Mark 3 Seeley frame

I agree with you however my frame is a light weight built for a G50. I think standard T45 or Renolds 303 would be better for a Commando engine. I've been bitten lol, heavy duty & build to last is best for me.

Hello Gentlemen!

I really appreciate the tremendous insights and advice. Most informative. My two cents ... Ken and Colin would be proud .

Trust me, there is a whole lot less engineering and experience happening here on my end, but I think I hear what you are saying about the comparative structural strength of the Mk2 chassis relative to the Mk3 in the area behind the headstock. The Minnovation solution on the Mk2 makes me envious, as I do like the idea of the power unit being more "locked in," perhaps contributing to the strength of the triangulated structure (of the 'half frame,' I should say!). I am looking at how my former Commando's Norvil h/s (w/isolastic) lines up, in situ, as a design inspiration.

I went ahead and ordered a Triumph 675 sidestand on eBay and I will give it a test fit upon arrival. I see what you mean, Chris, about the Commando primary clearance and the thin section of the plates under the motor. Primary-wise, my hope is to use a JPN outrigger type primary I have from Norman White, so there may be a bit more clearance underneath to work with (I'd attach a photo if I knew how!). Did you use one of your lower case bolts to secure your stand, i.e., a longer through-bolt?

One last question (for today, anyway!) if you wouldn't mind? As I await the sidestand, I am considering the other "essential" of a street Seeley ... the kickstart/rearset arrangement. Did you go with a folding footrest, any special k/s arm? Again, any sage advice would be greatly appreciated!

Best wishes for a great weekend!

Rob

Fast Eddie said:

But… I don’t see the mk3 as being well triangulated. There is a point at which the headstock triangulation and main frame triangulation meet (red arrow in pic below) and at that point there is no triangulation.

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The triangulation has to be viewed for the complete frame. Forces are transferred axially along the tubes because tubular axial stiffness is high, even through bends. Transverse stiffness is low.
At the indicated joint, the sloped tubes create an inward force (towards the frame C/L) while the horizontal tubes create an opposite outward force, in equilibrium with the former. Thus, the triangular force diagram is maintained.
Partial weight of the powerplant has to be introduced at this joint. The gravity forces are decomposed into a force component acting downward at the sloped tubes, and a component acting forward at the horizontal tubes.
Both components will reduce the respective static chassis loads, which is beneficial.

- Knut

mdt-son said:

The triangulation has to be viewed for the complete frame. Forces are transferred axially along the tubes because tubular axial stiffness is high, even through bends. Transverse stiffness is low.
At the indicated joint, the sloped tubes create an inward force (towards the frame C/L) while the horizontal tubes create an opposite outward force, in equilibrium with the former. Thus, the triangular force diagram is maintained.
Partial weight of the powerplant has to be introduced at this joint. The gravity forces are decomposed into a force component acting downward at the sloped tubes, and a component acting forward at the horizontal tubes.
Both components will reduce the respective static chassis loads, which is beneficial.

- Knut

Click to expand...

what are the input forces to the frame that you are starting with?

Hi Rob
Yes I drilled the stand bracket & used the engine to engine plates mounting bolt to hold the front of the stand. I ran an extended kick-start with a crank in it from Avery products (John's passed away) but I think the company is still going. Its a generic one as I also got one from Sammy Miller but not chromed. The new incarnation will have a long kick-start from RGM. There is a fair bit of clearance with the footpegs mounted on the swinging arm. Again on my reincarnation I have bosses welded on to put footplates to give me the opportunity to adjust the footpeg heights. I did a straight linkage to the gearbox nothing special its just clearance with the kick-start.

Perfect! Thank YOU, Chris!

We shall see how the Triumph 675 stand fares, soon enough, with the front through-bolt solution as Option 1. Much appreciated!

I did believe I could discern a folding k/s in the photo of your (fantastic!) machine. Thank you for the follow-up details!

Classic Kickstarts List - Terry Weedy - Avery Products https://share.google/ru31en93xxHUaaFTP

Yes, Avery may still be trading?

This RGM one is attractive as well:

KICKSTART, OUR OWN DESIGN, SWIVELS AT BASE https://share.google/d0XJRyd8BQJwtyDxH

Wonderful problem-solving assists, Chris!

Today, I am eyeing the gearbox cutout in the right side engine plate. I am not seeing any manner of rotation (no matter how convoluted, and I've made my self dizzy with effort!) which would enable me to squeeze that 'box through the hole. Next choice seems to be to leave it as-is, requiring more disassembly in the (hopefully unlikely) need for a g/b removal, or extend my plate-fitting efforts to include expanding the hole, allowing suitable clearance to remove the box through it.

I am putting on the surgical mask now ...

Rob

I do not know how a side-stand can be fitted to a Mk3 Seeley - there might be some way of attaching it near a footrest, but it would need to remain clear of the road. The Mk3 Seeley frame is immensely superior to a Featherbed. With a Featherbed, the motor must be as far forward as possible, and the exhaust pipes usually collide with the front down tubes of the frame. The Mk2 Seeley frame has the same problem. The 2 into1 exhaust usually ends-up with unequal lengths in the header pipe - which is OK if you believe the exhaust is only there to get the gas out - under the frame is better. The Mk3 Seeley frame does not flex. Often what feels like flex can be due to the motor being back a bit. We usually ride with our brain glued to the rear tyre contact patch, but light in the front is a big deterrent to high speed cornering. Smooth power delivery is important. I think that with my bike - the gusseted piece of chrome-moly tube in front of the motor makes a difference. The Gus Kuhn 750s probably had the ladder in front of the motor - it would allow the motor to move sideways at the bottom. On my bike that tube is very strong and almost a spring. The mounts are offset and there is a bend in the tube. For the frame to flex, it needs to distort that tube. - There is a fairly long distance from the tube to the pivot.

my engine plates are shaped as Commando ones ie different each side with one supposedly for you to pass the complete box through. What I have found is it is not worth the effort!
I build everything in with the engine on a Jack, front plates & bolts loosely in & stick the box in from the drive side, add the bolts & studs & get things in position before adding the drive side plate. Again loosely nip everything up & tie it all in with the rear frame mounting bolts. I've found this is the best way to deal with the bottom gearbox mounting stud, although on one set up I did tap out the gearbox M10 & use short bolts! I may find working on it a bit trickier as I'm getting older but I did nick the engine a few years ago & race it in the Mk2 frame at Snetterton after a late call to say my mate had done the engine in! It only took me an hour & a half to strip & less than an hour to drop it into the Mk4 as I had help.

