prawnabie
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| posted on 22/1/16 at 11:34 AM |
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If enough people report the posts hopefully the management will let the "Gibbs" axe fall on both of them (or the one of them - I do have
my suspicions!)
Back on topic, do you have a date when the pans are going to be made available, I fancy building one of these as a side project to the Herald
restoration!
Thanks,
Shaun
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Neville Jones
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| posted on 22/1/16 at 12:51 PM |
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I've just taken the time to search the bearings and do the numbers for Dereks little 600cc car.
Front corner weights will be about 110kg's max for an all up of 450kg's. (I'll keep forces and weights in kg's, so the
majority of readers can understand readily, although in engineering calcs these should be Newtons) I'll round out some of the numbers for
simplicity.
If we assume a wishbone length of 500mm, and a pushrod angle of 40 degrees to the horizontal then the pushrod will have a compression load of about
170 kg's. We double this for shock loads, so 340kg's. This is the push on the rocker. We have to make an assumption on the rocker ratio,
as this affects the load on the rocker central pivot. At 1:1, this gives a load at the rocker pivot of about 960kg's, with the coilover load and
reaction added.
The pushrod moves up and down relative to the rocker, so an assumption of the angle again has to be made. Say 5 degrees. This is to estimate the side
thrust loads on the rocker. But, the load acting at this angle is the pushrod 340 kg's. so, about 30 kgs. (The coilover stays coplanar with the
rocker.)
A needle roller to do the job will cost about £5~£6. a pair of thrust bearings will be about the same again, then about £4 for a proper needle inner.
So, about £16 for the bearings.
The 32002RS bearings are £18+ on the i'net, and a couple of £'s cheaper if you get the metal shielded items Two of these per rocker then
costs at least £32.
Then you've got the extra work to make the bearing sections, which is straightforward for the needle, with a straight bore and a couple of
circlips; not quite so for the double double angular contact bearings.
I've been through this design exercise a number of times, and keep coming up with the same end result, taking into account material costs and
labour.
Then there's the added complexity of the double bearing setup, and not to mention the added weight of the bigger housing for the double double
bearings and the bearings themselves.
For his purpose, Dereks sphericals with maybe the thrusts top and bottom will do the job satisfactorily, with good lubrication. And do it in a light
and economical, cost effective manner.
The numbers above for loads are quick and approximate but shouldn't far off.
Cheers,
Nev.
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Sam_68
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| posted on 22/1/16 at 01:48 PM |
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The DU bearings I recommended for Derek's application (budget, low-mileage race) are typically about £0.70 each, from memory. You can get them
as plain bushes, top-hat bushes, or thrust washers. Their wear and friction is comparable with spherical bearings, but they're not suitable for
any application in which you need to accommodate some mis-alignment (which you don't with a rocker pivot)
Throw 'em away after each hillclimb run, if you like, and your bank account probably still won't notice the difference. They're also
much lighter, much neater and much simpler than any other solution.
As previously stated, needle rollers are the usual solution for race cars, but they tend to have limited life: the individual needles flatten and so
flat-spot the bearing under the localised loads and limited range of rotation you get with a rocker. Fine for a race car, where you can rely on the
components being 'lifed' and regularly checked, but not so clever for a road car, where 'servicing' in most people's
mind consists of an oil and filter change every 12K miles. Decent quality needle rollers - like decent quality rod ends - also tend to be
rather more expensive. Hence for road-gong applications I prefer something with service qualities closer to those you'd expect for a wheel
bearing.
For what it's worth, if I was going to use sphericals, I'd use a pair in the form of, erm, spherical bearings (rather than rod ends),
housed in the rocker rather than mounted to the chassis (so that the chassis mounts could just be a pair of tabs like normal wishbone mounts, with a
bolt though the rocker assembly. Slightly increases the inertia of the rocker assembly, but looks a damned sight neater than
'free-standing' rod ends fixed to the chassis.
You pays yer money, and you takes yer choice, but the optimal solution depends on application. 
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Badger_McLetcher
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| posted on 22/1/16 at 07:03 PM |
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quote:
Originally posted by Sam_68
The DU bearings I recommended
I wouldn't recommend Depleted Uranium for bearings personally, it's quite heavy and tends to catch fire 
If disfunction is a function, then I must be some kind of genius.
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