Rear Hub Assembly - Please Explain

[Dilkris]

For many years now I have been reading threads and posts regarding the recognized approach of assembling the rear hubs and as I look at the details of the arrangement, (see photo's), I really don't understand and my personal problem is, I have to. (It's an illness....   

Can somebody please throw some light on the following 2 queries:-

Question 1
Why is the hub nut torqued to a high 150 ft/lbs?? I can see no technical reason for this whatsoever and in consideration of comments posted whereby it is suggested that the stub axles, ex Hilman Imp (?), are "soft" - is it not possible that the stub axles are actually being stretched?
 
Question 2
Why is a Loctite Compound, (638?), used in between the splines when fitting the hubs to the drive shafts? I have never seen this practice ever, on any application, (cars. motorbikes, industrial process plants etc), between the interface of a splined shaft and hub. So why here? 

Please understand, I am not suggesting that the above accepted practices are wrong, I am simply wanting to understand why they are so, as starting with a blank sheet of paper, they are "unusual".           

[Pfreen]

The nut pulls the inner races of the bearings together via the spacer.   That is why the spacer should be hardened so it doesn't relax and let the nut loosen.  If the nut does loosen, there will be lateral movement of the shaft in the bearings.

The loctite prevents fretting of the splines due to alternating loads on the splines.  This will slowly loosen the spline fit in the hub.

That's my take.

[Bainford]

Answer 1
Yes, you are stretching the axel when you torque the nut. That's the point of torqueing any fastener. The idea is to stretch the threaded portion of the axel within it's elastic limit, in many cases the torque spec is 70-80% of the elastic limit of the materials. The low quality steel of the Europa axel is a problem, but like any fastener it must be stretched in order to maintain the clamping force that retains the nut tight, and ensures that the components being clamped (bearings and spacer) remain clamped. If the nut was merely snugged-up without being torque tightened, then the axel remains free to stretch in use, thereby causing the axel components to become loose or 'unclamped'. If you apply too much torque force, you exceed the elastic limit and incur plastic deformation, aka a pooched axel.

Answer 2
In a former life as a millwright, I used various spline setting compounds from time to time, usually Loctite products. Often times these were attempts to save worn splines amidst the hectic pace of a plant shut-down or on the instruction of an obstinate and cheap equipment owner, but on occasion it was on newly fitted parts on the instruction of the equipment manufacturer. I recall some rock crusher installations in particular. Much of the decision to do so is based on the service duty of the splined component at hand. Though our cars are light and engines of moderate power, the interface between the splined components can be tumultuous, with power provided in both directions in an environment of shock & vibration. This can cause fretting at the spline interface, a problem exacerbated by the small size spline and the solidified crap from which the axel is produced, and the fact that the axels are nearly irreplaceable. Spline setting compounds can deal with the wear that has taken place already (provided it's not too bad) and help prevent further wear from occurring by filling the voids in the spline assembly and preventing the relative movement of the assembled components.

I hope that helps. Questions?

[jbcollier]

The rear stub axles are straight off a low-hp Sunbeam Imp.  Even a completely stock Renault powered Europa puts out 30% more power.  It gets worse.  In order to line up the brake drum properly they added a 3/8" spacer between the hub and the outer bearing.  This means the outer bearing is only partially on the stub axle's bearing seat so it's also partially on the splines!  And, the hub is not fully engaged with the splines!!  Still think it can't get any worse?  Think again.  Lotus uses spacers made seam-welded, mild-steel, in other words, exhaust tubing.  Next we add the sealed bearings have a reduced inner area for the spacers to butt against.  Now can you see how marginal the system is?

Thanks to stress analysis by a lister, we know it is the poor contact between the spacers and bearings that causes the fretting which leads to a bending movement on the end of the axle.

Lotus struggled and updated their procedures and tried to improve the parts as well but largely to no avail as they didn't seem to understand the issue.

So, your questions:

1) The high torque is to try and reduce the fretting.

2) 635 Loctite is used to stabilize the hub on the splines as they found fretting was causing excessive wear.  635 is a high-strength and slow-setting adhesive.  The slow-setting rate is critical to give you time to assemble and seat everything before it hardens.

If you want to stick with the stock system do the following:

- make sure your stub axles and hubs are in PERFECT condition.  If not, REPLACE them, period, full-stop.

- consider using these stub axles instead:

http://www.pamotorsport.com/for_sale/index.php?option=com_virtuemart&view=productdetails&virtuemart_product_id=279&virtuemart_category_id=36&Itemid=109

They are much, much stronger.  As they are made to order, specify a 30mm ID inner bearing seat.

