ISO Seeley ??

I'm new to Commandos, and I'm still in the novelty phase of appreciating how good the ISOs are at containing the harm done by vibes especially of big tuned motors.

But I do love Seeleys'...

So, the obvious question: has anyone built an ISO equipped Seeley?

Is it possible? If not... Why not?

The main virtue of the Seeley frame is the extremely firm link between the handle bars, your backside and the rear tyre's contact patch. Vibration is not a problem when you balance the crankshaft correctly. ISOs were invented to cope with the conundrum of a big vertical twin motor and rider comfort - not an issue on road racing bikes on smaller circuits.

I don't see the point. An isolastic Seeley would have the swingarm cradle mounted, as is on a Commando, to prevent chain tension pulling the cradle off line and 'locking' the iso's, which would then transmit vibration. Despite the incorrect assumption from some experts on this forum - it's not the design of the Commando or the frame which is the problem. Also, you might struggle finding anywhere to put three mounting points to form a plane on a standard Seeley due to no front downtubes.

Its a weekend so most likely away from work stations to respond, so just me right now. Not many have or ever will it seems but some folks, like racers, keep pressing faster and faster in turns to discover and explore limits of their cycle and skill and either live within those limits or seek better performance at expense of pilot comfrort/health and bike parts. Most effective cycles so far are very rigid in frames/engine which transmit damaging vibes, so frame must be made to take that but then gets so rigid it can have trouble taking up all the conflicting forces from tires, road texture and wind forces. Some folks have put iso's in Featherbeds and love it but don't know of any racing that combo or reporting riding track days or in public to limits to compare with standard Feather bed or against rigid-solid mounted engines. I've seen recent post that state the C'do frame is stiffer and about as light or lighter than Featherbed.

Seely's & others are made as light & solid as possible for best control of power/speed on tire patches to get ahead of other manic rider-racers so abhor any rubber looseness, so to put iso's in them is taboo and against whole concept behind current rigid as can be frames. Seeley's are known to break with Commando engines, usually just above the rear engine mount tubes so vibration lowering by crank BF and light piston/rods is a list topper concern when spending. Maybe you could be the first one to soften the Seeley and still stay in full control comfortably. Only isolastic Commando powered racer that can compete with the solids is Herb Becker's, Doug MaRae ridden example with 3 robust swash plates that tie power unit-rear tire to frame forks/front tire. Kennie Cummings and Dough swapped rides to compare, but only Kennie reported back here - that he felt Doug's front steering was not as sure or easy as his Seeley but definitely smoother. Doesn't seem to hinder Doug though.

Published interviews with Fast Freddie Spencer, goes into some detail on the too solid vs too wiggly frames and forks/swing arms, said so far attempts to build in compliance in swing arm and forks to leaned over forces are either too weak to control or just break. Set ups for Freddie can not be ridden well by other racers both he and Honda stated, so put that into pipe to smoke on.

Personally I think I've solved both sides of the upset equation with compliantly tri-linked rod links, smooth as can be to point of completely disappearing to my sense of a motorcycle under me, yet have not been able to induce any rebound or other upsetting surprises at'all and even provides a way to press rear harder into surface for more power hook up on edges, till point i've run out of power to go around sharper faster. Nothing else like it so far so unbelievable to everyone but plans to demo what I mean someday as main motivator in furious fun side of my life left.

I think you could successfully put ISOs on a Mk2 or Mk4 Seeley, however it would be essential to fix the swing arm spindle so that the system was not dependent on the adjustment of the ISOs or flex in the engine plates. You could still have ISOs with the vibratory motion in the engine gearbox assembly forced to be circular about the swing arm spindle (and that is probably the only important direction anyway). I think it is essential to maintain the rigidity offered by the tube from the steering head to the end of the swing arm spindle. It is all about the rear ISO mount and the construction of the swing arm mount on the Seeley frame. You would have to do a lot of thinking about how the engine gearbox assembly is pulled by the rear chain. The design of the head steady would need to accommodate the change in concept - probably need rose joints.

Acotel, what CR ratio are you running? That has a big effect on vibes.
I raced a Norton crank in a Triumph engined Triton, so it was solidly mounted, dynamically balanced to 80%, it was smoother than any other Triton I've ridden. Yet still, under racing conditions, breakages were a problem. Undoubtedly, some of this was down to my engineering / fabrication mistakes, but some was simply down to the vibes. It was running 11.25:1 CR and revving to 7500rpm.

Regarding your comments about pivoting an ISO motor on the swinging arm spindle, I nearly agree with you, I believe Triumph made a linkage system on their AV models, that would probably be the design to copy here.

I'd like to know what the solidly mounted 920s are like. Can anyone on here enlighten me?

Al-otment, some Seeleys did have a full cradle, so fitting 3 ISOs (inc a PR style head steady) should be possible. I'm just trying to explore whether or not it would be beneficial.

Fast Eddie said:

I'd like to know what the solidly mounted 920s are like. Can anyone on here enlighten me?

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Back in the '80s I tried putting a 920 engine balanced at 62% (for my Commando racer) into a Vendetta copy of a Seeley frame, and it shook so bad on the track at Riverside that you couldn't ride it more than a couple laps before loosing all feeling in your hands. It was a temporary swap to try to get the bike ready for a race, but didn't work out. I later put the original 878 cc engine back in, after a rebuild, balanced to a little over 80%, and it worked fine, managing to complete an AMA Battle of the Twins race at Daytona with no problems. I think the answer to your question is that a 920 can work out in a rigid mount, but it needs to be balanced properly for the frame design and intended use. Light weight reciprocating parts would also help. The 920s I built back in the day had pretty heavy pistons, although the stock rods we used were about as light in the small end as you can get and still have reliability.

