Opinions Sought: Commando 850 in Featherbed
- Thread starter sns
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It's reasonably straightforward. Rebalance your crank to 78% and you can bolt it up solid. You can make a set of engine plates quite easily, or you can buy a ready made set from Unity Equipe in the UK....I'm sure people in the US make them too. It's up to you whether you want it to look like a dommi or a caff racer!
http://i588.photobucket.com/albums/ss32 ... 009101.jpg
http://i588.photobucket.com/albums/ss32 ... 009101.jpg
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Seeley920 said:
Before I rebalanced I'd try the lightweight rods and pistons. Not sure if you need to rebalance with those.
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RennieK said:
Rebalancing might move the vibrations around in the rev range but the lighter pistons are suppose to greatly diminish them. Considering how much someone put into an Isolastic Featherbead to reduce the vibration, a grand doesn't seem like much.
The reason the the lighter pistons reduce vibration in this scenario is because they altar the balance factor more so than reducing the reciprocating weight. Having your crank balanced is a lot more accurate a way to balance a motor and reduce vibrations than trying lighter pistons. Personally I would do both if I had the budget for the lighter pistons and rods.
sns said:
If you are thinking of having the engine tilted like a Commando, then Cookie has one, I have one too. I think Cookie bought his plates and I made mine, it's not too difficult to do and in my case even store bought plates would have needed some modification, wasted money for me. If you do decide to make your own, bear in mind the front ones must be made from 3/16" plate or have some milling done to make thicker plates fit. The back plates can be ¼" or more (5/16").
If on the other hand, you want the engine sitting up straight, then you can just copy the steel plates in alloy or carve the back plates to move the transmission forward so you can use a Commando primary drive and covers.
In both cases, you have room to put the battery behind the transmission, there is even a bracket sold by Clubman Racing (and others I'm sure) for that purpose.
Jean
RennieK said:
Sorry, but that is just wrong. Obviously the intensity of the vibes depends on the mass involved. The longer rod also helps reducing them as they rotate less the longer they are (which is the main factor for 2nd order vibrations).
There is nothing on a Norton Twin to reduce vibes unless you change the masses involved (and I don't mean the few grams you drill out for balancing). All the balance factor determines is whether the thing will shake up and down or back and forth. The human body is more sensitive to vertical vibes IIRC that is one reason why some BF work better than others. Another one is that every construction has a certain stiffness so by changing the BF you'll simply change the direction at which the main excitement takes place and therefore depending on the stiffness at that direction you change the resonance frequency of the whole bike (yes, I know that is a little bit oversimplified).
Now that's something I can wholeheartedly agree too. :wink:
Tim
I am talking about this particular scenario of rigidly mounting a commando engine in a feather bed frame. The ultimate goal is to change the balance factor significantly. I assume the rods and pistons referred to are those discussed in this thread:Tintin said:
lightweight-pistons-and-carillo-rods-bay-usa-t5130.html
Jim had played around a lot with these and has reported outstanding results however just bolting in different weight pistons and rods without balancing is a bad idea in general. As has been reported by Jim this worked favorably on his production level crank in his ISO Commando. I agree that lightening the reciprocating weight and the longer rods is a positive step in reducing vibrations but altering the balance factor by an estimated 12% is a significant change and not even half way to the recommended 78% of the rigid triton factor. Keep in mind these are hypothetical balance factors too. I haven't read anywhere yet where the said cranks were actually balanced to a known balance factor. This is why I would recommend
A: balancing the crank with your present rods and pistons
or
B: using Jim's light weight rods and pistons and balancing the crank (best if it fits your budget but maybe you would rather put the cash into a drive belt or fcr carbs etc. etc.)
RennieK said:
Yes, I agree to that - but not to the statement that the lighter pistons and longer rods do not reduce vibes in total - however I understand that you didn't mean the later anyway.
