Front undertray hardware improvements

[wooooody]

Doing a few jobs so had to remove the front undertray over the weekend. It wasn't the most fun job I've ever done as I'd to lie under the car, goggles on, to drill out three of the M8 bolts, galvanically corroded to their rivnut.

I'm considering a few options and whatever goes one will have duralac as required and graphite based anti-seize on threads. 

Has anyone converted to a rivnut, stud & nut over the rivnut and bolt set up? Might even help installation? 

 

[Seb]

following, I tried to remove front undertray to clean the sand out, found the same issue, there are 3 rivnuts just spinning in place 

[wooooody]

You should be able to drill out the three spinning of course and replace the rivnuts. It's what's the best option long term. Unfortunately looks like there's no access possible to the nut side for the inboard fixings.

Stainless of course must be avoided in contact with aluminium.

[Roobarb]

4 hours ago, wooooody said:

Stainless of course must be avoided in contact with aluminium.

Interested in this as I think the Lotus aluminium is sort of galvanised isn't it (certainly it's not bare aluminium) so maybe not such an issue perhaps? But I know very little about metallurgy hence my interest as replacing such fixings with SS seems to be a standard update across most of the aluminium platformed Lotus cars - is this definitely a no-no then??

[Ginettaman]

Surely just use plenty of alloy anti seizure grease (not copper slip) as I don’t think it would have been any originally hence why they seize up. What the argument against stainless and alloy?

[wooooody]

Galvanic corrosion. Stainless acts faster than mild steel paired with aluminium, especially in wet conditions and more so if there's any salt present. I used aerospace stainless washers for my Elise undertray 16 years ago despite knowing it could be an issue. You could see the effects within months. 

[Ginettaman]

So what's the best option for fasteners.

[ADF]

Since rebuilding my S1 and making it nice I SORN over winter and it lives In a garage so its less exposed but galvanic corrosion is a major issue with the aluminium chassis mine had some serious issues, rusty fixings seem to have the greatest effect (probably because it holds moisture)

One thing I did change on the front  undertray was to junk the spire fixings on the sides and replaced with a strip of stainless with rivnuts set in,  saves a lot of fafing about with the front one as well as providing better support.

I use stainless fixings on my undertray with plastic washers under the SS washer very cheap and just replace them when they crack. I use either grease or a touch of wax oil to keep the moisture out. Don't use stainless for any load bearing bolts but there fine clamping any plastic bits.

The Aluminium chassis is anodised which does help reduce corrosion, but its easily damaged.

Note the rivnuts are aluminium, I've had to replace a few. My advice is use the serated ones and a little epoxy on the outside the slow/strong stuff this then bonds and seals the joint, never had one come loose again.  Not sure graphite is a good idea, same for copper grease I never use either near the chassis just in case (don't know wether you can get galvanic corrosion from metal loaded greases as you need to have an electrolyte in contact,  any tribologists out there?)

Best of luck, I remember also having to cut my front undertray off with a grinder and same with the wheel arch liners none of it was fun but well worth doing.

 

 

[wooooody]

On the graphite, I've been using it for 17+ years on the Elise and not had an issue. Forgot I have tef gel now, so will use that.

Still haven't decided what way to go, did discover a large stash of fibre washers this week that might be an idea to isolate the tray from a washer. Also looked at aluminium Bolts, might be possibly up to to M10 rivnuts for those. https://www.ebay.co.uk/itm/304566946719?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=IGZ6SQ9TQ96&sssrc=4429486&ssuid=kvzANOirTT2&var=&widget_ver=artemis&media=COPY

[ADF]

I would steer clear of aluminium bolts for this use myself. I use a couple of gold anodised fairing bolts on the rear number plate and they are really soft compared to steel.

The added benefit of the wax oil (dinitrol) is it acts as a bit of a mild thread locker when it sets and dissolves easily in white spirit. I don't use a lot, just abit in the threads.

As I understand it you need an electrolyte for the galvanic corrosion process.

So my thinking is use SS but isolate with plastic washer under the SS washer and use something to block any moisture getting to the joint.

I believe zinc acts a sacrificial barrier so I suppose you could use SS fixings with steel BZP washers but would need changing as the plating reduces.

A bit of topic,  but whenever I have an undertray off I give it spray of polish/wax (I use Williams stuff for this) it seals the surface a bit and cuts down the moisture and dirt with the additional benefit of making the underneath shiny.

Keep us updated, I would be interested to know what you settle on.

[wooooody]

I happened across these studs today. Unfortunately M10 and A4-80 stainless, but will assess lengths against requirements. Could be a nice solution with an isolated washer and nyloc nut. At least then if the stainless corrodes to a rivnut in the chassis, the nut should still come off fine.

[ADF]

I like your enthusiasm, I don't wish to seem negative and its your car. 

But I could see a few issues with that approach.

1. Setting them firmly enough may require bonding, as you can't tighten them up much into the ally.

2. Wouldn't be able to slide the panel into place. Maybe not an issue.

3. Main reason for me is anything sticking out the bottom of the chassis is going to get really hammered (I managed to loose the entire leading edge of a sill from a shed load of flints)

I use button head SS (A2) on mine with a spring washer, makes for a low profile and neat finish. The only issue is the danger of rounding off the Allen if there overtightened.

[wooooody]

Feedback is appreciated, it's why I've posted on here. Tbh, I'd probably missed how the tray slides out, so you're absolutely correct on that. 

The Evora, I think having owned a sport 160 for a long time, rides quite high, so my thinking was another 5mm of fastener protrusion should be ok, but again, I take your point. 

I've probably been over thinking this and an improved version of the standard set up would be best; 8.8 steel M8 bolt with a standard hex head rather than the ones Lotus fitted with the 10mm flanged head, tef gel and either a zinc or stainless washer with some sort of isolation washer between it and the undertray. 

[Ginettaman]

The Evora engine tray bolts into steel so I've ordered some stainless bolts and nylon washers to isolate the alloy sheet. All will be lubed up too.  I haven't worked out how the exhaust rear cover comes off which is next on my list. Is it just the Alan bolts into the plastic sides? 

[Spinney]

On my previous Exige and Elise before that, I used aeronautical grade anodised aluminium alloy Allen socket head screws similar to these:-

https://www.aliexpress.us/item/3256803866354163.html?src=google&aff_fcid=18471d14ccf744c783809afbc7560b00-1704704614373-07269-UneMJZVf&aff_fsk=UneMJZVf&aff_platform=aaf&sk=UneMJZVf&aff_trace_key=18471d14ccf744c783809afbc7560b00-1704704614373-07269-UneMJZVf&terminal_id=b5163e8072914614ad7727fe38684d6d&afSmartRedirect=y&gatewayAdapt=glo2usa4itemAdapt
 

A smear of graphite grease when fitting et voila, never a problem with them seizing in the Rivnut bushes. 

[Spinney]

That link above is just the example that came up on Google since I’m not currently in the U.K.  You can get a good range of sizes from many U.K. suppliers. I think mine came from RS Components. 

Being aero grade they are very strong and won’t cause galvanic corrosion in the Rivnuts as they are not dissimilar metals. 

Just a note on fitting new Rivnuts too is to use Loctite around the shoulders when installing them. This keeps them nice and tight in the sheet metal. 

[Spinney]

My apologies for keep replying to this but I’ve only just thought of one last point and that is I used hard nylon washers which also came from RS Components.