Short lived aluminium pressure plate.

Reggie · Jul 2, 2009

I have received an email asking for advice from a friend whos runs a Commando 920, whos aftermarket "aluminium pressure plate .050" thicker than standard" has worn away in a very short time..500 miles. I notice in another thread by bigstu, that he says avoid the aluminium pressure plates. I have copied the email that I have received below so that you can get a full picture of events.

Does anybody on the forum have any experience of these plates, and was it good or similar to my friends? Also, is it likely to be excessive heat from slipping that caused this?

Update for my Norton clutch :-
Got it all apart now (bear in mind this clutch was completely new, and only did about 500 miles.)

I'd thought the prob' (started slipping again....) must have been because of the oil that was getting into the primary from the poor crankshaft seal / clutch pushrod, and maybe it's got something to do with it, I don't know, but... when I got the diaphram spring off, I could see that the clutch basket was full of aluminium "paste"... I had to prise out the pressure plate, & each of the plates individually, as they were stuck in with alu' gunge!

The Al' had come off the inside surface of the thick pressure plate! - across it's complete surface, but how / why? - any ideas?

The 1st plate in, ie. the 1st in after the pressure plate is a Surflex one, and it's surface had picked up loads of the Al, ie. really quite suprisingly thick on the surface of the surflex plate in most places, where it had picked up Al from the pressure plate... but had it rubbed the Al off it? - or just picked it up after it had been rubbed off?

The other plates were OK - sods to get out due to all the Al gunge, but relatively OK.
The other surflex ones looked like they'd been soaking in oil (probably this knackers them? - I'm not sure) but were free of Al.
The steel plates looked slightly discoloured maybe... ie. not bright (maybe excess heat?)

I've no ideas as to why the Al's been taken off the pressure plate.

bigstu · Jul 2, 2009

Hi, Stu here..
I did say avoid the aluminium pressure plate, only because I have heard from a number of folk that it doesn't work well.
I have no experience of it personnally but I do have experience of the steel one, it works well.
I know one thing. When I am designing machine tools, I would not use hard anodised aluminium as a choice of material for a fast sliding component with heat. The depth of hardness is not acceptable, neither is the chemical composition. If you want to know what aluminium is llike for picking up, look in the slide of an amal carb! Steel is better. Cast Iron could be even better. Save weight by going on a diet!
You can buy the steel one instead of the aluminium one from RGM, I gave someone the part number a while ago on this site.
Stu.

bigstu · Jul 2, 2009

One further point. I see this person is running dry....I bet the ali plate runs better in oil. So if you use sureflex plates but not running dry I bet the life is better. Still wouln't go for one myself.
Stu.

swooshdave · Jul 2, 2009

bigstu said:
If you want to know what aluminium is llike for picking up, look in the slide of an amal carb!

I don't think the Amals are aluminum.

Cookie · Jul 2, 2009

My opinion is much like Bigstu's. The only way I'd use that would be in a racing situation where you throw everything away in 500 miles. Racing bits are not always the best stuff to ride off the track. In oil it probably would last better but why bother?

Seeley920 · Jul 2, 2009

I use the ali pressure plates in both my bikes...BUT...I machine the thickness of a plain steel plate off the back, and insert an extra steel plate last, then the pressure plate, no problems as the ali and extra steel plate turn together. My fibre plates are on their 4th season's racing with almost no wear...I just strip it and blow out a little dust at the end of the season.....oh and it is running dry!

swooshdave · Jul 2, 2009

Seeley920 said:
I use the ali pressure plates in both my bikes...BUT...I machine the thickness of a plain steel plate off the back, and insert an extra steel plate last, then the pressure plate, no problems as the ali and extra steel plate turn together.

That sounds like the logical solution. Steel turning against aluminum sounds like a bad idea.

The good news is that the friend's aluminum plate is probbaly thin enough now to try the two steel plates. :mrgreen:

marinatlas · Jul 3, 2009

Hi there, got the same situation, with that beefy alloy pressure plate in few hundred miles on a fast road going 920 , belt drive cdo, and now as it had been "eaten" , have it turn down and put an extra steel plate right after , will see what happen then, I am interested into , as I had to fit in my next project , the belt drive made by a friend of mine ( Dan Parker, based in Sussex) which have the normal alloy centre hub from a cdo but the drum had been machined to accept outside plates with outside lugs as the one on Featherbed clutches, and so the pressure plate had lugs too and is alloy, so i think I will fit a steel plate right after this alloy pressure plate instead of a fiber one, of course will try to play with the thickness of all plates to just arrive to the good measurement for the stack height

Reggie · Jul 3, 2009

Thanks for the replies.

