featherbed frame

WOOD ! the Brakes feel a bit Wooden , :D :p :lol:

featherbed frame


Quite a few things were wooden , like Mosquitos , DeH 88s , the Spruce Goose ( actuall BIRCH Ply ) & the odd Boat . Not to mention CLOGS .

featherbed frame
 
Morgan cars had a bit of wood behind the metal skins. Good substitute for a chrome moly subframe. I might make a Seeley frame out of bamboo and fit a Chinese motor. I could sell it as an artifact, or a souvenir for tourists who want to take up road racing. They could give them to people as they leave the IOM ferry at Douglas along with free rider credentials.
 
It is mentioned various places that Egli frames weren't nearly stiff enough in the large central backbone.
It wasn't until someone came up with a honeycomb stiffening fix that went into the backbone that they were any good.
You sometimes see early ones with (considerable) additional tubing for bracing...

Without isolastics and a Commando motor, do Seeley frames make your teeth c-h-a-t-t-e-r ??


acotrel said:
Matt, the bike looks good fitted with the Trident engine. I doubt it would handle well if pushed hard. Even a standard Trident tends to wheel stand. Hard to beat a Rob North frame for that motor. If you look at the frames around previous to the Featherbed, it was an earth-shattering improvement. Seeleys etc were made 15+ years later, after guys had ridden featherbeds to death. Colin Seeley know more about handling than most of us ever knew back in those days. For a commando engine, the early Egli frame is probably better than most.

featherbed frame
Click to expand...
 
Trident engined Tritons are not the best handlers. I had the privilege of a ride on one. It had been very nicely built, sounded gorgeous, went like steam in a straight line but didn't handle very well at all compared to my bike. I had just got off my 650SS which was nicely set up, steered and handled beautifully. The Triton showed all the characteristics of having too high a CG. Compared to my bike, it was difficult to change direction, felt heavy although it wasn't much heavier than my 650SS, I'm sure that wheelies would have been a piece of cake.
Rob North got it right for Trident power!!
cheers
wakeup
 
Rohan, I don't think you believe in rebalancing crankshafts. The crank in my 850 motor is balanced to 72 %. When it is idling the Seeley actually rocks backwards and forwards. As soon as you start riding it the vibration disappears and it is very smooth and the motor spins up extremely easily. So much so that you must be very careful to change gears so as not to let it exceed 7,000 rpm. If it made my teeth chatter at high revs , I'd either fix it or sell it. I won't tolerate that crap these days - been there, done that ! With the motor set up to pull hard, my main problem has been getting the gearing right. With a 4 speed close box, first gear is too high when the overall gearing is high enough, so you have to cook the clutch off the start line. Once the bike is mobile, you really have to watch your revs. I hate to think what is happening to the aluminium conrods with those heavy 850 pistons flying up and down at 7,500 RPM.
 
Rohan, I suggest that if you want to fit an 850 commando motor into a featherbed frame, you must think about your bike's primary application. If it is to be used for commuting, the standard 58% balance factor is probably OK, as long as you don't take the freeway going to work. Or you could gear the bike really high and stay off the back roads. Personally, I don't care if the bike shakes the shit out of itself at low revs as long as it smooths out when you ride it hard, however I never commute by motorcycle.
 
I don't have a Seeley, nor have I ever considered one, so this point is somewhat moot.
Since you have never ridden a Commando, and the balance factor is 52%, some of those comments are rather suspect. ??
Since the engine is free to move - and not transfer its vibes to the rider, within limits - spreading the vibes both fore-and-aft AND up-and-down equally with that 52% probably suggests that the folks at Nortons knew what they were doing.
Altering balance factors, or adding a balance shaft, doesn't affect the bearing loads to any noticeable degree - so something that is more, or less, comfortable to the rider is not going to affect engine life. Unless something is badly wrong...
 
Is a commando 750 motor with a 58% balance factor as reliable as an Atlas 750 motor with a 72% balance factor ? I know of Atlas 750 engines which have had the barrel flange break, however never heard of one splitting the crankcases through the main bearings through over-revving. Does a commando 750 handle better than a swing arm framed Matchless pushrod single or as well as a unit construction Triumph 650 ? I suggest that if the Triumph had power equal to a standard commando it would make the commando look stupid on a race track. The torque characteristics might give the commando the edge, however otherwise ..... ?
 
Matt, the Gus Kuhn short circuit racer shown in that link is what I've modeled my bike on. I don't know about the Boyer Seeley Trident, I wouldn't go that way, the engine is too heavy and it could handle like a bag of shit.. If I was going to do it differently a Walmsley G50 engine would be beautiful and possibly faster, but it is hard to beat cubes.

https://www.youtube.com/watch?v=eXcNgWqHDNw
 
Matt, You should be able to build yourself a Period 4 Seeley racer with a two valve Jawa engine relatively cheaply. When I was building mine, I looked at a 70s DOHC speedway Jawa engine, however the elgibility requirements for our historic racing classes stuffed that idea. It would have made a really great bike with such a light and powerful motor. Those speedway engines are still bloody cheap ! You can buy a brand new one for about $5000. There are plenty of second hand ones about too.

http://www.ebay.com.au/sch/i.html?_saca ... 26_arr%3D1
 
Rohan,
'Altering balance factors, or adding a balance shaft, doesn't affect the bearing loads to any noticeable degree - so something that is more, or less, comfortable to the rider is not going to affect engine life. Unless something is badly wrong...'

You've said two things quickly. I agree that adding balance shafts does not affect bearing loads, in relation to balance factor you are wrong. The difference between a 750 Norton crank 'in balance' at 7,000 RPM (running fairly vibrationless) , and a standard commando crank at the same revs is about half a kilogram being spun around at the big ends with the pistons and rods. That is why the isolastics are there. Isolastics help the bearings because the impacts (pulses) are absorbed to some extent when the engine moves. History shows that there have been a lot of bearing and case failures in commando engines through over-revving - why is this so ? I suspect that the crank in the new 961 Norton is balanced to be smooth at high revs, with the balance shafts possibly effective at low revs. Are isolastics used on the new Norton commando ?
 
Too many things thrown together there to reply to.
Remember - reciprocating forces can never be perfectly balanced by rotating weights.
"Balance' in this instance being a relative term, its only a best compromise.

Early Atlas engines had thin cylinder walls and flanges, which were subsequently strengthened.
Note how thick the flange has to be in alloy cylinders...
 
acotrel said:
Is a commando 750 motor with a 58% balance factor as reliable as an Atlas 750 motor with a 72% balance factor ? I know of Atlas 750 engines which have had the barrel flange break, however never heard of one splitting the crankcases through the main bearings through over-revving. Does a commando 750 handle better than a swing arm framed Matchless pushrod single or as well as a unit construction Triumph 650 ? I suggest that if the Triumph had power equal to a standard commando it would make the commando look stupid on a race track. The torque characteristics might give the commando the edge, however otherwise ..... ?
Click to expand...

I raced AHRMA Historic Production Heavyweight on a near-bone-stock late 60s Bonneville 650 on Dunlop Arrowmax tires.

I believe that if I took my Combat and swapped the bodywork & pegs to fit the same class, fit similar tires, and attempted to run the same races I've done in the past, I don't believe I could better my lap times (even though the Commando has lots more torque, not to mention 100ccs more displacement). The fact is, it is heavier by more than enough to make up the engine's advantage, and it just feels "piggy" in comparison to the little Bonny.

-just an observation/opinion, and one that is not likely to be tested for confirmation; so "for whatever it's worth"
 
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