Rear hub taper question

[Elanman99]

I have had to lap-in the taper of one of the rear hub/shaft assemblies
beacause of wear caused by usibng the car when the Nyloc nut was not
correctly tightened. With care I was able to achieve more than 90% metal to
metal contact, checked with engineers blue, but the hub now fits too far on
the taper with the result that the inner roadwheel rim makes contact with
the bottom suspension boltheads.

As a temporary measure I have made a 3mm thick spacer to offset the wheel so
that I can use the car. The wheels are bolt-on Minilites that have aluminium
nuts which now have 3mm less thread engagement.

I have calculated that 5 thou thick shim material curved to fit between the
taper shaft and the hub will give about 3mm of offset.

Does anyone have any opinions as to whether the shim would be best made from
brass or steel? I would assemble using loctite. Is this a bodge too far? I
dont want to be a DPO!

Ian Phillips

1968 S4 DHC

[gobw2]

DPO - dead previous owner??? Some people have broken rear axles.
Shimming sounds risky to me - I would (aI am cheap) break down and get a
new one. George

On Tue, 29 Jul 2003 15:21:35 +0100 "Ian Phillips"
<***@***.***> writes:
I have had to lap-in the taper of one of the rear hub/shaft assemblies
beacause of wear caused by usibng the car when the Nyloc nut was not
correctly tightened. With care I was able to achieve more than 90% metal
to
metal contact, checked with engineers blue, but the hub now fits too far
on
the taper with the result that the inner roadwheel rim makes contact with
the bottom suspension boltheads.

As a temporary measure I have made a 3mm thick spacer to offset the wheel
so
that I can use the car. The wheels are bolt-on Minilites that have
aluminium
nuts which now have 3mm less thread engagement.

I have calculated that 5 thou thick shim material curved to fit between
the
taper shaft and the hub will give about 3mm of offset.

Does anyone have any opinions as to whether the shim would be best made
from
brass or steel? I would assemble using loctite. Is this a bodge too far?
I
dont want to be a DPO!

Ian Phillips

1968 S4 DHC

[Elanman99]

I thought DPO was 'Dubious Previous Owner'!

The shim would really be no more than a conical spacer and would be a lot
cheaper than a new hub and shaft, and probably new bearings.

Ian

----- Original Message -----


Sent: Wednesday, July 30, 2003 4:43 AM
Subject: Re: [LotusElan.net] Rear hub taper question


DPO - dead previous owner??? Some people have broken rear axles.
Shimming sounds risky to me - I would (aI am cheap) break down and get a
new one. George

On Tue, 29 Jul 2003 15:21:35 +0100 "Ian Phillips"
<***@***.***> writes:
I have had to lap-in the taper of one of the rear hub/shaft assemblies
beacause of wear caused by usibng the car when the Nyloc nut was not
correctly tightened. With care I was able to achieve more than 90% metal
to
metal contact, checked with engineers blue, but the hub now fits too far
on
the taper with the result that the inner roadwheel rim makes contact with
the bottom suspension boltheads.

As a temporary measure I have made a 3mm thick spacer to offset the wheel
so
that I can use the car. The wheels are bolt-on Minilites that have
aluminium
nuts which now have 3mm less thread engagement.

I have calculated that 5 thou thick shim material curved to fit between
the
taper shaft and the hub will give about 3mm of offset.

Does anyone have any opinions as to whether the shim would be best made
from
brass or steel? I would assemble using loctite. Is this a bodge too far?
I
dont want to be a DPO!

Ian Phillips

1968 S4 DHC

[elansprint71]

Ian,
Evidently "standard procedure" when fitting 2 wheels to S4 Elans is to relieve the bolt head by filing to avoid exactly the situation you have. Removing a small portion of the head from one side will not compromise safety as the bolt is only there (in a linear sense) to stop the bushes falling out!
Shimming a locking taper is the first step on the road to madness!

Pete

[rgh0]

I would be very concerned that introduction of any shim material in the hub
to shaft taper would fail to carry the loads.

