Re: TC Front Axle Repairs

[m.jablonski@mei.unimelb.edu.au]

Back in December I wrote to the list with my problem of stretched or
worn front axle eyes. These had become bell-mouthed and ovalled, with
the largest clearance on the kingpins being about 0.015" on diameter.
There was a bit of interest in the solution and I undertook to get back
to the list with my findings.

There are three options for repairing the eyes -

1. Shrinking by heating the eyes to cherry red and forging back into
shape. They have to be reamed after re-sizing.

2. Reaming the eyes out to a parallel bore and then using new, oversize
king pins. Suitable materials would be 4140 or EN33, these are case
hardenable steels. One would need to rough machine, case harden and
then finish grind. Hardened bar with a soft core is available which
permits drilling and tapping at the top, but the bar still needs
grinding to the new diameter. Standard bushes can be used in the
knuckle providing the amount of oversize is limited (to say 0.015").
These can be reamed oversize with an expanding reamer. Cost of new
kingpins plus reaming is about double that of Option 1.

3. Boring the eye out 1/8" oversize and fitting a sleeve with 1/16"
wall thickness to bring the eye back to standard.

I found an axle repairer who has been in business for long enough to
have worked on beam-axled cars. He was happy to use any of the three
methods. For those in Australia the repairer is R. Kent & Sons at 66
- 70 Renver Road, Clayton, Victoria telephone (03) 9544 7326. The
person to speak to is Tom Kent.

Each method has its problems:

1. Shrinking involves heating the eye and probably losing its state of
heat treatment. I say "probably" because I'm not entirely sure that
the axles were heat treated. However, assuming they were hardened and
tempered, to regain the original state one would have to harden after
forging, by heating and quenching and then temper by heating for 1 hour
per inch of section and quenching again. Kent does not harden or
temper. If one could get an accurate material analysis it would be
possible to work out the appropriate heat treatment temperatures to
regain the original hardness of the axle.

2. The use of oversize kingpins means that every time these require
replacement, special kingpins have to the made. They have to be
hardened and ground and the little cutouts ground in, as well as the
top drilled and tapped. The process is irreversible (except perhaps by
reverting to method 1).

3. Sleeving increases the stress in the axle eyes by about 1/3
depending on original wall thickness and sleeve thickness. Mike Card
and I carried out some rough stress calculations but had to make so
many assumptions re the material, loading conditions, etc that I felt
it was too risky to be increasing the stress by this amount. Tom Kent
however, said that he had seen axles with sleeved eyes coming in for
straightening without any obvious problems. He had crack tested the
eyes and the ones he had seen were OK. (Though, unless he'd carried
out the sleeving he wouldn't have seen any broken eyes.) He did say
that an essential prerequisite was a central bore in the eye.
Sometimes the bore can be offset in the forging causing a thin wall
section on one side.

I chose the first option. I did this on the basis of not wanting the
problem of non-standard components or the risk of excessive stress. I
also spoke to Mike Sherrell who said he'd had his axle repaired this
way "a hundred years ago" and had had no trouble so far. I reason
that, if the eye does stretch due to softening of the metal, I will get
the eyes shrunk again but this time have the axle hardened and tempered.

During my investigations I checked the axle hardness and had a material
analysis of some filings from the axle done on a scanning electron
microscope. For the technically minded, the results follow.

The hardness readings varied quite a bit over the axle ranging from 185
Brinell to 222. The average was 205 BHN. Interestingly, there is a
small dimple on the underside of the axle, the sort made by a Brinell
hardness test (I have two axles with this). Making some assumptions on
load and ball diameter the dimple corresponds to 226 BHN (my adjacent
readings - were 222 and 187.5).

The results of the material analysis are:
sample 1 sample 2 EN17
(for comparison)
Carbon 0.36% (approx.) 0.3 - 0.4%
Silicon 0.25% 0.27% 0.1 - 0.35%
Manganese 1.87% 1.88% 1.3 - 1.8%
Molybdenum 1.22% 0.64% 0.2 - 0.35%
Sulphur 0 0 0 - 0.05%
Phosphorous not given 0 - 0.05%

The carbon content is only approximate and this is critical for working
out the heat treatment. So this composition is only a guide. If I were
to heat treat the axle, I would have a more accurate analysis carried
out. Interestingly, (apart from molybdenum content) the composition
appears to be close to EN17 which is the material specification stamped
onto the side of a spare steering knuckle I have (suspected to be
pre-war).

