Isolastic Links

Someone stated the Commando frame is three times stiffer torsionally than a featherbed so that blows your twisting from stem to stern theory out of the water - and what about the Proddy racer lapping at an average of 96.53mph?

Rod end replacements for isolastics don't improve anything over a freshly adjusted isolastic.

Sealed rod ends just stay like a freshly adjusted isolastic indefinitely. Jim

Thanks for pointing that out, Jim. I was under the impression that the rod-ends were being fitted as a cure to correct handling problems for which the isolastics were, incorrectly IMO, identified as the cause.

Extra lateral control -either rod ends or isolastics -on the head and under the swingarm do help stiffen things up quite a bit. Jim

how come Peter Williams on the Monocoque averaged 105.47mph during the 1973 F750 TT win using iso's and averaged 96.53mph on the proddy racer Commando using iso's

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excellent question!

and your point is that correctly set up isos work just fine

my question: did Peter Williams have a rod linkage head steady in 1973 TT win or stock donuts?

also, anyone know is Peter's bike was equipped with an underneath swing arm additional stiffeners?

I can't seem to find any information about this

I would suspect [but I don't know] that he would have used a third idolastic on the head as was normal in that period.

I would hate to think of getting on the track with a stock headsteady, not because of the rubber mounts as much as the fact that they tend to break when you need them the most. Jim

He just had the three isolastics on the monocoque. No need for a fourth if the three form as big an (near to) equilateral triangle as possible for maximum torsional and lateral resistance from the engine/cradle/frame assembly.

I agree with replacing the standard head steady for an iso unit or a rod end. I think below or above the swing arm is a compromise for the rear iso position. I guess they placed the rear iso where it is as it's away from the road dirt and in a more accessible place than if it were low down. I can see the point of a fourth iso below the swingarm - but to increase torsional resistance not lateral.

comnoz said:

This has been my front mount for many years. Maybe I will get the rear done this winter. Jim

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That looks like a more sensible approach especially if it is dome at both ends of the engine plate assemblies. I would try to gusset and reinforce the attachment points for the frame mounts, or the mod could result in cracking. If there is such a thing as a double ended Heim joint you could put in the middle under the rear of the gearbox and attach it to the frame tubes on both sides in a straight assembly. All you need to achieve is elimination of sideways movement of the pivot. If you made the Z plates out of chrome moly steel you could hang it off those.

Al-otment said:

The iso's don't require taming. This is a misconception which has been perpetuated ever since it was realised that some Commando's didn't handle as well as the Featherbeds. I've asked this question before - and still none of the isolastic critics have answered it - how come Peter Williams on the Monocoque averaged 105.47mph during the 1973 F750 TT win using iso's and averaged 96.53mph on the proddy racer Commando using iso's, finishing second to a Triumph but also ahead of a Triumph in third during the 1972 production TT?

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I'm not so much an isolastic "critic" as I am someone (among hundreds) who has FELT the difference that ADDING rod links makes. We're not ELIMINATING the isolastics, just limiting their range of motion to fall as closely in line with the parallel and perpendiculars in the rolling chassis (or, as mentioned, reducing torsional forces and reactions).

Now, as to why Peter Williams averaged 105+ in the '73 TT; well, that has something to do with the ENTIRE PACKAGE - chassis, suspension, brakes, engine, and RIDER.

Shall we argue that the Triumph NOT having isolastics was the reason it won in '72? I don't think so.

3'x's stiffer than a Featherbed, cool, so takes 3x's more tire load to twist it and that gives extra thrilling cornering control to experience in a ole clunker. The other thing that impressed me too was how well tri-links worked in raw woods and pasture and ravines and woopty-doo's. When I tried the RD350 in same paths,it was too wiggley and hi CoG for me to have as much fun on so stayed on the paths till back on Peel to head off the path for some freaked out deer in chest hi brush. The trial bikes had hi center advantage but not the grunt to power up ravines like Peel, so could catch up after hesitating in fear shoving over an edge she'd hung up on - temporarily. Trouble comes on pavement where ordinary C'do power ain't enough to hit the speeds balloon tire sports bikes can in turns leaning to 45', unless bad surface then they jitter bug while Peel just passed that shit through like a flag wired to the tire patches. The C'dp teeter tooter pivot is the rear isolastic, unless only linked at front and top then the front iso becomes the pivot point with similar Hinge onset at only some what higher load imbalances and more sudden harsh higher freq rates of terror. I wonder if a steering damper set on high might be even better as front link. I love the sense of front tire on another vertical angle than rear, just not the snap backs that rebound past N. Peel had to leave iso gaps pretty close to factory or would buzz if too tight and got a bit sloppy if too loose, so tended to run rear looser over .01" and front somewhat under that. Maybe we can contact Peter Williams and quizz him on various issues. I think I'm the only one her stating and claiming I can't use any better handling its so solved so only seeking better power to weight to take more advantage and maybe find limits I just couldn't with what performed like 70 hp/350 lb package. Modern cycles are only corner cripples when compared to vintage cycles over 45' w/o power to wheelie above hi way speed. I rather have a date with a movie start than a track day on any other cycle i've tried or seen, but Peel's multiple road orgasms have spoiled me to even use human sex as bench mark of the highs, more like psychedelics to me. Don't yet know about hot battery pack robot sex though.