The taper is required to lock on tightly with good metal to metal contact
over most of its area to carry the torque loads. It would be very difficult
to get a shim to fit well enough to achieve the degree of taper lock needed
to carry the torque and to be exactly centralised and to not cause wheel run
out.

The taper has to also resist signficant cyclic bending stress that causes
fretting between the hub and the taper over the inner 20 to 30 mm of the
taper. Under racing cornering loads with modern sticky tyres this leads to
deterioration of the fit over time due to fretting wear. Most of the wear
occurs in the relativly soft hubs if you are using a modern high strength
steel for the shaft.

Relapping the hubs to the shafts causes it to move in rapidly as you have
observed. I have had to replace hubs over the years as they had worn and
moved in to much

Interference between the wishbone bolts and the inside of the wheel is a
common issue with most cast alloy wheels and depending on the width and
offsets this can happen with the hubs and shafts at as new dimensions. You
can try to find wheels with a slghtly bigger ID in the area of concern, most
wheels have taper in this area and the design of the taper and thickness of
the machined casting at the point of interference varies from wheel to wheel
even of the same wheel make and type. Three piece wheels with thinner spun
alloy rims solves this problem but at huge cost so for most people its not
an option

Ensure you are also using the very thin bolt heads of the original Lotus
bolts and that they have not been replaced with normal bolts. I have filed a
small bevel on the heads of these bolts to avoid interference with the wheel
and align with bevel with the wheel to get the needed static clearance of
about 2mm with my alloy wheels. Under cornering loads this clearance closes
up to about zero as the rubber bushes compress and the wheel components
bend.

regards
Rohan

[Elanman99]

Rohan

I have taken on board your concerns about using a shim and will probably get
a new hub, but I have added some questions/comments to your reply.


----- Original Message -----
From: "Rohan Hodges" <***@***.***>

Sent: Wednesday, July 30, 2003 2:09 PM
Subject: [LotusElan.net] Re: Rear hub taper question


I would be very concerned that introduction of any shim material in the hub
to shaft taper would fail to carry the loads.

The taper is required to lock on tightly with good metal to metal contact
over most of its area to carry the torque loads. It would be very difficult
to get a shim to fit well enough to achieve the degree of taper lock needed
to carry the torque and to be exactly centralised and to not cause wheel run
out.

I was considering brass as the material and rolling into a cone before
assembling with Loctite.

The taper has to also resist signficant cyclic bending stress that causes
fretting between the hub and the taper over the inner 20 to 30 mm of the
taper. Under racing cornering loads with modern sticky tyres this leads to
deterioration of the fit over time due to fretting wear. Most of the wear
occurs in the relativly soft hubs if you are using a modern high strength
steel for the shaft.

Is the fretting likely on a car only used on the road? and why does it occur
at one (inner=larger?) end of the taper only? I have the standard shafts so
are probably harder than the hub. Presumably when I lapped in the taper,
more metal was removed from the shaft rather than the hub, so maybe its the
shaft I should replace.

Relapping the hubs to the shafts causes it to move in rapidly as you have
observed. I have had to replace hubs over the years as they had worn and
moved in to much

Interference between the wishbone bolts and the inside of the wheel is a
common issue with most cast alloy wheels and depending on the width and
offsets this can happen with the hubs and shafts at as new dimensions. You
can try to find wheels with a slghtly bigger ID in the area of concern, most
wheels have taper in this area and the design of the taper and thickness of
the machined casting at the point of interference varies from wheel to wheel
even of the same wheel make and type. Three piece wheels with thinner spun
alloy rims solves this problem but at huge cost so for most people its not
an option

Ensure you are also using the very thin bolt heads of the original Lotus
bolts and that they have not been replaced with normal bolts. I have filed a
small bevel on the heads of these bolts to avoid interference with the wheel
and align with bevel with the wheel to get the needed static clearance of
about 2mm with my alloy wheels. Under cornering loads this clearance closes
up to about zero as the rubber bushes compress and the wheel components
bend.

I have the standard reduced head bolts and alloy wheels. I could remove part
of the bolt head to give clearance but that seems as much as a bodge as my
shim idea.

