Fuel filler assembly metal composition?

[Knorbert]

Hello All,

I’ve just bought my first stag after approx 40yrs of wanting one but never getting round to actually buying one. It now resides on the Isle of Mull with me and hence will be continually undersealed and waxoiled to prevent the salty atmosphere eating my new pride and joy!

It’s a 1977 MkII in Brooklands Green and in good condition having had a complete mechanical rebuild by the previous owner. Still lots to tinker with to get it how I want it (yes, car OCD!) and I’ve just bought a fuel filler assembly without a bent fuel stopper shaft (a common issue?).

This is my first post on the Forum as I need a bit of advice. I want to get the new one chromed, but I’ve been asked by our local chromer what material it’s made from.

Can anyone help me with experience of the metal composition?

all the best

Mark

Dr Mark Aston

[DJT]

Hi and welcome to the wonderful world of Stag ownership.

Post moved to general Forum section where you are likely to get more responses.

[Philip Wardle]

I believe the material is MAZAC, which was an original trademark name for a group of alloys comprising zinc and small amounts of aluminium, magnesium with the generic name ZAMAC or ZAMAC. The issue with this material is that, if not cast carefully, the finished part may not be perfectly homoginous, e.g. it may have micro cavities which reveal themselves as pits in the surface during the polishing stages of the re-chroming process.

This is a typical problem with other parts made from the same material on the Stag including the door handles, air intake grill, rear lamp bodies, and lock down plates behind the door pillars. It's not impossible to obtain good results from rechroming, albeit not perfect in most cases, but it very much depends on initial condition of the part and skills of the rechromer. I've found that they generally won't guarantee outcomes, which is understandable, but its possible to negotiate a price to allow for some additional time spent and/or repetition of some or all stages in the proces in order to get the best result.

The quality of some rechromed parts on Ebay (as an example) sometimes illustrates the problem, you will often see that parts have been so heaviliy polished in an attempt to eliminate pits that they have lost their overall shape or definition of features. Excessive polishing doesn't resolve the problem because if you remove the pits on the surface you often expose more underneath. The better companies will try to build-up the surface with the copper and nickel layers, filling in the pits, and then polish back each layer to get the best possible finish before applying the chrome layer. Even then, it isn't possible for them to be certain that pits will not re-appear.

[Philip Wardle]

PS I also have a bent stopper shaft (on the car, not me ho ho) and have wondered whether anyone has tried straightening it? I do have a spare filler assembly (in very poor condition) and was thinking of sacrificing it in the interests of science, but not sure of the best approach.

[Knorbert]

Thanks Philip,

That’s really useful info. Unfortunately, it doesn’t look like my local chromers want to touch this, so I’ll have to look for a specialist.

I have been reticent to try bending the shaft back in a cold state, and very pleased I didn’t try. Now I know it’s primarily a zinc amalgam, it’s more likely to crack than not at the pivot point of the bend. The only way to possibly straighten would be with local heat applied, but there’s a danger in that as the melting point of the material is going to be somewhere between 379°C and 390°C. That’s quite low and it is easily exceeded locally unless one keeps a very critical eye on the heating (once you know what to look for).

It’s probably a specialist repair in this case.

All the best

Mark

[Philip Wardle]

No problem Mark, the company I've used for years is http://www.derbyplating.co.uk/ - not the cheapest but I've found them very capable and helpful, they made a good job of some MAZAC parts for me once they were sure I had realistic expectations. They like to see the parts and discuss with you before quoting, as I should imagine others do, but if you are based some distance away you can probably arrange to send by post for them to look at. "Other chrome platers are available" and other people here will suggest these based on their own experience. Hope you can find a suitable firm anyhow.

I take your point about the melting point and local heating, I've done a bit of forge work and gas welding where the colour tells you the temperature of iron or steel but with MAZAC it's going to be like welding aluminium where judging termperature is a bit more difficult !

[Paulfrazer]

Regarding the bent stopper shaft, are you sure it is actually bent? The rubber stopper on mine is far from central on the filler hole when closed but I assume it was always a rather hit and miss fit in true 1970s BL mode. I think that trying to straighten it would lead to disaster! I have found a source of stopper rubbers that last more then 3 days before cutting through though https://coh-baines.co.uk/products/st...cap-fuel-cap02

[Knorbert]

Definitely bent on mine and probably not unusual through many decades of pushing the filler cap down on the fuel neck from the hinged angle it presents. The reason I bought a 2nd one is because the rubber cap is now right on the edge of the filler neck and I can occasionally smell fuel from the neck (nothing to do with enthusiastic cornering, of course ). I did take the spring assembly off and the shaft is quite badly canted in the direction of the cap latch bar…

[jbuckl]

Ok zamac or mazak is a good material for these cosmetic parts.

The car industry chose to chrome the parts to a cost….

The cheaper chrome is porous…. Allowing corrosion to begin after only a few years.

Better plating has shown that chrome on mazak can last…. Some American cars prove that where 60 plus year old chrome on zinc has lasted well.

imho the latch pin on the fixed part of the stag filler should bend back.


not sure if that is the issue here though?

The pin on the moving part is replaceable.


however have seen ones that have bent due to user abuse / error or an oversized rubber seal.

good news:- the pin can be straightened.

good news:- the chrome can be re-chromed.

good news:- the seal can be trimmed to fit.

my 2p is treat a filler cap as if it’s the car’s jewellery… which it is really.

[Philip Wardle]

Some more info re what's involved in chrome plating MAZAC parts in this excellent YouTube ... https://youtu.be/CvrPNJ7v-v8?si=DIMOWg46SrAJ-t2f

[Knorbert]

Thanks Philip, I had the complete fuel filler unit rechromed by Castle Chrome in the West Midlands. Only cost £80 + postage back, which was amazing value compared to some quotes I received. Very pleased with the final result, which was nicer than I’d hoped.

[Philip Wardle]

That's great, as you that was a very reasonable price. I seem to remember other good reports of Castle Chrome.