Is this control arm twisted?

[StillIC]

Every two bored holes ever made by humans are misaligned. There is no such thing as perfect. The question is, what tolerance of misalignment is acceptable??

Engineers design parts with the knowledge that it is impossible to make them perfectly aligned/round/straight/flat/smooth etc., so allow for this in the overall design of an assembly. The misalignment seen on the control arm seems usual to me and rubber bushes will account for this with ease.

I will never ever use a poly bush again in a rotating joint, as the bearing surface. Porsche doesn't, Lotus doesn't, no manufacturer does. Why should I (or anyone)? I have done so when I was young and less, well, less everything, but learnt my lessons over the course of two cars.

[greenMachine]

Every two bored holes ever made by humans are misaligned. There is no such thing as perfect. The question is, what tolerance of misalignment is acceptable??

Funny that, I was mulling exactly this as I took the SE into town today.

How far does castor adjustment move the bores out of nominal alignment? I am thinking that it would be something like the 'misalignment' shown.

Bottom line, castor and/or toe adjustment is introducing 'misalignment' into the nominal bore/axis. All bushes (in such locations) will suffer from it, therefore need to be able to tolerate it. Rubber and poly are flexible, and therefore can adjust to accommodate it - but perhaps there are differences in their resilience to the forces within the bushing as the arm moves about the axis (bolt).

[RS2000]

You've lost me gM. I don't believe caster, camber or toe-in adjustments affect bore alignment or misalignment at all.

On the rear, the whole lower arm moves for camber & toe adjustments, with the bolts moving in slotted holes in the cross-member. Likewise on the front lower arm for caster & camber adjustments.
You could easily introduce misalignment of the offset bore type poly bushes, where the crush tube bolt hole is not central.

I agree that the misalignment in the photos is from factory fabrication, & would be within tolerances allowed. They could get the bores spot on if line-bored after fabrication, but not worth the cost when it doesn't matter with rubber bushes.

[greenMachine]

RS, it's a bit difficult to explain, if I get time later I will try and do some drawings.

Taking the inner mounts, the two bolts have a common axis (are co-axial) when the adjusters are set identical (this is an assumption on my part, I have not seen anything to suggest otherwise). However when the adjusters are moved differentially (say to set toe or caster), they are no longer co-axial, their axes are different, but still parallel. That is, the horizontal suspension arm has moved forward or back at its outer end, twisting at the two bushes which are still held in a strict fore-aft axis.

As a necessary consequence of that twist, the inner bores of the bushes (the surfaces in contact with the sleeves) are no longer parallel (no longer on the same axis) as the surface in contact with the bore of its housing on the arm.

Put another way, the pressures are no longer uniform within the poly. The displacement of the axes means that in each of the two polys , at each end of the polys there is more pressure on one side than the other.

Remember that the adjusters simply slide in or out in the slots, they remain perpendicular to their chassis mounts - that is the key to understanding the change to the geometry of the bushes, the sleeves and the bushes' inner and outer surfaces.

[RS2000]

Yes, you're correct gM. My apologies.
I was forgetting that the inner mounts are 2 separate bolts that stay perpendicular to the chassis mounts when torqued.
The housing bores stay co-axial, but the crush tubes don't.
Cheers

[Roadrunner]

It's an interesting one for sure. What I find peculiar is that of all the comments on the Delrin threads, no one has mentioned misalignment of these 2 bores. Delrin is harder than poly, so you'd seriously struggle to get the long bolt through both bushes in my arm. If this arm is like this from the factory how haven't others had the same issue?

Am I unique? Don't answer that

[greenMachine]

Delrin requires a compliant bush in one of the two misaligned/non-coaxial bushes, this is set out in the MT.net megathread. SADfab sell a poly/bronze for this purpose, and specify a set of four, one for each corner of the car when installing delrin (one for each of the four LCAs). Having worked this through in my mind, I now wonder if that is the full solution - I am thinking that just doing one is only fixing half the problem, and that in fact both LCA-I bushes (ie eight, rather than four locations) should be poly/bronze. I am going to take this up there, and if I survive I will report back .

The issue is much more manageable with rubber or poly, because their compliance is greater than delrin. Nevertheless, I wonder about the failures in poly bushes (Luke, are you there?), and whether the flexing of the poly when the arm rotates (especially when heavily loaded under high-G on the track) is playing a part in the failures. The movement of the high/low pressure zones within the poly as the arm moves up and down could lead to friction and potentially tearing in the the material, and there would be a level of heating with the pressure changes as well. I'll have to leave it to the material scientists to have the final say on that though.

