Date: Thu, 11 Apr 1996 09:34:28 -0800
From: Stephen Hill
Finally getting around to adjusting the isolastics on my 73 Norton Interstate.
When I measure the clearances (total of left and right clearances) I get
.012" on the rear and .024" on the front. Checking my info sources, I get
the following advice:
My conclusions: Haynes and Clymer are ambiguous as to technique
and total clearance. And the Tech Digest and the Factory Manual are clearly
contradictory. I am inclined to go with the Factory Manual and set total
clearance at a total clearance of .010".
Comments?
And is anybody aware of the Tech Digest correcting the error in a later version?
Stephen Hill
"Life's too short to own one bike at a time".
Date: Thu, 11 Apr 1996 15:06:17 -0500
From: Kenneth Miller
I just did this on a '73 Roadster. I only have a bootleg factory manual so was blissfully ignorant of any contradictions. The front one's easy. The rear one's easy to measure, but a bitch to get at if you want to disassemble it (I decided mine wasn't that bad). The factory manual (bear with me, I'm doing this from memory) gives two methods; an easy and a preferred. The preferred suggests removing the front engine mount from the frame and crankcase. This is easy once you support the engine on a trolley jack or the like (not terribly stable though, still sitting on the centerstand, not a technique for those of you with curious kids, dogs, wives, the faint of heart or those with nervous ticks).
I'm getting ahead of myself, though. To measure, the factory manual
advises you to slacken the mounting bolt and nut, lever the engine to one
side and use a feeler gauge to determine the gap. The only trouble I had
was being able to sandwich enough feeler gauge blades together to get a
rough measurement of the gap (in my case about 10x what is recommended
or 0.10"). OK, couldn't ignore that. I didn't have any trouble measuring
the rear either except that I did it on the other side (rear on the right,
front on the left). In my case, I decided to remove the front mount and
completely rebuild it since my rubber bits showed
significant wear (BTW, this can be done on early model Commandos without
using the special drift-if anyone's interested). ANYWAY...With the engine
mount free of the bike and containing fresh rubber bits, re-insert the
mounting bolt with associated washers/spacers/etc. and torque to spec (sorry,
I don't remember the figure). Now, measure the clearance on one side (the
left), subtract 0.01", add that many shims (I tried to balance them left
vs. right side). Reassemble and re-measure (lather, rinse, repeat) until
you get something greater that 0.05", but less than 0.01" (the shims are
available 0.005", 0.010", and 0.030" I think). Best to be a little tight
rather than loose...that exhaust port repair thing is expensive and I've
done it more than once...but I digress.
A comment: I found the torque spec for the engine mount to be inadequate, I suggest a little stronger pull on the wrench than is recommended.
Regards,
Ken
'73 850 Roadster-just completed it's first uneventful road test since
its latest re-heading.
'70 BSA B44VS (x2)-someone remind me why I took these apart...
'75 BMW R75/6-annoyingly boring for tinkerers like me
Date: Thu, 11 Apr 1996 17:59:25 -0400 (EDT)
From: Klaus Kaak
>Finally getting around to adjusting the isolastics on my 73 Norton
>Interstate. When I measure the clearances (total of left and right
>clearances) I get .012" on the rear and .024" on the front. Checking
my
>info sources, I get the following advice:
[Snip]
I've also been frustrated over the years with contradictory info from different. sources. In the end I converted to MkIII isolastics and followed good old fashion trial and error methods. Start out with about 5 thou on each side and go for a test. If you feel excessive vibrations coming through handlebar and footpegs, back off a little. By the time you reach approximately. 7-8thou on each side you should be fine. If they are too lose, you will also notice quickly by sloppy handling and that infamous "commando wobble" even at lower speeds. If you use pre MkIII isolastics, call in sick for a day and have a 12 pack of premium beer ready, but otherwise refer to above comments. so long
klaus
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