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Lambretta rear shock absorber stud replacement.
Posted: Sat Sep 05, 2020 4:39 pm
by kevspeed
Hi all,not something i have ever had to do before,so better to ask for advice from somebody who has!
The rear shock stud/pin is spinning in the cases,ive managed to hold it enough to get the nut and shocker off,but i should imagine it will need replacing,or the cases repairing. Any advice gratefully accepted,thanks in advance.........Kev
Re: Lambretta rear shock absorber stud replacement.
Posted: Mon Sep 07, 2020 1:43 pm
by Warkton Tornado No.1
I had this occur in the 70's & got the whole pin out, tapped it to whatever size would fit, & bolted it in place.
Subsequently, many years later & with more engineering knowledge, removed it, scrupulously cleaned it & refitted with a Loctite product suitable for retention of shafts in bores.
Re: Lambretta rear shock absorber stud replacement.
Posted: Mon Sep 07, 2020 3:47 pm
by kevspeed
Sounds good,i may drill and tap for a grub screw to stop it turning,plus the loctite method,belt and braces,thanks for the reply
Re: Lambretta rear shock absorber stud replacement.
Posted: Wed Sep 09, 2020 8:19 pm
by Grumpy225
These are press fit with teeth to keep them from rotating.
It's too important of a piece of suspension to trust to a little grub screw. The hole is already damaged and will only get worse. The grub screw might hold for a little while but will fail. Have it welded and repaired correctly.
Or not, it's your scoot.
Re: Lambretta rear shock absorber stud replacement.
Posted: Sun Sep 13, 2020 2:09 pm
by Warkton Tornado No.1
As a lifetime engineer that had to have some kind of cheap transport from 1973 onwards, the consequences were that Lambrettas & I have never been apart.
I am not saying that alternative views are wrong, but IME, the problem with welding the alloy used in Lambrettas are the high Zinc content, which boils, causing porosity. If that were not enough to contend with, removing every trace of oil is not easy. Personally, I have witnessed dirty welds, despite coded welders being employed. Distortion may be of little consequence in certain areas, but naturally occurs.
It's not just Lambretta that have this issue. Theoretically, we should be able to weld up tiny failures within pistons, be they Honda, Suzuki or Yamaha. Just try it. It will fail.
Personally, I will shy away from welding of Lambretta components, particuarly those associated with the engine.
I once had an oversize bearing journal in a disc backplate welded & machined to size. After very little use (admittedly in racing) the hammering through braking made the journal oversize & the disc hub was actually rubbing on the backplate. Obviously, the weld was soft....
Loctite will work in scrupulously clean prepared areas if the correct grade is selected. So will other transition methods, such as an alternative pin that is larger, or the existing pin knurled on it's surface, a sleeve shrunk on.
The case itself may also be countersunk to allow the pin's hollow end to be peened into the enlarged countersink.
I just wish it to be understood that there are many ways to achieve the same aim. Fundamentally, safety & peace of mind are the objectives.
A proprietary product used extensively in Engineering will work if within it's limitations.
Re: Lambretta rear shock absorber stud replacement.
Posted: Tue Sep 15, 2020 8:27 pm
by Grumpy225
Warkton Tornado No.1 wrote: ↑Sun Sep 13, 2020 2:09 pm
As a lifetime engineer that had to have some kind of cheap transport from 1973 onwards, the consequences were that Lambrettas & I have never been apart.
I am not saying that alternative views are wrong, but IME, the problem with welding the alloy used in Lambrettas are the high Zinc content, which boils, causing porosity. If that were not enough to contend with, removing every trace of oil is not easy. Personally, I have witnessed dirty welds, despite coded welders being employed. Distortion may be of little consequence in certain areas, but naturally occurs.
It's not just Lambretta that have this issue. Theoretically, we should be able to weld up tiny failures within pistons, be they Honda, Suzuki or Yamaha. Just try it. It will fail.
Personally, I will shy away from welding of Lambretta components, particuarly those associated with the engine.
I once had an oversize bearing journal in a disc backplate welded & machined to size. After very little use (admittedly in racing) the hammering through braking made the journal oversize & the disc hub was actually rubbing on the backplate. Obviously, the weld was soft....
Loctite will work in scrupulously clean prepared areas if the correct grade is selected. So will other transition methods, such as an alternative pin that is larger, or the existing pin knurled on it's surface, a sleeve shrunk on.
The case itself may also be countersunk to allow the pin's hollow end to be peened into the enlarged countersink.
I just wish it to be understood that there are many ways to achieve the same aim. Fundamentally, safety & peace of mind are the objectives.
A proprietary product used extensively in Engineering will work if within it's limitations.
Makes me wonder how the shops that convert cases are handling the welding?
Re: Lambretta rear shock absorber stud replacement.
Posted: Tue Sep 15, 2020 11:06 pm
by wrecklessrobbie
Re: Lambretta rear shock absorber stud replacement.
Posted: Wed Sep 16, 2020 2:11 pm
by Warkton Tornado No.1
Grumpy225 wrote: ↑Tue Sep 15, 2020 8:27 pm
Makes me wonder how the shops that convert cases are handling the welding?
Apparently not very well....
Re: Lambretta rear shock absorber stud replacement.
Posted: Thu Sep 17, 2020 10:07 pm
by Grumpy225
The takeaway to me is if you want a big block you need to buy a big block but I don't see why there would be any problems with doing a case conversion if it is done correctly.
Some people do really well at it
https://www.mbscooters.co.uk/info/mb-*- ... n+260.html
I've had lots of cases welded and repaired locally and so far no issues. These cases are old/dirty aluminum and there will be porosity issues if they are not prepared right.
Re: Lambretta rear shock absorber stud replacement.
Posted: Fri Sep 18, 2020 3:36 pm
by Warkton Tornado No.1
Grumpy225 wrote: ↑Thu Sep 17, 2020 10:07 pm
The takeaway to me is if you want a big block you need to buy a big block but I don't see why there would be any problems with doing a case conversion if it is done correctly.
Some people do really well at it
https://www.mbscooters.co.uk/info/mb-*- ... n+260.html
I've had lots of cases welded and repaired locally and so far no issues. These cases are old/dirty aluminum and there will be porosity issues if they are not prepared right.
I'm pleased that you have not experienced the issues that some of us have endured
However, I doubt that in the Post (see above) that details the problems with welding that "they are not prepared right" or that the coded welders I have had repair cases would take too kindly were it suggested they had skimped on thorough preparation
The fact is that having fell foul of the presumption that welding may be the best way, I wanted to make the OP aware that alternatives may work as well, if not better. In the example of a front hub that had been welded, there was no visual sign that the bore for the bearing was in effect getting bigger. The rear suspension pin in the crankcase strikes me as being in a very similar scenario, transmitting all road shocks to the suspension, it is the first in line for that specific task......