Lower-Trunnion-Bushes

Refurbishing Worn Out Trunnion Bushes.

The time could arrive where the lower trunnion bushes will have considerable wear, the suspension could become noticeably sloppy, and there will be a noticeable fall off with the handling of the elan.

And as with any precise instrument, they perform better if maintained within the given tolerances.

The elan, if maintained correctly, is a very precise handling car, each component within the suspension, will play its part in delivering the unique driving experience that the Lotus elan is well known for.

Before we delve into the refurbishing and part redesign of the lower trunnion bushes, we should describe this important piece of the elan suspension… maybe it will be better to use the factory workshop manual exploded diagram.

Which include the three inch high tensile bolt, dust cover, steel spacer tube, sealing ring, top hat bush X 2 (Hard Nylon), and the bronze trunnion.

Much of the elan front suspension is made up of several Triumph Herald components, they are mostly strong and lightweight, and generally ideal for the Lotus elan application, but to be honest the lower trunnion bushes are possibly not the most ideal design.

In the writers opinion, they are not really the sort component that is ideal for a high performance sports car like the elan. The photo below shows some old and damaged trunnion bushing parts.

Understand, that the bits above were found in a disused parts box during preparation for this article.

The photo clearly shows the thin sheet metal dust covers, and grease seals, (Disregarding the HT bolt) the bush assembly is probably fine when brand new, but the  components of concern are the two top hat style bushes, which appear to of a hard nylon material, if not maintained and lubricated will suffer from premature wear.

Even if the DIY mechanic managed to achieve the proper fit of these old technology bushes, I would imagine that they would soon require further servicing and maintenance, which would be ongoing on a regular basis, so why would one continue to put up with this constant maintenance work when time could be spent on installing custom made urethane bushes that would eliminate the majority of servicing work for many many years, it makes sense.

Above photo is of the first set of red urethane bushes we manufactured way back in 1983.

The original Triumph Herald bush kit was totally knackered, and to be honest, the writer simply did not like the arrangement. So, at the time, all of the suspension bushes were being converted over to urethane, which have lasted for more than thirty years, and the trunnions were treated to new urethane bushes as well.

Sure, you would have noticed that one of the top hat style bushes has split around the flange… but this bush has been in service for more that thirty years, and covered about 80,000 miles in that time… not a bad run.

The original bronze trunnion bush housing was worn slightly oval shape from the old hard bush, the trunnions was degreased, cleaned, then mounted in a four jaw lathe chuck and bored out to true it up, then the urethane bush kit was machined to suit…which is simple and easy to do.

It does not take much mechanical knowledge to understand how vague the handling of the elan may become if these bushes are neglected and they become extremely worn and loose, be assured there would be plenty of annoying suspension rattles, as well as a very vague and wandering elan front end.

That is not what the Lotus elan is about.

During the first rebuild/restoration of the elan way back in the early 1980s, the original hard trunnion bushes were discarded in favour of custom machined Red Urethane bushes. Red urethane was available (And still is) in round solid rod form of varying diameters, so it matters little what size bush is required, there is a suitable size available, the round urethane solid rod is supplied in 12″ or 300mm length.

There are several companies offering ready made polyurethane bushing materials, some are good, some are very bad.

The hardness grades are generally indicated by the colour, and only three colours existed… Black = Hard, Yellow = Soft, and Red = medium grade, the preferred material for automotive suspension bush applications, and this is what we are dealing with here. Urethane is impervious to grease – oil – petrol – thinners – water and road muck, and is generally self lubricating, so why wouldn’t it make sense to convert the trunnion bushes to red urethane material…

It really is a no brainer… fit and forget for a couple of decades, at least. 

The rod can be easily turned in the lathe, but a high spindle speed is required, and a knife like cutting edge turning tool for best results, it takes a bit of trial and error to get it right.

If the bronze trunnion housings are worn oval shape, they can be carefully mounted in the independent four jaw lathe chuck, trued up, and over bored to correct the ovality, but only remove enough metal to create a true bore, the original bore size is 3/4″.

The bronze metal in the housing is generous enough to allow over boring to the next size, but the actual bore size is not that critical, because the urethane bush will be machined to fit the housing, in other words, a custom fit will be achieved. (Hand Press In Fit)

At this point, you may be wondering about the longevity of the urethane bushes…. let me say this, you can rest assured that they will last two or three decades if the bushes are correctly made and installed, the bonus is that there will never be a problem with worn trunnion bushes, the urethane provides extra compliance and flex, and the suspension will always feel tight and precise.

The photo above illustrates the split Top Hat design bushes, and the stainless steel crush tube. It is very important to make the crush tube the correct length… just proud of the urethane bush, the stainless crush sleeve controls the amount of pressure applied to the bush when the high tensile nut is tightened. The side washers have been discarded with the new bush set.

BTW, there’s bound to be someone wondering what type of tires are fitted to the S2 elan – Falken Azenis RT615K – 195/60R14 – Street legal motor-sport high performance tire – And yes, they stick like a limpet when cornering hard. (Grin)

If the nut is too tight the suspension joint will bind, but you don’t want it to loose either, a good guide is when things can be moved by hand, with a bit of effort… again, employing a bit of trial and error.

With the trunnion housing being previously bored out, there will be no need to dismantle the entire front suspension, the bushes can be machined and trial fitted to the car (This project was carried out while the body was off the chassis for an engine rebuild).

The sleeve is pressed in using a simple press tool, made up from w length of all thread, two nuts, and a rear press plate, assemble as shown and just wind the nut down the threaded rod, and the sleeve will be easily pressed in and installed.
Do not try to hammer or drift the sleeve in… it wont work, pressing as shown is best.

With an all urethane front suspension set up, the complete system works in harmony with out any binding, there should not be any rattles from any component, and the urethane bushes provide correct compliance with out allowing the suspension to walk around under hard cornering, or during hard braking as would occur with standard rubber suspension bushes.

You may be totally happy with your elan as it is. You don’t have to carry out this modification, but drawing on the driving experience of the writers elan, the handling has been improved significantly over what the standard rubber bushing provides.

Make no mistake, converting any car over to urethane suspension bushing involves a lot of work and effort, but the results speak for them selves.

On several mountain drives we have organised, there has been a standard S4 elan that could not match the writers S2 elan in the challenging, twisting and winding mountain roads… where the elan truly excels.

If you are tired of maintaining the poor quality and original triumph herald suspension components, then you might want to investigate the conversion we have illustrated and explained above.

And to answer your questions, no, we don’t supply bushing kits, this is a DIY project that most advanced home mechanics should be able to carry out providing you have access to a lathe, and a supply of Urethane rod… the red stuff is best.

Once the original lower trunnion bushes have been converted to urethane bushes, all of the old bushes and fiddly sheet metal bits and pieces can be thrown in the bin, because they wont be required any more.

Hope you have enjoyed reading and learning – This is another technical article sharing with other elan and lotus marque owners.