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dracko Offline OP
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I’m in the process of cleaning up and repainting a pre-1968 swingarm.

I have a later one on hand, that has seal cup washers on each end with o-rings to seal in the grease, but that swingarm has been modified in the past so I’m using the earlier one.

Looking at it after disassembly, it looks as though there is no seal or o-ring to keep the grease from squeezing out. Just a washer on each side. What am I missing here?

I’d post pictures but since photobucket shut down I don’t know how. Would be nice if you could upload pictures from your phone directly to the site.

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Drako, do you have parts books?

They're pretty much all here for free download: https://partsbooks.britishonly.com/

The o-rings show up first in Parts Book #6 - 1968. Prior to that there are only 'end plates' with no o-ring.

End plate Reference 7, page 41 in Parts #5 - F6730 (and F7675, .015" thicker).

HTH


Bruce Miller
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The Bonnie Ref: https://www.hermit.cc/tmc/om/manual.htm
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dracko Offline OP
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Thanks Hermit, I looked at a few parts diagrams, most I could fine were for the later forks but I’ll check that link you posted. Thanks for that.

I guess I have all the parts I need. But I’m surprised there is no seal on the ends. Thanks for the help!

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It would have surprised me before i disassembled the unit on my '69 Bonnie the other day. Before disassembly I noted that there was, by eye, a fat 1/8" side-to-side play of the swing arm - side-to-side as in perpendicular to the wheel base - like a shuttle, back and forth. I was very concerned by this, but upon further disassembly I realized the play was just due to the o-ring seals having been flattened right out.

In spite of the o-rings not having been sealing, the only time grease seemed to ever come out was when I was pumping it in, and the cavity seemed to be well-filled with grease. So I wonder if the o-rings were added to keep grease in, or road grit out?

The first time I replaced the bushes was at 53,000 miles and the o-rings weren't flat like the current ones ( I know because I still have the originals bagged and tagged).

Now the bushes need replacing again at 85,000 miles, so 32,000 mile interval compared to 53,000 the first time. Could premature wear of bushes be due to inferior 0-rings that compressed and failed to keep out road grit from gravel roads?

Would be interesting to compare replacement interval for swing arms with and without seals.


Bruce Miller
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The Bonnie Ref: https://www.hermit.cc/tmc/om/manual.htm
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dracko Offline OP
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That is interesting. Looking at the later swingarm I have on hand, it looks as though the O-rings just sit on the outside of the swingarm (inside the cup washer) so I don’t really see how they could get flattened. The ones in this swingarm are dried right out but not flattened in any way. When you tighten up the swingarm bolt are they in a position that they’re getting squashed?

In regards to changing them, I decided to not do the bushings in this swingarm because I heard they need to be line reamed afterwards, is that right? If it’s just a matter of pound the old out and new ones in I might reconsider.

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Dracko -

In this photo you can probably make out the flattening on the inside of the o-rings. Funny thing is that I thought I remembered them being flattened on the 'sidewalls' as it were - which is what I thought explained the lateral play in the swinging arm frame. I also remember them as being more flattened then they appear to be now. Possible that they reconstituted themselves when removed from the stress? Or I was just mistaken.

[Linked Image from hermit.cc\tmc\om\images\forum_images\swingarm_o-ring.jpg]

If the lateral play in the swinging arm frame - 1/8th inch back and forth at the pivot from side-to-side - wasn't due to the o-rings, then what else would explain it? Or is that normal? Hoping someone would chime in on this question.

As for changing the bushes, if they need it (play) and you are reasonably skilled mechanically, I'd say do it while you have the opportunity. I have no mechanical skills, but I know the ones on my Bonnie need replacing so I'm going for it. After all, I've already done it once. Nevertheless, I've been procrastinating for over a week because I can't decide which one of my sockets I should deface by grinding flat for the job (if it weren't for Covid lockdown I'd just go out and buy a cheap one).

But I wonder if anyone knows whether or not you could swap your old style end caps for newer ones with o-rings?

One last comment: I did look again at the o-rings I removed at 53,000 miles and they have no flattening at all. Neither are their inside radius pitted like the ones that just came out after 32,000 miles. What else could cause the pitting other than road grit? And if the road grit penetrated to there, why wouldn't it have made it inside the swing arm and the bushes?

So many questions. So little time and knowledge!

Cheers!


Bruce Miller
aka The Hermit
The Bonnie Ref: https://www.hermit.cc/tmc/om/manual.htm
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The ends of the later swinging arm that take the o ring end caps are different. Also, the o rings don't affect side to side movement. Th ink that the op has the whole later swinging arm that has the o rings, etc.

The bushes are suppose to be ready sized but this is only so if the insides of the swinging arm is clean.

Side to side movement can be taken up by shortening the spacer tube and fitting thicker side plates. What happens is that the swinging arm itself wears so that the bobbins protrude. They have to be flush with the swinging arm. You can also flip the side plates so that the worn area is on the outside.

Dave

Last edited by dave jones; 02/15/21 8:19 am.

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