Featherbed: Twin vs Manx, handling, weight, etc

Ashley,
FWIW and IMHO…
You already have a Commando featherbed, so why build another?
The 650 engine is sweet. And JS does extra lightweight rods and pistons for those. You could build a super sweet, tight, crisp, revvy 650…
Nigel I am just toying with the idea, I have the parts to build the 650 and going down the road with JS motor parts is really out of my budget, but it's good to dream, the 650 motor isn't the original motor for the Manxman frame the numbers are close but out by 64, it's an ex race bike the crank has been balanced, has high compression pistons, I have a new 2S cam for it, the head was missing when I bought the bike and bits and took me some time, well 2 years in fact to chase up a head for it, not sure what happened to the head that it was raced with, had all the internals for the head + extra bits - valves.
I paid $1k for this project bike, he wanted $2.5k for it I talked him down to $1.5k but when loading the parts on the truck my mate who was with me notice no head so when I asked about the head he dropped $500 straight off the price, so he knew the head was missing, I looked world wide for a head and after 2 years of looking found a guy in South Aus who had 2 heads so he sent me the best one with new valves for $400, so still way in front.
I have had many ideas pop into my head for this Slimline frame, I did a complete strip down of CBR 250 Honda race bike and thinking of using the front end and Nissan disc race brakes on this project bike with out to much modification, the idea of running single leading drum on the front don't appeal to me.
I nearly sold this project Norton 3 weeks ago, had someone interested but I put on a high price for what I had done so far, but lucky I had a change of heart and will start back on this project soon, I was originally building this Norton for my youngest daughter but she has now bought a newest Triumph Triple 660.

Ashley
 
Nigel I am just toying with the idea, I have the parts to build the 650 and going down the road with JS motor parts is really out of my budget, but it's good to dream, the 650 motor isn't the original motor for the Manxman frame the numbers are close but out by 64, it's an ex race bike the crank has been balanced, has high compression pistons, I have a new 2S cam for it, the head was missing when I bought the bike and bits and took me some time, well 2 years in fact to chase up a head for it, not sure what happened to the head that it was raced with, had all the internals for the head + extra bits - valves.
I paid $1k for this project bike, he wanted $2.5k for it I talked him down to $1.5k but when loading the parts on the truck my mate who was with me notice no head so when I asked about the head he dropped $500 straight off the price, so he knew the head was missing, I looked world wide for a head and after 2 years of looking found a guy in South Aus who had 2 heads so he sent me the best one with new valves for $400, so still way in front.
I have had many ideas pop into my head for this Slimline frame, I did a complete strip down of CBR 250 Honda race bike and thinking of using the front end and Nissan disc race brakes on this project bike with out to much modification, the idea of running single leading drum on the front don't appeal to me.
I nearly sold this project Norton 3 weeks ago, had someone interested but I put on a high price for what I had done so far, but lucky I had a change of heart and will start back on this project soon, I was originally building this Norton for my youngest daughter but she has now bought a newest Triumph Triple 660.

Ashley
I’d still keep it 650 and enjoy it for what it is. Keep it light, throw on some modern running gear, etc. Sweet !
 
A featherbed frame with a Jawa speedway motor is almost good. But anything else which is not Manx is a waste of effort. I raced with featherbed frames for too long to be deluded about them. I will not brag about the Seeley frame - it just happens to be much better. You need to try them both, and make an objective assessment. I once led an Allpowers race at Winton in the early 70s with my Triton 500. My Seeley 850 would make it look stupid. THe bikes I raced against after Y2K were 1100cc methanol fuelled CB750 Honda. My Seeley is as fat down the straights, and much faster around corners.
I am not bullshitting. If you ever come south, I will let you ride it at Winton Raceway. I definitely intend to do an onboard video, so you guys can see.
 