My apologies if I've ended up being too long-winded. Your comments are
invited.

Mark Jablonski
TC6022

[Harry Pyle]

Mark,

Some years ago I had the front axle off my TA Special analysed prior to
straightening.
We felt it needed to be re-heatreated afterward as it had been badly bent.
The results were taken from a 1/8x1/4 x1/2 taper sliver off the 4-hole flat
spring mount flange.

The following is extract from the Metallurgical Test/Recommendation Report.

The scanning Electron Microscope EDS analysis gave;

Silicon 0.09%
Chromium 0.20%
Iron 97.82%
Manganese 1.89%

The annealed specimen had a microstructure of 60% pearlite 40% ferrite
indicating a carbon content of between 0.4% and 0.5%.

The tests showed that the axle was made from carbon manganese steel similar
to SAE 1541 (EN15) and was in a hardened and tempered condition.

For this steel the best balance between strength and toughness is considered
to be at a nominal hardness of 300HB. At this hardness level the steel would
have an approximate tensile strength of 1000MPa and an expected yield
strenth of 900 MPa
.
The recommended heat treatment cycle to achieve this this hardness would be;
a) heat to 850C hold for 1 hour
b) oil quench to below 70C..as quenched hardness to be above 500HB
c) Temper to 290 - 330HB at an estimated temperature of 500C.

Hardness tests on the original axle were 218 - 255HB.
After the repair..hardenss tests on different parts of the axle were between
245 - 258HB

The above axle was 1937 MG TA. We have also tested and reheatreated a 1932
MG J2 axle with almost identical results.

I hope the above information will help others and spare expense in
reinventing the wheel.

Regards Harry TC62446, TB0440, TA1089

----- Original Message -----
From:
To:
Sent: Thursday, March 09, 2000 10:34 AM
Subject: [mg-tabc] TC Front Axle Repairs


