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.
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.
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