In The Garage April 2022 Issue 15
April 2022 Issue 15 Welcome to Issue 15 of In The Garage. We are always looking for content so please let us know what is going on in your garage especially if you are a new contributor.
Martin Lovell – TR6 Dodgy Trailing Arm Bush Martin writes
In March 2008, two years after purchase, I cleaned up, painted and rebuilt the front and rear suspension of my TR6. I used uprated and slightly lowered springs and a set of red poly bushes branded ‘Polybush’, which I’ve since discovered aren’t necessarily quality polyurethane, see photos Fig 1, Fig 2, Fig 3 & Fig 4.
At the time I put a lot of effort into setting up the ride height and wheel cambers to give a slightly more aggressive than normal setup with negative camber of approx. -2.5 degrees front and -1 degree rear, and with ride height 20mm lower than standard at the front and 10mm lower at the rear. Some 14 years later I noticed that the o/s rear wheel camber was increasing and had reached about -3 degrees i.e. 2 degrees more than when I set it up. I also noticed that the progression of this increase in negative camber had accelerated over the past 12 months or so. I had previously noticed on regular inspections that one trailing arm bush, the rear o/s inner, was beginning to show signs of cracking but I could never directly link this to why the camber was increasing as the bush installed in the trailing arm bracket could not easily be seen in detail and total failure of the bush was not a thought that went through my mind. A detailed investigation, dismantling and rebuild with replacement parts as necessary was added to my winter 2021/22 list of jobs.
When I finally got around to start the job, a detailed inspection prior to disassembly revealed that the situation was worse than I had expected and sections of the visible shoulder of the rear o/s inner bush were seen to be breaking away, see photos Fig 5.
I immediately ordered a set of blue ‘Super Pro’ polyurethane bushes and dismantled the rear suspension of the car. With the suspension fully dismantled I was shocked to discover that the rear o/s inner bush had actually failed completely as can be seen in photos Fig 6 & Fig 7. Fortunately, there was no damage to the trailing arm casting. I had caught it just in time.
With reference to measurements of the wheel cambers which I had carefully recorded during my first rebuild, measurement of the additional offset introduced by of the now fully visible failed bush, and referring to information from a very helpful rear suspension technical bulletin published by Buckeye Triumphs, the situation became clear. Using the data I was able calculate that the worn bush damage and subsequent unwanted offset was causing an additional -2 degrees of negative camber to the rear o/s wheel, which agreed with my observation that the negative camber was gradually increasing. I was able to make the calculation using the Buckeye Triumph data table of ‘Relative Camber Angle and Ride Height for Various Trailing Arm Bracket Configurations’ for every possible combination of 1, 2 & 3 notch trailing arm bracket in either the top or bottom notch mounting position and comparing how the unwanted movement of the bush sleeve would change the camber, See Fig 8, Fig 9 and the Buckeye Link at the end of this feature.
As always with trailing arm bush replacement you need a press or in my case a big vice and a combination of three short pieces of tube ranging from 25mm to 60mm diameter to push the old bush out and then push new bush in. It looks like an easy job but it is actually very tricky to do. Having four hands would have been helpful! After several attempts with the steel tubes either flying around the garage when under pressure or falling on the floor just as you’re trying balance the trailing arm, hold it all the bits together and turn the vice handle all at the same time, I got the job done.
Initial measurements and calculations indicate that my rear suspension is now back to how I set it up 14 years ago in 2008 but final confirmation won’t be available until I get the full weight of the car back on the ground in April.
Four tips coming from this story are:
1. Get your suspension set up how you want it not just as it is.
2. Check cambers and visually check your suspension bushes annually.
3. Ask me if you want to know how to push the bushes out and into the trailing arms. 4. Get a mate to help with the bushes, as you need at least four hands!
Here’s a link to the Buckeye Triumph technical bulletin - TR250 & TR6 Steering & Suspension Adjusting Rear Suspension Camber:https://static1.squarespace.co... djusting+Rear+Suspension.pdf
Martin
Andrew Willmott – TR4 and TR3 TR4 Engine and Gearbox Rebuild
Following on from last issue’s report revealing that the TR4 engine would require a major repair subsequent to dropping a valve seat the decision was made to remove the engine and gearbox for a full rebuild.
Initial survey revealed water marked liners and one piston damaged by the dropped valve seat, erosion on the face of one cam follower, deformed securing nut seating on the rocker pedestals, worn rocker shaft and a crank which had never seen a balancing machine.
I won’t bore you with a full workshop report but the engine was rebuilt with a balanced rotating assembly, new shell bearings, a “Mad Marx” crankshaft rear seal kit, 87mm pistons with Racetorations uprated liners and a Kent Hi- Torque cam with a reworked cylinder head to cap it all off.
