Outer sill: function in load bearing?

tyroguru · May 17, 2020

Franky made a comment recently about not wanting to replace sills whilst the car was on a rollover jog and it made me wonder: How much does the *outer sill* contribute to the load bearing ability of the monocoque design? I'm interested in the 240Z in this instance but maybe it applies to all cars of interest here.

I've seen photo's of many people replacing outer sills on rotisseries as it's quite a common problem and I can't think that I've seen any using bracing (though I know that doesn't mean you necessarily shouldn't!). Can outer sills be replaced safely without compromising the structure whilst on a rotisserie?

ben240z · May 17, 2020

if the inner sills and floors are sound then yes you can cut off the outer sill. They do form part of the strength of the whole monocoque but if you are confident in replacing them then do it on the rotiserie.

Turn & Burn · May 17, 2020

It could depend how rotten the inners are. Just make sure everything is braced before u chop, u can’t really see the inner workings before you chop the outer off.

tyroguru · May 18, 2020

Thanks Gents. I have an endoscope (just a cheap iOS thing) and the inner looks to be pretty good, at least from what I can see. I think it has to be replaced at some point and I was thinking of removing it before it went for blasting if the inner sill was in a good condition so that it can be exposed and blasted.

ben240z · May 18, 2020

if you are sending it for blasting without the outer sills I would make a temp brace that goes across the door aperture from hinge to lock area to give it extra support during transport.

tyroguru · May 18, 2020

ben240z said:
if you are sending it for blasting without the outer sills I would make a temp brace that goes across the door aperture from hinge to lock area to give it extra support during transport.

Thanks Ben - I'll do that.

Ian · May 18, 2020

Its fine to do on a rotisserie as long as your floors and rails are ok, and best to only do one side at a time. Mine was measured pre removal for any flex as there seems to be none.

Alphabettispaghetti · May 18, 2020

Ian said:
Its fine to do on a rotisserie as long as your floors and rails are ok, and best to only do one side at a time. Mine was measured pre removal for any flex as there seems to be none.

the floor support rails provide no real strength, i can’t see how it wouldn’t move without temporary bracing?

Bazzateer · May 18, 2020

Agree with Franky, as I understand it the rails are just there to stop the floorpans from flexing, they are not structural?

ben240z · May 18, 2020

The inner sill structure is designed to give strength and prevent flex with the door open. The outer sill is structural but more of a finishing cover to the inner structure. The floor rails are more useful in preventing the floor pan drumming.

tyroguru · May 18, 2020

Thanks all for the input. I'll probably just weld some box section in as a support for it to go to be blasted as Ben suggested. I'll only have the driver side outer sill removed and the floors are reasonably strong though not great. The bracing seems a reasonably simple thing to do so probably better safe than sorry.

ben240z · May 19, 2020

I would not weld a brace in. Use the hinge bolt holes on the A pillar then the door lock bolt holes. Welding a brace in runs the risk of pulling the door aperture as it cools and also you then have to grind the welds off already thin metal ( usually around 0.9mm thin)
A bodyshop would use an adjustable bar that has clamps on each end that clamp to the door rubber seams.

tyroguru · May 19, 2020

Thanks again Ben for the advice - makes sense. At least that's a non-destructive fabbing exercise that I can get wrong multiple times with no bad outcome

. I'll report back on what I come up with.

Turn & Burn · May 19, 2020

tyroguru said:
Thanks again Ben for the advice - makes sense. At least that's a non-destructive fabbing exercise that I can get wrong multiple times with no bad outcome . I'll report back on what I come up with.

As suggested by Ben is exactly what I did. I made braces from 1.5” angle at a length to suit the door opening. I bolted plates at the end that allowed me to clamp /pinch across the seams

tyroguru · May 19, 2020

So pretty much the same approach as these Sealey ones then Andy?

Ian · May 19, 2020

Yes, same as the ones on my car at the moment.

Turn & Burn · May 19, 2020

tyroguru said:
So pretty much the same approach as these Sealey ones then Andy?

View attachment 38631

Yep, exactly

Alphabettispaghetti · May 19, 2020

tyroguru said:
So pretty much the same approach as these Sealey ones then Andy?

View attachment 38631

thats exactly what I mean. I'd like to see a triangulated version though.