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Suspension rocker/ bell crank question
dan8400 - 12/5/14 at 07:42 PM

Hi everyone

I am making some suspension rocker arms for a single seater. Do I need to mount them on bearings or can I use a bush of some sort?

Thanks
Dan

[Edited on 12/5/14 by dan8400]

bi22le - 12/5/14 at 07:57 PM

JPSC cars used to be on bushes and were changes to roller bearing to reduce wear and cope with the excessive forces going through them.

By excessive I mean more than required. Do a search and you will see that inboard suspension and rocker arm style trick stuff has its faults.

dan8400 - 12/5/14 at 08:14 PM

These are what I want

http://img832.imageshack.us/img832/350/ra15.jpg

I have this chassis. Bought it second hand (although it's NOS). Can't get hold of the company that made it for parts though. So I am unsure how the rockers are bushed/bearinged up

Thanks
Dan

adithorp - 12/5/14 at 08:24 PM

Most Fury's are on nylon bushed rocker arms. Problems have arisen where the pivot has seized/corroded; One of mine went tight after the first year. Adding a grease nipple and regularly checks and service cure that. 6 years of use and I've had no further problems.

Some have been converted to needle roller bearings, though there are reports of them failing prematurely, as the range of motion in the rocker is limited and the load is constantly on the same bearing.

dan8400 - 12/5/14 at 08:28 PM

So by adding a grease nipple you can use nylon bushes no problem?

Which grease do you use? I have a grease gun

Thanks
Dan

Sam_68 - 12/5/14 at 08:36 PM

The image you picture is just a 'rocker' rather than a 'rocker arm' (the latter tends to imply a rocking wishbone, a la Sylva or Lotus 25).

That arrangement tends to develop some axial thrust, which needle rollers on their own can't cope with.

You need to use either a taper roller bearing (which tends to be quite heavy/bulky), or a combined needle roller/needle thrust bearing (eg the Nadella), which are expensive, hard to source (though you can get separate needle roller and needle thrust bearings and use them in combination) and tend to develop 'flat spots' through excessively loading just 2 or 3 of the needles, or else you use DU style shell bearings and thrust washers and replace them regularly as a 'service item'.

Nylon bushes, as used on the rocking wishbones of some (most?) Sylvas and Fishers won't last two minute on a rocker (pushrod/pullrod) set-up.

You pays yer money, and you takes yer choice... as bi22le suggests, there's no perfect solution.

dan8400 - 12/5/14 at 08:38 PM

I have seen the nadella bearings and, yes, they are very expensive

Did you look at picture I posted? Just wondered how they mounted that. Just looks as if it's bolted straight through the chassis

Not saying that would work just trying to fathom out how they've done it

Thanks
Dan

dan8400 - 12/5/14 at 08:39 PM

quote:
Originally posted by Sam_68
The image you picture is just a 'rocker' rather than a 'rocker arm' (the latter tends to imply a rocking wishbone, a la Sylva or Lotus 25).

That arrangement tends to develop some axial thrust, which needle rollers on their own can't cope with.

You need to use either a taper roller bearing (which tends to be quite heavy/bulky), or a combined needle roller/needle thrust bearing (eg the Nadella), which are expensive, hard to source (though you can get separate needle roller and needle thrust bearings and use them in combination) and tend to develop 'flat spots' through excessively loading just 2 or 3 of the needles, or else you use DU style shell bearings and thrust washers and replace them regularly as a 'service item'.

Nylon bushes, as used on the rocking wishbones of some (most?) Sylvas and Fishers won't last two minute on a rocker (pushrod/pullrod) set-up.

You pays yer money, and you takes yer choice... as bi22le suggests, there's no perfect solution.



Edited to amend title error

Thanks
Dan

dan8400 - 12/5/14 at 08:49 PM

I take it something like this is no good?

http://www.bearingboys.co.uk/OB101316_Plain_Oilite_Bearing_Bush-3654-p

Thanks
Dan

adithorp - 12/5/14 at 08:52 PM

quote:
Originally posted by dan8400
So by adding a grease nipple you can use nylon bushes no problem?

Which grease do you use? I have a grease gun

Thanks
Dan


Sorry, wrote my reply based on the original title/info before you posted the bell-crank picture. No I wouldn't use nylon bushes for those.

dan8400 - 12/5/14 at 08:54 PM

Ok no problem.

Thanks
Dan

Sam_68 - 12/5/14 at 09:04 PM

quote:
Originally posted by dan8400
Did you look at picture I posted? Just wondered how they mounted that.


Yes, it may well be a DU bearing with DU thrust washers (in which case it may well be bolted straight through the chassis with a DU bush as a 'sleeve' and DU thrust washers either side... or with needle rollers/needle thrust bearings doing the same job), but people use all sorts of solutions - some completely half-arsed - so I wouldn't like to guess!

Personally, I wouldn't touch a nylon or poly bush in that application - you need a good long axial distance along the rocker pivot (as you have with the Sylva/Fisher rocking wishbone arrangement) to avoid excessive distortion of the bush with something as soft as plastic, but that's not to say that someone might not have tried!

FWIIW, I tend to prefer the DU bearing as a solution myself; slightly higher friction than a needle roller, perhaps, but it's cheap, simple, light and strong and doesn't 'flat-spot' like a needle roller can. I can accept arguments in favour of other solutions though - as I said, there isn't a perfect solution that stands out above all others, I don't think.

dan8400 - 12/5/14 at 09:07 PM

Thanks for that Sam


Thanks
Dan

Sam_68 - 12/5/14 at 09:10 PM

quote:
Originally posted by dan8400
I take it something like this is no good?

http://www.bearingboys.co.uk/OB101316_Plain_Oilite_Bearing_Bush-3654-p

Thanks
Dan


Yes, plain oilite bearings are another solution, though you'd need thrust washers/thrusts bearings to take the axial thrust with those, too, and I don't think their friction/wear characteristics are quite as good as DU bearings.

dan8400 - 12/5/14 at 09:10 PM

Good info Sam. Thanks