AC fuel pump

[Hamish Coutts]

Guys,

It's great that you're rebuilding mechanical pumps ~ that keeps things original and nice and simple (there's no extra wiring for an electrical pump, oil pressure cut off switches, fuel pressure regulators and so on).

However (and there is always is a, 'however'), please, please be aware that if the diaphram of a mechanical pump leaks or even worse, fails; a lot of the leaking petrol will end up in the sump and dilute the oil. That happened to me a while ago before I rebuilt my engine. I clearly remember draining the oil and thinking there was the hell of a smell of petrol.

Stating the blatently obvious, this is not the best thing for an engine.

It's always a question of balance (Would the Moody Blues agree? ). Personally, I chose to avoid the risk of diaphram failure again and went for a Facet pump, filter and pressure regulator. That way if anything fails all that happens is the engine stops through fuel failure, not bearing failure. You may think this a bit alarmist but I think not. Try weighing up the extra cost of an electric pump + ancilliaries against the unnecessary rebuild of a twink?

I know racers will have to operate under certain conditions but otherwise, you have a choice.

What do you think?

Hamish.

[types26/36]

Guys I chose to avoid the risk of diaphram failure again and went for a Facet pump, filter and pressure regulator. That way if anything fails all What do you think Hamish.

Hamish,
There are no guarantees in life, you can say "however" "what if" " this can happen" sure the diaphragm can fail, the single circuit brakes can fail, the drive shafts can disintegrate but we are driving 40 year old cars and despite total rebuilds anything can happen.........if you want total reliability by a Toyota!

[Frank Howard]

Hamish,

You make a good point. One thing I'd like to add.

Years ago I had a Ford straight six. I noticed that the oil level seemed to be rising rather and falling. The car ran worse and worse until one day, after I got a block from my house, the car would barely move. I nursed it around the block back to my garage and it was my neighbor who correctly diagnosed the problem as soon as he took a whiff of the dip stick.

The crank case was so full of petrol that the liquid was interfering with the downward stroke of the pistons. A new mechanical fuel pump along with an oil and filter change solved the problem. I lucked out as the rings and bearings were OK.

I'm not advocating letting your crank case fill up with petrol to the point that the pistons cannot operate properly. I only want to point out that if you check your oil regularly and you notice it begin to rise, this is the first signal that the fuel pump diaphragm is broken. The second signal is the engine will barely run. The third is the oil pressure drops as the bearings are trashed. During any of these scenarios, the car becomes a rolling bomb. You should fix the pump when you see the first signal.

[dusty]

I'd like to think that fitting a new (genuine AC part) Diaphram would mean it won't fail! But I guess its a possibility.

[elanmac]

If the diaphram splits how does the pump still work. If the split is big enough to allow a large amount of petrol into the sump where does the pressure come from to pump the petrol. Below the diaphram there is a seal to prevent the crankcase fumes damaging it. The seal is not in the kit off ebay but does need to be changed when overhauling the pump. The seal looks like a small clutch or brake slave cylinder seal, the one fitted on the end of the cylinders. I have tried to buy one but without success, as I found a small amount of carbon below my diaphram.