Chain Guard Alignment '74 850

Saber

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My son and I have been restoring a '74 850 for almost two years and we have enjoyed riding it as progress has permitted us to do so. Its looking good and running pretty well. One puzzling item is that our drive chain to chain guard is way off center to the point it appears to be rubbing. Did we assemble something wrong? If not, how do we get some clearane in there?20200914_210349.jpg
 

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The chainguard looks to be mounted correctly, your brake drum is too far over. Prime candidate is you are missing
SPACER - REAR BRAKE PLATE - OUTER 06.0334

number 14 on this page


 

L.A.B.

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One puzzling item is that our drive chain to chain guard is way off center to the point it appears to be rubbing.
The chain rubbing against the outer section of the chainguard is a problem that has been mentioned before.
 
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had the same clearance problem on my 74 to the point that the chain rubbed and wore away a small section of my black chainguard extension toward the outboard side. BTW, that seems to be a Mk3 feature and i'm guessing somehow it made it into my late production Mk2 - does not show up on the Mk2 parts drawing and is not showing on from your 74 - ???

I rebuilt my rear brake assembly, and upgraded several components to stainless, including the #14 spacer. clearance issue gone. didn't take any before/after measurements on old vs. new part - all I can is now I have about 1/8 inch space between the chain guard extension and the chain. still not perfectly centered though - I don't know if it was the spacer, or how I reassembled things, but the problem's gone and i'll take it. hope this helps....



question to maylar (if you're monitoring this thread) - since our bike's VIN number is "nine" apart, and most likely built within hours of each other, does your 74 have the black chainguard extension?
 
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L.A.B.

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BTW, that seems to be a Mk3 feature and i'm guessing somehow it made it into my late production Mk2 - does not show up on the Mk2 parts drawing and is not showing on from your 74 - ???
The holes are there so it is the 'extension' chainguard .

According to Norton Service Release N3/55, May '73, the 064837 chainguard with holes for the extension was introduced "subsequent to engine number 307091" so pre-Mk2/2A.
As you said, the extension parts are missing from the Mk2/2A supplement although the 064837 chainguard is listed.

The later 065818 slotted chainguard also has the holes and is for the 850 Mk2 and Mk2A (from January '74) not just "850Mk2a"

064837 therefore, is also not just for the "850 Mk3".
The Mk3 reverted to the earlier 064837 non-slotted chainguard as with the rear disc brake the slot was no longer required.
 
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The holes are there so it is the 'extension' chainguard .

According to Norton Service Release N3/55, May '73, the 064837 chainguard with holes for the extension was introduced "subsequent to engine number 307091" so pre-Mk2/2A.
As you said, the extension parts are missing from the Mk2/2A supplement although the 064837 chainguard is listed.

The later 065818 slotted chainguard also has the holes and is for the 850 Mk2 and Mk2A (from January '74) not just "850Mk2a"

064837 therefore, is also not just for the "850 Mk3".
The Mk3 reverted to the earlier 064837 non-slotted chainguard as with the rear disc brake the slot was no longer required.
thanks for clearing things up. from your posted information, I have the Mk2a chainguard.
 
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I replaced my chainguard recently and it looks nice and shiny but the chain hits it on the outside. Nothing else changed. Found that the AN chainguard is a thinner gauge metal and does not hold its shape well when bolted up. The clearances are very tight in that area. I left it off for now. I need to do some more fooling with it this winter. The original chainguard is close too but just makes it.
 

Saber

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Thank you guys. My #14 spacer is in place. I do have the chain guard extension, I just took it off for the photo. My chain guard is the slotted one 06.5818.
LAB I read that older post somewhere along my research but the only item in there that is still un-checked on my part is the last post from HoveToo about the circlip. I dont think I took it out when we went over the rear wheel last year. Adding any spacers or putting in a thicker spacer between the swing arm mounts doesn't seem right as I have to pry the swing arms open when mounting the rear wheel assembly as is. Perhaps tearing it down and putting it back together might result in something (similar to Joe's luck/skill). I may also look at doing something at the front end of the chain guard to cant the rear edge outward. I haven't checked clearance in the front yet though.
 

maylar

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According to Norton Service Release N3/55, May '73, the 064837 chainguard with holes for the extension was introduced "subsequent to engine number 307091" so pre-Mk2/2A.
As you said, the extension parts are missing from the Mk2/2A supplement although the 064837 chainguard is listed.
So is the extension available as a spare part?
 

