Commando Cradle Reinforcing

lcrken

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I was rummaging through my accumulation of Commando engine cradles yesterday, looking for a replacement for the 750 I'm rebuilding, and ran accross several that had been reinforced for road racing. I'm showing them here just to show the variety of techniques folks used in the '70s and '80s. They all included welded on nuts with bolts to lock down the swingarm pivot shaft. The first set of pictures shows them in a row, with a stock cradle at the right hand end.

Cradles in a Row Rear 1200.jpg


Cradles in a Row Front 1200.jpg


Cradles in a Row Top 1200.jpg


To show a little more detail of them, I'm including a couple shots of the second from the left cradle above. It's interesting in that it has reinforcing bars on both the left and right side engine mounting lugs. I've only seen the one on the right side break, so that's all I ever reinforced on my bikes. This one is also the only one I've seen with an added cross tube at the bottom. Plus, it has a partial needle bearing swingarm conversion, where the stock bronze bush i left in place, but shortened, and a needle bearing pressed in next to it. That's not shown in the pictures, but I thought it was an interesting approach. It's the cradle that was in Fred Eiker's racing Commando, for those that know Fred.

Racer B Cradle 1 1200.jpg


Ken
 

Fast Eddie

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Great pics Ken, thanks for posting.

When I first rebuilt my Commando Norman White converted the swinging arm pivot tube to cotter pin, other than that I left it stock and never gave it a second thought.

But later when I had it apart again it really struck me how unsupported the whole, swinging arm pivot tube is. There is a LOT of potential for flex there. Not that it’s an issue for me and how I ride, but I can see why racers would do as they have in those pics.
 

Chris

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Thanks Ken
Really an eye opener!
The swinging arm & cradle are so heavy you don't think of this area being unsupported. On my proddie a bolt in cross brace had been added. Just a little bit of rule bending. All that did was hasten the breaking of the area around the bottom engine mount. When I had it repaired I had it strengthened a bit. Looks like I could have gone a lot further.
I tried to buy one made in alloy (like Ludwig) for my road bike. I wonder what other attempts have been made to alter this area.
 
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The one in the middle looks like it would be the strongest. Has anyone run up an entire cradle out of higher grade steel?
 

lcrken

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I've seen several made out of 6061 aluminum. Not likely to see one out of 7075 because it is not a weldable alloy. Might be able to come up with a bolted-together design using 7075. The problem with making them out of aluminum is that the plates have to be thicker if you want the same strength, so you aren't saving as much weight as one might think. I was at one point planning to make a cradle from 6AL4V titanium for the restomod MK3 I'm building. I needed a special pattern to accommodate the electric starter conversion (Old Britts partsI was using. I had the material and drawings, and had a water jet guy who was going cut the plates out. But when I discovered that Old Britts had a batch of steel ones made, and still had one on the shelf, I bought it instead, saving a lot of time and effort. I'd still like to do the ti one someday, but I'm starting to run out of somedays.

This is a picture of an alloy cradle made back around 2005 by Les Loudon, shown before welding.

Timing Side 1 1200.jpg


Ken
 
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I once looked at a Commando frame when I was thinking about building another race bike. It looked all too difficult to me. I think you always need to decide what you are building - a race bike, or a road bike - because once you start, the road back is often very expensive.
 
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