For an 850 Commando rigidtly bolted to the frame I'd go for as light as possible for rods and pistons (with Jim's stuff the best option I'm aware of) and definetly have the crank balanced to this weight and the BF which best suits the intended use - lazy sunday touring or red banner race track attacks.
Tim
sns said:
The Featherlastic is well known - but I can't really see the point unless you want the 60ies style with Isos. However it's a lot of effort to do and the JS pistons and rods together with a careful engine build should bring the vibes to an acceptable level already.
If you want Isos stay with the Commando, if you want a Featherbed I'd recommend a rigid mount. The Featherlastic is a bit of the worst of both (heavier frame without handling benefit) IMHO.
Tim
My featherbed handles well but has no sweet cruise spot like a Commando. It would be pretty fatigueing to ride a long distance, works fine for what I use it for which is mountain road cruiseing.
I think my engine plates were an English kit, I've only ever seen one similar set. As far as rebalance goes I'd say do it. I had one done years back and it was a great improvement over factory settings.
My bike is not a handmade unit like Jean's just a kit bike with a few good features like using tthe commando primary case.
I suspect it may be using Dominator gearing, either 18 0r 19 tooth front sprocket as it rips off pretty quickly but I think it could only hit about 100. I've never bothered to look since I'm happy enough with that area. It comes out of a mountain corner pretty quickly and by the time you get woulnd up it's time to brake and down shift.
On my bike everything you look at says old hot rod and 1970, on Jean's bike everywhere you look there is hand made jewelry.
I think my engine plates were an English kit, I've only ever seen one similar set. As far as rebalance goes I'd say do it. I had one done years back and it was a great improvement over factory settings.
My bike is not a handmade unit like Jean's just a kit bike with a few good features like using tthe commando primary case.
I suspect it may be using Dominator gearing, either 18 0r 19 tooth front sprocket as it rips off pretty quickly but I think it could only hit about 100. I've never bothered to look since I'm happy enough with that area. It comes out of a mountain corner pretty quickly and by the time you get woulnd up it's time to brake and down shift.
On my bike everything you look at says old hot rod and 1970, on Jean's bike everywhere you look there is hand made jewelry.
Go the 90 degree crank. Theres a bloke in Montreal who converts stock Norton cranks. Joe Fox in here Mildura (Australia) has recently got one and is building up the motor into a Featherbed. OK sounds like a Ducati but its a heck of lot easier to live with than anything resembling the Atlas where you'd need to visit the physiotherapist after every ride.
Mick
Mick
Sorry, I did blow by your link.sns said:
As soon as some one says I sent this there and shipped that to this guy and ordered bla bla bla... all I can think of is $$$$$$$$. That bike must have cost a fortune and not including the gosee trip he made. I'd love to have that bike though and I wouldn't put anyone off doing a similar build.
It may not be as bad as it sounds. The accelerating part takes energy but the deacceleration gives some of it back. But it does take energy to stretch and compress rods, bend cranks, and deform cases. Add to that the shaking of everythings else on the bike including the rider and that would be a significant amount of energy. The amplitude of the vibration is a function of the reciprocating mass, and that's all bad. It's like free power if you can reduce that mass and engine builders would swoon at the numbers Jim got compared to stock without even getting radical about it. The stock pistons are lumps by today's 'standard'.ludwig said:
Gday SNS, well Im currently going down the road of slotting a 74 850 Commando in a 64 Featherbed frame! I started out drouling over this picture below and decided thats what I want.
I dont know who owns this awsome bike but they are guilty of inspiring me to spend lotsa money. Anyway back to the motor side of it, my motor now sports an RGM 920 kit, being 920 cc, bound to vibrate! Phil Irving, famous Australian engineer, developer of the Vincent V twin and author of motorcycle technical books(TUNING for SPEED), believed that a parallel twin shouldnt be any larger than 500cc unless it had an offset crank firing 90 or 76 degrees. This smooths out the virbrations, making the motor think its a V twin like a Ducati, Honda VTR, Yamaha TRX 850, all riggid mounted. Phil tried to convince the British motorcycle industry this was the way to manufacture twins and to their detrament, fell only on deaf ears.
