Lotus Elan

Replacing right rear hub key?

PostPost by: lotusroads » Mon Aug 16, 2010 6:03 pm

Had a scare this weekend when I lost power to the right wheel following a couple of roto-flex surges. The surges were nothing out of the ordinary and I wasn't hitting the throttle hard when the power went. After jacking up the rear wheels I found the right wheel spinning freely on the outboard shaft and following removal of the hub it was clear this hub key (dowel) had given out.

Has anyone had a similar experience and had to replace this small but significant part? I talked with Dave Bean Eng. and they said they didn't have the part in stock. Do you know who may stock this part or if it can be cut to length from a suitable metal dowel? Any details would be greatly appreciated.

Cheers,
Greg
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PostPost by: types26/36 » Mon Aug 16, 2010 7:41 pm

lotusroads wrote: Do you know who may stock this part or if it can be cut to length from a suitable metal dowel? Any details would be greatly appreciated.Greg


Its listed in the S & J parts list http://www.sjsportscars.co.uk/index.php?mod=10
X026D0002Z REAR HUB DRIVE KEY although I think if the hub spun on the shaft you may well have damage, as far as I remember the two parts should be lapped in.
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PostPost by: lotusroads » Mon Aug 16, 2010 11:00 pm

Thanks for the input and part number. This should help a lot. I didn't notice any major damage other than some rounding to the edge of the groove in the outboard shaft that takes the pressure on acceleration. Perhaps this is a problem. The shaft looked good other than the edge of the groove, however I'll take a closer look and at the hub as well.

Regards,
Greg
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PostPost by: GrUmPyBoDgEr » Tue Aug 17, 2010 8:01 am

Hi Greg,

I hope you're still there?
I've been using this Forum for a few years & as far as I can recall yours is the first posting that describes the problem that you have.
There have been many discussions about matching the Tapers on the Shaft & Hub by "lapping in" & the method of torque tightening the Nut.
For that reason I'll not go into detail but it's worth having a scan through the Archives here.
I think you'll find that the damaged Key is not the cause of your problem but the result.
The drive from the Shaft to the Hub is done via the very close fit of the Taper & the clamping force exerted by the tightened Nut & load spreading Washer.
The Key (sometimes called the Pin) is there to "Locate" the Hub on the Shaft, not to provide "Drive"
You've described that the Wheel & Hub were spinning, which will mean that the Taper Contact Faces will have become damaged & must at least be re-lapped! (The damage could be beyond lapping!)
You will also need a new self locking Nyloc Nut; these must not be re-used.
I have read that in some cases the load spreading Washer (about 4mm thick) can bottom out on the Shoulder of the Shaft instead of the face of the Hub.
This would prevent the Nut from providing the very important clamping load onto the Taper assembly.
I strongly recommend that you give all of the parts a thorough checking to ensure that the correct assembly requirements are met.
If you cannot source a replacement Pin, a piece of Mild Steel Rod of the correct Diameter will do the job.

Good luck!
John
Last edited by GrUmPyBoDgEr on Tue Aug 17, 2010 8:04 am, edited 1 time in total.
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PostPost by: types26/36 » Tue Aug 17, 2010 8:03 am

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PostPost by: GrUmPyBoDgEr » Tue Aug 17, 2010 8:34 am




Hi Brian,

looks like the old "Bag of Worms" has been re-opened.
I am strongly opposed to the use of either Heat or any form of Loctite for assembling those Hubs to the Shafts.
Correctly matched parts, via lapping & correct tightening are the only design requirements to obtain the required results.
Once cooled a heated Hub will sit firmly on the Shaft (providing it was sitting correctly in the first place) but more heat will be needed to remove it when needed.
Loctite interferes with the required Metal to Metal Joint & will also provide major problems with future dis-assembly.
I've not voiced my opinion previously but advocating the heating Hubs or Loctite has irritated me each time the Subject comes to light.
Such methods may be used on more modern Designs where "all" of Components are designed "for Life" but in the case of Elan rear Hubs that is not applicable.

