Front ISO gap setting(s)

Saturday morning greetings from a new member. I recently purchased a 73 850 Commando that was/is in pretty good shape,,,nonetheless, I decided to go through refurbing some bits and pieces; the top, front and rear ISO mounts being one of the refurb projects. I purchased a new front ISO mount kit from Andover via OldBritts (the style that does not require modifying the mounting bracket). It's a very nice kit. And from the looks of the rubbers and the internals of the bracket I just removed I'm pretty sure these have never been changed.
Question I have is setting the gap,,,the instructions say .006" (equivalent to 1 1/2 holes loosened from snug on timing side of the assembly). Instructions say to check for and achieve this gap by "levering" (my word) engine to one side and then checking gap and adjusting timing side end gap. But,,,,if the end goal is a .006" gap couldn't I set the primary side end cap at .003" (by bottoming out the end cap internal shoulder on the threaded shaft and then backing off .003") and then tighten the primary side end cap at that position using the provided set screw? And, then, set the timing side end cap at a position equal to about "one hole" backed off from snug,,,(instructions say 1 1/2 holes is equal to .006" gap). Just curious if this would work,,,any suggestions/advice greatly appreciated, many thanks

By levering to one side the 6 thou gap you are aiming for is at the opposite side to where the gap should be zero if you lever hard enough. Once you have the 6 thou and stop levering then it should then be 3 thou each side in theory but I very much doubt it in practise. It's only a starting point anyway as once you set it by the book you then play around to find your preferred setting trading off handling for comfort. Never set to zero or you risk cracking your frame, think I ended up with 8 to 6 thou front and back but it's hard to tell as the actual components wear unevenly but it handles well and the vibration disappears above 2500 rpm.

Welcome Schilling.

Schilling said:

Question I have is setting the gap,,,the instructions say .006" (equivalent to 1 1/2 holes loosened from snug on timing side of the assembly).

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I don't recommend you rely the "backing off by 1 1/2 holes" method as you may find the clearance is reduced or even disappears completely when the through-bolt is tightened. I suggest you always check the clearance after the bolt (or rear Iso. stud) is fully tightened.

Schilling said:

Instructions say to check for and achieve this gap by "levering" (my word) engine to one side and then checking gap and adjusting timing side end gap. But,,,,if the end goal is a .006" gap couldn't I set the primary side end cap at .003" (by bottoming out the end cap internal shoulder on the threaded shaft and then backing off .003") and then tighten the primary side end cap at that position using the provided set screw? And, then, set the timing side end cap at a position equal to about "one hole" backed off from snug,,,(instructions say 1 1/2 holes is equal to .006" gap). Just curious if this would work,

Click to expand...

It might work but due to the constant side-to-side movement of the Iso. tubes when the bike is being ridden I doubt there's anything to be gained over levering the assembly to one side and checking the total play.

kommando said:

By levering to one side the 6 thou gap you are aiming for is at the opposite side to where the gap should be zero if you lever hard enough. Once you have the 6 thou and stop levering then it should then be 3 thou each side in theory but I very much doubt it in practise. It's only a starting point anyway as once you set it by the book you then play around to find your preferred setting trading off handling for comfort. Never set to zero or you risk cracking your frame, think I ended up with 8 to 6 thou front and back but it's hard to tell as the actual components wear unevenly but it handles well and the vibration disappears above 2500 rpm.

Click to expand...

got it,,,thanks much for your reply, much appreciated!

L.A.B. said:

Welcome Schilling.



I don't recommend you rely the "backing off by 1 1/2 holes" method as you may find the clearance is reduced or even disappears completely when the through-bolt is tightened. I suggest you always check the clearance after the bolt (or rear Iso. stud) is fully tightened.

Click to expand...

Thank you very much for your reply and advice,,,quick follow-on question; once the through-bolt is tightened will it still be possible to introduce the required gap by turning the timing side end cap to achieve the recommended gap?

FYI there is a nice series of videos showing front iso upgrade on an 850 here from Mi Ty:

Schilling said:

quick follow-on question; once the through-bolt is tightened will it still be possible to introduce the required gap by turning the timing side end cap to achieve the recommended gap?

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No, not the AN* type. Tightening the through-bolt will clamp the assembly (as it must do to maintain the clearance).

*(Unlike the 'Hemmings' vernier kit which can be adjusted with the through-bolt tightened)

Tornado said:

FYI there is a nice series of videos showing front iso upgrade on an 850 here from Mi Ty:

Click to expand...

Yes, thank you,,,excellent set of videos they are indeed.

L.A.B. said:

No, not the AN* type. Tightening the through-bolt will clamp the assembly (as it must do to maintain the clearance).

*(Unlike the 'Hemmings' vernier kit which can be adjusted with the through-bolt tightened)

Click to expand...

Roger that,,,,I tightened the through-bolt to 20 ft/lbs,,,,checked the clearance on the timing side,(there was none, not a surprise really considering how much wiggling there was needed to get the bracket/assembly mounted again), adjusted the end cap out by 1 1/2 holes,,,,tightened the bolt the rest of the way,,,,,went for a ride and noticed an improvement (keeping in mind I have not done the rear ISOs yet),,,smooth at 4k and above in 2nd, 3rd or 4th gear,,,a buzz in pegs and seat and grips at 3.5k in 2nd,,,,not intolerable at all

If you get to the rear iso, would love to have photos/video of the process...this job seems to be poorly documented on the net.

Wow that AN packaged 'Iso went in unbelievably easy (loose) compared to the RGM version.
The 'RGM's were not hard to install but the fit between the rubber and tube is much tighter than that even with lubricant.

Tornado said:

If you get to the rear iso, would love to have photos/video of the process...this job seems to be poorly documented on the net.

Click to expand...

I'm not yet adept at embedding previous posts in a reply,,,but I found one process for the rears from "trinorman" posted on this forum on May 17 2007 that seems to be pretty well documented,,,text only no pics or videos that I'm aware of,,,,I'm going to try his process next for the rears

After a second ride i checked the clearance (tried to check is a more accurate phrase) on both sides,,there was no gap at all on either side,,,,so, I loosened the through bolt again,,,turned the timing side end cap an additional 2 1/2 holes out and then had ten thou gap on the timing side,,,tightened the through bolt again and then had 6-7 thou gap on the timing side (no gap on the primary side even though during initial set-up i locked the primary side end cap via the set screw at 4 thou gap).

Good job! Thanks for write up.

Well, it's been a couple of hundred miles on my bike since I installed the front ISOs from Andover (via Oldbritts). Yesterday I installed the Dave Taylor head steady (with spring ). I set the spring tension right in the middle of the recommended tolerance band (recommended 1.2-1.5"),,,the rose joint and associated bits went together really well with the rose joint shaft horizontal and at 90 degrees to the tube. Everything seemed to be ok. I went for a ride and noticed a slight reduction in vibes coming thru the grips but an increased amount of vibes coming through the foot pegs (I have not yet installed, but have purchased, the rear ISO assembly bits, again from Andover via OldBritts). The bike handles quite nicely but I wouldn't say it was a world of difference, granted the instructions did say to make adjustments as necessary,,,but I'm not sure which way adjustments should be made,,,,tightened (introduce more tension) the spring to reduce vibes?,,,,or loosen (remove tension) in the spring? Any suggestions? thanks much in advance