Ian Phillips

[lotuselan2]

That was a lot of LAPPING!!!!

[gobw2]

Yes, Ian it is Dubious... - I was telling you with a bit of humor, that
in my opinion, because of the type of loading involved, and marginal
strength,shimming a locking conical taper might result in Dead previous
owner - IE - you.
You can turn the half height bolt head so the flat side is facing wheel,
and dress the head a bit Almost all loading on this bolt is shear. If you
have bolt on wheels, it might be possible to insert a spacer between hub
and wheel, however, I would query the list first. If your wheels are KO,
I strongly recomend against this. George

On Wed, 30 Jul 2003 08:06:46 +0100 "Ian Phillips"
<***@***.***> writes:
I thought DPO was 'Dubious Previous Owner'!

The shim would really be no more than a conical spacer and would be a lot
cheaper than a new hub and shaft, and probably new bearings.

Ian


DPO - dead previous owner??? Some people have broken rear axles.
Shimming sounds risky to me - I would (aI am cheap) break down and get a
new one. George

[rgh0]

Ian

A couple of responses on your questions / comments
Comment:

"I was considering brass as the material and rolling into a cone before
assembling with Loctite"

Response:
If you could get a cone which was a perfect fit with the hub and shaft then
conceptually you could do it. It would need to be a very high strength grade
of brass to achieve the strength and hardness required to adquately carry
the loads and achieve the taper lock on both its inside and outside surface.
Most high strength brass allloys are relatively brittle and you would
struggle to roll them into a cone without forming it hot and then you would
struggle even more to get it accurate enough to get a good fit. The taper
lock requires a much higher surface shear stress than any loctite can carry
on its own over the area between the hub and shaft. Use of loctite on this
join is really only there to add a little extra stength by filling in the
microscopic areas where you dont get a surface to surface contact. For a
well lapped join this adds little or no extra strength as the non contact
areas are very small. It may also help later separation by helping prevent
corrosion in the join and providing some lubriucation as it decomposes when
you heat the hub to get it to come off.

Comment:
"Is the fretting likely on a car only used on the road? and why does it
occur
at one (inner=larger?) end of the taper only? I have the standard shafts so
are probably harder than the hub. Presumably when I lapped in the taper,
more metal was removed from the shaft rather than the hub, so maybe its the
shaft I should replace"

Response:
I dont see the fretting on my road use plus 2. I find in the Elan I
continually need to retorque the rear hubs nuts to ensure the hubs stay well
locked on the shafts, I have spun shafts in the hubs a couple of times when
I did not do this regularly. The fretting starts at the inside of the hub
because this is the point of maximum bending stress in the shaft where it
contacts the hub, thus you get maximum strain distortion along the direction
of the shaft ( strain is "stretch" in engineering talk). The hub however is
not under bending stress and thus does not undergo the same strain
distortion at this point. This differential strain leads to fretting wear,
the wear then progresses down the shaft as a gap opens up between the two
components progressively with the wear. My experience lapping both standard
and high strength shafts to the hubs is that almost all the metal comes of
the softer cast iron hub, easy to see after lapping if you have a step
lapped in the shaft taper between the contact nd non contact areas. I have
never got a signficant one after lapping and never had to replace a shaft
due to this.

If the hub has moved in with wear / lapping and refitting you need to ensure
it has not also fouled the aluminum bearing carrier or bearing on the inside
or that the nut / washer has not bottomed on the based of the thread on the
outside of the hub. You also need to check that the tyre has not come to
close to the spring also.

Comment:

" I have the standard reduced head bolts and alloy wheels. I could remove
part
of the bolt head to give clearance but that seems as much as a bodge as my
shim idea".

Response:

I agree putting a bevel on the bolt head is a "bodge". However a 3mm bevel
is a small and easy to do effective "bodge" the does not affect the strength
or funtionality of the component and is a lot cheaper than 3 piece allow
wheels. A brass shim is a bodge that is difficult, if not impossible to do
and and make work and has a major effect on the strenght and functionality
of the taper lock join.

regards
Rohan