Replacing right rear hub key?

[GrUmPyBoDgEr]

One thing not specificially said here: the key should not be a tight fit nor should it
be allowed to get to the inner part of the keyway (the key should be kept
at the outer end). If tight-fit or slipped-in-too-far applies the key will
distort the hub and prevent the taper surfaces from touching near the key.

Well done that Man; a point that all of us overlooked to mention
Cheers
John

[gerrym]

From the LotusElan.net archives

Regards
Gerry



Mon Apr 01, 2002 5:15 am

Dan Wise Rear Drive Tapered Hubs

I have worked with flexible drive couplings on turbomachinery in
refineries that are installed on tapered shafts(4000 to 10,000 HP). In
order for the taper to provide drive it must have both adequate "pull up"
of interference fit and the mating pieces must have perfect contact.
Otherwise fretting of the mating tapered surfaces will occur and the
drive will eventually fail.

To achieve perfect taper contact we used tapered lapping mandrels and
lapping paste to get the desired result. After lapping, the compound was
cleaned off and prussian blue was applied to the tapered shaft and the
coupling hub test fit. Absolute minimum allowable was 85% contact area.
95 to 100% was usually obtained with a bit more patience. We did not use
loctite.

On Elan hubs, too much lapping and the hub pulls up too far on the taper
for the nut to load the hub on the taper for adequate interference fit.
The loctite serves to fill the imperfections on the taper and provide
additional contact. The loctite also serves as a lubricant when you heat
it up to melting point to expand the taper from its interference fit.

When you have the puller mounted on the hub and tightened up for removal
there is an enormous amount of potential energy stored in the puller.
Stand clear, don't have anything valuable in the way.

The keyway is on the shaft to provide drive if the hub to taper
interference fit fails. It will easily shear if the taper is not pulled
up tight enough. The Dave Bean recommendations to round and fillet the
end of the keyway are accepted practice to reduce the chance of stress
risers at a very critical area.

Some of the service shops who subscribe to this list are capable of
safely removing the hubs, replacing the bearings, non-destructive
inspection and proper reassembly. If in doubt about what to do, use
their services. Having a wheel/hub assembly come adrift at speed is very
exciting.

[GrUmPyBoDgEr]

I still can't agree to the use of heat or Loctite during assembly.
A top quality fit between the Shaft & hub via Lapping is not difficult to achieve, with some patience & Elbow grease & provides IMHO the best solution.
Heat & Loctite may provide an assembly solution(?) but dismantling those Parts at a later stage could be extremely difficult

The keyway is on the shaft to provide drive if the hub to taper
interference fit fails. It will easily shear if the taper is not pulled
up tight enough.
A two sentence contradiction; is this a "specialist"?

Belligerently yours
John

[gerrym]

John, hi.

Amazing how topics were covered so long ago. I found that one in the archives (and don't necessarily agree to all the content).

I must confess to supervising some field work myself on main turbine drives: not everything that must be done there is appropriate for the little Lotus hub shafts. However, thinking about the near universal application of hydraulic fitting methods for large drive hubs, I'm slowly coming around to the thought that loctite with a suitably low melting point might be the closest appropriate method and a very good idea.

Certainly it will act as a valuable lubricate during the pull up of the hub on the shaft. It might even have a use in preventing corrosion in service (purely as a void filler).

Overall, it's mos5 valuable use must be as a "lubricant" during dissasembly (after enough applied heat).

Putting my head up to be shot.
Gerry

PS, best blueing compound to use on a good shaft taper is just a little permanent marker, likely already in the house

Anyway, I have a spare hub and might buy a new TTR shaft for a litle bench expeiment.

[garyeanderson]

I still can't agree to the use of heat or Loctite during assembly.
A top quality fit between the Shaft & hub via Lapping is not difficult to achieve, with some patience & Elbow grease & provides IMHO the best solution.
Heat & Loctite may provide an assembly solution(?) but dismantling those Parts at a later stage could be extremely difficult

The keyway is on the shaft to provide drive if the hub to taper
interference fit fails. It will easily shear if the taper is not pulled
up tight enough.
A two sentence contradiction; is this a "specialist"?

Belligerently yours
John

Dan is still on the forum, we met back in 2000 at Mike Ostrov's shop when I was visiting Mike after picking up 14/1115, Dan is a nice guy with and Elan Coupe. Not sure he'll read this or not but my understanding is that the loctite is used for assembly, and the heat is used to melt the loctite on disassembly, not when assembling the hub. Have a read in your spare time. Dave Bean has been around Elans for a couple of weeks, maybe a bit longer and may have something to offer. I guess the $7 keeps folks from buying the catalog, I know that's a lot these days but sometimes you need to pay the big dollars to get info. Anyway this is the page from the catalog on HUB assembly and disassembly, it is posted with out permission but buy the catalog and maybe it will stay around. it's too large to post here it would mess up the page and then folk would have to use the scroll bar to read my trash.