The aluminium water gallery plug in the top of the cylinder head was replaced as although these often look fine from the top they can be corroded away on the underside which is exposed to the coolant and this can go undetected until coolant starts to leak into the rocker cover.
I was lucky that I had a serviceable set of rocker pedestals in my spares stock. The damage caused by not using the correct heavy-duty machined washers is evidenced by the cupping of the top surface as seen in the first picture.
The machining of the cylinder head mating face brings the rocker shaft closer to the cam altering the rocker geometry. The ideal solution to correct the geometry is to shorten the pushrods but raising the shaft with shims under the rocker pedestals is adequate for a road car.
A set of shims were made from a piece of copper sheet of the correct thickness, not forgetting that the rocker oil feed passes up through the rear pedestal and an oil hole is required in the matching shim. Although not strictly necessary I made mine with tabs to locate them on the head and hold them in position during assembly.
The combustion chambers were cleaned up and ground to remove the standard inlet valve shrouding and introduce a chamfer between the combustion chamber and squish area similar to a later TR4a head. The valve seats were then re-cut. I selected the best valves I could find from my used spares stock and had them re-cut prior to a very light grind by hand with an old school “sucker on a stick” and grinding paste. With the valves installed the chambers were fettled again with the die grinder to match the volumes across the four cylinders. A new copper head gasket was then re shaped to match the cylinder head and oversized 87mm bores.
The higher lift cam fitted required TR4a double valve springs to avoid coil binding on the standard TR3 inner springs. They were fitted together with matching TR4a spring caps; a bit too hastily as it transpired. After the car had been back on the road for some time I was looking at John Blake’s newly rebuilt cylinder head and noticed that it had progressively wound valve springs. On asking which valve springs he was using I was surprised to find that they were TR4a items the same as I had just fitted to my rebuilt head. Every days’ a school day! A quick check revealed that mine were indeed the same and even though probability dictates that 50% of them should have been correctly orientated six of the eight were upside down.
With rope fed down the plug hole and the piston squeezing it against the valve heads I was able to swap them all over in an hour. It wouldn’t have made much difference at standard revs but reduces the reciprocating mass a bit and knowing that it was now correct made me feel a lot better. Close examination of the following photo will reveal which of the springs were incorrectly fitted.
While waiting for machining work on the engine parts I couldn’t ignore the gearbox and overdrive. It seemed an ideal time to refresh the assembly as it was already out of the car and sat on the bench.
A morning’s work saw the whole lot stripped and a quick survey revealed no obvious problems and that the gearbox had previously been rebuilt with steel bushes in place of the standard bronze items which tend to fail prematurely. The lay-gear machined to take a third needle roller bearing and treated to a new shaft. All the main bearings were cleaned and inspection revealed that they were all serviceable.
It’s worth pointing out that there are a few different versions of main bearing which are subtly different as I discovered on re assembly. I couldn’t get one of the bearings to seat correctly against the shoulder on the main shaft. Close examination revealed that this version didn’t feature the radius on the inner bore to clear the radius on the main shaft but was square edged to seat against a spacer. Swapping the position of the two bearings allowed them to both seat correctly.
Although it had never caused a problem the gearbox had tended to jump out of 2nd gear on the overrun since before it had come into my ownership so the setting of the syncro-hub release loads and selector shaft detent loads received special attention. It transpired that the settings were arbitrary at best so a few hours were spent on the bench with a set of bathroom scales and a pile of shims to get the syncro loads as close as possible to the settings given in the workshop manual before moving on to the selector shafts.
The selector shafts are usually set with a spring gauge but I find it difficult to read the release point consistently so I secure the selector assembly vertically in a vice and hang a fixed weight from the selector forks in the form of cans of
water so that the weight can be easily varied to give the correct force. Some more work with spare springs and shims saw the selector shaft release loads matching the workshop manual figures.
The gearbox and overdrive re assembly went quickly as I’ve built a few now and with the aid of John Blake’s test kit the gearbox and overdrive were test run on the bench prior to being re fitted to the car.
Road testing revealed that 2nd gear was now secure on the overrun even under harsh provocation and that the action at the gear lever is much improved.
TR4 Heater Valve Mounting
As always when dismantling TRs we find ways in which things can be improved when we come to re-assembly.
The heater valve connection to the cylinder head is always problematic, more so when the angled adaptor requires removal.
I rummaged through my hydraulic fittings box and found a 3/8” BSP male/female swivel that mounts the valve upright, allows removal without having to disconnect the valve to unscrew it and simple orientation of the valve to suit the hose and operating cable. The fitting is sealed into the cylinder head port with a bonded washer although a copper washer and some Welseal would serve just as well.
