Uprights - What would you do if you were making new ones?

[LotusJoe]

If you were making new uprights would you change the bearing landing to accommodate a different type of bearing?

Maybe leave the material inside the upright so you don't need the bearing spacer any longer?


 Or maybe make an upright that would fit the S-2, Twin Cam and the Special, if that is possible. 


 

[EuropaTC]

I'm guessing you're all about to start designing & fabricating then Joe ?  Well, as you asked, here's my (possibly controversial ?) 2c worth.

Yep, I'd certainly change the bearings. Despite the theories stated about low loading and the way some folks claim the bearings last well, that's not been my experience.  When I used my car daily it wasn't unusual for me to have to change the rear bearings at 2yrs because I had an MoT garage that was very strict about wheel play and any play would get a fail on the annual test.

So, in an ideal world with machine shop facilities my first step would be to fit a modern and better sealed design of bearing, which would probably mean a complete new casting. My first thoughts would be to try to use something like Lotus have used on the Elise, which is a double row taper roller bearing. (picture attached)  That would do away with the spacer as well, but be aware that the Elise has an entirely different design of rear suspension using CV joints and twin links.

The steel spacer is an interesting one.  I can see why it's present in the OEM design, but given how Chapman was ever trying to lose weight (and costs) it did make me wonder why he didn't do away with it and rely on an internal shoulder in the housing to support the bearings. I can only think that he decided it wasn't strong enough or perhaps might wear in service, making the infamous "hub falling off" sequence a bit more likely ?

Finally, why not incorporate a small lug on the top of the bearing carrier itself to allow an optional upper link to be added ?  There's quite a few folks with twin link suspensions these days and it might increase the potential market for any future production run ?  I would have thought that as long as the critical external/suspension dimensions are the same for S2 & TC's then anything you design should be applicable to both markets.

Brian

[Bainford]

Very interesting question, Joe, and Brian has some equally interesting suggestions. A bit of thought would be required on my part if I were to suggest a significant design change. I have yet to change my rear bearings ( a job I'll likely be tackling next year) so I have yet to get intimate with that part of the car, at which point I would probably have thought out some ideas (... why the hell did they do it that way? It would have been much better if they did it this way...).

Anyway, right off the top of my head, I think the current design could be improved if it were altered to include a steel sleeve in the bearing bore. This would require more material around the exterior portion of the housing to maintain a suitable robust assembly. An aluminum bearing housing is always a bad idea in a long term assembly. The steel suffers wear & tear much better, is more dimensionally stable, is easier to install bearings (allows better 'feel'), and, when worse comes to worse, a steel sleeve can be replaced. Comments and critisims on this idea accepted.

That's one quick though for the moment. If anything else comes to mind I'll post it. I'm sure discussion will ensue.

[LotusJoe]

The inside of the upright is hollow as I'm sure most of you know. I suspect this was a product of the casting process. My thought would be to leave the upright solid with a hole slightly bigger than the stub axle to eliminate the need for the steel spacer. Taking Trevor's idea a step further, maybe pressing in a steel spacer on the inner bore and a steel sleeve for the outer bore. This would make the landing for the back side of the bearings larger and help eliminate movement in the upright. I also like the addition of the circlips.  An update on the bearings I think would be in order. I'm not an expert on what that would be, so more research is needed. I am thinking of having them made in 6061 aluminum which would be far superior to the aluminum cast. Being able to accommodate all the models would help eliminate the need for multiple designs. But it would have to be done in such a way that didn't require a bunch of additional modifications to any of the ancillary parts. It looks to me that the main difference, aside from the bearings is the attachment of the lower link. The S-2s lower link looks to be offset so it can attach to the upright on the same side as the shock, where the TC Special is straight and attaches to the opposite side. That may be a simple as boring both attachment holes. I haven't measured the different uprights so I'm not sure if it is that simple.

     

[EuropaTC]

I think your interpretation of the lower link/damper assembly is right, the casting looks (from pictures at least) to be able to work with both designs.

A solid casting would be quite a bit heavier and might raise another problem with the potential for shrinkage cavities inside the section; there are lots of ways to combat this and of course you can make much thicker Al castings, but it will complicate the casting procedure. So maybe there might have been good reasons for having a hollow casting ?

But you could still have a thicker bearing section with a built-in spacer and personally I think it's very possible to come up with a design to appeal to the S2 & TC owners.  The snag in my mind is exactly what loads you get from having the driveshaft as the upper link, if it wasn't there it would be much easier.  The Elise for instance uses a thick Aluminium extrusion as a carrier - yep, they just squirt out a length of extrusion and slice it up into hub carriers ! ( ok, maybe it's not quite that simple....       )

Brian

[Bainford]

Brian mentions weight, and I think this is an important consideration. As Lotus owners, the weight of any component or mod is always on the mind, sometimes to a ridiculous degree. However, this is unsprung weight, and its effect on a very light weight car can be significant.

Just food for thought...

[pboedker]

The inside of the upright is hollow as I'm sure most of you know. I suspect this was a product of the casting process. My thought would be to leave the upright solid with a hole slightly bigger than the stub axle to eliminate the need for the steel spacer.