http://s248.photobucket.com/albums/gg17 ... 460202.jpg

[GrUmPyBoDgEr]

This exchange of views does crop up quite frequently.
There seem to be advocates of Hub Heating & the use of various "Loctites" when assembling these parts.
Fair enough, it was not my intention to tell anyone how to do it; to each his own, as they say.
When I dismantled the Hubs during the rebuild of my very neglected Elan (by the previous Owners) I had no trouble at all.
When re-assembling, with new Shafts, I did it the way I was taught:- Lap in, clean, align with Pin & tighten.
No trouble in the past 10 Years; I'll wish I never said that now
But we've come a long way from the original discussion about the role of the Pin, Key whatever you care to call it, which is why I highlighted the previous comment:-
"The keyway is on the shaft to provide drive if the hub to taper
interference fit fails. It will easily shear if the taper is not pulled
up tight enough".
A two sentence contradiction; is this a "specialist"?

Cheers
John

[garyeanderson]

This exchange of views does crop up quite frequently.
There seem to be advocates of Hub Heating & the use of various "Loctites" when assembling these parts.
Fair enough, it was not my intention to tell anyone how to do it; to each his own, as they say.
When I dismantled the Hubs during the rebuild of my very neglected Elan (by the previous Owners) I had no trouble at all.
When re-assembling, with new Shafts, I did it the way I was taught:- Lap in, clean, align with Pin & tighten.
No trouble in the past 10 Years; I'll wish I never said that now
But we've come a long way from the original discussion about the role of the Pin, Key whatever you care to call it, which is why I highlighted the previous comment:-
"The keyway is on the shaft to provide drive if the hub to taper
interference fit fails. It will easily shear if the taper is not pulled
up tight enough".
A two sentence contradiction; is this a "specialist"?

Cheers
John

Hi DJ

I agree that you have the perfect right to express your view. You do it very well most of the time. Sometimes we say things (or in this case, write) that can be read differently by others. When you and I are discussing something, I am near by a keyboard as you are to make the discussion a two-way conversation and I can correct or explain what was written. I am not perfect and I get things wrong, read things wrong or sometime just don't understand what it is someone is saying without photos. Anyway when Jerry brings up a topic from eight years ago as part of the discussion and you pick the part that you don't agree with without Dan being here to counter explain what it was he was saying.

"The keyway is on the shaft to provide drive if the hub to taper
interference fit fails. It will easily shear if the taper is not pulled
up tight enough.
A two sentence contradiction; is this a "specialist"?"

"A two sentence contradiction" is a fine statement and that?s your right.

The next part you seem to be questioning his professional ability
"specialist"?

I just see it as that Dan doesn't have the opportunity to offer up what it is he said or meant to say 8 years ago. Dan?s last visit to the forum was a couple weeks ago, his profile is here

stresscraxx-u401.html

Maybe you could PM him and ask what it was he was saying at that time.

Here is a topic where Dan and Roger didn't quite agree on and they had the opportunity to discuss it to clear up the question.

post61787.html
p.s. did you look at the link I posted and read it?

[gerrym]

Gary and DJ, really sorry if my dredging up from the archives has caused any disagreeable disagreement.

Originally my view and my own previous assembling of hubs to the shafts was always based on getting good mechanical contact over the surface area (like DJ). However, as I said in my previous post, I'm slowly changing my view and maybe Loctite has a valuable role to play. I personally don't see Loctite as a way of making a bad contact good. Instead if it provides a more reliable way of disassembling the hub to shaft taper, then it is potentially a very good thing.

So historically at least, it is interesting that Dave Bean (thanks Gary for the extract) and Dan advocate the use of Loctite. Looking at the Loctite 242 datasheet, it seems that it loses strength pretty rapidly at 150 degrees C and 250 degrees C is the recommended temperature for disassembly of difficult to remove parts.

Gary just to clarify, I didn't suggest melting the loctite as part of the assembly routine.

Regarding the stress raiser from the keyway and keyend in contact with the shaft, both of these issues can be completely eliminated by TTR's option of a keyless shaft. maybe just a little more tricky to assemble? Has anyone got one of these keyless shafts and how did the assemble work out.

On the heavy hub machinery comparisons, hydraulic fitting is almost exclusively used today. For an Elan, one realisation would be an axial drilling in the shaft end (to provide a conduit for the pressure) together with a radial connection into the centre drilling, plus 2 radial grooves for O rings/backup rings (one at each end of the shaft inside the hub). Very stress raising. But then again no heat or Loctite would be required.

Regards all

Gerry

[GrUmPyBoDgEr]

My mistake & no excuses,
it was silly of me to use those derogatory words & I appologise to Dan for having written that.

John

[CBUEB1771]

it was silly of me to use those derogatory words

Pelly, Esq.
Just use the royal wave and we'll move on in bliss. Had fun with the lads at historic races at Lime Rock Park today. Images from Gary and me to follow.
Russ