TR4 Steering Wheel Replacement
TR4 entry and exit have always been a wriggle even for someone as compact as me, and more so after the MX5 seats were installed. The problem has always been the gap, or lack of it, between the steering wheel and the seat bolster. I’ve always felt that the 15” Moto Lita steering wheel was a bit too big so a nice condition 13” version was sourced from eBay. The new wheel allows for easier access and feels better suited to the car, weighting up the steering noticeably but not enough to make parking difficult.
TR4 Battery Isolator
The TR4 has had a battery isolator fitted to the battery terminal since soon after I got it but it has been less than convenient to use when out-and-about as the bonnet needs opening to switch it on and off.
I had a period Lucas battery isolator in my spares stock so a quick hole in the bulkhead next to the battery tray and half an hour making up new leads saw me with a much more convenient switch accessible from the passenger’s foot-well.
TR4 Braided Brake Hoses
I’d had the TR4 up on the lift to for a springtime grease and check over and all seemed well until I gave the brake hoses a bend test. Although they looked fine under casual inspection the outer hose layer cracked up when bent double so replacement was in order. Goodridge braided hoses were sourced at a good price and while I was working on the brakes I remade some of the hard lines from Kunifer tube to tuck them away a bit more than they had been.
TR3 LED Headlights
I’ve been impressed by LED headlamp conversions made by other members of the Devon Group and as all the other bulbs on the TR3 had already been upgraded to LEDs I decided to upgrade the headlamps to match. The Lucas headlight reflectors had turned a bit hazy with age decided to go the whole hog and replace the units too. I sourced some quality German Hella units that included a small pilot bulb in the bottom of the reflector for a sidelight that could be used as a daylight running light or improved sidelight.
The LED headlight bulbs were supplied by Classic Car LEDs and feature a “black box” driver unit that allows them to be powered by anything from 9 to 32 volts. Although they can be squeezed into the headlamp bucket I used the optional extension cable and mount them on the inner wings with industrial self adhesive Velcro. The wire access hole in the buckets need opening up and a larger grommet fitting to allow the connecting plug through but apart from that it was a simple bolt on job.
The pictures below show the difference between the white LED and the yellow halogen bulb. The Hella beam pattern is well focused and is remarkably well cut off on dipped beam. I’ve yet to be “flashed” at all with the new bulbs in use
and the difference in night visibility is remarkable. A slight downside is that I’ve found reflective road signs to create a bit of dazzle on main beam but I’ll put up with that
When in use the pilot bulbs are almost indistinguishable from dipped headlamps but there is almost no projection of the light due to the positioning of the LED away from the focal point; so no chance of dazzling oncoming drivers.
TR3 Steering Column Modification
The cockpit of a sidescreen TR is compact at best and the steering wheel is quite close to the driver. The rack and pinion conversion (detailed in issue 7) had put the wheel closer still so a further modification was in order. A spare steering column was cut in half and machined on each end to form an interference fit spigot location and shortening it by an inch or so. The two parts were pressed together and welded by ace welder Mikey Dove from Bob Dove Racing. A quick spin on the lathe confirmed that it was true and the weld was cleaned up before it was painted and fitted back on the car. The modification has improved the driving position and made the cockpit feel more spacious out of proportion with the small change.
Andrew
John Blake – TR4
John will be campaigning his TR4 in the Revington TR Register Sprint and Hillclimb Championship this season so in the interest of not missing any events due to mechanical failure he has been building a complete replacement engine and transmission assembly which can be quickly changed as a unit. I’ve already offered to fit it in the TR3 to run it in but my kind offer fell on stony ground J
As always John is happy to pounce on any marginal gain and with the biggest valves that the combustion chamber will take fitted the gas flow is impeded by the edge of the cylinder liner. An hour or so was spent with a die grinder to improve things by chamfering the edge of the liner in the inlet area. The following photos show the modification. It’s interesting to compare the photo of the combustion chamber with oversize valves to the picture of my TR4 combustion chamber with standard sized valves shown earlier in this issue taking note of the shape of the chamber and the gap between the valves.
Tony Bunch – Ouch!
Tony posted this little reminder on our Devon Group Facebook Page. I’ve seen this a few times over the years so it’s worth another airing if it saves a bit of grief for someone somewhere.
You – Your Car
Thanks to all our contributors to this issue.
Contributions and feedback (positive or negative) are always welcome.
What’s happening in your garage?
Please make a few notes about your garage exploits and email them to me for the next issue. Contributions are best managed by sending in plain text with attached photos or in Word format.
Mail your notes and pictures to: andrewawillmott@gmail.com Andrew W