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JohnD

Fuel Resistant Seals

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All,

This conversation started under a different heading, so you can see the preamble at: http://sideways-technologies.co.uk/forums/index.php/topic/7071-running-in-a-new-engine/page-2?do=findComment&comment=100130

 

This all started when I hoped to go to Spa with the CSCC, but blew my engine (broken ARP big end bolt! Pah!).  The Club told entrants that the Belgian scrutes were red hot for full FIA compliance, including fuel tank 'safety'  foam.    This is reliably 'antislosh' but IMHO isn't 'safety' as if there's a hole in thte tank all the fuel comes out, just not as quickly.   But I complied and filled the tank with foam, with the result that it became impossible to fill it from empty in less than ten minutes, as the fuel would not drain away from the filler neck and bubbled and spat as the air came out.    This I got around by making a tight fitting collar for a large funnel, so the air had more space to escape in, but at Crystal Palace, I found that the foam was not just slow to fill, but slow to deliver too.  If you recall, I have a fuel system designed to prevent air getting into the injectors due to fuel slosh (lifter pump and swirl pot, before main pump), but the car started to behave exactly as if it was suffereing from fuel surge, missing on the exit from corners, and when starting showing excessively low fuel pressure (70-80psi, when it should be 100-110).    I put in the remaining fuel in my spare can and this solved that problem for my last run, confirming the diagnosis.

 

I was running the tank at less than half full, because of the problem mentioned in the previous thread.    To put in the foam, I had to remove the tank cover plate, the old seal had shrunk and I used a silicone  gasket maker (Loctite 5922), but that had failed.   Anything over half full (the tank is angled) and it seeped out, so I ran half empty.   Removing the plate confirmed that sealant was missing just where it leaked, but all around, where it had been exposed to fuel, the sealant had changed.  Where it should be black and sticky, it was grey, and flaked off.     The foam was stained with the black pigment, so clearly this stuff isn't fuel resistant, but anyway, the foam is coming out! 

 

But what to use to reseal the coverplate?    I related before my test experiment with some rubber sheet I though might be suitable, which had a webbing sealed between two layers.  A few hours in a petrol bath and the petriol was discoloured; 24hrs and the webbing was destroyed.      I've repeated that with some new sheet, "NBR (acrylonitrile butadiene) rubber at 60° Shore hardness, with excellent mechanical and physical characteristics and excellent resistance to Petroleum based fluids, oils, solvents and greases"  according to the eBay seller.     I cut a strip from the sheet, cut it in two and one has been soaking overnight.  The test piece is softer, less stiff and slightly expanded, longer and thicker, than the control, but there is no discolouration of the petrol.  So I conclude it will do.  Swelling will assist the seal.    

 

But!    When I fitted the foam, I had to fit a different fuel sensor, one that floats in a tube rather than the old one with a float on a lever, as that would foul the foam.  I made a new hole in the cover plate, easier to do on the bench, rather than in the tank, but this mounts the new sensor near the centre, when the tank is angled, so it reads 'Empty' when about half full!    The old sensor hole, I covered with a cover plate for the cover plate (!) and sealed it with some gasket paper and a different sealant - and this has stayed fuel proof!.     It was in my drawer, three quarters used and I thought it was Red Hermatite - but now I unroll the tube, and it's called  "GasTite".   The blurb says, "Resistant to petrol, diesel, oil, water, steam and anti-freeze" !  This is the stuff to use, so I rush off to Eurocar and buy up their remaining two tubes!

 

Which leaves me with a quandary.     Gasket paper and "GasTite", or fancy "BA60 Nitrile rubber sheet", +/- Gastite?   The blurb for BA60 mentions a sealant. so use some with that, and I've bought the stuff anyway.    Also, the tank cover plate is 300mm across, so more flexible than a 50mm mini cover plate, so the rubber may be better.

 

I'll let you know!

 

Meanwhile...    To get this stiff I had to buy a roll, 1.4 long x 0.5 Meters wide, 3mm thick.   I very much doubt I shall need this much specialist rubber in my remaining lifetime!   If anyone wants some, I'll gladly cut you a slice, merely for the promise of a donation to a charity.  Any charity, as long as it's Help for Heroes!

 

John

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