Lotus Elan

alignment

PostPost by: Donels » Tue Feb 12, 2019 7:12 pm

I once had a Triumph Spitfire that had little self centring and then the bottom snapped off the upright. Grease had been used in the trunnions and set hard giving no lubrication, hence lots of friction and no self centring. The Elan +2 uses the same bits.

I doubt the chassis is wrong and something major would be required for the castor to be way out. I would start with the obvious, as someone else has suggested, and strip and service the trunnions, then check the steering rack is not binding.
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PostPost by: JonB » Wed Feb 13, 2019 8:34 am

My car's rack isn't binding, has new uprights, trunnions and ball joints. Trunnions are lubricated with EP90. This after I read all about Spitfires and snapping kingpins on a Triumph forum (I had several Spitfires over the years and never knew about this, or lubricated the trunnions. Just thinking about it gives me the shivers!).

According to the Hunter 4 wheel alignment measurement, I have 6 minutes of castor on the left and 25 minutes on the right. It should be easy to do as you say, but the OP should also do a 4 wheel alignment check, so he is dealing with proper measurements. Otherwise, he is using trial and error to rectify the problem (expensive).
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PostPost by: rgh0 » Wed Feb 13, 2019 9:37 am

While wheel alignment on a static test bench is useful how it changes under braking, turning and acceleration loads is also critically important. The Plus 2 with its longer and more flexible chassis and long suspension arms suffers much more from this than the Elan does. How you set up a Plus 2 on modern tyres is something that has not been worked much unfortunately compared to Elans.

Lots complexity down this path :evil:

cheers
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PostPost by: john.p.clegg » Wed Feb 13, 2019 10:11 am

While we're here does anyone have the book settings for the front , toe, castor , camber ?

Thanks
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PostPost by: JonB » Wed Feb 13, 2019 2:26 pm

Well, I have the settings from the Hunter system, which may or may not be "as book".

front-alignment.jpeg and


Interpolating from this diagram with +2 book values from the Brooklands manual:
  • Front camber 0.5 degrees per side - book = 0 to 1mm
  • Front caster 3 degrees - book = 3 degrees +- 5 (!)
  • Front toe in 12.5 minutes per side (doesn't seem like much!) - book = 4.76mm
  • Rear camber -0.5 degrees per side - book = -1 to 0 mm
  • Rear caster (NOT SHOWN)
  • Rear toe in 12.5 minutes per side - book = 0-4.76mm

The age old question is "How do you convert these angular values to the distance values in the book?" - and I have seen much debate but few authoritative replies.

A second question (about the Hunter settings) is this: They use the same settings for the Elan and Plus 2. That can't be right given the different chassis geometry, can it? The book shows some different values (camber and caster) between early and late models.
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PostPost by: john.p.clegg » Wed Feb 13, 2019 2:52 pm

If the elan and plus2 share the same "trapezoid " configuration then yes,the front and rear toe-in is correct ( the same ) as for the rest of your figures , trying not to be too brutal , I think I'd like to get a sledge hammer to the frame...??

All they've done is adjust the toe-in,the castor and camber figures are all over the place , even different before/after with no adjustment ??

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PostPost by: RonR » Thu Feb 14, 2019 5:59 pm

JonB wrote:How do you convert these angular values to the distance values in the book?


Here's the figures from the WSM, which agrees with your Hunter sheet:

FRONT SUSPENSION
Camber Zero to +1° (Positive) - Not 1mm as in Brooklands
Castor 3° +/- 30' (Positive)
Toe - in 3/16 in. (4.76 mm.) to Zero

REAR SUSPENSION
Wheel camber 1° to Zero (Negative)
Toe – in 3/16 in. (4.76 mm.) to Zero

To convert the Toe-in figures, I use secondary school trigonometry (SOH-CAH-TOA), and the wheel size (13").

3/16 = 0.1875

Sin X = Opposite over Hypotenuse = 0.1875 / 13 = 0.014423

X = Inverse Sin(0.014423) = 0.8264 Degrees

X * 60 = 49.58 Minutes - giving approx. 25 Minutes per Side.
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PostPost by: vincereynard » Thu Feb 14, 2019 6:19 pm

The figures can / will also change with load. Remember the +2 has rear weight bias (a bit).

Half a tank of fuel and 2 passengers will drop the back and increase castor. (a bit).

The 4 wheel tracking must be done with the correct loading (not necessarily as recommmended) but
what the car will be generally used with. Actually it would be interesting to see how much the figure changed before anf after heaving a sack of sand in the boot!

I seem to recall that when set up correctly the 4 wheels basically form a trapezium (?) The rear wheels point at the centre of the front. I intend to get a small laser, attach it to the rear hubs and tweak until it is pointing at the front hub thread. (Once the wishbones are set correctly!)

Trig. Calculator - http://www.carbidedepot.com/formulas-trigright.asp
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PostPost by: JonB » Thu Feb 14, 2019 7:53 pm

Regarding my Hunter results.

  • Done with weight of 2x adult passengers and spare wheel in boot.
  • Alignment was done on a ramp. It's possible that when the ramp came down and stopped, the suspension settled slightly. Might have been better if they'd measured, adjusted then remeasured without moving the ramp.
  • At the time, the bushes were all shot and have been replaced.

Anyway there you have it. Get it 4 wheel aligned so you know what you are dealing with.
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PostPost by: bitsobrits » Thu Feb 14, 2019 8:56 pm

When chasing Elan front camber or caster differences from side to side, don't overlook the possibility of a bent upright. After much head scratching, and after disassembly/cleaning and carefully measuring my two uprights, I discovered the RF to be bent in both the fore/aft plane and L/R plane. The fore/aft/ bend was in the area just above the trunnion thread, the L/R bend at the top of the thread. Not at all detectable when on the car, somewhat visible to just looking at the disassembled parts, and verified with straightedge and calipers. Probably a curb hit years ago, put right by another unbent upright.
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PostPost by: Lotus 50 » Fri Feb 15, 2019 2:01 am

New tires, strip and service the trunions, and then check alignment. The steering is light enough that I'm sure it's not binding.

Sounds like a plan. Mid April.
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PostPost by: mbell » Fri Feb 15, 2019 2:42 am

I'd take a careful look at the suspension arms to. Not sure if they are sided but if they are traveling them reversed could be the cause of your issue.
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PostPost by: miked » Fri Feb 15, 2019 9:37 am

Re vertical links. I also had one snap on a spitfire in 1975, when parking. Young fellow who was not up to speed with lube or examination. :shock: :shock:
I have separated quite a few and found varying degrees of corrosion. Even wasting of threads near top. Scary on a Plus 2 i had. :?
I won't use them with any surface pitting on the neck curve as this were they go. My understanding of surface pitting is that there are small cavities beneath. It is the first thing I do. Make sure the are is clean and not corroded. Then regular lube.

Mike :D
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PostPost by: JonB » Fri Feb 15, 2019 4:11 pm

The micro fractures that lead to the kingpin shearing off are called "stress risers".

Fortunately it usually happens when you have the steering on full lock (when manoeuvring at low speed). It's difficult to buy uprights with good threads on them. There seem to be chatter marks all the time ( = stress risers). I agonised about this for ages on this thread: lotus-suspension-f42/another-post-about-uprights-trunnions-t40847.html

..but never found a decent set. In the end I bought a pair from Sue Miller, also with a dodgy thread but it was that or nothing.
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