Magneto shield.

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Magneto shield.

Postby Invicta » Mon Sep 09, 2019 4:07 pm

Photo0569.jpg
I am rebuilding a basket case 1949 AJS model 18 and the magneto shield, if that is what this piece of steel is called , is bent as per the photographs. My question is did it start life in this state or has the bend has been caused by over tightening of the clamp bolts around the frame tube.
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Re: Magneto shield.

Postby Rob Harknett » Mon Sep 09, 2019 7:22 pm

I am sure my mag shields have C clips round the frame tube with flat bar the other side. The guard flat against the bar flat. Could be your shield was fitted with C clips only and got bent. Try a test. Stick a piece cardboard on the guard. So it just buts up to the tube. Will it fit? clear the mag etc. Or does it need the indent round to go the tube for clearance? I could not refit a guard on one of my prewar bikes as Armours could not get the exhaust pipe bend right. If I fitted it, it needed to go higher up the front tube. All it would do then would be prevent air flow to the barrel for cooling.

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Re: Magneto shield.

Postby Invicta » Mon Sep 09, 2019 10:30 pm

Thanks for that Rob.
I can't try it just yet as the engine and mag are still out of the frame. I was taking it along with other bits to the powder coaters, and was going to straighten it first, but I think I will hang onto it until I can test fit it as you suggest prior to flattening it. What you say about it being fitted without a bar in place makes sense as it does look as though the two "C" clips have been over tightened casing it to distort.

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Re: Magneto shield.

Postby Rob Harknett » Mon Sep 09, 2019 11:05 pm

Invicta wrote:Thanks for that Rob.
I can't try it just yet as the engine and mag are still out of the frame. I was taking it along with other bits to the powder coaters, and was going to straighten it first, but I think I will hang onto it until I can test fit it as you suggest prior to flattening it. What you say about it being fitted without a bar in place makes sense as it does look as though the two "C" clips have been over tightened casing it to distort.

Perhaps someone with the same model as yours will confirm Dave. 39 /49 has the same clip, but 49 shows the 38 no. has been given, also a 6 digit 49 no.
The bar and shield for 38 has old no's, but for 49 shows a new 6 digit no. only. Maybe in the morning I'll look and take a photo of my 38 for you to compare

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Re: Magneto shield.

Postby Rob Harknett » Tue Sep 10, 2019 2:18 pm

Only the clip has the same pt. no. for 1938 & 1949. This suggests to me, as the clip accommodates the down tube diameter, the plate should be bent to accommodate any of the tube diameter. My 39 shield looks like yours inc. the hole for the mag AR cable. It is flat apart from the top bend. Not a good picture, but you should see the clips circle the tube. At the rear of the tube there is the flat plate then mag shield. I would still wait for a 49 owner to confirm if your shield should bend a bit to except the tube before you make it flat.
SDC15329.JPG
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Re: Magneto shield.

Postby Invicta » Wed Sep 11, 2019 9:02 pm

Thanks for the information Rob. I am missing the flat bar that goes between the shield and the clips. Could you please let me have the dimensions from yours and I will make one. Incidentally the shield on my 1950 model 18 is made of aluminium and is held in place by one "C" clip and also has a hole for the Mag Ht lead to pass through as well as one for the mag AR cable. It has the flat bar that matches the flat part of the "C" clip. The base of it sits on the mag platform plate so one clip is enough to hold it in place as it can not twist.

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Re: Magneto shield.

Postby Duncan » Mon Sep 16, 2019 9:47 pm

Hi David

I have just had a look at the shield for my 1947 16m, the crease between the mounting bolts is present on mine as is a bend on the adjacent timing side of the shield but this might be damage rather than intentional, I also have the backing plates these also have a slight bend in the middle of them they are approximately 3/4" wide, 3" to 3 1/16" long and approximately 3/8" deflection, the bolt holes are slotted along the line of the plate 90 degrees to the bolt slots in the shield.

The pipe clamp that goes around the frame is some 1 1/4" deep, 1 3/8" across and its feet are slightly bent back.

It is difficult to say if all of the parts were designed this way or started square and have been bent in use but the clip may be too shallow if the back bar is square.

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Re: Magneto shield.

Postby Rob Harknett » Mon Sep 16, 2019 11:54 pm

Invicta wrote:Thanks for the information Rob. I am missing the flat bar that goes between the shield and the clips. Could you please let me have the dimensions from yours and I will make one. Incidentally the shield on my 1950 model 18 is made of aluminium and is held in place by one "C" clip and also has a hole for the Mag Ht lead to pass through as well as one for the mag AR cable. It has the flat bar that matches the flat part of the "C" clip. The base of it sits on the mag platform plate so one clip is enough to hold it in place as it can not twist.

The bar will match the clip in length also rads at each end. See from my pic. nothing is visible as the clip hides it. Bar thickness the same as the clip. Two clips will prevent vibration. Vibrating metal could damage cables, Even through the holes should have ring groments to stop this.

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Re: Magneto shield.

Postby SPRIDDLER » Tue Sep 17, 2019 4:11 am

If it helps at all here's the best pic I can find of my '47 Model 18 shield. The one owner before me was an AMC dealer so very original.

Mag shield.JPG
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Re: Magneto shield.

Postby Rob Harknett » Tue Sep 17, 2019 10:57 am

SPRIDDLER wrote:If it helps at all here's the best pic I can find of my '47 Model 18 shield. The one owner before me was an AMC dealer so very original.

Mag shield.JPG

The fitting looks the same as, also position fitted as on my 1938 AJS Nevile. Also your cover has just the AR cable hole as mine. My cover as yours shields the spark plug cable and fittings. I am missing the rubber gromet for the AR cable hole. To prevent water flow down the cable.

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