> Back in December I wrote to the list with my problem of stretched or
> worn front axle eyes. These had become bell-mouthed and ovalled, with
> the largest clearance on the kingpins being about 0.015" on diameter.
> There was a bit of interest in the solution and I undertook to get back
> to the list with my findings.
>
> There are three options for repairing the eyes -
>
> 1. Shrinking by heating the eyes to cherry red and forging back into
> shape. They have to be reamed after re-sizing.
>
> 2. Reaming the eyes out to a parallel bore and then using new, oversize
> king pins. Suitable materials would be 4140 or EN33, these are case
> hardenable steels. One would need to rough machine, case harden and
> then finish grind. Hardened bar with a soft core is available which
> permits drilling and tapping at the top, but the bar still needs
> grinding to the new diameter. Standard bushes can be used in the
> knuckle providing the amount of oversize is limited (to say 0.015").
> These can be reamed oversize with an expanding reamer. Cost of new
> kingpins plus reaming is about double that of Option 1.
>
> 3. Boring the eye out 1/8" oversize and fitting a sleeve with 1/16"
> wall thickness to bring the eye back to standard.
>
> I found an axle repairer who has been in business for long enough to
> have worked on beam-axled cars. He was happy to use any of the three
> methods. For those in Australia the repairer is R. Kent & Sons at 66
> - 70 Renver Road, Clayton, Victoria telephone (03) 9544 7326. The
> person to speak to is Tom Kent.
>
> Each method has its problems:
>
> 1. Shrinking involves heating the eye and probably losing its state of
> heat treatment. I say "probably" because I'm not entirely sure that
> the axles were heat treated. However, assuming they were hardened and
> tempered, to regain the original state one would have to harden after
> forging, by heating and quenching and then temper by heating for 1 hour
> per inch of section and quenching again. Kent does not harden or
> temper. If one could get an accurate material analysis it would be
> possible to work out the appropriate heat treatment temperatures to
> regain the original hardness of the axle.
>
> 2. The use of oversize kingpins means that every time these require
> replacement, special kingpins have to the made. They have to be
> hardened and ground and the little cutouts ground in, as well as the
> top drilled and tapped. The process is irreversible (except perhaps by
> reverting to method 1).
>
> 3. Sleeving increases the stress in the axle eyes by about 1/3
> depending on original wall thickness and sleeve thickness. Mike Card
> and I carried out some rough stress calculations but had to make so
> many assumptions re the material, loading conditions, etc that I felt
> it was too risky to be increasing the stress by this amount. Tom Kent
> however, said that he had seen axles with sleeved eyes coming in for
> straightening without any obvious problems. He had crack tested the
> eyes and the ones he had seen were OK. (Though, unless he'd carried
> out the sleeving he wouldn't have seen any broken eyes.) He did say
> that an essential prerequisite was a central bore in the eye.
> Sometimes the bore can be offset in the forging causing a thin wall
> section on one side.
>
> I chose the first option. I did this on the basis of not wanting the
> problem of non-standard components or the risk of excessive stress. I
> also spoke to Mike Sherrell who said he'd had his axle repaired this
> way "a hundred years ago" and had had no trouble so far. I reason
> that, if the eye does stretch due to softening of the metal, I will get
> the eyes shrunk again but this time have the axle hardened and tempered.
>
> During my investigations I checked the axle hardness and had a material
> analysis of some filings from the axle done on a scanning electron
> microscope. For the technically minded, the results follow.
>
> The hardness readings varied quite a bit over the axle ranging from 185
> Brinell to 222. The average was 205 BHN. Interestingly, there is a
> small dimple on the underside of the axle, the sort made by a Brinell
> hardness test (I have two axles with this). Making some assumptions on
> load and ball diameter the dimple corresponds to 226 BHN (my adjacent
> readings - were 222 and 187.5).
>
> The results of the material analysis are:
> sample 1 sample 2 EN17
> (for comparison)
> Carbon 0.36% (approx.) 0.3 - 0.4%
> Silicon 0.25% 0.27% 0.1 - 0.35%
> Manganese 1.87% 1.88% 1.3 - 1.8%
> Molybdenum 1.22% 0.64% 0.2 - 0.35%
> Sulphur 0 0 0 - 0.05%
> Phosphorous not given 0 - 0.05%
>
> The carbon content is only approximate and this is critical for working
> out the heat treatment. So this composition is only a guide. If I were
> to heat treat the axle, I would have a more accurate analysis carried
> out. Interestingly, (apart from molybdenum content) the composition
> appears to be close to EN17 which is the material specification stamped
> onto the side of a spare steering knuckle I have (suspected to be
> pre-war).
>
> My apologies if I've ended up being too long-winded. Your comments are
> invited.
>
> Mark Jablonski
> TC6022
>
>
>
> ------------------------------------------------------------------------
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> -- http://www.egroups.com/ChatPage?listName=mg-tabc&m=1
>
>

[Roger Furneaux]

Mark - absolutely NO apology at all is needed, in fact this is EXACTLY the
sort of info we all need, and I congratulate you heartily on going to all
the trouble! One comment is that EN33 is not available off-the -shelf in the
U.K., so we would use EN36, which is better, and used to make Crown Wheels &
Pinions. However, anybody going down the larger king-pin route would have to
have good product-liability insurance....

These wonderful little cars of ours are going to be around for much longer
than any of us temporary custodians, and a lot of the component parts are
nearing the end of their working lives NOW, and will have to be replaced
soon. Whether you use Moss (mostly Taiwan, and many think that really means
China) or Abingdon Spares (who source a lot of their parts in England),
Japanese, Australain or whatever is up to you.

We don't want too many more of the shouting matches that took place
recently: let us all just calm down and take in the fact that there are two
sorts of T-typers, the "keep it all as it left Abingdon brigade" (many of
whom will have restored their cars, with new wood, panelling, trim, paint,
etc. etc.), and the "modify to drive it Safely and Fast" faction (many of
whom have kept all the original parts).

Of course, this is over-simplification, because my TC0978, for example, has
most of its original wood and metal-work but quite a few go-faster goodies
such as Derrington exhaust, TF carbs, 16" wheels and Alfin drums (from Bob
G.). However, in the steering department, a previous owner fitted a TA 'box
(does that please you Geoff?) which means that I have one of those lovely
springy three-spoke steering wheels, as fitted to MMM cars.

Keep on MotorinG!

Roger