The simplicity of T-Types has encouraged their high survival rate, despite the early years of being driven by impoverished students. Numerous rebuilders will have come across some ingenious bodges to mask problems and it’s tempting to give some examples, but the concern that I could be feeding ideas to unprincipled owners overcomes what could be a good tale.
Most potential problem areas can be sorted out with the good supply of available spare parts. However, there’s one area that’s particularly challenging – worn axle eyes that support the king-pins on the TA/B/Cs. Just looking at the forces on the wheel when cornering and then realising that such forces are multiplied when applied to the king-pin, leaves one wondering how it all copes, especially after some 60 years.
It’s not surprising that some axle eyes have become oval, resulting in a loose king-pin, a potential MOT failure. An oval axle eye can allow the king pin to rock back and forth repeatedly, thereby exaggerating the initial problem with time. So how did the initial problem occur? The answer may come from batches of undersized king-pins. One such king-pin I looked at was over 2 thou. under-sized, and the resultant wear in the axle eye necessitated the eye being bored out and a sleeve fitted. This is an expensive operation and one that weakens the axle eye.
Recently, whilst replacing some king-pin sets on three beam axles, I discovered that all the front axle eyes were worn oval, and to compound the situation the new king-pins were 0.5 thou. undersized. This may not seem much, but given a worn axle eye, the last thing one needs is an under-sized king-pin. Ideally the king-pin should be drifted in with light blows from a plastic headed hammer.
Approaches to some spares’ stockists failed to convince them that this was a problem worth pursuing, one suggestion made was that just tightening up the cotter pin would solve the matter; not so. The cotter pin being at the fulcrum of the king-pin is unable to prevent it rocking. The possibility of trying other stockists may not help as many new king-pin sets seem to be made by just one company.
By good chance I learnt that Gerry Brown was commissioning some oversized king-pins from a precision engineering company. We decided on an initial batch of 5 sets of plus 2 thou. oversized king-pins and will wait to see how effective these are. However, king-pins need bushes so I’ve placed an order with the supplier who provided the last batch that John James and I ordered some time ago.
What seems to be a general lack of awareness of the problems associated with worn axle eyes is possibly explained by the fact that some (many?) TA/TB/TC owners no longer submit their cars to an annual MOT inspection where such issues would be picked up
This is concerning, as early detection allows the much simpler remedy of using over-sized king-pins to be used. The alternative remedies for badly worn axle eyes are really not worth contemplating as finding engineering firms willing to undertake such work is becoming increasingly difficult and expensive.
Given that there is currently a lack of demand from owners for oversized king-pins, it is hardly surprising that suppliers don’t stock them. However, if after reading this article you feel that you would like to be associated with a case to be put forward to suppliers to stock them, please let us know.
In conclusion, I now realise that the main way axle eyes have become worn was due to the fitting of undersized king-pins. This was brought home to me whilst comparing the effect of using a 0.5 thou. undersized king-pin with a “spot on” king-pin in an unworn axle eye. The correctly sized king-pin was a reassuringly tight fit whilst the 0.5 thou. undersized king-pin not only fell through the axle eye, but was able to rock significantly when held in the axle eye.
Undersized king-pins should be rejected
Most precision engineering workshops should be able to grind the king-pins to the accuracy required, there’s no valid excuse for undersized king-pins.
Fitting undersized king-pins will cause the axle eyes to wear
An additional issue is finding small engineering concerns willing to undertake fitting and reaming out king-pin bushes. However, a “garden shed” model engineer might be able to help using a technique suggested by Peter Cole (see photo 1).
A ¾” reamer is mounted in the chuck of a lathe and the stub axle with new bushes is slid on to a mandrel mounted in the tail stock. The object is to slide the stub axle’s king-pin bushes along the mandrel to meet the rotating reamer in the chuck, thereby assuring alignment. The reamer is set to rotate slowly and with plenty of lubricant, a firm gloved hand will be needed to hold the stub axle’s spindle as the reamer is engaged.
The rotating force is considerable, so engage the reamer slowly.
Photo 1 – The reaming method suggested by Peter Cole
If fitting oversized king-pins, the axle eyes and bushes will need an expanding reamer for the final cut. Reaming the bushes in alignment needs an expanding reamer with an extension guide shaft.
There are two types of expanding reamer; the first is a conventional expanding reamer that has a guide shaft screwed on and uses a sliding collar whose tapered end locates in the bush at the far end of the stub axle. The second type has the extended shaft as part of the reamer body, these are rare and expensive but more accurate.
Photo 2 – Showing how the final oversize ream is accomplished using an adjustable reamer with a guide.
The cutting blades on expanding reamers are not long enough to engage both bushes at the same time, so having reamed the first bush using the sliding collar located in the opposite bush, the reamer needs to be withdrawn and inserted in the second bush with the sliding collar engaged in the freshly reamed bush.
Photo 3 – Showing two types of adjustable reamer incorporating a fixed guide and a screw on guide. Both have sliding collars which locate in the king-pin bush at the far end of the stub axle.
Reaming the bushes needs a sharp expanding reamer to achieve a good finish, so these ought to be done first as reaming the tough steel axle eye may dull the edges of the reamer. Adjustment of the expanding reamer can be painstaking as a light slide fit of the king-pin in the bushes is aimed for, whilst light blows with a plastic/wooden hammer on the king-pin is recommended for its fit in the axle eye.
Once the cotter pin is located and the securing nut tightened, hammer home the cotter pin before finally tightening the nut. Make sure the cotter pin is made from tough steel (eg EN24T) and not low carbon steel such as EN8 as the flat taper surface can “ruck up” when sliding over the locating flat on the king-pin.
Ed’s note: As mentioned in Eric’s article, he has ordered a quantity of bi-metal (known as ‘wrapped’) king-pin bushes. These are the same as originally fitted when the cars were new. Price to be advised.
Bi-metal ‘wrapped’ king pin bushes – note the oil/grease groove which has a spur take off that feeds lubrication to the thrust faces of the beam axle’s eye.