Settiing up New Isolastics

Greetings.

I am new to this board, but have been around British/Italian motorcycles for about 30 years. For the first time in my life, however, I am doing a 100% rebuild/restoration of a '75 MK III Roadster; my goal is to have the finished product fully updated to the current knowledge base and to have it look very much like some of CNW creations.

I am at the stage where the engine plates and swing arm need to go back into the frame. I have noticed that left and right sides of the Isos protrude from their respective tubes at different lengths; I can also see that with the verniers that you could shift the plates/swingarm left or right about an inch or cock them up to, maybe 5 degrees (not that you would).

When I install the new Iso centers what is the criteria for how deep I set them, how much metal center should protrude from each side?

RS

Tire interference with chain is a big consideration. Beyond that, the adjustable isos are side-dependent (I forget if it's front or rear / left or right, but they are opposite). The fixed side is fixed on one side, adjustable side on the other, reversed front to back.

I'd dearly love to see a Norton with the rear tire centered, and both tires in alignment and perfectly vertical.

Rigid head steadies, properly installed and adjusted can contribute the final key ingredient to getting as close as possible.

Old Britts ought to have thier e-start kit available by the time you get to the stage where you'll implement it. You might offer to prototype for/with them, get a discount...

RoadScholar said:

When I install the new Iso centers what is the criteria for how deep I set them, how much metal center should protrude from each side?

Click to expand...

Welcome RoadScholar,

I think I understand, but the positions of the engine cradle and front mounting relative to the frame shouldn't be affected by the Iso. tube position, as the tube itself shouldn't protrude out from either the fixed or adjustable end caps once they are screwed into position (if it does, then something isn't assembled correctly?)

Therefore the position of the Iso. tube shouldn't affect the cradle or front mounting positions.

If the correct Iso. clearances are set on both assemblies then nothing should be out of line?

Just be aware that the engine cradle is not set central to the frame.

SAme page?

Grandpaul: Thank you for stepping up on this.The Mk III came from the factory with a starter, just need a couple more commutator brushes to do the job. My question is really about port and starbord, L.A.B. has made enough of a stab that my next question should yield the answer that gives me the proper confidence to make reassembly of the engine cradle a check mark.

L.A.B.: Thank you also, your response leads me to believe that we are almost there. I see the Isos as, essentially, three parts: the central threaded tube and the two threaded end cap assemblies, both of which can push or pull the central tube left or right within the larger exterior tube. I'd guess that using the cap assemblies you could actually cock the engine cradle in the frame, if you set each at opposite extreams (not that you would); more to the point you can move the engine cradle left and right a good 1/4 to 3/16 just using the central tubes threads.

I have my front mount here with me now, it is exactly as it was when it left the factory in 1975. I have the cap assemblies off and what I see is the two threaded ends, one with shoulder, one fully threaded. The fully threaded end (for the non adjustment cap assembly) protrudes 15/16 beyond the exterior tube, the left hand side--with the shoulder--(for the adjustable cap assembly) protrudes 7/16. I could duplicate this and move on, but I am trying to understand why there is such desparity and see if some improvement is sleeping here. I believe that the goal here is to see if both tires can run on the same center line, or at the least to insure that the offset results in a parallelogram.

Put another way: When you push out the guts of an ISO what criteria do you use to decide when the new guts are pused in far enough?

RS

Re: SAme page?

RoadScholar said:

I see the Isos as, essentially, three parts: the central threaded tube and the two threaded end cap assemblies, both of which can push or pull the central tube left or right within the larger exterior tube. I'd guess that using the cap assemblies you could actually cock the engine cradle in the frame, if you set each at opposite extreams (not that you would); more to the point you can move the engine cradle left and right a good 1/4 to 3/16 just using the central tubes threads.

Click to expand...

If I've understood correctly, I believe you think that the position of either the cradle or front mounting can somehow be adjusted by altering the positions of the abutment and adjustable cap along the Iso. tube threads?


As I see it, that's not really possible, as there isn't any way that the cradle or front mount can move laterally between the frame once the assembly is fitted into position, there simply isn't any room, as the space between the frame mountings is completely taken up by the outer cradle/fr. mount tube, tube caps, PTFE washers, fixed abutment and adjuster, the abutment and aduster should both be hard up against the frame on either side?

The Iso. tube also has no positive location inside the outer cradle/ fr. mount tube as it's free to move inside it, as it is only located by the fixed abutment.
Unless you were to attempt to expand the frame by screwing the adjuster out too far, in which case you would end up with far too much Iso clearance I don't think you could achieve what you have suggested?

Re: SAme page?

RoadScholar said:

I believe that the goal here is to see if both tires can run on the same center line, or at the least to insure that the offset results in a parallelogram.
RS

Click to expand...

I've been out of the scene for 20 years and am just getting immersed in Norton Mania again. My experience precludes the vernier mounts but as I recall the purpose of shims or vernier adjustments is solely to restrain sideways play on the mount system. Shims were to be added equally on each side to achieve the .010" tolerance of side play. For the sake of chain alignment parallax must be maintained between the engine, trans., and rear sprocket. I suppose by shifting the shims (vernier settings) more to one side than another and using spacers on the front and rear axles and also shimming the brake rotors one could align the wheels on the same center line whilst maintaining the overall balance or center of gravity close enough that you could still sit centrally on the seat.