It would seem then that the solution is to put the original steel pressure plate back in with an extra steel plate to keep the clutch light, or turn down the alloy pressure plate the thickness of a steel plate, and then add a steel plate directly behind it to stop the wear issues :!:

bigstu wrote;

I would not use hard anodised aluminium as a choice of material for a fast sliding component with heat. The depth of hardness is not acceptable, neither is the chemical composition.

With the evidence of my friends clutch, I couldn't argue with your reasoning.

bigstu · Jul 6, 2009

Just a quick reply to Swooshdave.
This is my reply from Burlen Fuel sytems, the manufacturer(?) of amals
You are correct to question the material amals are made from.....The term I have heard used in the Uk many times is 'monkey metal'. I assume this is not a term of endearment.

"Unfortunately we are not privileged to such top secret information! Seriously though, they are both now made in a form of Aluminium alloy, maybe Zinc content" (Quote from Burlen)

I believe they are correct. The bodies are made from what some people call 'zinc alloy'. It is in fact an aluminium zinc alloy.
So I feel I am correct in stating that Amal carbs are made from Aluminium.
It is interesting that I believe Mikuni carbs are not made from an aluminium zinc alloy, but a better grade of aluminium alloy.
I wonder if this is why they last longer? Is it the zinc content that makes Amals wear so bad?

Stu.

swooshdave · Jul 6, 2009

bigstu said:
Just a quick reply to Swooshdave.

"Unfortunately we are not privileged to such top secret information! Seriously though, they are both now made in a form of Aluminium alloy, maybe Zinc content" (Quote from Burlen)

My best guess is that it's a zinc alloy, with a small percentage of aluminum.

I wonder if this is why they last longer? Is it the zinc content that makes Amals wear so bad?

Stu.

I've always heard that it's the same material on the body and slide which causes the wear, which is why chromed slides or brass sleeves are so popular. That, and it's a zinc alloy which is not the toughest material in the world...

kebra · Jul 6, 2009

I experienced too, the ultra fast wear of anodized plate,
and unfortunately after that, the sleep of the Barnett kit, this kit contain normally one plate less
but each one is more thick but not enough on my bike.
So I still not have a solution for a smoother clutch lever.

littlefield · Jul 6, 2009

I bet the zinc alloy was selected as much for easy casting of the thin sections as for good material properties.

Reggie · Jul 6, 2009

kebra wrote;

but each one is more thick but not enough on my bike.

Have you tried putting two plain metal plates together in the clutch to raise the stack height?

Keith1069 · Jul 6, 2009

this kit contain normally one plate less
but each one is more thick but not enough on my bike.
So I still not have a solution for a smoother clutch lever.

Have done a few of these on 750's and what works every time is 4 steels, 4 Surflex and the standard thick steel 750 pressure plate. With a nylon lined cable (Venhill nylocable) the clutch lever action is positive and light (two -three fingers). Have you tried this set-up?
If you want truly featherlight action you can use a Dominator actuating lever but the travel is reduced and neutral finding not so good.

JimC · Jul 6, 2009

The Venhill cable probably contributes 90% to reducing clutch pull. Great little "invention".

kebra · Jul 6, 2009

Keith1069 said:
Have done a few of these on 750's and what works every time is 4 steels, 4 Surflex and the standard thick steel 750 pressure plate. With a nylon lined cable (Venhill nylocable) the clutch lever action is positive and light (two -three fingers). Have you tried this set-up?

Thanks I will try this solution asap...

bigstu · Jul 7, 2009

I agree with Kebra and JimC
I use a Venhill 'featherlight' tethlon lined cable and sureflex plates. I bought the thicker steel plate from rgm, rather than the aluminium plate. I guess the thicker steel plate I bought is a std 750 pressure plate?
My clutch is also 2 fingers...no slip or drag.
Stu

rbt11548 · Jul 8, 2009

kebra said:
Keith1069 said:

Have done a few of these on 750's and what works every time is 4 steels, 4 Surflex and the standard thick steel 750 pressure plate. With a nylon lined cable (Venhill nylocable) the clutch lever action is positive and light (two -three fingers). Have you tried this set-up?

Click to expand...

How thick is the standard 750 pressure plate?, when I pulled the cluctch off my Mk3 the PO had fitted 4 sureflex & 3 steel, I have 4 & 4 now but not sure what pressure plate.
Thanks

mike provence · Jul 8, 2009

Ladies and Gents,

We've got two discussions going here. As far as mkI Amals are concerned, the carbs are cast from die-cast zinc. Die-castings are expensive and most aluminum parts of our old bikes are made from low precision sand-cast aluminum.

Die-casting is higher precision than sand-casting, but dies are expensive. The sad fact is that dies for zinc casting cost half what dies for aluminum cost. So some Amal accountant ca 1965 decided to pay for cheap dies for soft zinc, instead of expensive dies for longer-wearing aluminum alloy.

Our quickly worn out carbs over the past 45 years are the result. Steel sleeves are the solution.

Short lived aluminium pressure plate.

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