Monoshock Commandos

There's been a lot of discussion on this forum about grandpauls adventures with building his monoshock Commando, everything from accolades to pretty much calling it a death trap. I just wondered if people are aware that Norton built and raced their own monoshock John Player and Gulf sponsored F750 racer back in 1974? There's a picture of it in Roy Bacon's book, with Dave Croxford on it, and a brief mention of it in Mick Wollett's book. Mick says that the bike was originally designed for the Cosworth Challenge, but was fitted with a Commando engine because the Cosworth wasn't ready in time. As far as I know, all the other F750 bikes, including the down-sized Commando style, the monocoque, and the space frame used isolastics. I'm curious if the monoshock also used them. Does anyone on the list know more about this bike?

Ken

lcrken said:

There's been a lot of discussion on this forum about grandpauls adventures with building his monoshock Commando, everything from accolades to pretty much calling it a death trap. I just wondered if people are aware that Norton built and raced their own monoshock John Player and Gulf sponsored F750 racer back in 1974? There's a picture of it in Roy Bacon's book, with Dave Croxford on it, and a brief mention of it in Mick Wollett's book. Mick says that the bike was originally designed for the Cosworth Challenge, but was fitted with a Commando engine because the Cosworth wasn't ready in time. As far as I know, all the other F750 bikes, including the down-sized Commando style, the monocoque, and the space frame used isolastics. I'm curious if the monoshock also used them. Does anyone on the list know more about this bike?

Ken

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NO, BUT BE CAREFULL! HE WASN'T CALLED ""CRASHER ""CROXFORD! FOR NOTHING :!:

Any pictures to post along with your writeup :?:

As far as I am concerned, loading or unloading the ISOs doesn't make the Commando more or less of a death trap, sure the handling could change, the vibration could be worse, but nothing lethal. I am sure the factory did far worse with their first "widowmaker" frames and all the "fixes" they came up with over the years. The Commando series still is an amazing motorcycle able to be modified and improved in many ways.

Jean

Jeandr said:

Any pictures to post along with your writeup :?:

As far as I am concerned, loading or unloading the ISOs doesn't make the Commando more or less of a death trap, sure the handling could change, the vibration could be worse, but nothing lethal. I am sure the factory did far worse with their first "widowmaker" frames and all the "fixes" they came up with over the years. The Commando series still is an amazing motorcycle able to be modified and improved in many ways.

Jean

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"Widow maker" frames .and riders called "Crasher" Not a good picture was it? Feather bed ,None isolastic and jeff Duke...now theres a another story :wink:

What really Pigs me off is guys on this Forum raving about the "great" handling the commando with is Rubber machine mounts gives...well you are all living is cloud cookoo land..infact 99 % of you have never riden one hard! Back in 1971 i had a susi 350 and my mate had a fastback. ..on many race's we had i have seen the Norton well out of shape. "Deca " would grind stands away with ease, Ask Hobit i recon he's been there!
Pottering down to the local pub[these days] at 30mph is no test! Riden hard the Commando will take no prisoners. Grand pauls Mono shock looks great. but i would like to see Gary Thwaite on board around Darly moor,,,Mayby Not :!:

Riden hard the Commando will take no prisoners

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Amend to that dear John, I have firmly sworn off trying to press a factory rubber baby buggy into its flopping fish off the deck states. I've piloted two mono's to out of control and ran Peel against very upset dangerous aggressive squids and have lost my respect for mono shocks or fat ass tires, plus the buzz bomb engine vibes that get though. Mono's are very interesting engineering but I only go by my ass and wrist strain G's meters so I'm very hard to please anymore. Would love to see what Norton crew came up with and why it didn't show up on market.

hobot said:

Riden hard the Commando will take no prisoners

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Amend to that dear John, I have firmly sworn off trying to press a factory rubber baby buggy into its flopping fish off the deck states. I've piloted two mono's to out of control and ran Peel against very upset dangerous aggressive squids and have lost my respect for mono shocks or fat ass tires, plus the buzz bomb engine vibes that get though. Mono's are very interesting engineering but I only go by my ass and wrist strain G's meters so I'm very hard to please anymore. Would love to see what Norton crew came up with and why it didn't show up on market.

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Steve, you are a real test pilot. i have great respect for you, I bet when you where 20, there was no living with you!

I'll be posting .jpg images of my raw CAD design and the best photos I have of the swingarms I built. As mentioned in the other thread, I don't believe the imposed loads on the isolastics are any different from those on a standard frame, and MAY be less. I do NOT run oversize tires in the rear, 110/90 only (others run 120s, not me).

I will admit, my monoshock bikes haven't been raced hard or even thrashed to within an inch of thier lives on gravel roads. I already have a race bike, and I've moderated my street behavior considerably after completing racing school and actually being on many race tracks. It's just not worth it on the street at excessive speed any more (not to mention the 3 times I've been clobbered). Also, none of the monoshock bikes I built were for racing.

I still maintain that the design is more than adequate, safe, and effective. Whether it's SUPERIOR can only be proven with two otherwise identical bikes and the same rider, on the same track. Any further criticism should be relegated to finite element / structural analysis.

I, too, would love to see detailed pix and information regarding the factory racing monoshock setup. Very interested to know whether they implemented any sort of rising rate linkage.

For what it's worth, Kenny Dreer's original prototype (I have the swingarm & cradle on my blue bike) has a rising rate linkage, "unconventional" to say the least. He had it configured with the shock laying down and bolted to a fabbed-up bracket UNDER the rear frame web, just under and behind the injectors. That bike never ran (dummy mock-up of the 952 engine), so the highest speeds it attained were walking speeds on and off trailers.

