Outdrives - Weak point or bad luck?

[Northy]

Nah, colour makes no difference, it's the material



G

[AmiSMB]

Yeah you have the get some rings made with real 'O'. I think the purer 'O' the harder!!

[showtime]

i wont ask what colour your ring is Grant

[ryan]

Originally Posted by showtime

i wont ask what colour your ring is Grant

Is that because you already no? Haha

[showtime]

well it would just be a guess but i'd say.........................................

[AmiSMB]

LMAO

[chris68nufc]

Anybody know if you can buy the losi hard spacers seperatley that people are using as limiters. I have 2 o rings on at the moment but they dont work. Ive done 2 outdrives already.

[Chrislong]

Originally Posted by chris68nufc

Anybody know if you can buy the losi hard spacers seperatley that people are using as limiters. I have 2 o rings on at the moment but they dont work. Ive done 2 outdrives already.

Chris, when are you racing next? I think I have some spare limiters like I use, if I find them I will put them asside for you and you can have them at Worksop.

Alternatively if you need something sooner - then AE sell a pack of those 0.3 shims (were white, are black in newer kits), and I reckon 3 of those per shock will be just right.

[waggz]

AE makes some limiters that are about 3mm in size. I found them in my dirt oval parts that I have for my custom works sprint cars. I think they might be called bump stops? I will check to see if I can get a part number on these.

Has anybody heard if there will be a new batch of outdrives made from a different material?

[Cam]

All,

Are the spacers/limiters you are using fitted onto the piston shaft inside the shock or on the outside of the shock?

Cam

[showtime]

they need to be on the outside of the shock to limit uptravel dude
spacers fitted on the inside limit droop

[Cam]

tvm

[Richard Lowe]

After having a good look at lil Bens SX at York this week it's pretty obvious what's causing all these broken outdrives, and it's not the outdrives or up travel

[glypo]

It is...?

They are over hardened for sure, anyone with smallest bit of materials knowledge can see that.

[Richard Lowe]

But its not the main reason IMO

[Southwell]

Down travel?

[Chrislong]

Originally Posted by Richard Lowe

But its not the main reason IMO

Well do share the info Rich, don't be shy, your not usually.

[waggz]

edit

[glypo]

To be fair, Schumacher do you give you the tools for making the diff. The weird composite tools which also deals with turnbuckles and ball grippa (rod ends). Using this would put the out-drive under less strain then gripping using a mole wrench, or pliers or whatever you used.

Either way, unacceptable really. I am beyond certain the outdrives are over-hardened. I have been saying it for ages (since the start of this thread at least) and Schumacher hasn't denied it.

I have been looking at the fractures under a microscope and the size of the crystals suggest over-hardened steel. Out of the 5 types of possible fracture (ductile, brittle, creep, fatigue and environmental) brittle is the most obvious for hardened steel. A brittle fracture is not a bad thing by itself, and is indeed expected from the high strength steels.

The last time I studied fractures, it was in structural integrity where there is always assumed a crack present. However I feel I am right in saying that the same will apply for any material as you just assume the crack or defect is close to infinitely small to begin with, and the same relationships withhold? When you look at the brittle fracture toughness (KIC) of something like high strength steel it is in the region of 70 MPa(root)m and a toughness (GIC) of around 30-90 kJ/m^2. When you compare this to mild steel which has KIC of 140 and GIC of 100 and even a ductile metal like Aluminium with a KIC of 300 and GIC of 500-1000!

This by no means implies hardened steel is weak, it’s the strength of the material that deals with that. However a small difference between yield strength and ultimate tensile strength is what defines a brittle fracture – and is associated with this low fracture toughness. Basically, the lower the fracture toughness is you will typically find the smaller the zone of plastic deformation (lower elasticity). As I say, it’s not bad, you want hard driveshafts otherwise they will mark easily. However by hardening the material initially you reduce the zone of plastic deformation (between YS and UTS). If you harden too much you actually start to reduce the UTS and the YS tends towards the UTS. In summary a small zone of plasticity is fine, it's just when you overharden you loose strength and you loose any ductility to slow the fracture.

On the front end of my car, I am convinced the driveshafts are well clear of fowling the outdrives, yet I am sat here with 3 broken outdrives in front of me from the front of my car. 2 of them had broken when nothing else had broken either. Whether Schumacher admit it or not, I am sure over hardening is the case. I would like to hear your alternate theory Richard although I am not sure I will agree.

I just wish Schumacher would admit more openly about this issue (as in some circumstances it is due to this driveshaft issue, but most it isn’t) so that we can hear what the proposed solution and timescale is.

[MattW]

I'm not sure what you mean when you talk of a driveshaft problem??