Rant over & not aimed at you Brian, just the Purveyors of Sorcery.
Cheers
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PostPost by: types26/36 » Tue Aug 17, 2010 9:14 am

D.J.Pelly wrote:Rant over & not aimed at you Brian, just the Purveyors of Sorcery.CheersJohn


John, I'm not advocating the use of heat or locktite just linking Greg to the threads on the subject, I myself have never used heat,loctite or even lapped them in and I have not had a problem so "you pays your money and you take your chance" ...or as they say "Que Sera, Sera"
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PostPost by: GrUmPyBoDgEr » Tue Aug 17, 2010 9:20 am

types26/36/74 wrote:
D.J.Pelly wrote:Rant over & not aimed at you Brian, just the Purveyors of Sorcery.CheersJohn


John, I'm not advocating the use of heat or locktite just linking Greg to the threads on the subject, I myself have never used heat,loctite or even lapped them in and I have not had a problem so "you pays your money and you take your chance" ...or as they say "Que Sera, Sera"


I know Brian, hence the:- Rant over & not aimed at you Brian, just the Purveyors of Sorcery.
Cheers
John :)
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PostPost by: gerrym » Tue Aug 17, 2010 12:11 pm

Greg, DJ is spot on when he talks about the role of the dowel. It's only function is to keep the hub/shaft aligned when initially tightening the retaining nut.

The taper is what will transmit the drive. Suggest that you carefully visually check inside the hub and surface of shaft for any burrs.

Then you need to check the fit and that the bore of the hub has not stretched out of shape.

Blue the inside of the hub (Prussion blue or permanent ink marker). Mate the hub to the shaft with a good solid knock. Remove shaft and check for a good fit which is usually defined as one which has mating over at least 70% of the area.

Now is the tricky bit. If it looks as though there are just a few high spots on the shaft, flatten these down with fine emery paper and then check as to whether fit is acceptable. If not improving, you are at a cross roads because whilst shafts can be bought new and to a good taper tolerance, hubs are unobtainable for Plus 2s.

Don't try lapping, you will create a shoulder which will cause serious mating problems.

Regards
Gerry
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PostPost by: bcmc33 » Tue Aug 17, 2010 12:50 pm

D.J.Pelly wrote:I've not voiced my opinion previously but advocating the heating Hubs or Loctite has irritated me each time the Subject comes to light.

Rant over & not aimed at you Brian, just the Purveyors of Sorcery

Clearly aimed at this Brian then, John.

As my old dad taught me - "If you want to know something, ask an expert, and if you want to know how to do something watch an expert"

I am aware of two well known Elan racers who advised to heat the hubs before assembly. Now this made some sort of sense to me because as a young plant engineer in the 60's I well remember the old machine tool fitters always heating female tapered gears and flywheels even though they had 'proper' keys. I also well remember that they were real b*st*rds to get apart.
However, I would not consider using any sort of Loctite type adhesive - this would certainly compromise such an assembly.

I remain your Sorcery Friend
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PostPost by: GrUmPyBoDgEr » Tue Aug 17, 2010 1:46 pm

bcmc33 wrote:
D.J.Pelly wrote:I've not voiced my opinion previously but advocating the heating Hubs or Loctite has irritated me each time the Subject comes to light.

Rant over & not aimed at you Brian, just the Purveyors of Sorcery

Clearly aimed at this Brian then, John.

As my old dad taught me - "If you want to know something, ask an expert, and if you want to know how to do something watch an expert"

I am aware of two well known Elan racers who advised to heat the hubs before assembly. Now this made some sort of sense to me because as a young plant engineer in the 60's I well remember the old machine tool fitters always heating female tapered gears and flywheels even though they had 'proper' keys. I also well remember that they were real b*st*rds to get apart.
However, I would not consider using any sort of Loctite type adhesive - this would certainly compromise such an assembly.

I remain your Sorcery Friend


I've made my case (at long last) Brian,
I think you'll find those "proper Keys" were made of what "the old machine tool fitters" would have called "Soft Iron" ~ Mild Steel.
I'm pleased that you agree by saying:- "I also well remember that they were real b*st*rds to get apart".
I'm sure that by heating the Hub before assembly onto the Taper will provide a large interference fit, that won't be going anywhere; on or off!
My personal "Fitting" experience was limited to Aero Engines where only Splines or Serrations were considered acceptable.
Your Dad was a wise Man; mine was similar, bless 'em!