I’d still keep it 650 and enjoy it for what it is. Keep it light, throw on some modern running gear, etc. Sweet !
A 650ss is a very nice bike. One of my mates had a Manxman. They were probably the best ever. The Atlas had problems- the first in Melbourne broke it's barrel flange.
As I said previously, I watched Jack Forrest beast all the Manxes at Bathurst in an Allpowers race, in about 1963 with a 650SS. That was no mean feat. He was a works rider for BMW in Europe. But the guys on the Manxes in Australia were extremely fast.
 
Nigel comparing a featherbed frame with a Seeley frame is chalk and cheese. Tom Phillis did a 100 MPH lap of the IOM on a Domiracer. That does not mean that you could do it. Tom died on the IOM while riding a 4 cylinder Honda. - an excellent motorcycle. When the good guys die while racing, you know you really have a problem. Some guys ride beyond their capabilities. I do not believe I am a good rider, but I do one thing well - I do not crash. I learned to be that way by riding a Triton, often - over about a 12 year period.
I can still feel the pain.
In Australia a Domiracer would be in Period 3 Historic, a Seeley frame is not eligible - it is post-1962. Where you are might be different. The motor in my Seeley is 1973 - theoretically, it is not eligble for Period 4. which ends at 1974.
What you need to realise is that road racing changed in 1963. The two-strokes arrived. We needed more than featherbed frames.
 
NIgel,
Perhaps you need to think about what you are trying to achieve. When I build a race motorcycle, I like it to be of a certain type. To me it does not matter if it is pre-1963 or post-1963. But those two types of motorcycle are quite distinct. In 1963, the two-strokes arrived, so the guys with four-strokes had to lift their game. I raced a 1950s 500cc Triton against 60s and 70s bikes, because that was what I could afford. When you do silly things like that, you learn to race the hard way. I do not believe I am a good rider, I just know how to avoid crashing. A good rider such as Mike Hailwood or Ago, thinks differently , because they have been conditioned by riding better motorcycles.
 
NIgel,
Perhaps you need to think about what you are trying to achieve.
Al,

Perhaps you should accept that others come to different conclusions than you do and have a fine life.

@Fast Eddie is no fool, has been around the block a time or two, and is planning a new project to ride. You are sitting at your computer talking about the past, seemingly with no intention of ever riding your motorcycle again, or participate in your loved sport, beyond posting on this forum. We've heard your opinions and value your experience, but we intend to proceed with our lives under our own steam.

The constant harping about what you perceive as everyone's poor choices, is old hat. Please stop.
 
A featherbed frame with a Jawa speedway motor is almost good. But anything else which is not Manx is a waste of effort. I raced with featherbed frames for too long to be deluded about them. I will not brag about the Seeley frame - it just happens to be much better. You need to try them both, and make an objective assessment. I once led an Allpowers race at Winton in the early 70s with my Triton 500. My Seeley 850 would make it look stupid. THe bikes I raced against after Y2K were 1100cc methanol fuelled CB750 Honda. My Seeley is as fat down the straights, and much faster around corners.
I am not bullshitting. If you ever come south, I will let you ride it at Winton Raceway. I definitely intend to do an onboard video, so you guys can see.
Al I think you are already deluded, as a well set up Featherbed with a Commando motor that is built for the Featherbed and having someone who been riding it for a long time and know how to ride it, it's one of the best things I have done, get it up in the tight twisties it's so much fun and even better when there are other bikes in front, I play games with them, they don't know I am there till I cut under them in corners, it handle so well that sometimes I got to look back to see if I did go around that corner or bend and using the torque of the motor to push it through the corner is such a thrill, well for me anyway.
Of course a 850 should make a 500 look stupid and the best thing about riding on the road I get to enjoy my great handling Norton anytime I feel like it, it's still my favourite ride and play bike (why else would I have kept it for over 40 years in the Featherbed if it wasn't any good), but as well I also love riding my 1200 Thruxton, riding a bike once in the blue moon on a track is really not my idea of enjoying what I have.
I look forward in seeing what plan Nigel comes out with and a 920 Featherbed, now that could be a lot of fun.
Talking about the past at lease Nigel is looking at the future and building something for himself and only time will tell what comes out of it, I look forward to the seeing the result.

