unfortunately it doesn't talk about C (dynamic load rating) but let's assume the same applies.

Using 25mm bore just as a benchmark,

6205 deep groove (25/52mm)
I would normally call a 62xx a light series, but by their definition...
C(o) = 7,800 N
C = 14,000 N
So let's assume C (axial) = 7,000 N

7205 angular contact ball (25/52mm)
There is a complicated calculation for axial but I'll be simplistic and say it's the same as radial if they were just used as a thrust bearing.
C(o) = 10,200 N
C = 15,600 N

Now a built up needle roller thrust 25/42mm
C(o) = 60,000 N
C = 13,400 N
or 35/52mm
C(o) = 83,000 N
C = 16,600 N

Dynamic is lower than static on the needles (presumably, being flat, the needles will be trying to do different speeds at their inner and outer ends, so it probably screws up the oil film) but they are comparable to an angular contact ball bearing - the deep groove ball bearing is about half.

The trick is going to be working out the side load from helix angle and engine torque - I can only do it simplistically with a static load diagram once I figure out how to measure the helix angle - and then guessing what safety factor to add for shock loadings, torque reversals etc.....

Schrödinger's cat - so which one am I ???

COULD YOU USE SHAR OF OIL FILM ?oops caps ,
eg ,surface area of washer to idler ,then oil viscocity ,then how much force it takes to shear through that psi,and since on a stock engine it works ,use that as your margin for safety.

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

i just have the timkin (sp) idler bearing

That’s Great stuff Rod S now we are really starting to get into the meat and potatoes of the thing,
right a few problems jump out at me the first and foremost,
If we use a needle roller bearing we are going to have to create two bearing surfaces one on the gear and on the alloy cacesings as most of the needle bearings don’t come with inner and outer races that might be a problem?

I have looked at the 7000 series
before as a very good alternative it is possible to get the series with inner and outer races which would be ideal we could machine the caceings to take a slightly larger bearing if need be
,
<runs off to find slide rule and brain>

but would not the primary gear to idler gear create thrust forces in one direction, and the input gear to idler gear create thrust forces the other way around?

7000 series being the angular contct ball bearings....

The problem is my simplistic statement above "There is a complicated calculation for axial but I'll be simplistic and say it's the same as radial if they were just used as a thrust bearing."

Once you use them to carry radial load, ie, if you re-machine the casing to replace the cylindrical needle rollers and thrust washers with just an angular contact ball bearing, the axial capacity will drop as it carries radial load.

They are also very sensitive to have the right axial preload (ie, no end float) so machining would have to be very accurate.

The needle roller thrust bearings I'm looking at have no inner or outer races, as you say, but you pick the appropriate sized raceway washer, thrust washer, shaft washer, housing washer from the catalogue, or make and heat treat your own.

Schrödinger's cat - so which one am I ???

setting the preload would be a piece of piss simply assemble the hole lot on a gear box with out an engine block measure the gap between the gear face and the inner race and get shims to take this up and add the correct preload job done just like the diff bearings.

again the problem I see with the needle roller and using thrust washers is that there wont be enough room the current trust washers are between 3 and 4 mm that’s not giving us a lot of room for a bearing and two thrust washers, you could machine the gear to allow some more room but the gear is as hard as the hob of hell at this point because it is a thrust face and their is bugger all room on the gear box caceing for machining ?

My thoughts with the angular contact bearings would be to fix a shaft in place of the existing journal bearings and but a bearing each side of the idler outer ring. That way the preload could be set on the shaft before it is installed.

Similar to the MED setup but with two angular contact bearings rather than one roller.

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."

Schrödinger's cat - so which one am I ???

Schrödinger's cat - so which one am I ???

the way its been explained to me after mine went years ago is helical idlers will want to 'twist' if the thrusts get worn, which will take out the bearings in no time

another point, which probably is not an issue but i though i would raise anyway is transfer case flex, i doubt very much that is an issue, but does anyone know for sure?
no point designing a superduper thrust bearing if the casing its held in flexes...

granted it would be nice on a road car to cure the side loading issue associated with helical idler gears as you would have reduced noise, greater strength, but they would still 'sap' power, its just the axial force generated would be dealt with in a more civilised way

on a race/drag car, sc spurs are still going to transfer power more efficiently, which means more power at the wheels, which is a bonus, but at the cost of increased wear

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

the med solution is ideal for sc spurs, but the old jkd system that used timken bearings would be better suited for side loadings

maybe after someone more intelligent than me calcs the axial force generated by the idler, we can find out if the timken taper roller bearings they use (LL52549) is suitable, then its just a case of machining the idler for these?

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

That part number took a bit of tracking down, it's an imperial series !!!

Dynamic load rating 14,400 N

It will probably be hard to source nowadays and the closest metrics are quite a bit wider (although that gives them a higher load capacity

Schrödinger's cat - so which one am I ???