Oil leaks - Pierburg “Chinese hat” type fuel pump

[simonvolvo]

If your Pierburg “Chinese hat” type fuel pump leaks oil don’t immediately assume that a set of new gaskets will fix the leak.

Supposedly knowledgeable people claim that the cause of the problem is a warped pump flange. The flange is warped, so they say, by over-tightening the bolts that fix the pump to the block and attempts to stop the leak by tightening the bolts even further just exacerbate the problem. This all sounds very plausible but is WRONG.

The Pierburg pump has a pivot pin which passes through holes in the pump body and is held in place by a pair of circlips on the outside of the pump body. Two things happen as an engine gets older: One, in the case of the fuel pump (and I’m guessing here), the fit of the pin in the relatively soft die-cast material of the pump base becomes less and less tight, so widening the capillary gap between the pin and the pump base; and, two, the crankcase pressure of the engine increases. As a consequence, minute but ever-increasing quantities of oil are driven out past the pivot pin. Once outside the pump the oil finds its way to the lowest point, which is where the pump joins the block, making it appear as if that is where the oil has come through.

What I did eventually, after literally years of faffing around with the gaskets and attempting to straighten the flange - yes it was slightly warped: Remove the pump, remove one of the circlips on the pivot pin, and withdraw the pin. Thoroughly degrease the pin and the rest of the pump below the diaphragm, using brake cleaner for example. Re-insert the pin and put some suitable sealing fluid on the pin where it passes through the holes in the pump base. I used Loctite Thread Locker 242 which I happened to have lying around. (There may well be other, perhaps better, products that will do the trick.) Allow to dry overnight. The pin does not have to be able to rotate in the pump base, so it doesn’t matter that the Loctite, when dried, prevents the pin from rotating.

That stopped the leak COMPLETELY.

The fact that the flange was slightly warped proved to be of no consequence.

[niveketak]

Well I had a look at my leak and lo and behold it is leaking at the pin not the gasket. Don't have any loctite but do have some epoxy resin which should do the trick.

[simonvolvo]

Originally Posted by niveketak

Don't have any loctite but do have some epoxy resin which should do the trick.

You could try epoxy resin but I have an idea it will not really want to "wick" into the capillary, which is where you want it to be. Something like shellac may work, or what about some nail polish?

[Ron Kwas]

Simon;

I expect that just about any gasket sealer which is liquid during assembly but then dries and hardens to a hydrocarbon impervious seal will have the desired result...but my compliments on analyzing a commonly occurring situation and coming up with the true cause and solution!...I wonder...are the other pumps less susceptible to this due to a different or better design/construction?

Cheers from Connecticut!

[simonvolvo]

Originally Posted by Ron Kwas

I wonder...are the other pumps less susceptible to this due to a different or better design/construction?

The only after-market fuel pump I have seen has the pivot pin entirely inside the pump base (it is crimped in position), so there is no capillary gap through which oil can leak. In this sense it is an improvement over the Pierburg design. However, the downside is that you can’t take the pump apart, which means that if something/anything goes wrong you have to toss the entire pump and buy a new one.