L.A.B.

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So is the extension available as a spare part?
(x2)
 
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Looking at your photo's the shock looks to be pressing against the chainguard, you may need a longer bolt for the bottom shock mount with a spacer behind the shock on the bolt to move the shock out to provide clearance. The bolt used by the factory has a thin head so I turned the head down to match, if you do not use a longer bolt then if the nut does not fully engage then it risks coming loose. Or fit shocks that are thinner at that point.
 

MichaelB

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This is part of the Commando 'fettling'.
Part #21 fits on the back side of the braking plate.
It is as required shim/washer to move the sprocket over, keeping the brake in line with the cable, sort of.
Yes, it does move the brake shoes out a little but still in contact with the drum.
One shim did it for me.
Or, you can machine a new longer spacer as others have done.
Another tip, turn the master link around to the inside to minimize contact with the guard.
 
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This is part of the Commando 'fettling'.
Part #21 fits on the back side of the braking plate.
BINGO #21 A/R as required
The thickness of the bolt head inside the bracket can be thin or regular even with a thin washer to help support the thin sheet metal...what ever fits is OK.
Move the drum with #21 as the factory allowed them in the IPL . Any correct shock will not hit the chain guard. However aftermarket chainguards with "thick" supports loop can be a nuisance and should be avoided.
 

marshg246

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My son and I have been restoring a '74 850 for almost two years and we have enjoyed riding it as progress has permitted us to do so. Its looking good and running pretty well. One puzzling item is that our drive chain to chain guard is way off center to the point it appears to be rubbing. Did we assemble something wrong? If not, how do we get some clearane in there?View attachment 18727
Are you sure you have the real wheel aligned properly? When everything is right, there's very little clearance there so having the wheel crooked can make t look like what you have. Also, if your shock is interfering with the chainguard, that may be a problem. Some aftermarket shocks are too short at the bottom - especially if the shock is adjusted to the lower setting.
 
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one thing I forgot to mention - I did fab new lower shock mounting bolts from stainless, but they are dimensionally identical to the originals. the heads are a low profile as needed on the LH side to clear the chainguard mounting bracket. I doubt that has anything to do with the chainguard interference. when I rebuilt my rear brake assembly, I did press out/press in the bearing assembly - not sure if that had anything to do with it. the dummy axle is the original, with one #21 spacer which I kept as originally configured. whatever did, I went from interference to non-interference condition. puzzled....
 

NickZ

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My son and I have been restoring a '74 850 for almost two years and we have enjoyed riding it as progress has permitted us to do so. Its looking good and running pretty well. One puzzling item is that our drive chain to chain guard is way off center to the point it appears to be rubbing. Did we assemble something wrong?
When I had this issue, it was a result of the brake hub bearing holding circlip (#47) not being in its groove. This allowed the bearing to shift relative to the hub (or vice versa).
 

NickZ

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Adding any spacers or putting in a thicker spacer between the swing arm mounts doesn't seem right as I have to pry the swing arms open when mounting the rear wheel assembly as is.
Adding to #21 spacer width will help relieve the chain/guard contact, but will also increase the amount of swing arm prying required while mounting rear wheel. Make sure you have the cush drive paddles fully inserted into the hub and this will be minimal.
 

olympus

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had the same clearance problem on my 74 to the point that the chain rubbed and wore away a small section of my black chainguard extension toward the outboard side. BTW, that seems to be a Mk3 feature and i'm guessing somehow it made it into my late production Mk2 - does not show up on the Mk2 parts drawing and is not showing on from your 74 - ???

I rebuilt my rear brake assembly, and upgraded several components to stainless, including the #14 spacer. clearance issue gone. didn't take any before/after measurements on old vs. new part - all I can is now I have about 1/8 inch space between the chain guard extension and the chain. still not perfectly centered though - I don't know if it was the spacer, or how I reassembled things, but the problem's gone and i'll take it. hope this helps....



question to maylar (if you're monitoring this thread) - since our bike's VIN number is "nine" apart, and most likely built within hours of each other, does your 74 have the black chainguard extension?
Can I ask what that compression spring is for pinched between the guard side plates....
 
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