early style fuel pump domed cover

[roy mawbey]

I guess its possible there are a few out there with 356A and 356 early B domed cover vertical fuel pumps and that they might have experienced similar problems to mine.

My pump is now 60 years old made of aluminium and supplied new on 356 and Mercedes cars. Really its a wonderful bit of kit and although I bought a rebuild kit some years ago I have never used it. But....the domed cover that has the rubber seal and the 10mm bolt securing it has been the problem for me over the past 50 years of use.

In the early years of ownership I used to remove the cap to inspect the fuel filter inside the pump body quite often. That was not necessary as the number of times that 10mm bolt is undone and replaced again is not good for the thread in the pump body. It slowly wears the thread. And also to stop the rubber seal from leaking more pleasure each time is applied to the 10mm bolt which eventually distorts the top of the cover.

So, ten years I flattened the top cover with a file and found a new 10mm bolt and made it slightly longer to take advantage of the last few unused threads in the blind bore of pump body. I also used the new rubber seal from the rebuild kit bought those years ago from the USA.

Then some weeks ago I saw the seal and top bolt with the fibre washer leaking! I tightened the bolt made it worse! Established there is a guy in the States who can supply the no longer available pump covers and rebuild pumps. The cover alone is around £75- Other than that, the later horizontal pump can be fitted or of course an electric one fitted.

The thread in the blind hole of the body was stripped, the peg the tapped hole is in has a thin wall in one place and I thought a helicoil might not be easy. So... I looked at my chances at re-tapping a new thread. Well, a 1/4" UNF old style British thread had a thread diameter that would work. The tapping drill was 7/32 " and when I tried one in the stripped thread it showed me the 1/4" UNF tap could be used without having to drill! I took the chance of making a cardboard cover to go on top of the fuel pump body and then taped in place so no swarf could get in. I have a small tap wrench that allowed me to re-tap the hole without removing the pump. Turned out perfect. Also the head of the 1/4 UNF set screw accepts an 11mm spanner perfectly.

I then found in Hove near Brighton the company Namrick.co.uk who can supply every type of the old imperial nuts and bolts. I bought 6 off 1/4 " UNF x on inch long set screws and cut the length down on one to suit the hole. I also drilled the cap hole to make a fine clearance for the new bolt. As well, I found a fibre washer 2mm thick that I drilled and tapped 1/4 UNF. On the bolt I placed a steel washer the same diameter as the fibre washer. The fibre washer was then screwed onto the bolt.
Finally I bought a new rubber seal gasket to replace the USA one. The new one supplied by Roger Bray had all Porsche markings on the bag and was half the thickness of the USA one!

Cleaned to perfection the tapped hole, replaced the cap and tightened not too hard. Perfect after one run put a little more torque on the bolt and its been perfect ever since.

If you are not finally bored it will probably be of help to you.

Roy

[louis356]

I'm not too sure if I need to rebuild my pump yet. But have taken to top off to look inside. This is only the second time I have done this in 25 years!! So here's hoping I don't have to go through what you have done (or could I send it to you for a refurb if I do?).

I think I've got a blockage somewhere!! Just haven't had time to investigate.

Thanks for the description.

[neilbardsley]

I've heard that the filter by the fuel stopcock can be a good place to start looking. Might we worth checking the tank too? Sorry if you have already done both.

[roy mawbey]

Louis,

With the gravity feed from the tank there is enough pressure to easily send petrol to the pump. It will in fact flow very fast! If with the pump domed top off you have no fuel with the lever in the on position then it might be worth while trying the reserve position too. Take the fuel cap off when you do this.

The petcock controls the on and off supply and unless there is a real kink in the fuel braided pipe then I would suspect the petcock. Maybe try a little hand forward pressure on the on/off handle as you turn it.There is a gasket inside the petcock that might have moved round blocking it.

You are the same as me in never needing to take the domed top off to inspect the fuel filter. I reckon in th early sixties the owner who had my car must have it taken off on every service the thread was so bad. If you can tighten the 10mm bolt you are probably okay.

Let us know what you find Louis.

Roy