FT: Frame (Twin) Rear shock absorber alignment

[Albervin]

I have now done some fine measurements. The UFM where F28/1 mounts was 5 thou out of alignment. The shaft on the IKON was nearly 20 thou out of true! And so a simple job gets more complex. The UFM was straightened with moderate brute force and now a Koni is a good fit. The Ikon will be sent back to the factory for rebuilding. At no stage would I have considered fitting what Vic suggested until I had explored all avenues. I will fit spacers either side of the shock to keep it centralised and prevent any side torque.

 

[BigEd]

Ed, do you regard those spacers as necessary? I assumed that the idea was that the damper was allowed to float to find its own position.

The SP4's that screw into the brass SP/1 at the bottom of the spring boxes fit outside the RFM so the spacers just substitute for the thickness of the SP4's when fitting the nuts and washers to the F28/2 spindle.

 

[timetraveller]

Yes, I understand that and I explain that to people who buy the whole front and rear suspension kit. What I don't understand it the mention of 'plastic' bushes in the email I got. The question I asked was whether you think that it is necessary to use your spacers inside the lugs on the RFM to keep the bottom of the AVO damper central. If you do then in future I should be mentioning this to people who buy the rear suspension units.

 

[BigEd]

Yes, I understand that and I explain that to people who buy the whole front and rear suspension kit. What I don't understand it the mention of 'plastic' bushes in the email I got. The question I asked was whether you think that it is necessary to use your spacers inside the lugs on the RFM to keep the bottom of the AVO damper central. If you do then in future I should be mentioning this to people who buy the rear suspension units.

I have no spacers on the inside of the UFM. There is a total of 3-4 mm side clearance between the width of the bottom coil-over mount and the inside of the RFM castings. On my setup most of that clearance is over to one side, due maybe to some misalignment at either and of the coil-over or the RFM itself.
Re: plastic bushes, I've no idea as there are definitely no plastic bushes fitted to my AVO coil-over.
P.S. I'd marked up the outer spacers incorrectly in the photograph in my earlier post #12. I have since edited it.

 

[timetraveller]

OK Ed. I had looked at the corrected photo but not understood which was the lug on the RFM. It looks as though the AVO tube just nicely fits into the gap which is what I had understood. The gent with the 'plastic' query has still not come back to me so perhaps he realises he has misunderstood something.

 

[oexing]

So when that AVO cross tube is that wide, why could it bend the pin ??
Anybody today should be prepared for all sorts of defects like bent rear frames or flaws in welded AVO tubes . So it is a good idea to have some scope for dealing with mismatching parts by finding spacers according to what the shocker requires to meet the upper position at the oil tank lugs. At this joint you could ask for sperical bushes on the AVO as nobody can know how the individual condition on these bikes is. We had photos of a broken piston rod on Girdraulic , same risk there for non-parallel joints both ends of the shocker. It is definitely wrong not to have some way of selfadjusting joints at these places like rubber bushes or special bushes like the Igus type.

Vic

 

[Albervin]

Many of the early Koni shock absorbers had a twisted/bent bottom mount due to welding. This caused many a bent spindle at the rear and even partially locked front forks. Maybe forgotten in the mists of time.

 

[highbury731]

There are no plastic bushes in the AVO coil-over for a Vincent. Maybe he has one of their other units as these so have plastic bushes. Where did he get his AVO unit from?

I hesitate to contradict you on technical matters, but... I have an AVO coil-over which I have just been working on, and it most definitely has plastic lower bushes. They were supplied with the damper, and I had to press them in. The lower mount spindle F28/2 went easily into them after installation. It was rather more effort to get the lower end of the damper to fit into the RFM, due to the greater diameter of the AVO's lower mount.
Paul

 

[BigEd]

I hesitate to contradict you on technical matters, but... I have an AVO coil-over which I have just been working on, and it most definitely has plastic lower bushes. They were supplied with the damper, and I had to press them in. The lower mount spindle F28/2 went easily into them after installation. It was rather more effort to get the lower end of the damper to fit into the RFM, due to the greater diameter of the AVO's lower mount.
Paul

Dear Paul,
Not a contradiction but new information. My coil-over unit for a Vincent is one of the first made by AVO and it definitely has no bushes plastic bushes. When did you get your unit? (Any photographs?) It is quite possible that AVO has changed the design to incorporate plastic bushes. They use red plastic bushes in many of their car units.

 

[highbury731]

Here's a pic of the lower mount of my AVO coil-over. You can see the plastic bush: