Frame rust (warning)

[bossman]

Hi all.
Just wanted to give every body the heads up on the problems i'm having and others might have but not be aware of.
I have a 2010 factory build which as never been out in the rain and lives in a dry frost proof garage.
I became aware of what looked like cracks in the powder coat finish, this turned out to be rust that had lifted the
paint finish around every hole where the floor pan had been pop riveted to the frame.
Fortunately I've caught it before it had crept up the outside of the frame but the rust was extensive through out the frame.
It as been a nightmare to work work on stood on blocks treating it so i am very reluctant to pop rivet it again in case
i need to remove it in the future.
iv'e tapped the holes and was planning on putting pan head screws in with spring washers.
wondered if anybody else as done this or anybody had a view on a better solution?.
thanks John.

[jason82]

I know that the old Caterhams suffered badley with this. Especially where aluminium & steel meet, they react against each other quite badly. Maybe one solution from the beginning would have been a gasket in the kit which runs between the ally & steel in chassis. In the classic car world I have known people put engine oil into the chassis frames for protection, or even a cavity wax.

Every single place where aluminium touches steel could be a problem. Even though the chassis is painted it's not enough. Best solution is the rubber gasket & use stainless pop rivets , with a bead of tiger seal down the outside edge of the chassis beams to stop water getting between the two metals.

A good example of this is on car sos, they restored an old Caterham with this exact issue.

[jason82]

Another option could be to install steel floors welded in. 1mm should be plenty, then use a bed liner or something like that inside & out. I know it adds weight to the kit, but it adds extra strength to the chassis itself.

[kiwicanfly]

Stainless and aluminium is the biggest problem, it causes cathodic corrosion when aluminium stainless and moisture are present but it is the aluminium that suffers.

My floor is held on with rivnuts, m4 rivnuts require a 6mm or 1/4" (depending on make) hole so that would see the rust on the edges of your holes removed by the drill.

I also used blind rivnuts to reduce the chance of water ingress.

I also sprayed a wax coating inside my chassis to prevent the rust, the stuff I used dries to form a film which will protect bare metal for up to a year and dries,well, dry.

[kiwicanfly]

If you do use rivnuts,closed or open end, ensure you get them the correct crimping thickness for the tube and its curvature. Many are designed for thin sheets only.

[bossman]

Many thanks for that info Jason.
Kiwicanfly.
thanks for getting back to me, my original choice was rivnuts but i had concerns about them holding with the shape of the tube but if it's worked for you that's good enough for me.
Did you use anything to lock your bolts in place?, as i was concerned about the possibility of them rattling loose.
I was considering either thread lock or a spring washer.
thanks John.

[carlyd]

Feb 4, 2019 13:27:54 GMT bossman said:

Many thanks for that info Jason.
Kiwicanfly.
thanks for getting back to me, my original choice was rivnuts but i had concerns about them holding with the shape of the tube but if it's worked for you that's good enough for me.
Did you use anything to lock your bolts in place?, as i was concerned about the possibility of them rattling loose.
I was considering either thread lock or a spring washer.
thanks John.

I used rivnuts too. I was also concerned about them holding as you tend to put a lot of pressure on the floor as you get in and out so I put a long bolt right through the chassis tube and floor in 4 places. This ensure that the floor could not drop even if all 200 ish rivnuts dropped out.
I used some adhesive foam strip (approx 5mm thick) that I purchased from amazon to sandwich in between the floor and the chassis to stop vibration. This meant I didn't need to use anything to 'Stick' the floor to the chassis which made removal and refitting easy. It worked well and never had any vibrations etc.

[jason82]

Use rtv or a sealant on the body of the rivnut itself which comes into contact with the steel, then use loctite. That's how I have done my gearbox tunnel & bulk head.

One idea slightly different, I remember a company that used to sell fibreglass floors for the old vw beetle, they were really good.

[bossman]

Hi Carl.
Good to hear from you, i'll call by in the summer to have a look how your getting on with the all terrain beast your building.
Yes sounds like I've got the same foam as you for sandwiching the floor to the frame but i was mainly referring to the bolts
going into the rivnuts regarding them rattling and working loose.
Did you do anything to lock them in? or have they been fine without.
regards John.

[carlyd]

Feb 4, 2019 14:09:24 GMT bossman said:

Hi Carl.
Good to hear from you, i'll call by in the summer to have a look how your getting on with the all terrain beast your building.
Yes sounds like I've got the same foam as you for sandwiching the floor to the frame but i was mainly referring to the bolts
going into the rivnuts regarding them rattling and working loose.
Did you do anything to lock them in? or have they been fine without.
regards John.

Hi John, I didn't locktight them in as the locktight I used sets like steel and I don't think you'd ever get them back out due to the rivnut spinning before the locktight giving way.
I just tightened them and checked them regularly and they were fine. I think the lack of vibration using that foam strip helped keep them in.

[carlyd]

I've not even started the strip down yet. Very busy with work at the moment and freezing weather isn't encouraging me to brave the garage anytime soon. It must be lovely where Kiwi lives this time of year, but I'm not jelous.... much! 

[bossman]

Freezing fingers are all part of the joy of the build some say!.
That was exactly my worry with using thread lock so it's reassuring to hear that yours haven't moved without it.

[kiwicanfly]

Here's a link to the test I did on the rivnuts I used for my build.

mevowners.proboards.com/post/72332/thread

Also Torx head screws can be tightened way more than allen key head screws without damaging the hole, the also have bigger flanes under the head. I once tightened one down so tight I ripped the whole head off (again a test, not in the car) you can't do that with an allen key.

Locktite comes in different strengths, I used the lightest grade. This can be undone easily but still holds nicely.

I think it is pink in colour but to be honest it's just too hot outside to venture to the garage to check

When using rivnuts ensure the screw runs in easily and doesn't bind on the threads or hole in the thing your fixing down (as in a bit of misalignment pushing the screw to one side), any binding like that is a major cause of rivnuts spinning.

[bossman]

thanks that's great.
So sorry to hear it's to hot to go outside, we have a similar problem here but ours is cold.

[carlyd]

Feb 4, 2019 18:34:02 GMT kiwicanfly said:

Also Torx head screws can be tightened way more than allen key head screws without damaging the hole, the also have bigger flanes under the head. I once tightened one down so tight I ripped the whole head off (again a test, not in the car) you can't do that with an allen key.

Locktite comes in different strengths, I used the lightest grade. This can be undone easily but still holds nicely.

I rounded a few allen bolts, they were only M4 then switched to Torx bolts, much better as you say.

I didn't know locktite comes in different strengths? I use a red one, it sets like weld so I was dubious about using it on rivnuts.