Soviet East German Radio

[Nowhere-Man]

One point to consider is we don't hear as often about the failings of work undertaken in an industrial setting. Living in a boat yard I see a lot of things that go wrong. To give an example, someone had a marinized but non-running VW GDR diesel in his boat. The mechanic concluded the problem was no fuel lift pump had been fitted so fuel couldn't rise above tank level. The customer started to pay for work to be done. However from a Hayne's manual I discovered the Bosch injection pump on this German engine needed 12 volts on it. It would then lift fuel as well as inject to the cylinders. Few marine engines have pumps like Bosch and most use crankcaase pressure to power a mechanical fuel pump. That's partly why I became to this day a bit zealous over schematics.
Also those here in the trade, consider doing marine electrics as they can't find people. There"s a huge shortage.

[Murphyv310]

Hi.
I'm intrigued by the version of the Diesel engine that has been converted to marine use.
It is unlikely to be a modern common rail version as trying to rig these up with ECU etc is a nightmare.
The older types use the Common enough Bosch pumps that require no fuel lift pump in a car but if the fuel tank is lower than 1-2 meters than the engine (fuel pump actually) then a supplementary low pressure pump will be required.
All of the Bosch pumps will have a 12 volt connection to the "stop" solenoid, 12 volts on it and the engine runs, cut the 12v and it stops.
On this pump it needs a feed in (suction) of fuel and a return back to the tank, this is for bleeding and part of the design, the fuel filter is in the feed line.

Your other statement "Most use crankcase pressure to power a mechanical fuel pump" I'm sorry you are wrong. A diesel fuel pump has to be timed correctly to the relative camshaft and crankshaft positions and this can only be done either electronically or on older engines by running the pump off the timing belt or chain or by using a toothed auxiliary belt.

The only other time you will see a pump on the side of a crankcase is a mechanical fuel lift pump (usually on petrol engines or very old diesels) that is driven from an eccentric on an auxiliary shaft (in OHC engines) or from the camshaft in OHV engines, nothing to do with crankcase pressures, If you had enough crankcase pressure to run a pump you have all the seals leaking oil!!!!!

[Nowhere-Man]

"In older types use the Common enough Bosch pumps that require no fuel lift pump in a car but if the fuel tank is lower than 1-2 meters than the engine (fuel pump actually) then a supplementary low pressure pump will be required."

In my view the mechanic got off on the wrong track altogether. I later found the engine had run fine in the past as it was. It was a mk 1 Golf (or was it mk 2, can't quite recall). The engine came to me in the end as unwanted.. I did the whole scenario of regrinding the valve ports and checking the bearing caps and so on. In the end it turned out all the piston rings were worn and bedded in the grooves. I soaked them in diesel to try and get them out. When I found the cost of fitting new rings I ceased. Too costly although looking back maybe there were options like a rebore. The usual approach would be to do a compression test but I just took off the head. I still have my valve removal tool.

[Murphyv310]

Hi.
You don't do compression tests on a diesel, it's a leakdown test. Gummed rings sounds like lack of oil changes.

[Crackle]

If you only took the head off how did you know the rings were "worn and bedded in the grooves" on all the engines I have rebuilt the piston rings are not visible until the crank shaft has been removed and piston taken out of the bore.

Mike

[Murphyv310]

You don't need to remove the crankshaft Mike, just the sump and big end shells, then push up the piston and Conrod.

[Nowhere-Man]

We're getting way off topic here. Very briefly. You can tell if there are issues once the head is off. In this case I followed through and removed each piston once the sump was off. Definitely no compression in that case.

[Murphyv310]

Error in posting

[Murphyv310]

We're getting way off topic here. Very briefly. You can tell if there are issues once the head is off. In this case I followed through and removed each piston once the sump was off. Definitely no compression in that case.

We are getting OT but NM you did bring this up in the first place. Looking at the last two or three threads of yours you seem to be quite the one for taking a thread OT.

[Nowhere-Man]

I referred back to Lawrence's summary of the Saalburg circuit. The main areas of focus for me at the moment are the two IF's and the EBF89 plus the EABC80. I am literally racking my brains to trace the diodes and, of course, there is the discriminator circuit. I think Lawrence indicated the centre tap between L23 and L24. Anyway maybe it will be understood why I take time out to address textbook theory. Discriminator circuits won't be understood without some grappling with ARRL tutorials.
I haven't fully grasped Lawrence's explanation yet but I will get there. Tomorrow I will print it.
Notice one diode on EBF89 is grounded out and the grid used instead. Likewise the diode on EABC80.
The Foster Seeley discriminator circuit may help me if I locate it.
When I step back and say all the circuit makes sense, then I will go to work more fully.