concours
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What brakes on the Seeley? Type of fuel?
Norton Desaxe cylinder offset
- Thread starter jseng1
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I only ever use methanol fuel, because it is easier to get right. I would never be able to get similar performance out of petrol. The front brake is a Honda CB750 hub with two 1970s Suzuki steel discs, and two Lockheed AP calipers with asbestos pads, the master cylinder was designed for one caliper, so I operate the front brake with my index finger while other finger operate a Yamaha dual cable quick-action throttle. I don't move my hand to use the brake - it is finger-tip control. The old asbestos pads in the front brake were the only ones which would work well enough.
I wish you well with your bike. I never believed in my Seeley 850, but now I love it. Grief stops me from even going near it. The only reason I contribute to this forum is I had a result which I never expected. An 850cc Commando engined race bike should not be able to beat an 1100cc methanol-fuelled CB750 Honda. It made them look stupid. I can probably ride fairly well, I can out-ride most other guys - but I was not even trying. Here is a photo of one of Rex Wolfenden's 1100cc Hondas ---
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cliffa
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@acotrel, may I ask why you said "Grief stops me from even going near it" ? I sympathize if you lost somebody close to you, but what has that to do with your Seeley? I have been a contributing member on here since 2013, and as far as I'm aware you have been lamenting a loss since then or possibly before. We only live once ( I'm reliably informedI only ever use methanol fuel, because it is easier to get right. I would never be able to get similar performance out of petrol. The front brake is a Honda CB750 hub with two 1970s Suzuki steel discs, and two Lockheed AP calipers with asbestos pads, the master cylinder was designed for one caliper, so I operate the front brake with my index finger while other finger operate a Yamaha dual cable quick-action throttle. I don't move my hand to use the brake - it is finger-tip control. The old asbestos pads in the front brake were the only ones which would work well enough.
I wish you well with your bike. I never believed in my Seeley 850, but now I love it. Grief stops me from even going near it. The only reason I contribute to this forum is I had a result which I never expected. An 850cc Commando engined race bike should not be able to beat an 1100cc methanol-fuelled CB750 Honda. It made them look stupid. I can probably ride fairly well, I can out-ride most other guys - but I was not even trying. Here is a photo of one of Rex Wolfenden's 1100cc Hondas ---
), so why not get your bike out, dust it off and parade it? Or even better let a younger rider race, parade or just enjoy it and bask in their enthusiasm? Youthfulness is infectious, and may give you a whole new lease of life! (but please don't let them (or you) near those asbestos brake pads).
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Did nobody notice my post #15 in which I gave the actual cylinder offset measured using the factory drawings .
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To do that now in Victoria is almost impossible. Those days have gone. One of my friends has a son and a grandson, both were into road racing - politics has turned them off it. There is a thing which happens in sports - some people get their jollies from leading clubs. In Australia, the clubs are supposed to be not-for-profit, and the articles of association shapes them to be democratic. But the guys who lead, often have not raced - so they do damage. I no longer have access to Winton Raceway because the car club members were abused at a motorcycle race meeting - due to in-fighting in a motorcycle club. It was all about petty jealousies - idiocy. My days of driving hundreds of kilometres to race are long gone, and to do it so some young kid can get hurt, would be stupid. I am now 83, an 18 year old kid would probably take 6 years to become as competent as myself, on my bike.@acotrel, may I ask why you said "Grief stops me from even going near it" ? I sympathize if you lost somebody close to you, but what has that to do with your Seeley? I have been a contributing member on here since 2013, and as far as I'm aware you have been lamenting a loss since then or possibly before. We only live once ( I'm reliably informed
My grief is about my mate when I was 18, he taught me how to build a race motor, and he had ridden my Seeley. At his funeral his kids' behaviour was disgusting - they had a family fight in the funeral parlour. So nobody spoke for my mate.
I am slowly improving, until recently I could not even think about reassembling the transmission of the Seeley.
This forum helps me - some of the guys are up and going. That is good.
I am probably a bit precious -over the last 20 years, I have been to too many funerals.
robs ss
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Yep - and that would make sense, as the bore of the (un-desaxe) 650 was 86mm whereas the 750 was 73mm.
If they shifted the bore CL backward so that the front of the bores were in the same place, the shift (theoretically) would be 2.5mm (0.098"), close to your measured 0.093"
The 850 has a bore of 77mm - did they further increase the desaxe for that? If so, that would be be another 2mm (0.079")
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Which happens to be nearly the same amount that the wedge base gasket will offset the cylinders forward (.097"). But the actual factory offset needs to be measured off existing cases/cylinders. Some say its less than what you see in the drawings.
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I have found that, particularly with a Commando motor, it is difficult to predict what might give a good result. Most motors give more power by revving higher. If you lower the gearing of a motorcycle when using a Commando motor, the result is not necessarily better acceleration. The effects of improved torque are best realised by raising the gearing, but the revs must stay within the power band. With my first race bike, I had all top-end and very little torque - a 2 into 1 exhaust made the bike rideable. When I first got it, it had separate pipes with megaphones. I found out the reason it had almost killed my mate at Bathurst.
robs ss
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Jim
The claims you have made there may be true in theory - have you any data on measurable change?
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Something which is not wrong cannot be corrected. Many things are a compromise - everything usually affects everything else. The rider adapts to the bike, and the bike is adapted to suit its use. When I develop a bike, I adjust to suit the race circuit which I use the most. That removes one variable. The other variables are the power characteristics and handling which suits the circuit. When a rider cannot ride the bike, they often blame themselves. However, more often than not- the bike is set-up incorrectly for the situation. When we race, we raise and lower the gearing to find out what suits. When I built my Seeley 850, my speculation was based on my previous experience. I still got it slightly wrong, and made changes. Even them the MK3 Seeley frame surprised me. I raced the bike in 3 places before I realised how to use it to get best performance.
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Back in 1987 I shortened and releveled the deck on my cases. In the vid below I'm racing against monoshock Ducatis, Doing my best with a 4 speed and biased tires against their 5 speeds and radial tires. You can see in the Vid that the Norton is holding its own power wise. The Ducati was able to down shift the last turn to the flag (I couldn't with my 4 speed). This was my last road race.
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The as-fitted bore centerlines on Norton Commando 750 and 850 barrels are identical. This was a deliberate design choice by Norton to maintain compatibility across engine variants. It is also the reason why Norton couldn't increase capacity to a full 850 cc.
-Knut
It's interesting to note that the highly efficient Matchless G2 designed in 1958 had a (measured) desaxe value of 1/8 inch (3.175 mm). Not particularly much by today's thinking, at the time it was considered state of the art.
Achieving the same effect in a revised Norton 750/850 engine would require a positive desaxe of 4.56 mm .
Addition: Apparently, the design envelope of the Unified 650 discussed in another thread does not contain a desaxe specification, which is surprising, given the fact that Dough Hele must have played a part in the design process.
- Knut
Achieving the same effect in a revised Norton 750/850 engine would require a positive desaxe of 4.56 mm .
Addition: Apparently, the design envelope of the Unified 650 discussed in another thread does not contain a desaxe specification, which is surprising, given the fact that Dough Hele must have played a part in the design process.
- Knut
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Scott engines have 0.375" / 9.525mm desaxe
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