"Abracadabra" & "Zim Zalla Bim" :D
John
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PostPost by: GrUmPyBoDgEr » Tue Aug 17, 2010 1:55 pm

gerrym wrote:Greg, DJ is spot on when he talks about the role of the dowel. It's only function is to keep the hub/shaft aligned when initially tightening the retaining nut.

The taper is what will transmit the drive. Suggest that you carefully visually check inside the hub and surface of shaft for any burrs.

Then you need to check the fit and that the bore of the hub has not stretched out of shape.

Blue the inside of the hub (Prussion blue or permanent ink marker). Mate the hub to the shaft with a good solid knock. Remove shaft and check for a good fit which is usually defined as one which has mating over at least 70% of the area.

Now is the tricky bit. If it looks as though there are just a few high spots on the shaft, flatten these down with fine emery paper and then check as to whether fit is acceptable. If not improving, you are at a cross roads because whilst shafts can be bought new and to a good taper tolerance, hubs are unobtainable for Plus 2s.

Don't try lapping, you will create a shoulder which will cause serious mating problems.

Regards
Gerry


That's a fair point about the possible Shoulder Gerry.
I've only lapped brand new Shafts into old Hubs.
Have you experienced the "Shoulder"?
"Theoretically" the Iron Hub should be softer than a heat treated Steel Shaft thus submitting to the Shaft rather than causing a shoulder to form?

P.S. Greg!
I hope you're still out there? :)
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PostPost by: gerrym » Tue Aug 17, 2010 2:24 pm

John, yes I have but not on an Elan drive shaft. A lap relies on hard abrasive particles imbedding into the softer of the surfaces (ie the hub) to rub away at the harder surface (the shaft).

Regards
Gerry
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PostPost by: lotusroads » Tue Aug 17, 2010 3:18 pm

Many thanks to John, DJ, Gerry and anyone else who gave advice.

Sounds like the problem may be worse than expected. The hub did spin freely on the shaft with the nylon nut tightened. When the hub key went the metal fragments may have machined some metal off the inner hub. The locating groove in the shaft is also damaged on the trailing edge such that the edge is rounded. I can get another shaft, but it looks like the hub could be where the trouble lies? The inner contact surface of the hub has some grooves, but doesn't seem to have any major damage. The inner washer (between hub and bearing) looks like it has lost some thickness as well and will need to be replaced.

I will definitely try the dye technique to see the % contact. And will give a thorough read of archives provided to hopefully get some more tips for replacing.

When it comes to tightening the hub on with the nylon nut, can I go really tight with the nut or will this have negative effects on the bearing?

Regards, Greg
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PostPost by: GrUmPyBoDgEr » Tue Aug 17, 2010 4:19 pm

Gerry,

thanks for the lapping explanation.
The only serious lapping I did as an Apprentice was Bristol Hercules & Centaurus Radial Engine Crankcase Joints; they had to be Air & Oil tight without Gaskets but a drop of the original "Hermatite"
The Casings were Aluminium Alloy & the enormous lapping Plate was Iron.
It took two to move the Casings around in the prescribed figure of Eight.
Oh & out of interest, being close to the subject.
The Steel Crankshafts were split in the middle longitudinally. The Joint consisted of a highly polished Shaft & Bore.
The Bore was tightened onto the Shaft by means of a long very tough Bolt passing through Bosses on the O/D of the Bored part & the Bolt extension measured to ensure the correct clamping loads had been achieved.
No Keys or Splines; perfect alignment was critical. (Achieved by a precision Ground rod that passed through precision Bores in both Crankshaft halves).

Greg,

You might like to contact Spyder for a 2nd Hand Hub. (or even a Shaft as well, if you feel brave enough :roll: )
A used Shaft should be thoroughly checked dimensionally & crack tested to be doubly sure.
They use the Ford Sierra/Scorpio parts & their own rear uprights for their Zetec Conversions so the +2 parts become excess to requirements.

Cheers
John
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