Ashley
 
Pardon my confusion but what constitutes a Commando motor in a Featherbed? Do the cases have to be commando? Does an Atlas rebuilt with superblend bearings, a six-start oil pump gear, flat top pistons and a 750 commando head and valve gear count? How bout adding concentrics and a Boyer ign. I went that far with my Atlas and it still looks like a stock Atlas.

I did a similar treatment to a G15 with swept back pipes and rearsets and 10:1 pistons and a much hotter cam though I don't remember where it came from; probably Pokes basement. To that I added a Commando primary but left the engine sitting straight up. That was a lot of work just to get a 3-row primary chain and I wouldn't do it again. Looked great though and was fast but it didn't handle like the Atlas which is also fast but not like the G15.
 
A featherbed frame with a Jawa speedway motor is almost good.
Only ridden JAWA speedway bikes in the sixties. A Speedway JAWA on methanol is a very nice ride with a wide usable rev span. When compared to the earlier JAP speedway bikes not very much more power. Much less servicing on the JAWA. And a vastly superior handling. But those featherbed framed ones I've seen running on petrol lacks power compared to a Manx.
 
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Pardon my confusion but what constitutes a Commando motor in a Featherbed? Do the cases have to be commando? Does an Atlas rebuilt with superblend bearings, a six-start oil pump gear, flat top pistons and a 750 commando head and valve gear count? How bout adding concentrics and a Boyer ign. I went that far with my Atlas and it still looks like a stock Atlas.

I did a similar treatment to a G15 with swept back pipes and rearsets and 10:1 pistons and a much hotter cam though I don't remember where it came from; probably Pokes basement. To that I added a Commando primary but left the engine sitting straight up. That was a lot of work just to get a 3-row primary chain and I wouldn't do it again. Looked great though and was fast but it didn't handle like the Atlas which is also fast but not like the G15.
A complete Commando motor, I went for complete 850 Commando and in 1980 converted as much Commando gear to use on my 1957 Wideline Featherbed frame, motor was built and balance to run on solid mounts for the Featherbed frame and the motor mounted the same as Commando, not straight up like the Dommies, exhaust pipes were made and bent as well stuck close to the frame for the Featherbed frame, so I run a complete Commando motor, primary and gear box, made my own engine mounts tilted forward.
Featherbed: Twin vs Manx, handling, weight, etc
 
Pardon my confusion but what constitutes a Commando motor in a Featherbed? Do the cases have to be commando? Does an Atlas rebuilt with superblend bearings, a six-start oil pump gear, flat top pistons and a 750 commando head and valve gear count? How bout adding concentrics and a Boyer ign. I went that far with my Atlas and it still looks like a stock Atlas.

I did a similar treatment to a G15 with swept back pipes and rearsets and 10:1 pistons and a much hotter cam though I don't remember where it came from; probably Pokes basement. To that I added a Commando primary but left the engine sitting straight up. That was a lot of work just to get a 3-row primary chain and I wouldn't do it again. Looked great though and was fast but it didn't handle like the Atlas which is also fast but not like the G15.
Well a Commando motor is not an Atlas motor, so that probably answers the question. You still have a different crank balance factor which may be in favor of the Atlas if rigid mounted. From ‘72, Commando case breathers are different and cases are stronger.
 
A Commando motor might be an Atlas motor which has been made to go slower. The low balance factor of the Commando is suited for operation at lower revs. An 850 Commando is as fast as an H2 Kawasaki, but not for long. When you build a bike, it is an exercise in pattern recognition. A bike with a 750 Atlas motor can be as fast as anything else, but it is the whole package which is important - NOT just the motor. Also different bikes suit different situations. What is good on winding roads with tight bends, is often not so good on open roads which have large sweeping bends.
When you road race a motorcycle, you cope with multivariate data - the type of circuit contributes. Changing only one variable e.g. power, is often not enough. With most bikes when you lower the overall gearing, they accelerate faster. A Norton with the heavy crank in the motor, does not behave like that. Close ratios with high overall gearing is better.
 
