Lotus Elan

rear hub shaft nuts

PostPost by: bob_rich » Thu Aug 12, 2010 9:39 am

Hi Folks

Has anyone got the information on the thread form used on the rear hub shaft? The nut that is visible down the bore if you remove wheel spinners. It looks like it might be 5/8" UNF diameter over the thread is around 0.617" to 0.623" but I wonder if it is of special or tapered form as I am finding the replacement nuts I got from are a VERY tight fit and I do not want to progress further until I clean up the threads on the shaft and convince myself that the torque I am putting on is correct.

There is no mention in the book that the nuts are of a use once as discard type but the ones I took off are very slack so intended to replace them but the new ones are very tight indeed

thanks for any responses

Bob
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PostPost by: alexblack13 » Thu Aug 12, 2010 10:35 am

Hello Bob,
Sorry to hear of your difficulties. First of all its not unusual to find the threaded area of the shafts somewhat riveted over or 'mushroomed' a bit. This happens when 'Someone' uses a hammer to drift out the shaft from the strut ass'y. A couple of whacks is enough to cause difficulty. The threaded areas should be parallel I am sure. Repair is possible (if the damage is light) with the use of the correct thread file, but a die nut or similar is better obviously. Be carefull if trying to fit a very tight nut, because if it grips up they can be difficult to remove. Best to repair the shaft. The nut should spin on (but not be slack!) up to the Nylock area. I always use a new nut and ditch the old ones. BUT.... You say the old are very slack & the new are very tight? Sounds like the new nuts are incorrect thread.

Not sure of the thread detail but its in the book. I am sure someone will give you the info' soon. If not I'll check for you.

Check the nuts 1st.. And Bob.... This is a safety critical detail. Any doubt at all about the integrity of the component's threaded area?? = Scrap the part. your life (s) could depend on it.



Best wishes.. & take care...


Alex...
Last edited by alexblack13 on Thu Aug 12, 2010 10:47 am, edited 2 times in total.
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PostPost by: rcraven » Thu Aug 12, 2010 10:41 am

Sorry, I don't know what the thread should be, but is it possible that the new nuts are tight because the old thread has stretched or distorted with age and perhaps occasional overtightening? I had something like this with another car with knock on wheels. When I bought new spinners because the old one were wearing I found they wouldn't fit and the culprit was the old hub not the new spinners.

PS I've now noticed you've already had a somewhat similar reply whilst I was typing this.
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PostPost by: bcmc33 » Thu Aug 12, 2010 11:17 am

The thread is 5/8 UNF(18tpi)

To play safe you will need to rethread using a die nut - I always get mine from eBay
http://cgi.ebay.co.uk/5-8-x-18-HSS-UNF- ... upplies_ET
New nyloc nuts will also be required.
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PostPost by: andyhodg » Thu Aug 12, 2010 12:21 pm

Hi

I had a similar problem with my hub shafts. The ends had been badly mushroomed and whilst I could remove the nut it became a very loose fit on the undamaged part of the thread. I could not get a relaible "square" start with a die nut. I ended up doing a relatively rough screw cut on the lathe just over the first couple of threads. Thsi was sufficient to allow the new nuts to fit, a bit loose on the start but adequate just beforew the nut was seated. I don't know where you are based Bob but I would be willing to help if you could bring your shafts over.

Regards

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PostPost by: bob_rich » Thu Aug 12, 2010 2:28 pm

Hi Folks

I think I may have two issues. firstly the thread does look like 5/8" UNF by 18tpi.
on one axle the nut will not even start. At first glance it look like the thread had gone on the axle but a close inspection and check with a micrometer on the diameter seems to suggest that the nut has failed and left its thread graunched into the stub axle thread. so plan to borrow a die and (carefully!) clean it up.

However on the other axle which was the one that the first post referred to the axle thread looks OK but a new nut gave the very solid resistance after just a 1 to 2 threads. I notice that for 5/8"UNF there are 6 fit grades 1A to 3B and was wondering if the selected nut was supposed to be very tight because if it wasn't the wheel might come off!

will update with what I find out

( had a problem with the computer and think an earlier reply got lost in cyberspace so maybe another post one this theme might be posted by me. sorry if it is

cheers

Bob
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PostPost by: AussieJohn » Thu Aug 12, 2010 3:41 pm

Try the new nuts on a known good bolt thread, I bought some nuts off a well-known lotus spares place and it turned out the new nuts were nearly 10 thou too small and chewed up the thread. The dealer said there had been no problems but as the bits were unusable I find his answer hard to believe, cheers, John.
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PostPost by: billwill » Thu Aug 12, 2010 8:04 pm

>was wondering if the selected nut was supposed to be very tight because if it wasn't the wheel might come off!


Surely it's a castellated nut, with a split pin to stop it coming undone, so you only need to be sure that it has sufficient thread to hold the sideways force of the hub on the nut. It doesn't matter if it is an easy fit on the shaft.
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PostPost by: gerrym » Thu Aug 12, 2010 8:16 pm

Bill, surely its a nyloc nut!

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PostPost by: bob_rich » Thu Aug 12, 2010 8:17 pm

Hi Bill

Its the rear hub axle and the nuts are Nylocs. The manual for the +2 does not show a split pin in this position and the shafts are not cross drilled. So a good fit and the ability to reliably take the 12kg-Metre torque is what is required.

will continue with investigation to morrow

cheers

Bob
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PostPost by: gerrym » Thu Aug 12, 2010 8:42 pm

Bob, re your comment that there are 6 tolerance grades, most of there are not used nor commercially available.

To check the nuts and rule out a gross mistake in their manufacture, it is worth measuring the internal bore (check against Zeus or equivalent).

Namrick sell individual 5/8" unf nuts (plain as well as nylocs) if you want to check out the thread on the axle shafts.

Regards
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PostPost by: billwill » Fri Aug 13, 2010 1:40 am

Are we all nutty?

I think we may be talking about two different nuts.

:lol:
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PostPost by: frearther » Fri Aug 13, 2010 10:48 am

billwill wrote:Are we all nutty?

I think we may be talking about two different nuts.

:lol:



Are you starting a new topic, Bill? :D
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PostPost by: bob_rich » Fri Aug 13, 2010 5:28 pm

Hi All

thanks 4 all the comments. the bottom line is I have one badly damaged shaft and its thread was too far gone. The other shaft is fine. Tested both by assembling up with hub, using new nuts, after , I though carefully, cleaning up the threads with a die. one took full torques of 120Lb-ft solid the other started to yield at around 70lb-ft and on strip down the thread had yielded. Currently reviewing all the options will chat with a mate, who is pretty good at turning work, with a view to machining off the old stud and grafting in a new one. other option is to but a new axle.

I think the problem was that the one axle had been re-cut once before after a previous owner had welted the end of the shaft so much that the thread had to be recut.

ah well life with a Lotus I guess!!

cheers
Bob
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PostPost by: alexblack13 » Fri Aug 13, 2010 6:29 pm

Yep.. As I said.. Very common to find the stub axles thus. Very badly treated...... Philistines are everywhere...Bodges galore eh!

Your ONLY option is to fit a new shaft. OR a good secondhand at a pinch...

What do you mean by 'grafting on' a new one? I can see a possibility of machining off OK and facing the end, center drilling, drilling to size, tapping resulting hole and fitting a new threaded part suitably glued in....

But I wouldn't do it! For the sake of a few quid why risk your neck? :shock:

Don't do it. Buy a new one and don't hit it with hammer when removing from housing... :wink:
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