Ken

I can't see the point/benefit of having the swingarm pivot and rear iso on a common axis. Important factor is for the swingarm to be cradle mounted as mentioned before, so as to ensure the iso's do not transmit vibration due to cradle assembly skew under otherwise external load from chain pull.

wakeup said:

...when I started at Andover the Commando frame came up in conversation. The comment was made that it was torsionally far stiffer than a featherbed frame. During the development of the Commando there were a series of tests to measure torsional stiffness, it seems that the Commando frame was (is) three times stiffer than a featherbed, and weighed far less.

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The above is presumably tested between swingarm and steering head axes.
I don't think there would be any benefit compared to a blueprinted Commando frame and it would be a lot more work.

The perimeter framed bike I built in the 90's used a suspended engine and four isloastic mounts with the swingarm attached to the trans. It was somooth as an electric motor and had none of the soggy handling attributed to isolastic mounts. Jim

comnoz said:

The perimeter framed bike I built in the 90's used a suspended engine and four isloastic mounts with the swingarm attached to the trans. It was somooth as an electric motor and had none of the soggy handling attributed to isolastic mounts. Jim

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Neat! Think I've spotted 3 of the mounts - 2 at the rear on the vertical tubing and 1 in front of the barrels. I assume No.4 is in the standard head steady position? If this is the case, Jim, I wonder if you tested with the front of barrel iso removed?

Al-otment said:

Neat! Think I've spotted 3 of the mounts - 2 at the rear on the vertical tubing and 1 in front of the barrels. I assume No.4 is in the standard head steady position? If this is the case, Jim, I wonder if you tested with the front of barrel iso removed?

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Yes, the fourth iso is on the head. I first built it without the front iso and hanger. It was good as long as the isos were adjusted very tight but that brought out some vibration.
After I installed the front hanger and mount it was like a riding a solid mount frame but without the vibs. Jim

Fast Eddie said:

has anyone built an ISO equipped Seeley?

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I don't know of any; not saying it has not been done. There's a few featherbeds converted to Isolastic (Featherlastic) and everything I have heard about them was positive.

Fast Eddie said:

Is it possible? If not... Why not?

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As acotrel stated above, the Seeley Mk2 is a full perimeter frame and would be the easiest candidate and in my opinion, yes, it is possible. There will be a sacrifice in frame stiffness with the loss of the engine/trans structure bolted tight inside the cradle but I cannot say whether it would be of any consequence. There's also of the two cross tubes that receive the rear trans plates; if you could get the swingarm and iso in there without having to cut & move these two tubes, all the better. I know of at least two Seeley Mk2's with a solid engine/trans mounts but without a solid head steady.

Really a neat idea.

Dances with Shrapnel said:

I don't know of any; not saying it has not been done. There's a few featherbeds converted to Isolastic (Featherlastic) and everything I have heard about them was positive.

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You need to ride one sometime. Jim

comnoz said:

You need to ride one sometime. Jim

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Are they good, bad or ??

I know how good a Commando can get having ridden one of Herb Beckers racers. I actually deliberated with Randy Illg of Framecrafters.net on going with a Featherelastic when we started the Featherbed road racer build a few years back.

As for the torsional stiffness of the iso Seeley concept, I wonder how much stiffness is lost when trying to transefer to bike rolling moment through to the rear wheel?

The Holy Grail is termed Flexural Rigidity aka Goldie Locks design.

http://www.motorcyclistonline.com/newsa ... _rr_frame/

Hm, Jim's frame really stirs me more restlessly. Uh oh. Factory or Fancy frame,
Lions and Tiggrs and Bears >Oh MY!

Its got all kinds of hard points for my needs and with so much rubber area - not a whitworth of effect on swing arm pivot mounted out board or inboard. With the rear travel I'd want a chain tensioner is needed on bottom and rub plate on top d/t sa dangle angle range so engine/trans unit could be only thing isolated. I can see a new hybrid breed Commando here with other current goodies - for the next generation and a few ahead of their time now. I've a good sense of what I want to feel happening under me and what I don't. I might want the swing arm to be rubber mounted separately too. Oh my oh my oh my no appointments as snow front hits so feels like a white lightening morning to calm down. Will look into the sheet metal shop in the woods nearby.

The neat thing about that frame was it weighed half of what a Commando frame weighed. The bike weighed 280 lbs with everything but gas. Jim

Uhu-A-hhhu-A-hhhh-A-uhh, of donkie honking and honking on a hunk a hunk of frame construction I can't get out of my mind and as I am out of my mind.... by the subject matter + two sNorts = all it took for this state of being a Commando crazy with a few tough surviving neurons to quiver...




Any id of where I'd be w/o this group therapy? Thanks for putting up and I mean it.

My 850 only runs standard petrol compression with methanol fuel. Rohan has taken me to task over the low comp ratio saying you need high comp. to get methanol working properly. High comp is an option with methanol, however not absolutely necessary. My friend's 50s 500 manx on 14 to one comp. ran two degrees ignition retard behind standard timing for petrol, my 850 runs 4 degrees more advance ahead of standard timing for petrol - if you think about burn times it is logical. And it dramatically affects the way power is delivered around TDC. We also run a speedway Vincent with flat top pistons on low comp. with methanol, it is as quick as the 12 to 1 comp motors. Any vibes I have with the Seeley are low frequency, however the bike is smooth and fast at 7,000 RPM. Crank is balanced at 72%.

I was running 8500 to 9000 rpm with the bike in the picture. 12-1 compression and the largest Norris grind cam. 42mm FCR carbs.
At 85% balance factor the cases lasted one weekend. With a 50% balance factor I could get a whole season out of a set of cases. Jim