Twin Engine Plates

Information relating to the Matchless G12 or AJS Model 31 650cc twin
TrevorCSR
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Twin Engine Plates

Post by TrevorCSR »

According to the parts book for 1960, there is a difference between the rear engine plates. One pair fit the standard G9, G12 and G12GL and the other pair fit the G12CS and G12CSR.

022291 Plate, Engine, Rear, Left G9 G12 G12GL
022292 Plate, Engine, Rear, Right G9 G12 G12GL

023643 Plate, Engine, Rear, Left G12CS G12CSR
023644 Plate, Engine, Rear, Right G12CS G12CSR

Does anybody know what the difference is?
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dave16mct
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Re: Twin Engine Plates

Post by dave16mct »

Didn't the CS have a round footrest rod? That would be one difference as the square holes on the engine plates prevent the footrests rotating on the road models.
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robcurrie
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Re: Twin Engine Plates

Post by robcurrie »

My '62 CSR has square holes for the footrest rod.
Might there be a difference for the twin down tube frame?

Rob C
TrevorCSR
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Re: Twin Engine Plates

Post by TrevorCSR »

Dave. I'm sure my 1960 31CSR has a square footrest stud. How would you stop them rotating? I know competition pegs fit around two frame tubes but I thought most CSRs had standard type footrests.
Rob C. I checked the 1959 parts book which has a single down tube. The part numbers are the same.
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dave16mct
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Re: Twin Engine Plates

Post by dave16mct »

No, it's the CS that has the round footrest rod, because of the comp footrests. I don't know why they gave the CSR the same pt number as the CS. Maybe it was an option to have comp footrests?
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Re: Twin Engine Plates

Post by TrevorCSR »

No, the CS does NOT NEED the round footrest rod BECAUSE of the comp footrests. Round rod or square, it makes no difference, CS footrests mount on the frame tubes.
BUT IF you wanted to fit ‘standard' footrests to a CSR you would have to change engine plates. that's not logical. There must be another difference between the two part numbers.
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ajscomboman
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Re: Twin Engine Plates

Post by ajscomboman »

I'd disagree Trevor, having 3 CS models and 2 CSR's it does make a difference. The CS foot rests do as stated sit over the bottom rails but the holes through the footrest match the holes in the frame and are designed so that the round rod fits snugly to ensure the rests do not rock around and are adequately supported. Using a square rod whilst in principle it works ok it's not as the makers designed it to be. The CSR's have a square rod and footrests that are broached to fit the square end snugly and pass through the engine plates with the square to ensure the rests don't twist under load.
hwilkinson
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Re: Twin Engine Plates

Post by hwilkinson »

According the parts books the 1960 G12 CSR had different left and right foot rests and same rod as CS, I assume round? The G9 G12 and G12 DL were different. In 61 they were all the same non-handed rests and rods except g80cs and G12cs. I think all plates had square holes and the round rod is a nice fit.

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ajscomboman
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Re: Twin Engine Plates

Post by ajscomboman »

You cant fit a round rod into the square engine plates it's a far bigger diameter.
TrevorCSR
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Re: Twin Engine Plates

Post by TrevorCSR »

I understand ajscomboman, the round rod is the same diameter as the across corners of the square bar. But if you wanted to fit standard pegs, you'd have to change engine plates as there is nothing to stop the square bar from spinning.
So, it seems AMC might have made a mistake in their 1960 spares catalogue! Only the CS plates are different with a round hole and the CSRs have the square rod?
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