This is a never-before published photo that Kenny sent me-



You can JUST make out the upper shock mount here...

(also, check out the carbon fiber primary case, 1 of only 3 ever made, I have that on the shelf as well, very trick)

Ken, you were one step ahead of me on starting this thread; thanx.

The first iteration required a "notch out" of the upper left main unit due to the drive chain path.

Second iteration eliminated that leg, as the forward uprights had almost all the structure required to carry & distribute the loads with the right side upper main unit triangulating.

First prototype-



Second iteration-

Failed concept - forward box section didn't allow rising rate linkage sufficient space to rotate through it's full arc, stopped about 1" short of max available tire travel



All three in one place-

Chain notch-out on the second version...

john robert bould said:

What really Pigs me off is guys on this Forum raving about the "great" handling the commando with is Rubber machine mounts gives...well you are all living is cloud cookoo land..infact 99 % of you have never riden one hard! Back in 1971 i had a susi 350 and my mate had a fastback. ..on many race's we had i have seen the Norton well out of shape. "Deca " would grind stands away with ease, Ask Hobit i recon he's been there!
Pottering down to the local pub[these days] at 30mph is no test! Riden hard the Commando will take no prisoners. Grand pauls Mono shock looks great. but i would like to see Gary Thwaite on board around Darly moor,,,Mayby Not :!:

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Would agree entirely.............any bike which has a in effect a rubber mounted rear wheel, which is able move entirely independently of the frame is never likely to handle that great! As to a monoshock conversion on a rubber mount bike, this will certainly provide much improved rear suspension action, but will do little to address the lack or rigidity which results from the rubber mounts.

My monoshock adaptations were never designed or intended to deal with the poor design of the Commando rear end.

As to the widely known and understood inherent drawback to having anything besides a single snug rotating pivot joint in a suspension system at the swingarm pivot, rendering the commando less-than-optimum, the fix is virtually plug and play: rod joint steadies on the front and top mounts, and a slightly more difficult lower/rear rod joint steady.

As long as you limit the available range of motion of the rubber isolated joints to strictly fore/aft and up/down, (would necessarily have to be a triangulated system to properly address the triangulated isolastics), the result is as good as it gets on a Commando with vibration isolation. Short of that, you have to have rigid mounts and the transmitted vibration from the engine. You can address the engine's vibration with rods & pistons and crankshaft modifications.

El Carbono, not to worry Ms Peel retains all the rubbery C'do advantages in spades.
I would love to see how Dreer did his under slung shock, that definitely has some appeal to me and Peel. Just can't put any clutter up above the cradle. Peel will have back up swing arm sway bars to focus all her stretching and twisting in one place, her rear beefed rubber pivot. I've read the mono-coupe frames invited hi speed drifts but that don't impress me any more, only tolerating higher inward directed loads w/o loosing grip to cause hesitation in the leaned acceleration does.

Mono's sure clear up the rear view in C'do's w/o sticking their ass up like a dog in heat.

Carbonfibre said:

john robert bould said:

What really Pigs me off is guys on this Forum raving about the "great" handling the commando with is Rubber machine mounts gives...well you are all living is cloud cookoo land..infact 99 % of you have never riden one hard! Back in 1971 i had a susi 350 and my mate had a fastback. ..on many race's we had i have seen the Norton well out of shape. "Deca " would grind stands away with ease, Ask Hobit i recon he's been there!
Pottering down to the local pub[these days] at 30mph is no test! Riden hard the Commando will take no prisoners. Grand pauls Mono shock looks great. but i would like to see Gary Thwaite on board around Darly moor,,,Mayby Not :!:

Click to expand...

Would agree entirely.............any bike which has a in effect a rubber mounted rear wheel, which is able move entirely independently of the frame is never likely to handle that great! As to a monoshock conversion on a rubber mount bike, this will certainly provide much improved rear suspension action, but will do little to address the lack or rigidity which results from the rubber mounts.

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Ok I have to bite, how does a monoshock provide improved suspension action? Granted it could well be better than some stuffed old commando shocks but compare it to something new and I dont see any advantage at all

The entire mods to the frame involve two small tabs under the main tube at the web, with holes drilled through to bolt the top of the shock. It can revert to stock in an afternoon with nothing else done to the frame AT ALL.

The backside of the oil tank needs to be lightly pressed in to allow clearance if you use a relatively fat monoshock; a thinner shock fits as-is.

Of course, you sacrifice two stock swingarms to make the one mono unit, but they are still relatively easy to find. If I had the scratch, I could just fabricate my own uppers, but I found this easier to do and meat to look kinda "stock"...

john robert bould said:

What really Pigs me off is guys on this Forum raving about the "great" handling the commando with is Rubber machine mounts gives...well you are all living is cloud cookoo land..infact 99 % of you have never riden one hard!

Click to expand...

Given that Peter Williams has lapped the IoM on a Commando faster, 107.x mph, than any old featherbed bike, we'd have to suggest that the above is just a load of old cobblers.

Yes, a manx has recently done 108.x mph, but that has more to do with how much more hp the dohc can be coaxed to these days. If PW on a Commando had more hp, he'd a gone faster !!

Cheers.

Carbonfibre said:

Would agree entirely.............any bike which has a in effect a rubber mounted rear wheel, which is able move entirely independently of the frame is never likely to handle that great! As to a monoshock conversion on a rubber mount bike, this will certainly provide much improved rear suspension action, but will do little to address the lack or rigidity which results from the rubber mounts.

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Presumeably this is why the isolastics have quite strict instructions on how much /how little side movement thay are to be shimmed to.

Its not as though they have unlimited movement....