Yeah, that’s fairly unlikely …
What race categories cater for Norton twins in the UK ? A lot depends on eligibility. In Australia, my Seeley 850 isc strictly not eligible for the class in which it can race. My motor isc 1973 - the class is pre-73. Also I use Yamaha fork yokes which are not legal. If the scrutimeer s do not worry, I do not worry. Nobody in Australian historic racing ever lodges a protest - it just notv done. Strictly speaking that 1600cc VIncent which was banned at Goodwood, is eligible to race against my Seeley 850. But it is usually up one class.
 
A Commando motor might be an Atlas motor which has been made to go slower. The low balance factor of the Commando is suited for operation at lower revs. An 850 Commando is as fast as an H2 Kawasaki, but not for long. When you build a bike, it is an exercise in pattern recognition. A bike with a 750 Atlas motor can be as fast as anything else, but it is the whole package which is important - NOT just the motor. Also different bikes suit different situations. What is good on winding roads with tight bends, is often not so good on open roads which have large sweeping bends.
When you road race a motorcycle, you cope with multivariate data - the type of circuit contributes. Changing only one variable e.g. power, is often not enough. With most bikes when you lower the overall gearing, they accelerate faster. A Norton with the heavy crank in the motor, does not behave like that. Close ratios with high overall gearing is better.
"A commando motor may be an atlas motor that's made to go slower" :D :D:D
 
So what is the difference between an Atlas 750 crank and a Commando 750 crank, aside from the balance factor? Ive had them both and 850 cranks apart to clean sludge traps and for re-grinding but never weighed one and didn't notice any difference, but then I wasn't looking either. Dealing with Atlas/G&N and P11 cranks, changing the balance factor did not involve major work. I never tried to drastically change the balance factor on any of them. That must involve a lot of drill-press time and other stuff I know nothing about. Pouring hot lead? How is it done?

Ashman, nice looking rig. Has a certain functional esthetic about it. What advantage have you found from the forward cant of the engine. I can see that it would move the CG forward a bit and perhaps a wee bit lower. What can you tell on the road? From this discussion I've learned that racers moved the CG forward and back by small amounts for best cornering but never having road raced or ridden a Manx or a Manxman I really am a babe in the woods or would that be a jaw-dropped corner worker at the end of the straight?
 
So what is the difference between an Atlas 750 crank and a Commando 750 crank, aside from the balance factor? Ive had them both and 850 cranks apart to clean sludge traps and for re-grinding but never weighed one and didn't notice any difference, but then I wasn't looking either. Dealing with Atlas/G&N and P11 cranks, changing the balance factor did not involve major work. I never tried to drastically change the balance factor on any of them. That must involve a lot of drill-press time and other stuff I know nothing about. Pouring hot lead? How is it done?

Ashman, nice looking rig. Has a certain functional esthetic about it. What advantage have you found from the forward cant of the engine. I can see that it would move the CG forward a bit and perhaps a wee bit lower. What can you tell on the road? From this discussion I've learned that racers moved the CG forward and back by small amounts for best cornering but never having road raced or ridden a Manx or a Manxman I really am a babe in the woods or would that be a jaw-dropped corner worker at the end of the straight?
I don't think there is any difference between the atlas crank and the commando 750 crank apart from the balance factor and the alternator keyway being in a different place?
 
I too would like to know a few things sorry if a bit OT.

1) As Thomasa asked, what are the benefits of a tilted engine in a featherbed vs straight up? (let's say 750 and 850 commando engine for discussion sake). And if I did this other than just buying a different set of plates are there any other things I have to take into consideration?

IMO there is no benefit in terms of handling that would be possible for a normal rider to detect. The main design benefits are styling. Plus packaging, ie making space for electric start components and big air boxes.

Yes there is a fair bit to do apart from engine plates: head steady, primary case mounting, exhaust pipes, intake manifolds. There may be internal oil system changes required too, but I’m not familiar enough with those engines to be sure.

Put simply, given all your other projects, and the fact that your Mercury is a running, functioning motorcycle, you’d be out of your freakin’ mind to consider this !
 
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