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Oversills, What They Are And Why You Want To Avoid Them

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#1 Down&Out


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Posted 15 September 2014 - 10:24 PM

It occurred to me the other day that although there was a few previous threads giving some coverage to the subject, there was no 'one stop shop' for information on oversills.

Oversills, or 'cover sills' are a sadly regular bodywork phenomenon. I have in fact never owned a mini without them, most people fit them for the sake of 12 months MOT, some fit them in error and a few people fit them thinking the problem is water getting into the sills, whereas in fact the sills are vented for the purpose of moisture being able to exit the sill.

Oversills block the venting, thus moisture builds up and rots the structural parts of your car from the inside out. I bought a project car recently and it came with oversills. I'd already fitted proper narrow heritage sills onto a different Mini so i used this opportunity to demonstrate to other mini owners what the difference is. (For those not super clued up on minis, this is a bodyshell on its side.)




Not a lot of difference to the untrained eye. Just as a comparison, here are the before shots. The car was fitted with oversills, the original sills were just handfuls of rust sliding about inside the sills and crossmember.




As a result of what was probably a two hour quick repair bodge job, ive had to replace a full length inner sill, the entire doorstep, rear bin strengthener, a section of the rear heelboard, the flitch panel, reinstate the jacking point and finally put the correct outer sill back on.


I just wanted to put this pictorial together to educate people out there as buyers and budding bodyworkers because oversills either mean the car has, or will have, hidden horrors. A quick repair it may be but down the line it will significantly damage the structure of a car, as well as its value, especially when you have to sell it needing all the welding ive just had to carry out.


I hope this helps at least one person in future anyway, if it stops at least one car from the peril of sill bodges then i've succeeded. Feel free to share it out and ask any questions if you should so desire.


#2 Cooperman


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Posted 15 September 2014 - 10:36 PM

Here is my current 850 project with the horrible oversills removed:





and repaired with M-Machine inner & outer sub-assembly:



#3 RossKnight


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Posted 15 September 2014 - 10:58 PM

I've seen the mess that the oversill did to the shell in the original post, first hand, that picture was very kind to how it actually looked in person. That area was a state, all because of one panel

#4 Ben_O


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Posted 15 September 2014 - 11:39 PM

This was a good idea putting this up on here. It is surprising how many Mini owners do not know what an oversill is or how to spot it.


I have lost count of the amount of rebuild threads i have read where the OP has put up pictures of the car they are doing and subsequently have fitted oversills.


People point out the fact that they have been fitted and the OP doesn't seem to even know what is meant by the term oversill.


I don't understand why they are still available? I think it is a complete waste of time fitting them for the sake of a few quid. Especially as Mini's are not the strongest car in the wrld. They need all the help they can get, not a piece of metal that is designed to fit over the top of the rusty remains of the original sill.




Thanks for this thread down&out, I think it should be pinned to help others out.



#5 Carlos W

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Posted 16 September 2014 - 04:37 AM

We'll look at getting this pinned

#6 megamini_jb


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Posted 16 September 2014 - 06:24 AM

Nice write up. If only there was something like this when I bought my second mini. Damn that thing was a mess under them

#7 stevearch0


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Posted 16 September 2014 - 06:50 AM

When I hacked the oversills off my project, the originals were in a bad way. Same consistency of ryvita!! Had three floors too!!

#8 MrIan


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Posted 16 September 2014 - 09:26 AM

Also those that don't repair their own cars need to watch out, i've seen a few restoration jobs done in garages advertising their restoration services on the internet with pictures clearly showing oversills fitted during the restoration. Yes they might have removed the old sill but they've stuck an oversill on with no drain holes to rot out anything in the area.

#9 geoff-d


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Posted 16 September 2014 - 12:08 PM

I fitted oversills to 1 of my cars about 4yrs ago no problems. The trick is to cut the holes into the moulded bump part before fitting also removed old cover & original sills 1st

#10 MrIan


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Posted 16 September 2014 - 01:59 PM

Yes it is very easy to make them drain by cutting slots but then also there's a lot of floorpan covered up by the wide type of oversill. Again it's the people that don't know that are at risk of wrecking the future of their own car by repairing it with these. The wide ones are by far the worse repair panels i've ever seen by allowing the repairer to cover rust n rot in the floor. If it's not rusty when you fit them it soon will be. The original sill runs onto the floorpan by what? an inch at the most? the wide cover sill as shown above runs onto it what? 4-5 inch ? that's 4 - 5 inch of floor and trapped moisture in the lap joint created. Sorry but a bit of a sore point with me as i'm removing oversills from my Jet Black at the mo !! flippin things !!

#11 Tommyboy12


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Posted 16 September 2014 - 02:11 PM

Is it worth pointing out about converting oversills? Im sure ive seen people cut 3-4 inches out of oversills to turn them into normal sills.

#12 sonikk4


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Posted 16 September 2014 - 02:19 PM

The biggest issue with oversills other than the rust issue is they form the wrong contour cross section and in doing so are not as strong as the original short sill. You can cut as many vents as you like in an oversill but as mentioned its the section right at the bottom where the sill welds to the floor that cause a lot of damage.


I had them on my Clubman. The old sill was cut off so no issues there but even though they had only been on for a short period of time there was water / moisture in the bottom which has started to attack the floor pan. Yes you can pump them full of a Waxoyl based product but if you are doing a proper job on your car then do not fit them. They are not correct, its as simple as that.

#13 RossKnight


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Posted 16 September 2014 - 03:05 PM

Is it worth pointing out about converting oversills? Im sure ive seen people cut 3-4 inches out of oversills to turn them into normal sills.


Might as well just fit normal sills?

#14 1984mini25


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Posted 16 September 2014 - 04:43 PM

You can see from the pics, just how rusty the oversill I paid £100 for to be fitted at a mini specialist in Northampton to get mine through it first mot, back in 05.


The oversill was only on the car for a MONTH and had been painted/under sealed on the outside. Its not until I went to patch the floor, thinking the sill was done and fixed 'properly' I end up having to remove the oversill and redo and weld on a proper sill instead.




And you can already see the tell tale signs of rust starting along the oversill to floor weld.



Edited by 1984mini25, 16 September 2014 - 04:44 PM.

#15 Bubblebobble


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Posted 16 September 2014 - 07:00 PM

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