>>>If I've understood correctly, I believe you think that the position of either the cradle or front mounting can somehow be adjusted by altering the positions of the abutment and adjustable cap along the Iso. tube threads? <<<<

Perfect understanding and well put, thanks!

Between the frame (front mount) and the guts of the ISO (no cap assemblies intsalled) there is 3/16 clearance that is made up, ultimately, by the cap assemblies. When I assemble the ISOs completely there is plenty to spare thread to move the mount laterally, without influencing the fit in the frame--tighten one side loosen the other, this moves the mount, but does not change the overall dimension. If the goal was to have the ISO guts centered and an equaly number of threads on both sides that would be enough information to properly set up the mounts. The fact that the ISO guts are not centered from the factory leads me to believe that the engine cases, where the mount attaches, is not centered either, but by how nuch?

Now, I could fit the mounts, engine plates, engine cases, swingarm and wheels and fiddle with the mounts until both wheels and on center or are in perfect parallelogram, and I will if I have to, but it would be so much easier if someone knew how to set the ISO guts relative to the mount that they live in and what to look for in the track.

I have a call into Matt at the Colorado Norton Works and will share what he tells me.

Happy New Year!!

RS

RoadScholar said:

When I assemble the ISOs completely there is plenty to spare thread to move the mount laterally, without influencing the fit in the frame--tighten one side loosen the other, this moves the mount, but does not change the overall dimension.

Click to expand...

As I see it, all you would succeed in doing would be to alter the position of the Iso tube within the assembly?
Moving the tube (Red) to either the left or right won't alter the cradle/front mount (Green) positions laterally, as they are located within the frame (Blue) by the fixed abutment (Fixed end cap) and adjuster (adjustable end cap) (Yellow) plus the tube caps and PTFE washers (Blue-Green).
If either end of the Iso tube extends out of the abutment or adjuster so that it rests against the frame, then something would appear to be wrong with the assembly?

As far as I remember, the fixed abutment is screwed all the way onto the Iso thread and then secured with the grub screw/set screw.

I agree with LAB's interpretation here. In the standard assembly notes, there is no suggestion that the isolastics are used as a centering device. The fixed abutment is screwed up tight and then locked with the grub screw.

The adjuster side, in my experience is correctly set with the the threaded tube perhaps 1/16" (from memory) beneath the top of the adjuster. If your threaded tubes are protruding, I would suspect that the copper loaded PTFE washers are missing or defective.

There remains, with the Mk111 as I understand it, the aspect that adjustment of the isolastics results in the frame being more or less sprung according to the position of the the threaded adjuster.

If one bears in mind how far a strong fitter can pull even a well-adjusted rear wheel out of line, I think that we have to accept that it's probably quite rare in use to have two wheels in line. That said, it seems to work although it works better on some than others :?

WHEW!

I like reading the book AND looking at the pictures!

We're There

L.A.B. You are right. Ultimately there is no descretion if properly installed. The person I spoke with at the Colorado Norton Works told me that the ISO guts are correctly installed when the fixed end cap goes just snug when it reaches the end of its threads.

I just finished installing the new ISO guts in my front mount. As in your picture the doing makes it much easier to see where and where you do not have clearance (or descretion). If the mount is adjusted properly it cannot shift, materially, to either side.

RS

Thinking about switching over my crazy-vibrating MK2 850 Roadster to new MK3 isolastics from CNW. Has anybody done this with their motor IN the bike? I have a lift that I can use to raise the motor, but I'm concerned about supporting the motor/frame to remove the front cradle (and the rear isos). Any experience/advice appreciated!

I've done the front mk3 with the motor in the frame. Bit tricky getting the mount back in as it's wider than the frame tubes, but not too bad. So yeah the front's possible as long as you support the engine, and aren't afraid to wack something with a rubber mallet.
Been putting the rear off for a month or two. Haven't decided if it'd be easier to just disconnect the top of the rear shocks and jack the frame up with engine supported, or to disconnect the bottom or the shock mounts and pull the whole cradle out. Having the gearbox still in there you would have to tilt and manuever to get it out PITA.

That does not sound very easy to me. How difficult/worthwhile to just pull the motor, pop in the isos and replace the motor in the frame? I do not have a centerstand, so it would have to be on the lift the whole time.

It'd be easier for you to pull it all out. I had to use the centerstand, a jack to hold the motor up, and something else to keep the front frame from falling.

I did it Pelican's way, on the centerstand but beyond that only using the hide mallet. And many, many swear words....

Looked into doing the rears when I had the gearbox out recently, but it looked like more than a bit more additional work and - touch wood - handling and vibration have been great to date, so I said the heck with it and stuffed the gearbox back in.

Great thread (til I got involved, anyway)!

I replaced the rear iso rubbers and installed the pre 75 vernier adjusters on both front and rear without removing anything.
I used a small floor jack under the crank to help support the front from falling, and placed the jack under the engine plates
between the motor and gearbox to support the rear. The front is is easy to remove, fiddly to put back.
Working on the rear iso requires patience and close quarter fiddling to do it without removing anything, but if I can do it,
so can anyone.
Kenny Cummings at New York City Norton website wrote an article detailing the procedure for replacing iso stuff while all in frame
his website is http://www.shelbynyc.com/nycnorton/74Commando.htm
contact him to find his article his email shows as nycnorton@gmail.com