bumper fitting

[morris]

I've been trying to work out how to fit my bumpers, not the usual issue of shims, sealant and how to screw them in place etc but more how far into the chassis tubes they are supposed to sit.

Are they supposed to slide into the chassis as far as possible until the outer tube touches or are you supposed to extend them out slightly? All the way in the shiny bits are a few mm away from touching the nose cone and further in than the extension of the wheels.

The Sportster manual talks about the the bumpers being designed to collapse progessively with the outer tube buckling but as far as I can tell they're just made of scaffold like tube that will simply transfer the entire force to the chassis. I had expected some sort of piston inside like a production car (or was that expecting too much)?

[peterux]

Originally Posted by morris

I've been trying to work out how to fit my bumpers, not the usual issue of shims, sealant and how to screw them in place etc but more how far into the chassis tubes they are supposed to sit.

Are they supposed to slide into the chassis as far as possible until the outer tube touches or are you supposed to extend them out slightly? All the way in the shiny bits are a few mm away from touching the nose cone and further in than the extension of the wheels.

The Sportster manual talks about the the bumpers being designed to collapse progessively with the outer tube buckling but as far as I can tell they're just made of scaffold like tube that will simply transfer the entire force to the chassis. I had expected some sort of piston inside like a production car (or was that expecting too much)?

Yep, you were expecting far too much
I fitted mine in as far as they would go with the outer tube touching the chassis. But when you drill the hole for the back bumper fixing screw make sure that you can get to it with the rear tub in place. (Or you'll be making a special Mike Garner spanner).
Good to see more progress and you'll be on the road for next spring!!

...peter

[morris]

I'll shove them all the way in then. Strikes me as a pretty ineffective solution to cushioning an impact though. I was sure the IVA manual had something to say on the matter of how bumpers were to be positioned and constructed but now can't find it. Maybe I just imagined it.

[cabrioman]

If they are the same as the Cabrio bumper struts I think the outer larger tube, which stops against the chassis, is a separate tube press fitted to the smaller diameter tube, which goes into the chassis. The general idea is that under impact the outer tube will concertina to take the impact, whether it does or not is another discussion.

John

[Mike]

Originally Posted by morris

I'll shove them all the way in then. Strikes me as a pretty ineffective solution to cushioning an impact though. I was sure the IVA manual had something to say on the matter of how bumpers were to be positioned and constructed but now can't find it. Maybe I just imagined it.

It always strikes me that we all go through the same emotions over the same things - I remeber having exactly the same thoughts.............the outer tube of the bumper is the same thickness and diameter as the chassis - how can that work as a concertina?

The bumpers are just for show, and Marlin's words are just for............Bullshit!

I hope none of us ever have an accident as there is not much of a crumple zone!

[peterux]

Originally Posted by Mike

I hope none of us ever have an accident as there is not much of a crumple zone!

Yes, but all modern tin-tops do crumple, so your Marlin will survive unscathed!!

[Patrick]

Just don't drive into an old car

[morris]

Ah, so it's the Volvo approach to engineering, build it like a tank and everyone else will absorb the impact for you