Injection Pump Pressure Valve Question

[mistral66]

I am nearing completion of a financially exhausting restoration on a '68 280SL California Coupe that has not been running for over 20 years. The fuel pump, fuel tank, injection lines, and fuel injectors have all been replaced. My injection pump control rack moves freely 1/2-in left and right, but fuel only comes out of the 1st, 2nd, and 4th pump outlets when I loosen the injection lines. Would I be correct in assuming that the injection pump pistons are ok since the rack moves freely, and the 3rd, 5th, and 6th pressure valves therefore need attention. Will WD-40 normally loosen these pressure valves or is replacement the better option (assuming I can find the tool to remove them and if these valves are even available). I have the R21 injection pump.

[Shvegel]

Hmmm.  that's an interesting one.  Just to make sure we are all on the same page by "rack" I assume you are talking about the toothed rod that runs through the length of the pump?  I think the first thing I would check before invading the pump would be to remove the long side cover under the fuel inlet and outlet and try moving one of the little levers (clamping gear segment) with the slotted screw through them back and forth and see if all 6 are moving?

 My next though although it sounds like a lot more work might be the best way to get it working would be to remove the pump and lay it on it's side with the fuel inlet facing up,  pour laquer thinner into the fuel supply fitting then run the pump carefully by using an electric drill with a 19mm socket.  I think what you have going on is the delivery valves may be gummed up and stuck closed and those cylinders are not able to purge the air in them so they are only building a few psi of air pressure.  by laying the pump on it's side with the fuel supply up it should allow thinner to flow into the cylinder by gravity and eliminate the air.  The pump will then develop a couple thousand psi and push the delivery valves open.  You could also access the valves by removing the outlet fittings but I don't recommend it.  the delivery valves seal to the pump barrels (Cylinders) with no sealant or gasket of any type.  They rely on a near perfectly flat machined surface.  If you get the smallest piece of dirt in there you can effect the seal or worse ruin the delivery valve.  You can clean around the outlet fittings but dirt will still find it's way down the threads and in the process of dropping the delivery valves in you may shake it loose.  You also won't have to source new nylon seals to go between the delivery valve and the outlet fitting.

From what I have read new delivery valves are not available from Bosch.  The common fix would be to buy the newer style ball valves and machine them down to fit.  The other option is to source used ones. 

[mistral66]

Many thanks for the advice and technical assistance. I will remove the injection pump and run lacquer thinner through it per your instructions. I'm also extremely happy not to have to remove the delivery valves and suffer the risk of further damage.