Perkins 4-108 fuel in engine oil

[skipperpete]

Here’s a CAV-DPA pump repair that a cruising sailor with a low budget, some mechanical ability, a bit of patience and a sump full of diesel might find useful. Once that the lift pump has been proven NOT to be the cause of the crossover, there remains one other culprit… the driveshaft seals on the injector pump. Initially its reasonable to assume that a return line restriction is causing the pump housing to be over pressurised, ( case pressure at the return line fitting on the pump should be close to zero) but if that’s not restricted it means the seals are worn. On a mechanically governed DPA pump this is a job for a tech but if you have a hydraulic governor model you’re in luck, for the cost of a seal kit and a pair of 90° circlip pliers you can do it yourself. Actually , the hardest part is taking off the manifold to get the injector pump off but once the pump’s on the saloon table the next bit is easy…. If you have the right circlip pliers.
Cleanliness is ultra important so seal the inlet port and outlet hp stocks and clean away any loose dirt or oil around the elliptical return line cover plate then undo the 2 screws that hold it to the pump body. Once the plate is off, clean again around that casing hole, no dirt should be allowed to get into the pump cavity.
Now with a small flashlight look into the cavity towards the bottom of the pump and you’ll see a steel circlip, slowly rotate the driveshaft till the ears of the clip are visible, put the end of the pliers into the pump window and with that flashlight to see, engage the pins of the pliers in the ears of the clip… squeeze …. and remove the clip to the window and leave it on the shaft. Then pull the shaft out of the pump housing complete with seals and circlip far enough to get the circlip off completely over the larger end of the shaft then pull out completely the splined shaft. The seals are unique inasmuch as they are fixed to and rotate with the shaft…. against an internal seal track….. so with an appropriate tool with no sharp edges, stretch the old rubber seals ( they’re pretty flexible and all rubber) until ya get em out of the groove then stretch on the new ones. I used a tool I made from the end of an old morse cable specifically for removing these and oring seals , a 1.8mm shaft screwdriver might work just as well, they have to be sort of rolled off with the 1.8mm rod under the seal. Once the soft seals are in place on the shaft, clean the seal track in the bottom of the pump, pop the shaft in far enough to get the circlipback over the big spline and ease the seals and shaft back into the pump base….. there’s even a taper built in to the seal track to make it easy. Easy peasy and no timing problems due to the master splines on the quill shaft.
If you ever do this seal change you’ll also have an understanding of how engine oil can get into the fuel ( the famous black tank) if the combination of high crankcase pressure and a blocked pcv valve combine to defeat the pump seals that are only facing light to zero fuel pressure from the pump case, but only on the hydraulic DPA pump and generally only the horizontal pumps. Total cost $20. Fixed!