MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - 1500 Thrust washers (again)

Hi everyone,

Sorry to bring this topic up again but...

1. I've discovered, through John initially and now through all the suppliers that replacement thrust washers use copper as the bearing surface? Does anyone know why? I was amazed as I expect copper to wear faster than white metal.

2. If forced to use copper, does that change the min clearance needed, with STD I have 7-8 thou clearance - Is that okay? should I be reducing that to 2-3 thou with a +5?

3. Does anyone know if I can still get white metal thrust washers? If so where?

Also I'm struggling to find +5 thou washers so John if you're reading this can I appeal to you again, I'll pop a message on the old thread too just in case.

Thanks in advance
Christian.
C L Carter

Copper is actually harder then white metal.
Alex G Matla

Yes - which means it doesn't perform well under elastohydrodynamic lubrication... which is what these thrusts are going to get... you need to force a deformed oil film (IMO) to keep these seperated... if you want hard... put steel in there!

C L Carter

Christian,

Out of interest, what is your background? You are clearly into your engineering. I did tribology as part of my degree a few years ago but have since forgotten it all! Clearly not the case for you.

Malcolm
Malcolm Le Chevalier

I did Mechanical engineering at Uni a year ago... I also did a tribology course - and I remembered some of it =]

I also did a lot at Uni with vintage vehicles (much older 1916-1926)

This copper idea is just confusing me, its almost like they made copper thrusts and forgot to tin the white metal to it.
C L Carter

They're copper faced on the 1275 too Christian. Maybe the materials available back then, were why copper alloy was chosen.

Read this.
http://www.customthrustwashers.com/custom_thrust_washers_002.htm


Here's another interesting piece on thrusts.
http://www.4secondsflat.com/Thrust_bearing_failures.html
Lawrence Slater

Well if I can't get anything else, then thats what it has to be I guess.

I don't understand your first sentence Lawrence - you're not suggesting they weren't able to alloy copper back then, are you?

As for the links, yes interesting, not sure I aggree about the material in the first link (although he isn't talking directly about the 1500 engine)

The second link pictures a white metal thrust face.

There must be a reason for not using a whitemetal thrust face. Perhaps its just cost! But I doubt it.
C L Carter

Presumably most of the time these thrust surfaces are just locating, and very lightly loaded, if at all. Only when the clutch pedal is depressed is there any significant load, and that should only be for a second or so at a time. I wonder if this has any material bearing on the choice of the bearing material?
Guy

Well, if you just got out of Mech E school, you ought to have learned something about materials. But, it wouldn't be the first deficiency of such schools.

They are not "copper", but some form of bronze, of which there are many, and many specifically for bearing materials. They are generally leaded. They tend to have much greater load bearing capacity than "white metal", itself a nebulous bunch of soft bearing alloys. Given that these things are known to be failure prone due to overloading, it would seem to be sensible to have changed the material. "White metal" is very soft, cannot take impact, and depends entirely on a good oil film for its continued existence. Some cars use "aluminum" Thrust (and other) bearings, also "white" but not "white metal".

These thrust washers do not carry a constant load, but are subject to some degree of impact, and they cannot establish a decent hydrodynamic film, so the harder material seems appropriate.

Clearance can be the same. Tight clearances are usually given in order to reduce time before they become excessive and let the washers fall out. The harder material should let you use greater initial clearance without this problem coming up too soon. I'd still try for .003, but don't let it keep your car off the road all summer!

FRM
FR Millmore

FR. I always thought the term "copper alloy" included bronze?

Hi Christian. No not suggesting that. I was suggesting that, maybe, copper alloy was chosen for want of a better material.


Lawrence Slater

Lawrence-
Indeed it does, but all references here were to "copper" except one of yours, and a sideways reference in Christian's response to you.
The term "copper" is normally reserved for pure copper, or a few low percentage alloys, usually stated, as "beryllium copper" or "chromium copper". Higher percentage alloys are referred to as "Brass" or "Bronze" depending on what other elements are used, but there is frequently no clear division between them. Most "copper" (red or yellow) coloured bearing materials are formally classed as bronzes.

FRM
FR Millmore

Right, well I haven't got my hands on one yet, I've just been told by 3 sources that they are "copper"... if they are infact bronze, be it phozzy or leaded I will be much happier.

C L Carter

Since what one is trying to combat is forward movement of the crank when the clutch is applied, I used to swap the thrust washers over. Putting the rear one which hardly wears at all in place of the front one. There is also no reason why one shouldn't mix one oversize with one standard, if that is what is needed to keep within the 3 thou or whatever it was.
Guy

Well I've received my new STD ones and thanks to John I now have a +5 too.

From visual appearance they are not any bronze that I'm familiar with and I've worked with Phozzy 1 and Leaded Bronze... SAE660. This really is a copper like coating in appearance. Whatever it is, it is a very thin coating on a steel washer. My plan is to check them after a year or 2 and see if there is any coating left.





C L Carter

Christian -
It is possible that the surface - what you are looking at - actually is pure copper, but it would be a few atoms thick, applied as a flash anticorrosion coat, or an artifact of processing. The grooves in the face are usually machined, exposing the steel and the interface with the bearing facing material, a common place for corrosion to start. This is likely done on flat sheets, before they are stamped out, so the sheets may sit around a while. This might explain a deliberate flash plating. Also, metals will self plate in the right solution; FI, iron in an acid solution that also had copper in it will self plate with copper. This would happen if the machined sheet were processed in an acid wash after machining.

A second possibility is that the supposed bronze has been surface modified in a similar but reversed process, which leaves a very thin layer of pure copper by removing everything else. The process is referred to as "depletion gilding" in the precious metals realm, where a thin layer of pure gold or silver can be produced on a low alloy base material.

Both the depletion gilding and the flash self plating can easily occur in the same process. I've done this by accident, very annoying on jewelery work, but useful sometimes.

Estimating layer thickness by eye in stamped laminated material is very deceptive. The top layers smear down over the lower ones. As example, looking at a US 25 cent piece edge, it looks like the "bottom" (as stamped) layer of nickle is 30-60% (variable around the circumference) of the thickness, with the center copper layer the balance, and the "top" nickle layer not visible at all. Actually, both nickle layers are the same thickness, and the total is about 92% copper and 8% nickle. So, to get a worthwhile idea of thickness of layers, you have to cut without smearing into the cross section of the part.

You might try asking the manufacturer, but they may consider the material and construction as proprietary.
At a guess, I'd say the bearing material is around .030".

FRM
FR Millmore

This thread was discussed between 22/05/2012 and 25/05/2012

MG Midget and Sprite Technical index

This thread is from the archives. Join the live MG Midget and Sprite Technical BBS now