Hi Al look at my first photos in this post, it is very easy to fit a side stand to a Seeley Mk3 frame. The Maney 2 into 1 & the one built in New Zealand by Brooking 850 have the same length primary. No the Mk2 does not have the same problem as a featherbed again look at a photo of my Mk4 it's as far forward as you can get it & the pipes dont get in the way of the frame tubes. The Mk3 frame does flex lol you cant have an engine out front like that & there not be flex. Your superior head steady & your ladder help but you have stated that you loaned the bike out & the rider said he 'felt' it move. Other than being petite, Seeley frames & Commando engines just go together & pretty much everything works & they always have done.

Indeed ... probably better part of valor to do it that way. I've got it setting on a flat jack, right now, as you described. You're right, drive side plate like a "lid," easy on and off. No stress and I'm not dizzy (!). Good advice, Chris.

Surgical mask stowed.

Rob by the way the RGM kick start (thanks Nige) had a cranked gearbox mount to throw it out further, as well as the advantage of the extra length. I ran a tiny leisure dry battery under the seat. Never had a problem as long as it held a bit of charge.

jan nelder said:

what are the input forces to the frame that you are starting with?

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Generalized chassis loads. The absolute load size is not important (decomposition can be dimensionless), but if you ask med for a figure, I will assume a gravity load of 90 kg*g = 883 Newton, fluids included.

- Knut

Chris said:

Hi Al look at my first photos in this post, it is very easy to fit a side stand to a Seeley Mk3 frame. The Maney 2 into 1 & the one built in New Zealand by Brooking 850 have the same length primary. No the Mk2 does not have the same problem as a featherbed again look at a photo of my Mk4 it's as far forward as you can get it & the pipes dont get in the way of the frame tubes. The Mk3 frame does flex lol you cant have an engine out front like that & there not be flex. Your superior head steady & your ladder help but you have stated that you loaned the bike out & the rider said he 'felt' it move. Other than being petite, Seeley frames & Commando engines just go together & pretty much everything works & they always have done.

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I did not loan my Seeley 850 to Bill Horsman. I asked him about the handling of the Jerry Kooistra Mk3 Seeley G50 before I rode my Seeley 850. He said that when he pushed the Seeley G50 really hard, he could feel the front move. I have never felt that with my Seeley 850. It makes most other bikes look stupid. When I come out of corners that fast, it takes a really fast 1000cc four cylinder bike to beat it to the end of the next straight - and if they get there first, it usually does not matter. My regret is that I will probably never get to race again. In road racing and life generally, many people are defeated by their own mindsets. The Seeley 850 has a methanol-fuelled 850cc engine - it has to do something when all the bits work together. Being defeatist is bullshit. When some guys get blown to the weeds on a straight, it knocks their backside in - 'patience is a virtue'. With any racing motorcycle, we do not know what it can do until we work with it. The first time it is raced, it will always go backwards. The first time the Seeley 850 was raced, I gave it to my mate to ride, so he had the problems. I am not stupid.
'A poor workman often blames his tools' ? -BULLSHIT ! - When you see a really top rider, you do not usually experience the bike they are riding. A really well-sorted bike is always fast, regardless of its horsepower. All this crap about better tyres is bullshit - 'the rider adjusts to the bike and the circuit'. If you have an ego -lose it. You will always be beaten until you become faster.

The last time I raced the Seeley850,I revved it to 6000 RPM on the start line to get it to keep up with the others to the first two corners, and I had waited until my last race to do it. I rode under and past the three leaders at turn 2, and was well out in front when the fuel line came off. The gearbox was AMC with a Manx close ratio gear cluster. I expected it to give-up. The bike now has a 6-speed TTI box. I will probably never race again. We have lost our local circuit, and I don't want to drive hundreds of kilometres to race. My mate has died and training another helper is a problem. We do not have many meetings these days. Times change and it is not 'as it was, so it always shall be'. The British have a better attitude towards old cars and motorcycles.

So swap out a G50 single for a 850 Commando lump. I think that answers the question.

Chris said:

So swap out a G50 single for a 850 Commando lump. I think that answers the question.

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The G50 might have been lighter in the front, but what happens with handling usually happens at the opposite end to where it feels to be. If the damping of the rear shocks is insufficient, it is usually felt as though it is because of the front jumping around. Bill Horsman was not a beginner. He raced once on the IOM and won the Junior Clubman's TT with an Aermacchi 350. Most people have never seen him race. He stopped racing after a guy rode a bike out of a gate on the back of Mount Gambier circuit. He hit it with an RG00 Suzuki and broke both of his legs. He was sponsored by Cornell Suzuki in Adelaide.
The reason I asked him about the Mk3 Seeley frame's handling was exactly the same doubt which you expressed. It does not flex - but two frame tubes run from the steering head to the pivot. I know of one Mk3 which bounced off a tyre barrier - it bent where the frame tubes cross over.