7 replies to this topic

[Kerrin]

Have been stripping the rear subframe off the car due to some rust on the boot floor.

I decided to strip the subframe down and check it all over and give it a paint up while it was off the car. When the radius arms were removed there seems to be no needle rollers in the inner end, just another bronze bush, the pivot pin is quite worn and damaged but strangely the wear looks like is from needle rollers, so the pins must have been re-used. There is no play in the bushes even with the worn arms, and using some good spare pins it is perfect.

Are these arms wrongly re-conned, are they ok to use? The car was used for autotests for the last 5 years before I bought it but done very little milage and it has stood up to that fine so far.

The radius arms are different to my other car, the handbrake quadrant is held on by a lock nut on a stud not a pin and split pin the diameter of the outer end of the radius arm near the outer mount also steps down for the last two inches not tapered. Are these early arms?

I have done lots of searching and not found anything yet!

Edited by Kerrin, 11 October 2010 - 06:15 PM.

[Big_Adam]

I believe DKLawson once said about people who knew who just reamed the whole arm out and put on long bushing rather than bearings etc.

Might be worth asking him about bushes and bearings.

[jayare]

It's not uncommon for cheap reconditioned arms to have two needle rollers as it does away with the need for reaming the bush after fitting, but the loads are not ideally suited to needle rollers. Two bushes should be fine with new pins as long as they have been correctly reamed, but make sure you keep them greased,

JR

[Kerrin]

BA Thanks for that, It may well be one long bush I will give it a clean out and see.

jayare I was looking for the post about the cheap recon arms as I couldnt remember if the needle rollers were the issue or the bushes, that is a relief>
It sounds like they are fine to re use.

The other mini, (with the 4 spotties) had one completely shot arm with loads of play, the needles had failed and eat into the casting, no way it would be any good to recon for this mini.

Edited by Kerrin, 11 October 2010 - 06:36 PM.

[dklawson]

Adam is correct that I know of some people who have bushes at both end of their car's radius arms. This was not done as a cheap rebuild, it was done as a way of increasing the load capacity for racing.

Needle bearings have low friction just like ball bearings. However, the rollers represent several discrete points of contact between the shaft and the arm. The contact stresses at those points are very high. You can see the effect on old radius arm shafts where even with proper lubrication the shaft is worn and/or peened by the needles. Bushings spread the load out over a larger area and thus minimize the contact stresses. Why BMC chose to design the arms with needle bearings on one end is beyond me.

Regardless, it is often possible to put new shafts in older arms and find most of the play is gone. It certainly pays to check the play by fitting a new shaft to an old arm before committing to fit new bushings/bearings.

[Kerrin]

Adam is correct that I know of some people who have bushes at both end of their car's radius arms. This was not done as a cheap rebuild, it was done as a way of increasing the load capacity for racing.

Needle bearings have low friction just like ball bearings. However, the rollers represent several discrete points of contact between the shaft and the arm. The contact stresses at those points are very high. You can see the effect on old radius arm shafts where even with proper lubrication the shaft is worn and/or peened by the needles. Bushings spread the load out over a larger area and thus minimize the contact stresses. Why BMC chose to design the arms with needle bearings on one end is beyond me.

Regardless, it is often possible to put new shafts in older arms and find most of the play is gone. It certainly pays to check the play by fitting a new shaft to an old arm before committing to fit new bushings/bearings.

Thank you for your comments, I have two mini's (see pic) and this one is gradually turning into a weekend toy/track car, leaving the other one more standard. so these arms will be fine to re-use. Great news.

The radius arms did not appear to have any play at all before I stripped them out of the sub frame, but the pins do have some wear and are peened by previous use with needle bearings. I will replace them with some spare unworn pins when it is built back up.

Saves a lot of work

[Kerrin]

As a bit of an update, I cleaned up the radius arms ready to re-fit on the car.

They are different to the normal radius arms, as in they have a flat steel handbrake quadrant mount and a nyloc nut rather than a pin through the cast of the arm.

Are these MK1 arms? they were on the car when I got it and its a 81 car? they appear to be cast iron. Are most Mk1 arms steel?

[Dan]

Early arms are fabricated from several parts made from sheet steel.