FT: Frame (Twin) Rear shock absorber alignment

Albervin

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VOC Member
I have four shock absorbers of varying provenance. The original Vincent one is totally shot and needs a full rebuild or throwing in the bin. I then have a couple of KONI and IKON units. My problem is that NONE seem to have have parallel eyes. If I fit the relevant studs into one of them the other will not line on. All mix sort of but NONE fit. I think all the eyes on these dampers are not true and so I am having a real problem with my rear end (SHUT UP!) .. The IKON has a bushed rear mount BUT the front mount is then the issue. The Koni units are not bushed at all. There is nearly 1/32-1/16 interference with fitting a stud between two of these, let alone trying to fit on an RFM!!! Has anyone else had issues with fitting? I have checked the alignment of the RFM with the UFM with a 3m straight edge and it is "very bloody close"! Any input welcome.
 

timetraveller

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VOC Member
Funnily enough I had a query last week from a member who had bought the whole front and rear suspension set up from me. He had just got round to fitting the rear coil over AVO and if the top spindle was fitted the lower one would not line up with the spindle. I have supplied a lot of these and this is the first time there has been a problem so the damper in question in now back on its way to AVO for them to look at it. I will keep people informed. And at the same time another person emailed to say that the plastic bushes for the lower fitting on an AVO coil over rear would not fit. I don't have one here but I do not recall any plastic bushes for the lower mounting!
 

Albervin

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I have just tried to fit three shock absorbers to F28/1 and F28/2 in a line . A standard/original, a Koni and an Ikon. NONE would easily slide on to a new spring bolt when more than one shock absorber was mounted. This can only mean the eyes of the shock absorbers are not parallel. The Ikon has a bushed rear mount. The Koni has no bushes. I have been told the Koni welded base will often have a twist and this seems to confirm it. It is also possible the same issue exists with the Ikon. I then tried to mix and match pairs and had the same problem. The F28/1 and F28/2 are brand new from the VOCS.
 

oexing

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From a technical side this design is not correct as you cannot be sure that all bolts front and rear on the bike are parallel - or bores in shockers parallel as well. So commonly some sort of rubberized bushes are fitted to shockers. In case nothing is found on your items you better find some way to modify for some flexibility . Else you could produce a cracked piston rod as shockers cannot bear side loads from cocked ends. I made sort of spherical ends on homemade air shocks but then big question: Is there material to do anything about this critical matter ?

Vic

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Albervin

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VOC Member
Fitting a rose joint is an option if there is enough metal. It seems you are always bringing up "possible" solutions where none may be possible . I have done this this with an old Maico but I can't see how to do it on a Vincent.
 

oexing

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VOC Member
Sometimes crazy ideas can lead to solutions when many more people think about them for a while. I see that the lower mounts of Konis cannot possibly modified for rubber or spherical bushes, not enough space around due to castings below. But it is allright to keep that end as is and have the upper end opened for a spherical bush like the IGUS type shown in photo. It is a type for 12 mm bolts, o.d. is 18 mm. But standard on Vincents is a 3/8 bolt I guess so a smaller 10 mm Igus , o.d. 16 mm, may easily fit there. These can handle 5 degrees deflection and you just look for lateral clearance between lugs at the oil tank rear end. Best to raise the swing arm to max. "compression" and see what the upper Koni end does with the lower end as is. So provided there is sufficient space both sides up there the spherical bush will care for zero side loads on the piston rod.
Same type of Igus bush could be used for new spring box lugs, no lubrication required with these.

Vic
IGUS spherical slim line bush

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Bobv07662

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Last year I went over the rear damper and springs on my C. All bushings and pivot studs were replaced as well as a new damper. All parts were supplied by John Healy at Coventry. Everything lined up with no issues.
 

BigEd

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VOC Forum Moderator
..... And at the same time another person emailed to say that the plastic bushes for the lower fitting on an AVO coil over rear would not fit. I don't have one here but I do not recall any plastic bushes for the lower mounting!
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?
 

b'knighted

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VOC Member
I think that the AVO rear coilover is supplied with spacers to replace the spring ends allowing the original studs to be used. I think that AVOCall them bushes.
 
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