Noob isolastic question

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Ghostbuster

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Hi again,

I want to adjust the isolastic system on my stock MK3 Commando (I have very bad foot peg vibrations below 3000RPM). I found many threads regarding gap clearance and what to expect at different RPM's vs. gap clearance but not much on the actual procedure. I need some basic knowledge, I know that I am supposed to loosen the "through-bolt" and the rotate the nut with the holes but where do you measure the gap? and are the front and the back isolastic adjusted in the same way etc.?
 
Pull back the rubber boot (gater) and you will see the gap, sliding Teflon washer between two parallel faces. Same as the front, except it's more confined. Your iso's may need replacing if they are 38 years old.
 
Ok, didn't know there was a teflon washer. Regarding replacement; what is most likely to have worn them; age or mileage?
 
Ghostbuster said:
Ok, didn't know there was a teflon washer. Regarding replacement; what is most likely to have worn them; age or mileage?
Click to expand...


Those washers aka PTFE's turn to dust after a few decades due to lack of lube from bad gaiters letting dirt in.
So if you peek in there and the gray washers are gone or wafer thin and dry it would time to replace them.
Hell, some people run then with out gaiters.
 
There seems to be climatic differences in how well isolastic components hold up. My '74 was a pile of rust when I brought it home after sitting for three and a half decades, but the isolastic rubbers were in terrific shape and the teflon washers looked like new. So I guess cold and wet is good for something! I am beginning to suspect that their condition has more to do with what they got lubed with.

Russ
 
" Vibration up to 3000 RPM - Rear tight, Front OK
Vibration 3000-5000 RPM - Front tight, Rear OK
Vibration up to 5000 RPM - Both tight"

Or isolastics are toast!
 
Welcome GhoustB, I hate to state the obviouse but it sounds like you do not have a "Parts book" and a workshop manual, both of them are important to have with a bike like these & you can go to the tech section here and down load them or buy them. Get familior with the stor "Old Britts" they have a great web site that will help too. The parts book has pictures of how it all goes together and gives part #'s so you can buy and ask questions about specific parts. Good luck & let us know how it goes.
 
Hi again, and thanks for all your answers, yes I guess it is time to get a workshop manual and a parts list, I'm slowly but steadily getting better at servicing this bike :)
 
By the way, I've been timing the bike with a timing light, and I might have around a 0,5-1 degree difference between cylinder 1 and 2, can/will that cause any vibration??
 
Are you running a points ignition? I suspect the timing difference is due to a difference in the gap on the point sets, such that one is firing a little earlier than the other. I don't honestly know how much gap difference it would take to translate to a 1-degree difference. I would make sure that both point sets are in good order and that one of the blocks isn't wearing faster than the other for some reason.

Russ
 
Yes I'm running with original points. I kinda like how the whole bike is stock, even though that points can be adjusted differently and a electronic ignition can't.

I actually didn't think that difference in contact gap would give different timing, I mean the spark fly when the contacts open right?
 
Ghostbuster said:
Yes I'm running with original points. I kinda like how the whole bike is stock, even though that points can be adjusted differently and a electronic ignition can't.

I actually didn't think that difference in contact gap would give different timing, I mean the spark fly when the contacts open right?
Click to expand...
Yes this is true. But, the points set at a wider gap will fire sooner and respectively the point with the tighter gap will fire later. This is a direct affect of when the points cam make contact with the points and changes the point in time (timing) when the points actually break (spark).
 
I recently bought an 850 Mk2A which despite having a rebuilt engine and gearbox appears to still have the original isos front and rear. The boots are heavily perished and their are no multi hole adjusters so I think I'm right. There are a few niggles, the first of concern is the vibration which is right the way through the rev range although is does seem smoother above 3000rpm which is unfortunately where the clutch slip starts on rough surfaces. Anyway, the first job is the isos. I want to fit a better system but am confused by the bewildering amount of info and types. I've tried checking the clearances, but at the risk of seeming daft, I cant see where the feeler gauge actually goes. Also it would appear I can do the conversion myself, but its a lot of work and if I'm honest I'm not that good at mechanics and nor do I have much garage/workshop space.

So. - How do I check the clearances for front and rear?
How do I tell what I've got in there right now?
What should I buy to replace the parts? Is there a 'kit' available?
Should I have a go or should I get a pro to do the job?
 
Thanks for that - I'm off to buy a trolley jack and visit ebay for a factory manual. The Haynes one I got with the bike is nowhere near as useful. :D
 
Rider5 said:
What should I buy to replace the parts? Is there a 'kit' available?
Should I have a go or should I get a pro to do the job?
Click to expand...

The front Iso is reasonably straightforward to service (or refurbish if the rubbers are perished) as the complete assembly can be removed. Some type of rubber lubricant will be needed (red rubber grease etc.)

The rear Iso is somewhat less easy to work on, as the cradle needs to be moved in order to replace the rubbers, and if you are unlucky, you may find the long Iso mounting stud is rusted solid.

Adjusting the Isos isn't a job you should have to do very often, however, the vernier kits do make it easier, if the rubbers require replacement then you might just as well buy the vernier kits in my opinion.

Some vernier Iso kits require the front Iso mounting tube to be machined down, the Hemmings vernier kit does not require any machining to fit, so, as you seem to be posting from within the UK I suggest you speak to Mick or Angela Hemmings (http://www.mickhemmings.com/) as the Hemmings vernier kit does not
 
Ghostbuster said:
By the way, I've been timing the bike with a timing light, and I might have around a 0,5-1 degree difference between cylinder 1 and 2, can/will that cause any vibration??
Click to expand...

Given that, kinematically, a 360 degree parallel twin is about the most efficient device for turning hydrocarbon fuel into vibration, I think a 1 degree difference in ignition timing is insignificant.
 
Yeah, kinematically! That's exactly what I was thinking!

Ok, seriously, I'll go look it up now. :)
 
Given that, kinematically, a 360 degree parallel twin is about the most efficient device for turning hydrocarbon fuel into vibration, I think a 1 degree difference in ignition timing is insignificant.
Click to expand...

LOL !!!

brilliant
 
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