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TR4/4A fuel cap lock

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while Christmas holiday I alway make some of these fuel cap locks,



fitts petrol / fuel cap Triumph TR4 / TR4A / TR5, some TR6 and other Triumph (some Spitfire, GT6, not TR3)
with round diameter 50 mm, small latch as on photos, base / lower part must be one cast, not srewed type (TR3)
lock is german trademark, no modification on fuel cap necessary, not visible by closed fuel cap,


if interested send me a personal message, price is 60 55 GPB shipping included,

shure - not a bargain but from evey sold lock I have to go out with my wife!

That´s the deal with her for the time I spend in my workshop.







Ciao Marco

Edited by Z320
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Hi Bob,


it would fit without any problem to a TR2-3,

but I own / have no TR2-3 fuel cap to make the insert suitable.


I only know the body is longer - so the hook does not grip.

Further the nozzle is a little taller - so it is not possible to stick the insert in.

And I´ve been told there should be 2 minimum different diameters on the TR2-3.


Ciao Marco

Edited by Z320
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I fitted a locking petrol cap to my 3A. I had a spare Mini Cooper 'Monza' locking cap. (Photo's. 1 and 2)

I bought a Mini Cooper 'fake' second petrol tank neck from MiniSport and adapted it to fit into the 3A petrol tank. (Photo. 3).

Very easy to do and it looks 'the business' on the TR.



Edited by Fireman049
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  • 2 weeks later...

post-11421-0-08336000-1515864497_thumb.jpgI bought one from Marco.


Really well made and fitted like a glove first time.


Takes about 2 seconds to fit:-)


Comes with 2 keys.


It arrived in a couple of days.


Well done Marco! Great bit of kit!



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Mine arrived from Germany yesterday morning.

Had to sign for delivery (good), very well packaged, very well made and fits like a glove.

This is something which I have thought about, on and off, for years because each re-fuelling takes some 65 litres of fuel and costs me about £77 (nominal 18 gallon tank), so I am very pleased that now I have a lock in place.

Thanks, Marco.

Ian Cornish

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Dear Ian,


thank you to let me work with you on this article, I like the result very much.

Because it explains exactly how it works and everybody with this idea in mind and a lathe can make one DIY.

The time I can spend on my car and bike hobby is very limited and more limited for this item.

So I appreciate help for self-help.


By the way - did anyone realise that the lock insert also fitts on the TR6 fuel cap ?!? -

when you put the body (without cap) on a lathe and bore / spindle it out by the dimentions of the lock?

This is my double DIY-advice, I will not offer to do that.


Ciao Marco

Edited by Z320
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  • 3 weeks later...

Just received my Locking full cap from Marco. Fits my TR5 really well (took 2 seconds). Nicely made and it will stop horrible people putting things in the tank. Thanks Marco.

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A nice piece of kit quickly fitted.

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  • 6 months later...

I suggest you contact Marco direct - details from my article in TR Action:


Lock insert for TR4/4A fuel filler

Ian Cornish


For many years, this is something which I have thought about on and off because the extended tank in 4VC holds a nominal 18 gallons, and each re-fuelling swallows some 65 litres of fuel, costing me about £77. I have no wish to fit a locking cap because the Works’ competition cars didn’t have such in 1962 – and these caps cost between £45-60. So, I am very pleased that now I have a lock in place thanks to Marco in Germany (Z320 on the Forum), who posted early in January that he makes a lock insert for the round 2” (50 mm) diameter filler of TR4/4A/5, some TR6, and other Triumphs (some Spitfires, GT6, but not TR2-3 – see below). The lock itself is German (trademarked) and is supplied with two keys. No modification is required to the filler cap or its tube, and the device is invisible when the cap is closed. It can be seen that there is a very small breather hole to prevent a vacuum being created inside the tank.


Mike Colman, also pleased with the unit, has mentioned another not insignificant benefit: “in addition to preventing fuel theft, it also stops intentional fuel contamination .... important to me”.


The cap part must have a filler tube descending 2” (50mm) to a small gap between the upper (cap) part and the lower part, which is attached to the tank and is also smooth inside, this gap being bridged by the large diameter rubber tube. When the key is rotated, the lock engages its operating bar into the gap. The sidescreen models (TR2/3/3A) have a 2-part screwed casting, with the bottom edge of the lower section being further from the top, and that’s the reason why this lock insert is not suitable for them. Marco is getting hold of a TR2/3 filler assembly in order to see whether he might be able to make a lock insert to fit.


If interested, send Marco a personal message (PM) via the Forum or via the email address below. The price to club members is £55.00 (GPB), inclusive of post & packing. Marco comments, “sure - not a bargain, but from every sold lock I have to go out with my wife! That´s the deal with her for the time I spend in my workshop!”


As I hadn’t set-up internet banking (I have now), I paid Marco via PayPal. I had to sign for delivery (that’s good) and the unit was packaged securely. The unit is very well made and finished, and fits like a glove, so I am a happy customer (note: I have no commercial connection with Marco, whom I’ve never met).


Marco can be contacted via Forum PM (Z320), or via email Z320@arcor.de

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Hi Matt,


thanks for your interest, I have no lock inserts ready at the moment

but will make some for TR4 and 4A fuel caps when the nights will be longer.

We stay in contact?


Ciao Marco

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