isolastics

Looks like my next job is to look over the isolastics. The clearance is about right, but I need to at least replace the gaitor.[img][/img]

yep, mine look like that too. Hopefully I can keep that for a winter project.

Finish tearing the gaitor off, then have a look (post us images) at the visual concentricity.

Are you trying to estimate the condition of the rubbers inside?

I was hoping to get to the isolastics, swingframe and so forth next winter. At least, the front isolastic is easier to get to than the rear. I also have a "spare" I could use from my friend's Commando (whose motor I blew up).
Every time I read a new chapter in the shop manual or a new section in the service notes, I find something new to work on (yesterday I rerouted the clutch cable per the service notes, which made the clutch much lighter.
My plan is to rebuild components as I go so I can ride the bike this year then next winter I can do a complete restoration by just rebuilding the motor and gearbox, repaint the frame and have the other major components already gone through.

Just trying to get a view on a few different ones.

would you like me to post a photo of one removed from a '72? It's late now but I can post it in a day or two.

I can tell ya after seeing 3 front sets of cushions in '71 and 72's and the photos above, the center tube will be off centered so one side of cushion mooshed out a bit wider and likely significantly softer than new. Its traditional to just flip em but I prefer new with beveled rims. If gaps were still in range then not much will be noticed by new ones but a bit later vibe isolation and a bit later onset of hinge closer to point of no return. If ya replace front save to put the old cushions in the rear for better isolation and handling load support.

Yup, new ones on order from Old Britts.
I hate the idea of replacing the rears at this point since they are so inacessable. It sounds like you have to disassemble the primary to get to them. I would plan on upgrading the alternator, rebuilding the clutch, rebuilding the swingarm, then might as well disassemble the gearbox for inspection, polish the covers, powdercoat the frame......

If you don't have the engine spring installed you may want to consider getting those parts and installing. It really doesn't do much for the vibes at speed but at idle it does, plus it pulls the front iso up more centered than without, and also helps center the rear one. You'll need the later boxed style head steady or some of the replacement head steadies have a place for the spring.

Dave
69S

DogT,
Are you referring the the Mark 3 head steady upgrade? I can do that. Many posts in the past about the Mk3 isolastic upgrades left me fairly unimpressed.

Yeah, I think that's the MKIII head steady. It's not a great upgrade or performance enhancement, but it does pull the front isolastic up so it may not compress over time as much. Just a thought and it's only a few bucks if you don't have to buy the head steady. I notice my eyeballs are not bouncing around in their sockets when I go down my drive in 2nd gear at about 2000 rpm, that's all.

Yeah can't blame ya leaving the rear isolastic be as any way its attacked, by hi stress-strain method leaving most the bike intact or taking it down far enough for easy access both suck out nicer ways to spend remaining life time. All this mechanical and mental exertion by others leaves me ready for a nap today : )
My ride is chain adjusted and oil topped off ready to do 40 miles commute vacation time to work and back. I do have to put out of mind all the things I've fixed or have stopped the show while riding, to get some pleasure w/o gritting teeth.

Has anyone ever replaced all the rubbers in the isolastics with poluurethane bushes ?

acotrel said:

Has anyone ever replaced all the rubbers in the isolastics with poluurethane bushes ?

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That would be just like hard mounting.

At least when I take the bike 3/4 of the way apart to get to the rear isolastic, I can at least mount the horn in the original location.
Thanks for not commenting on the rust spots and crud. I kinda like the overall patina. The bike is not as purdy as some in the gallery but not as ghastly as the "barn finds". This one was more of a "parking lot find". I've been polishing and repainting parts as I go through them rather than completely disassembling the bike and doing it all at once.

I like hard mounting.

acotrel said:

I like hard mounting.

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You know what to do.

Reuse old rubbers there, too?

concours said:

acotrel said:

Has anyone ever replaced all the rubbers in the isolastics with poluurethane bushes ?

Click to expand...

That would be just like hard mounting.

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As you point out, that would defeat the whole design idea of the isolastic system. Back in the '70s and '80s some racers used to tighten the isos down until they were essentially unable to move, thinking it would improve the handling, but all it did was make them vibrate a lot more. Same result for a racer I knew who machined some cups to go over the iso tubes and lock them up solid to the frame, along with a rigid top mount. The Commando 52% balance factor works fine with the iso mounts, but is really unpleasant to ride in pretty much any solid mount frame, including a Commando with the isos converted to solid. Properly set up, the isolastic Commando worked fine as a race bike, as demonstrated by Peter Williams, Dave Croxford, Mick Grant, Phil Read, and others. But a lot of racers back in the day just couldn't seem to accept the idea that rubber mounts had any place on a race bike, and insisted on trying to defeat the isos to "improve" the handling. Oh well, it's all ancient history now.

The only iso mods that look to me like they might work are the linkage systems that have surfaced in the last couple of decades (or maybe even earlier. I lose track of time a lot.), or maybe the addition of another iso tube below the engine, or both. I haven't tried those yet, but at least they still allow the isos to function as intended, and people who have tried them seem to like them a lot. All my racing experience with Commandos was with the original PR isos and top mount, and as long as they were maintained and adjusted properly, they worked fine for me, so I'm a little bit biased in favor of not trying to fix something that isn't broken. Some of the other mods to Commando frames do have value in terms of adding some stiffnes to the frame/swingarm/cradle and/or reducing the risk of bits cracking and breaking.

And once again I realize I'm just repeating stuff I've posted before, so I'll stop trying to preach to the unbelievers on the virtues of isolastics, at least for a while.

Ken

Ken

Ken, I am interested in your opinion. I cannot reconcile the swing arm being mounted to two steel engine plates without believing they must flex. On pre-unit Triumph 650s, you could feel the flex in the seat tube, - the post 62 unit Triumphs with the ends of the spindle secured to the rear subframe by plates, handled at least as good as a featherbed Norton frame.
If it was possible to extend the swing arm bearing tube and move the bearings outwards, and pick up the ends of the spindle by changing the zed plates to hold a couple of silentbloc bushes, the motor/gear box assembly would be forced to rotate about the swing arm spindle when vibrating. There is not enough movement in some silentbloc bushes to allow the feel in swing arm flex to be felt by the rider, especially if they are mounted out wide. Some featherbeds had them in the swing arm. If this was done, the vibration from the chain would be transferred through the frame, however the silentblocs would moderate most of it. Your thoughts ?