Wheel alignment

Monday 10 June 2024

Unplanned maintenance

Sometimes, we're just not sufficiently switched on to see warning signs over time that point to potential trouble.  We've owned the GT for nearly 3 years and apart from a rebuild of the carbs, expenditure has been in the routine maintenance category or minor improvements.  Overall, pretty good for a 52 year old car.

During ownership, there has always been a slight whiff of petrol, although no obvious source.  I just put it down to what one might expect from a non-injected engine.  However, that smell has recently been more noticeable after a drive when the tank is more than 3/4 full.  The baffles in the fuel tank are fairly rudimentary and with the relatively short filler pipe, I wondered whether it was possible that the fuel surges back up the pipe, particularly when cornering enthusiastically.  Time to jack the car up and have a good look round as a car fire is the last thing anyone wants.

Nothing obvious showed up until I noticed that some underseal was missing at the front of the tank - very hard to see in the narrow space.  That set the alarm bells ringing as a solvent such as petrol could cause underseal losses like that.  Time for a bit of research on the various MG internet forums and what I found was pretty worrying.  Apparently, the top of old MGB fuel tanks are prone to rusting over time, both from the inside and on the external upper surface where crap can build up.

Nothing obviously wrong at first glance

First job was to drain the tank.  Although there's a drain bolt at the bottom of the tank, I was worried about flow regulation and decided to siphon it instead into containers with a narrow neck.  Jennie was less concerned about me setting fire to myself than setting fire to the house so it was accomplished outside the garage with a fire extinguisher at the ready.

During the internet search, I found some excellent instructions for tank removal and replacement on a blog by US resident Eric Cloninger: Replacing an MGB Fuel Tank.  Very easy to read and also included a YouTube video link to an English chap who demonstrated how to do it.  Many thanks Eric - great when a plan comes together, eh?   I'm not going to give a blow by blow account but removing the tank was pretty easy, using the jack to support it, plus one or two well-aimed kicks to dislodge it from the threaded studs. As an engineer, I know when to apply brute force rather than careful leverage!

The following photo shows the tank being wheeled out on the jack.  The top of the tank had been undersealed but looking towards the top right hand side, it's clear that the underseal had been washed off over time by petrol leakage.  This part of the tank is close to the right hand rear wheel and I suspect that it collects more crap as a result.

Old fuel tank immediately following removal

One of the panels had severe corrosion pitting but the panel nearest the front edge actually had a number of small pin holes all the way through.  These are shown below.  It's a fair bet that as the underseal got progressively washed off, the leaks became significantly worse; particularly when the tank was fairly full and g forces caused the contents to slosh about.

Fuel tank right at the end of its life

A quick call to Paul Walbran Motors, the MG specialists in Auckland revealed that they had a tank in stock, together with a mounting kit. Not cheap at approx NZ$1000 (USD 610, AUD 927, GBP 479) but they're imported from the UK and being a high internal volume item, shipping costs are significant.  Not complaining though as Paul and his team always deliver outstanding service.  It was received in deepest Coromandel less than 24 hours after ordering.

Next job was to transfer the fuel gauge sender unit to the new tank.  Years of accumulated grime and corrosion on the locking ring required a bit more brute force and copious quantities of WD40 before it came free but a new locking ring and rubber seal made reassembly straightforward.  The original rubber strips to prevent fretting corrosion between the floor pan and tank were covered in sticky underseal.  The replacements were cunningly manufactured from the rear inner tube of Jennie's bicycle because it's been years since she used it.  Besides, it's easier to ask for forgiveness than permission.  Ummm... actually, it's better to say nothing at all.  The new seal round the filler neck and floor pan hole was cut from Jennie's yoga mat.  Not likely to get into grief with that as it's been some years since she last did any yoga and the mat was abandoned in the garage.  Fair game, I think.

New fuel tank being prepped for installation

Next job was to pop the tank onto the jack and gently raise it into place.  Not quite as easy as the previous sentence suggests as the filler pipe had to be eased through a hole in the floor pan at the same time.  Only a few obscenities uttered and 15 minutes or so wasted until the best method was discovered.  

Bolting up was no problem, apart from a 76 year old body laying on concrete for much of the day in a cramped position.  Connecting the tank filler pipe to the external filler pipe via a length of rubber piping which was an interference fit took some time to accomplish but all was well.  Hook up the fuel gauge sender unit to the power supply, connect the fuel line and that was the job done.

Connecting the filler pipe through the floor pan and filler cap assembly

Hooking up the fuel gauge sender unit

Refill the tank (outside because I know what's good for me), no leaks, no smell of petrol and all is fine and dandy.  Well, apart from the aches and pains of laying on a hard surface for a fair slice of the day - nothing that paracetamol can't fix. Kneeling is particularly uncomfortable after the knee replacement and with the other due in September, servicing the differential is a job that needs to be done fairly soon.  Keeps us from getting under our significant other's feet eh?

Ready to come off the axle stands


  1. Geez Jay, that you for your diagnosis description. My 74 B roadster is smelling gassy too. I’ve checked antirun, carbs, fuel lines, charcoal canister but not the fuel tank. New opportunity for aching bones and muscles, I’ll be 80 next birthday so laying on concrete for a day will be costly. 😳

    1. Hi Carl, thanks for responding! My GT was imported from the UK and doesn't have the emission controls which US models have. That made problem solving a little easier. Removal and replacement is quite straightforward, even easier with a mate to help if they can be bribed. I suspect that your issue will be the same as mine - an old body! I'm reasonably fit and mountain bike regularly but the following morning, I was sore and stiff. Nothing that paracetamol couldn't fix, but I won't make a habit of that type of work. Every good wish if it turns out to be your problem too!

  2. Well spotted Geoff, and a good fix. Empty petrol tanks aren't the sort of thing you would want to try to weld!!

    1. Many thanks! Yep, no welding of tanks as I'd prefer to live a little longer. A new tank will see me out - one less thing to worry about in future.


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