RR, I am agnostic about your misalignment issue. I am assuming that the arms ex-factory have co-axial inner bores. If they don't, presumably they are aligned to best accommodate the factory suspension settings, so that the conflict between the axis of the bolts/sleeves and the axis of the housing bores is minimised. It would follow that both inner bores would need to be parallel to achieve this effect. It would also follow that this would mean that the 'misalignment' is the default. I tend to think that this is overthinking the issue, and that for ease of manufacturing and servicing, co-axial housing bores are the default - remember they use rubber ex-factory, and that is very compliant if/when 'misalignment' is required for suspension adjustment.

[Roadrunner]

What I find peculiar is that of all the comments on the Delrin threads, no one has mentioned misalignment of these 2 bores.

Delrin requires a compliant bush in one of the two misaligned/non-coaxial bushes, this is set out in the MT.net megathread.

I was only referring to the outer bushes, where Sadfab use Delrin on both sides of the hub/knuckle.

[StillIC]

It's an interesting one for sure. What I find peculiar is that of all the comments on the Delrin threads, no one has mentioned misalignment of these 2 bores. Delrin is harder than poly, so you'd seriously struggle to get the long bolt through both bushes in my arm. If this arm is like this from the factory how haven't others had the same issue?

Am I unique? Don't answer that

I have installed poly bushes on non-MX5s, and normally don't worry about misalignment in bores. I just install the bushes in the arms, then bolt one end of the arm (loosely) then force the arm to the second locating bracket, then force the other bolt through. Then I leave the bolts finger tight, lower the car to the ground on a flat or levelled surface so the weight is evenly on the springs, then fully torque the bolts. This is *always* the technique I use (and require). Also true for rubber bushes.

I don't believe your car is unique. As for you, I can't possibly comment!

[greenMachine]

What I find peculiar is that of all the comments on the Delrin threads, no one has mentioned misalignment of these 2 bores.

Delrin requires a compliant bush in one of the two misaligned/non-coaxial bushes, this is set out in the MT.net megathread.

I was only referring to the outer bushes, where Sadfab use Delrin on both sides of the hub/knuckle.

My mistake

However my conclusions/concerns/whatever about the SADfab compliance bushing is unaffected by that.

I agree with StillIC, don't sweat the 'misalignment' they are flexible bushes so let them flex. A tad misalignment there is no big deal.

I disagree, or at least consider unnecessary, his tightening procedure for the polys, the whole point of poly is they (are supposed to) rotate with the movement of the arms - this is the big difference from the rubber.

Rubber does not rotate, it deflects. It is held at both the inner and outer surface, the inner is held by the sleeve, the outer by the housing bore. When the arm rotates, these surfaces do not, they remain firmly held, and the rubber twists between them. While that permits the arm to move, it also loads the arm with the resistance to twisting of the rubber, adding to the spring rate. It is also why, with rubber, it is necessary that the suspension bolts securing rubber bushes are only tightened with the suspension loaded with the car weight, so the rubber bush is neutrally held, twisting in neither direction.

[StillIC]

…..
I disagree, or at least consider unnecessary, his tightening procedure for the polys, the whole point of poly is they (are supposed to) rotate with the movement of the arms - this is the big difference from the rubber.
...

I agree that what you say is what is *supposed* to happen with polys (rotating not shear twist), but I don't trust them, even with gobs of grease (which often gets pushed out on install). Another reason for putting the weight on the suspension before bolt tightening allows other bits to settle to where they are likely to be, e.g. bolts in holes, although this is, arguably, not particularly important.

[greenMachine]

Seems like we are in furious agreement , at least on the drawbacks of poly!! Your method leaves nothing to chance with those crappy things, so I reckon I will concede the high ground to you - this time!

[Roadrunner]

Replacement lower control arm arrived. Long bolt went straight through with zero effort. Interestingly on a straight edge the bores were off the same amount as the original.
For curiosity's sake, I put the original rubber bushes in the original arm to see if it was the poly off centre. Long bolt still wouldn't go through without serious effort and binding.
Measuring every dimension and cross angle I can't see any bend or twist anywhere, but obviously it is bent.

[Magpie]

Looks like we need a local version of the SADFab bushings.

[rascal]

Looks like we need a local version of the SADFab bushings.

100%.
The exchange rate and wait time is a killer with sadfab...