I came across Geoff Collins web site http://offsetcrank.com/norton.htm . Geoff who is extremely great to get along with and very helpful with great knowledge, remanufactures various cranks to suit your needs. I thought this is the way to go for me, not cheap but my bike is a long term project and I want it to be somewhat unique and run smooth at any revs. This may not be the way for you, so I would stick with Seeley920,s advice as the man races them and has done so for many years. John gives good solid advice and mixes with the likes of Mick Hemmings, so has learned alot over the years.
Bob Cox,s featherlastic is very nice and the boys in Tucson do a real nice job, not cheap either but anything good comes at a price.
Ive purchased Converta dural enginge plates from Chris at Unitey in the UK,bolted staight up!
rgds FOXY
I dont know who owns this awsome bike but they are guilty of inspiring me to spend lotsa money. Anyway back to the motor side of it, my motor now sports an RGM 920 kit, being 920 cc, bound to vibrate! Phil Irving, famous Australian engineer, developer of the Vincent V twin and author of motorcycle technical books(TUNING for SPEED), believed that a parallel twin shouldnt be any larger than 500cc unless it had an offset crank firing 90 or 76 degrees. This smooths out the virbrations, making the motor think its a V twin like a Ducati, Honda VTR, Yamaha TRX 850, all riggid mounted. Phil tried to convince the British motorcycle industry this was the way to manufacture twins and to their detrament, fell only on deaf ears.
I came across Geoff Collins web site http://offsetcrank.com/norton.htm . Geoff who is extremely great to get along with and very helpful with great knowledge, remanufactures various cranks to suit your needs. I thought this is the way to go for me, not cheap but my bike is a long term project and I want it to be somewhat unique and run smooth at any revs. This may not be the way for you, so I would stick with Seeley920,s advice as the man races them and has done so for many years. John gives good solid advice and mixes with the likes of Mick Hemmings, so has learned alot over the years.
Bob Cox,s featherlastic is very nice and the boys in Tucson do a real nice job, not cheap either but anything good comes at a price.
Ive purchased Converta dural enginge plates from Chris at Unitey in the UK,bolted staight up!
rgds FOXY
Foxy said:
...guilty for designing some of the weirdest details to answer questions nobody asked. How on earth can you do a forked rocker engaging in the middle of the valve and claim it's a particularly clever design?
http://www.captain.norton.clara.net/cnn2sec14.html
http://dinamoto.it/DINAMOTO/8_on-line_p ... /twin.html
If you go for a different angle than IMHO 180deg makes far more sense as it kills primary forces (but produces the worst rocking couple). There is only one real reason to go for 90deg: Make it sound like a Ducati.
Because there is equally good reasons to do 360deg cranks - like even torque and lowest torsional vibration, no rocking couple etc - and Phil Irving was not the only engineer capable of doing the maths. There is only one way of minimizing the vibrations of a twin cylinder: Design an anti-vibration device such as balance shafts or levers. The best example is the current BMW F800, and Norton reportedly had a very similar design. Offset cranks do not really reduce the vibes but more or less just change the vector orientation. And whoever puts an offset crank into a Commando just has absolutely no clue of how the Isos work.
Tim
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Hi , I had allready fit a 750 Commando engine into my Atlas , but have the crank/rods statically balanced at 84%, then, the whole had been dynamically balanced , and it's far better than my previous Atlas, with a belt at 2/1 ratio and a 22 teeth , i could cruise at 4500/5000 rpm , easily.......now I had bought the Jim Schmidt set up , and will see the improvment it will bring , not cheap but nice items and well designed, it should according to Jim test and trials reduce the remaining vibes, and help the mill to rev more happily.........but take it easy as I am slow and lazy (old!!) that will take me some time to build up the power plant..........the Frog.
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