- throw the old spacers away!  Use new hardened spacers.

- use an open inner bearing (no built-in seals) for a larger contact area between the bearing and spacer.  Make sure it is a true open bearing and not a double-sealed bearing with the seals popped out.

- use a lock-tab with a hardened washer and the soft tab tack welded to it.

- assemble with 635 as per manual BUT do not bend the lock-tabs.  Go for a drive and corner hard.  Retorque the axle nut.  Repeat until the nut torque is stable.  Bend the lock tabs and you're done.

[Steve_Lindford]

S2 stub axles from Imp - Where do the twin cam axles come from??

Steve

[Dilkris]

Thankyou Pfreen, Bainford & JB for taking the trouble to come back to me on this, it's very much appreciated - questions? - sure - but I'm thinking about it. Chris

[SwiftDB4]

S2 stub axles from Imp - Where do the twin cam axles come from??

Steve

Obviously Hillman has been out of business for many years. My guess is both S2 and TC axles were made by an outside supplier, certainly not Lotus. Why did Lotus not get the outside supplier to improve the Imp design? Who is making the axles now that all the UK suppliers sell?

[Dilkris]

I believe the Hillman Imp was produced between 1966 and 1975 and the Europa and its variants between 63 and 76... seems like a reasonable fit. Who is making the axles as per original design now? Could still be emptying the parts bins....  A few people making improved versions though.

[TurboFource]

My Twin Cam was/is turbocharged and CWTech said he had no issues with axles, bearings or u-joints....he said the boost would spike to over 10lbs and that should have produced some nice torque numbers and they stood up to it....

[jbcollier]

TC/S axles are Lotus only AFAIK.  They probably got the chaps doing the Imp axles to do them.  Why not improve them further?  Changes cost $$$.

[lotusfanatic]

- make sure your stub axles and hubs are in PERFECT condition.  If not, REPLACE them, period, full-stop.

- consider using these stub axles instead:

http://www.pamotorsport.com/for_sale/index.php?option=com_virtuemart&view=productdetails&virtuemart_product_id=279&virtuemart_category_id=36&Itemid=109

They are much, much stronger.  As they are made to order, specify a 30mm ID inner bearing seat.

- throw the old spacers away!  Use new hardened spacers.

- use an open inner bearing (no built-in seals) for a larger contact area between the bearing and spacer.  Make sure it is a true open bearing and not a double-sealed bearing with the seals popped out.

- use a lock-tab with a hardened washer and the soft tab tack welded to it.

- assemble with 635 as per manual BUT do not bend the lock-tabs.  Go for a drive and corner hard.  Retorque the axle nut.  Repeat until the nut torque is stable.  Bend the lock tabs and you're done.

per JB's post, I understand that PA Motorsport make upgraded axles, it would be good to find the hubs, spacers and bearings all as a kit

Mark   

[S2Zetec54]

I was going to ask Peter of PA MS exactly this...what about a kit.

He'll need a hub carrier so I was vaguely thinking that I might do a winter strip down so he can see mine and develop something reliable based around his very strong en24 driveshaft.

He's an interesting and clearly talented chap who worked with Gordon Murray on the Rocket prototype apparently and he confirms that Gordon does indeed have a Europa 'kicking about' at his home. I'm sure he won't mind me mentioning that.

He is a long way from me but I am very tempted to put the miles in to meet him and pick up my driveshafts he's just turned down for me to 30mm

Anyway I'll let you know on the other thread how I get on in due course

[Bainford]

I'm quite excited about this new axel option. I am overhauling my axels this summer, and was planning to make a drawing of the axel and trot it around to the local machine shops to investigate the possibility/cost of making new ones from better material. My plan was to source new yokes (which I have yet to look into) to be welded to the new axels. Then news of these PA axels surfaced, Has there been any talk of producing a variant with a u-joint yoke sized for a TC/Special?

[jbcollier]

Kelvedon makes an axle kit which gets rid of all the wheel losing tendencies;

https://kelvedonlotus.co.uk/product/race-drive-shaft-kit/

[Bainford]

Kelvedon makes an axle kit which gets rid of all the wheel losing tendencies;

https://kelvedonlotus.co.uk/product/race-drive-shaft-kit/

Some nice looking stuff there. Pricy though, assuming the prices are 'per side'. It seems the axel and the hub are sold as an assembly. If so, an axel, yoke, nut, and bearing spacer comes to 920 pounds sterling. That translates to $3128 Canadian for a full set (both sides), before shipping.

I assume the axels offered by PA Motorsports do not include the hub flange. Can anyone confirm this?