ET: Engine (Twin) steady plate question

vibrac

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I was asked a question the other day that I was not sure I knew the answer to...
Why is the steady plate on the twin not in steel like the single?
I mumbled about expansion rates and saving weight, but I am not convinced, I certainly know that the ability of the alloy plate to deform means you need to be even more careful about pillar and spindle heights and I know from the inside faces of alloy plates against steel ones some of the misalignment that occurs. I have a feeling that a steel plate with some tasteful metal removed (a bit like our racing Comet below )would do I better job
1583853257706.png
 

Vincent Brake

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steel would bend the spindles due to differ expansion to alu.
in your picture it would bend a bit as you are not having a steel beam from spindle to spindle, apart from right hand side.


but U are right, the alu plate i use has on both sides at a spindle a steel washer to create more surface, so one can nip up ALL spindle nuts TIGHT.
i file the holes to suit spindle position, it would keep positon due to nip up and GLUE of course, Locktite 243.

specially for the follower spindles, i do a 1,5 mm recess in the steady plate, and fill with hardend steel washer 1,5 mm thick.
cam spindles are OK with 5/16 to 1/2 inch.

cheers
 

GBewley

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The twin steady plates, being much larger, would expand much more overall from one die to the other than the singles, so was made of a aluminum to compensate. I believe Clevor Trevor once told me he used steel ones on the twins, and someone mentioned using steel ones which were split for the twins. This could have been Trev as well.
 

Simon Dinsdale

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Looking up coefficient of thermal expansion:

Aluminium = 21-24
Bronze = 18-19
Steel = 10.8-12.5
Stainless austinitic 304 = 17.3

So aluminium expands twice as much as ordinary steel, but bronze & stainless 304 are a lot closer to aluminium. Food for thought?

Simon
 

GBewley

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Doing a quick calculation on aluminum and steel, I find that with a raise in temp from 70f to 350f the difference in expansion over a foot would be that the aluminum would expand 0.032” more. This would certainly stress the spindles.

The bottom line is that I think, once again, that the designers had it right. I’ve never found a reason to vary from their choices.

Looking up coefficient of thermal expansion:

Aluminium = 21-24
Bronze = 18-19
Steel = 10.8-12.5
Stainless austinitic 304 = 17.3

So aluminium expands twice as much as ordinary steel, but bronze & stainless 304 are a lot closer to aluminium. Food for thought?

Simon
 

G.L. Winter

Forum User
VOC Member
My B model Rapide is fitted with a steel steady plate --I had the timing chest to bits a couple of months ago for the first time-- and I just assumed that a steel plate was the standard item. I'm wrong, I guess, and aluminium is the material of choice? Should I replace my plate with an aluminium one?
 

GBewley

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VOC Member
I would likely replace, but as I stated above, others have used them. I have at least one in my spares. I wonder if perhaps the factory started with steel ones and found that the expansion was greater than expected and changed to aluminum ones, but I don't know.

My B model Rapide is fitted with a steel steady plate --I had the timing chest to bits a couple of months ago for the first time-- and I just assumed that a steel plate was the standard item. I'm wrong, I guess, and aluminium is the material of choice? Should I replace my plate with an aluminium one?
 
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