HELP! 3.5 liter oil pump priming issue LR 77 101 FC

[1bigfield]

OK, rare truck but common engine. I have a problem with the oil priming on the 3.5 LR V-8 in my 1977 military 101 Forward Control. (basically same 3.5 as early Range Rovers). For a while it became progressively more difficult to get engine oil pressure at start up. (The engine has under 10,000 original miles from brand new, no reason to expect anything to be worn out. I have both an electric oil pressure gauge plus a no-pressure light, so it is unlikely both are malfunctioning, plus I confirmed there was no oil flowing to the rockers). Eventually the oil pump would not prime at all. The pressure release valve seems free, not hung up, no step or wear issue I can feel. The oil filter is the proper anti back flow type and I changed it (and pre-filled with oil) to be sure it was the right one and not defective. The level of oil in the oil pan is fine. Still no pressure. I tried priming by pouring oil down a hose into one of the gauge ports in the pump before cranking with the coil wire removed. No pressure I tried priming by removing the distributor, machining a shaft to engage the oil pump and turning the pump with an electric drill for 15 minutes. No pressure. I pulled the pan and checked the oil pick up strainer. No blockage and looked clean.The oil pan was sludge free. I then bought two brand new genuine Land Rover gears for the oil pump and installed them packed with vaseline. No pressure. Repacked it again. Still no pressure. I am running out of ideas. I guess when the weather is better I'll pull the pan to see if the oil pickup into the pan is cracked or has come loose where it attaches. The official 101 parts manual doesn't even show the pickup part, (hard to figure that one other than having been created in the Leyland era corporate ownership ) but the 3.5 range rover parts manual which is the same basic engine shows a slightly different looking pick up (round rather than rectangular strainer) that bolts on with a gasket so I suppose it could be sucking air at that gasket or join. Any other suggestions from anybody???

[Team Idris]

There is the pick up pipe gasket and the timing cover gasket as suction seals? Timing cover gasket failure seems unlikely, but pick up pipes have fell off of all sorts of engines.

[rovernut]

Clouted the oil filter a couple of times whilst off roading with a mates 101. He always carried a spare filter just in case. No amount of pre priming the filter with oil would produce any pressure on first start up but packing the oil pump with Vaseline always did the trick.Until I saw this I always wondered why he carried the big jar of Vaseline around.

[Ash.Witty]

What grade of oil are you running? I used 10w40 in winter and 20/50 in summer as the later is very thick and took a while to gain pressure on my v8 in cold weather. When you used the pump priming tool did you set it to go clockwise? You might not create much pressure with the drill to put the light out, I tried this method and after a few seconds you hear the drill trying to stall or being put under load and this is when its primed and has a bit of pressure.

If you remove the pressure sender does oil come out if turned with the tool?

Now also not 100% but did you remove the rocker covers? Try looking at the end of the rocker shafts, there are plugs held in with split pins may be possible one has come loose.

[Bull Bar Cowboy]

Sounds like the oil pressure relief valve in the housing has jammed open. It’s a very common fault in the earlier V8’s and is due to a little scoring in the bore which causes the ball to stick.

Undo the cap and make sure the ball is pushed home onto its seat. If is really stuck fast then it will need a good sharp blow with a pencil drift to shift it.

If it is the problem, you can clean up the bore with a dremel and polishing mop …….. fitting a tadpole valve helps but is not a fool proof answer).

No need to pack the pump with vaso ………….. just give it a good stir with the drill and it will soon prime

[FridgeFreezer]

Worth also mentioning that you want proper spec oil - 20W50 or 15W40, if it's too thin it will struggle to prime.