TC Front Axle Repairs
Posted: Wed Mar 08, 2000 6:34 pm
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
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