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Misc: Everything Else Rear Damper Help

Steve Morris

Well Known and Active Website User
VOC Member
Hi all,
I noticed the rear of the bike has a rattle so on closer inspection the rear damper rearmost mount (the point where it mounts to the frame), was loose. Clearly its worn over the years, lack of lubrication etc..
So, i removed the rear damper and on inspection was clear it had no oil in it as there was little or no resistance when compressing it. So, i stripped it down and have found it could do with 2 new rubber seals and some fresh oil. Not a problem.
Second issue (and the original one), is the wear in the mounting hole at the pivot point. The aluminium has simply worn through (spoke to Bob at VOC and apparently they were never 'bushed' which came as some surprise to me?), anyway, i can make/get a new pin no problem, but i need to bush the damper. so, 2 questions for the 'learned'.

1. Which type and how much oil goes in the damper? (I have looked in KTB and Paul Richardsons book and cannot see any reference to this?) I know this depends on weight of rider/pillion/luggage/use etc, and have narrowed it down to 3, 5w or 10w fork oil OR brake fluid, any thoughts?

2. I need to 'bush' the damper. The way i view it is the damper is worn, so the worst case scenario is that I replace the damper, but, the damper is perfectly serviceable (new seals and oil given), except for this minor bushing issue. The standard pin/stud (F82/2) is available, so has anyone done this before and what type/size of bush would you recommend?

Many thanks in advance.

Best regards,

Steve.
 

chankly bore

Well Known and Active Website User
Non-VOC Member
There is a mention in the original literature recommending 20w. oil. There was an article about rebuilding the damper with bubble wrap inside and new seals some years ago. You might be able to use a 7/16" x 1/2" bush and add a grease nipple. Otherwise an exchange unit from Maughan's in Lincolnshire.
 

vibrac

Well Known and Active Website User
VOC Member
The reason that you have wear in the bottom of the damper is that it was not only meant to just rotate on the spindle F28/1 the spindle should also be rotating in the two bushes in the RFM and the two 3/8 nuts should not prevent that replace the FT117 bushes
 

Cyborg

Well Known and Active Website User
VOC Member
Page 23 in my Richardson book it refers to S.A.E 20 engine oil. KTB says non- detergent 20 or possibly 30. If the damper has been completely serviced, I don’t see the need for non- detergent. I wouldn’t stray to far from 20 ( in its stock form) if that is what it was designed for, but I’m not the resident expert.
I just assembled one, but tossed the part that holds the two O-rings and installed a modern lip seal. The seal itself fits without any machining, but in order to hold the internals together it requires a new spacer. The spacer protects the seal as well as holding everything in place.
Personally.... even though I have the equipment to install a thin wall bushing in the bottom of a damper, there isn’t a lot of extra room for removing material. My first choice would be to just replace that part of the damper. There are oodles of them around, so must be someone who will donate one to the cause. I suppose it depends on how close that existing hole is to the edge where the housing is machined for clearance. They aren’t all the same.
 
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Steve Morris

Well Known and Active Website User
VOC Member
Thanks all for the replies. I have been ‘experimenting’ with different weight oils. I spoke to Bob at VOC spares and he suggested fork oil, which kind of makes sense, but the weight will vary according to rider/riding style etc. I had some 5w racing fork oil, too light, damper has very little damping quality. Then some 10w. This felt OK, but wanted to try 20w. To be honest the 20w made the damper feel far too stiff in my opinion, I’m 14 stone and will only ever ride solo and not quickly, so I went back to 10w. I think that feels kind of right. The acid test of course is riding the bike, and now I’ve changed the rear damper oil I will need to do the same in the front, so I’ll let you all know how it feels.

The second part, the worn damper, I had a chat with Steve at Maughans. He does supply oil it’s bushes for this very problem, So it looks like that’s the route I’ll be taking, not sure if I may just send him the damper lower body so he can just ream and bush it yet, I want to do it myself but don’t have a decent reamer of the correct size so I’ll have a think about that one..
 

BigEd

Well Known and Active Website User
VOC Member
VOC Forum Moderator
Thanks all for the replies. I have been ‘experimenting’ with different weight oils. I spoke to Bob at VOC spares and he suggested fork oil, which kind of makes sense, but the weight will vary according to rider/riding style etc. I had some 5w racing fork oil, too light, damper has very little damping quality. Then some 10w. This felt OK, but wanted to try 20w. To be honest the 20w made the damper feel far too stiff in my opinion, I’m 14 stone and will only ever ride solo and not quickly, so I went back to 10w. I think that feels kind of right. The acid test of course is riding the bike, and now I’ve changed the rear damper oil I will need to do the same in the front, so I’ll let you all know how it feels.

The second part, the worn damper, I had a chat with Steve at Maughans. He does supply oil it’s bushes for this very problem, So it looks like that’s the route I’ll be taking, not sure if I may just send him the damper lower body so he can just ream and bush it yet, I want to do it myself but don’t have a decent reamer of the correct size so I’ll have a think about that one..
To "fine-tune" the damping you could do a 50/50 mix of 15 and 20 oil.
If you don't need 100% originality you can fit the AVO damper that doesn't leak and has an easy adjustment for damping force. It doesn't look to out of place and quite a few people use these. If you intend to do a lot of riding it is probably cheaper in the long run.
AVO also do a mono-shock unit that I now use.
 

timetraveller

Well Known and Active Website User
VOC Member
I don't want to be a damper (pun intended) on this but although dampers with the same resistance in both compression and extension strokes were considered adequate in 1950 only a few years later it was realised that one needed more damping on the extension than the compression stroke. If one wishes to use an original-looking Vincent damper for the look then fine but note that modern dampers like the AVO do have more damping on the extension than the compression stroke and, so far as I can tell, so do any other dampers used on modern machines. Keep it original by all means if you wish but if you want better comfort and handling then use a more modern damper.
 
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vibrac

Well Known and Active Website User
VOC Member
There is the recirculating ball valve modification that does impart some variation between compression and extension resistance, basically it is a hole up the end of the piston rod meeting a small cross hole above the piston and a ball bearing in the central drilling and a screw cap( I know I should search for it).
 

Bill Thomas

Well Known and Active Website User
VOC Member
I have found the Standard forks with the Comet don't work as well as with the Twin,
I think because of the less weight, So I have gone with as light an oil as I could do,
ATF. Cheers Bill.
 

Bill Thomas

Well Known and Active Website User
VOC Member
You have me there Martyn, I had forgot that, Should have looked in the book !,
Having had too many tank slappers, Including one that threw me over the top !,
I have been thinking too much on keeping the forks down,
As was said in an early Know thy Beast,
I think my thoughts where Side tracked ?.
Cheers Bill.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Thanks Martyn, I always fit an Hydraulic Damper now,
Strange how you can do so many miles and ride so many years as I have ,
Then have Big trouble, The roads in UK are very bad.
Cheers Bill.
 

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