I'm afraid this would not work since the bearing inner races would then jam on the upright and lock the stub axle to the upright. Remember that the original design locks the stub axle, the inner bearings inner race, the steel spacer, the outer bearings inner race and the hub flange firmly together. And then the outer bearings outer race is held in place in the upright by the square plate on the front link arm. While the inner bearings outer race is free to float in the upright and letting the balls roll freely in both bearings. I don't have the link ready, but the workshop manual has a very clear drawing of this.

But I really like the ideas you posted of steel inserts for the bearings or the idea of using some better material than originally. I have a Special, and had no problems sourcing the bearings, so making a uniform upright with these bearings would be an improvement for S1-2 and TC. I don't know enough about bearings to come up with yet another type that would beat the Special's configuration.

As I see the original design, it looks like someone took the smallest possible diameter to hold the bearings and then added the 'ears' for the front link arm and the 'hanging part' for the lower link. In my view a new upright might as well be square on the outside from the start, and maybe the part for the lower link could be a second part that attaches to the center part. And the part for an optional upper link could as well.

[LotusJoe]

I think in the case of the internal material of the upright we're not talking about much weight. When I was having some casting of Aluminum done the foundry was happy to cast my project in solid aluminum. However the guy actually doing the casting said "Hey you should put a plug in the center so you don't use so much Aluminum; cause you know we charge by the pound. I can cast this at half the weight...but it's your money." I'm thinking it was a cost savings for production purposes and not necessarily weight savings on the car.  Even today extrusions and castings are still popular due to the savings in cost. Also CNC technology didn't exist at that time.

I'm not suggesting that lighter isn't better. But I would be willing to give up a bit of weight for a superior carrier with updated bearings that wouldn't fail. I will know better about how much material we are talking about after the parts are scanned. I would be willing to guess that it is less than 1 pound. 

[LotusJoe]

The inside of the upright is hollow as I'm sure most of you know. I suspect this was a product of the casting process. My thought would be to leave the upright solid with a hole slightly bigger than the stub axle to eliminate the need for the steel spacer.

I'm afraid this would not work since the bearing inner races would then jam on the upright and lock the stub axle to the upright. Remember that the original design locks the stub axle, the inner bearings inner race, the steel spacer, the outer bearings inner race and the hub flange firmly together. And then the outer bearings outer race is held in place in the upright by the square plate on the front link arm. While the inner bearings outer race is free to float in the upright and letting the balls roll freely in both bearings. I don't have the link ready, but the workshop manual has a very clear drawing of this.

I found the drawings and put them in my previous post. I get what your saying...More thinking required 

[LotusJoe]

I got a pair of uprights from one of our members (Joji AKA Grumblebuns) they were however still assembled in the trailing arms. But with a little persuasion I was able to get them apart and cleaned up good enough to scan. More progress next week. If anyone is looking a set of slightly bent trailing arms he might want to sell them. 

[cal44]

I keep thinking about your question on the uprights.  Yes part is hollow, so how much would it weigh if it were solid vs. the current design?

Take a mid eighties 911 rear set up.  That stinkin' thing weighs a ton per side.  So, then we enter un-sprung weight.........since it has  a direct correlation with spings/shock........is it really going to make that much difference?
I ask because I don't know.

I get all dreamy thinking of uprights being milled on a C&C machine with the cutting water/oil and flying aluminum bits.........
oooooo'

Or....fad em' up out of steel plate, hollow and strong.

mike

[LotusJoe]

I thinking about solid 6061 Aluminum. I filled the void with water and it was just over a cup. So if you do the conversion it should be somewhere around 1.4 lbs of additional weight per upright. Too much? 

[cal44]

Soooo, just over one pound?  I must be missing something cuz that doesn't sound like a big deal to me.  If it was a big deal, get springs that have a bit more juice.

I wonder if the original design with the hollow area was more about saving money than weight.........hmmm.......

mike

[EuropaTC]

(part quote)
I wonder if the original design with the hollow area was more about saving money then weight.........hmmm.......
mike

Could well be Mike, although (allegedly) Chapman bawled out one of his mechanics for putting washers underneath the bolts on one of his cars with the phrase "why are you taking those washers for a ride on my car ?" 

But casting thicker sections can give you problems with shrinkage cavities as the outer skin solidifies leaving the inner core molten. Then as that finally solidifies it contracts and you get cavities forming. That's not an issue here because it's hollow anyway, but the snag is you might get a defect in an area you want to machine or use. 

The old way to prevent this was to either insulate/electrical trace heat the mold and have very slow cooling times, or "feed" the centre with new molten metal so you'd end up with the shrinkage taking place above the parts you needed. There's probably other ways of doing the job, but the main thing was that it extended the production times on a part, so it would cost more to make.  Not a big deal with low production runs, but Lotus were making thousands of these things so it would add pennies.

On the other hand, a simpler casting using less metal, would be cheaper on both counts - production & payment per pound. So you could well be on the money with the cost ! 

[LotusJoe]

Completed the Upright scan today!

I also weighed the stock carrier and it is 2.4 lbs.