Links placed close to the isolastics still act as pivot points even if essentially able to set iso gaps stable to almost no gap, still leaves long thin lever arms and torsion bars with tire patches on the ends.

1up3down said:

how come Peter Williams on the Monocoque averaged 105.47mph during the 1973 F750 TT win using iso's and averaged 96.53mph on the proddy racer Commando using iso's

Click to expand...

excellent question!

and your point is that correctly set up isos work just fine

my question: did Peter Williams have a rod linkage head steady in 1973 TT win or stock donuts?

also, anyone know is Peter's bike was equipped with an underneath swing arm additional stiffeners?

I can't seem to find any information about this

Click to expand...

My point is that the number one priority on any motorcycle frame with a swing arm is that the steering head and swingarm axes need to be as square as possible in two planes. If this is not established then typically additional mods are treating the symptoms of mis-alignment between these components.

Hmmmm, ................I wonder.................., anyone out there providing this most valuable service?

:roll:

Ugh I must be the only one in the world so far with a 2/3rds compliantly tri-linked isolastic cycle that reveals physics so plainly > a motorcycle MUST get its front and rear patches Out of Line in patches travel lines and out of vertical alignment to each other to steer well at speed by allowing the stem vertical axis to get out of square with the horizontal swing arm axle plane. A perfectly Neutral handling compliant load compensating tolerant frame also reveals every cycle has an innate Hinge pivot in front axle angle to gravity & relation to rear tire angle of thrust. If this makes no sense to anyone then more evidence none of ya know what you are missing out on yet. They should of had a race down unpaved Pikes Peak as power equalizer to see what really going on but might only be Peel that allows using Gravity Hinge racing down Mt's instead of just the easy way up, sheeze. If ya drop a bullet from your teeth at same time as firing a rifle out level, both hit ground at same time. If ya don't understand how that applies to two tire inline craft with a dual vertical and horizontal hinge in front, no matter I do.

grandpaul said:

Al-otment said:

The iso's don't require taming. This is a misconception which has been perpetuated ever since it was realised that some Commando's didn't handle as well as the Featherbeds. I've asked this question before - and still none of the isolastic critics have answered it - how come Peter Williams on the Monocoque averaged 105.47mph during the 1973 F750 TT win using iso's and averaged 96.53mph on the proddy racer Commando using iso's, finishing second to a Triumph but also ahead of a Triumph in third during the 1972 production TT?

Click to expand...

I'm not so much an isolastic "critic" as I am someone (among hundreds) who has FELT the difference that ADDING rod links makes. We're not ELIMINATING the isolastics, just limiting their range of motion to fall as closely in line with the parallel and perpendiculars in the rolling chassis (or, as mentioned, reducing torsional forces and reactions).

Click to expand...

Reducing torsional forces and reactions - really?

grandpaul said:

Now, as to why Peter Williams averaged 105+ in the '73 TT; well, that has something to do with the ENTIRE PACKAGE - chassis, suspension, brakes, engine, and RIDER.

Click to expand...

I agree, the entire package, including isolastics but not rod-ends. The rider is obviously important, but put a great rider on a badly handling motorbike and you've still got a badly handling motorbike - which the monocoque was not, as well as the 1972 TT production racer.

Man, talk about how to start an argument! Thanks so much for everyone's input, especially the links and images. Once my new MkIII verniers are installed and adjusted, I'll toy with the idea of installing links. 'Probably won't, but, since they work so well on the top mount, why not the other two?
Now, what should I bring up next...

Nathan

Thankgoodness a plain ole well fettered C'do is plenty good enough to have some sane thrills on but it you are into risking life and limb limits for a joy ride - un-tamed C'do can take ya down before traction is the limiting factor. I'd say if only doing one link do the breast support up above the mount some inches and tie both down tubes together so they don't twist in torsion spring backs. Ask us what grease is best handling inside isolastics and swing arm and chain too.

hobot said:

Ask us what grease is best handling inside isolastics and swing arm and chain too.

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No way, Steve! I already added fuel to that fire some months ago when I suggested silicone grease for the isolastics. Some people take this way too seriously!

So what's the problem with silicone grease? Isn't that what the factory recommended?

Red rubber grease?

Baby powder to red eye gravy would work fine. Swash plates, rod links and rubber bumpers and super magnets leaves lots of room to experiment.