Another 8N Not Starting Question

[Soundguy]

i don't have a manual with me, but if the spring was too long or strong, it would keep the plunger from lifting at 45 psi.

on the flip side of that argument, a worn N engine has a hard time making relief pressures anyway.

pull the plunger and reseat and see what you get.

 

[Rockfootball47]

i don't have a manual with me, but if the spring was too long or strong, it would keep the plunger from lifting at 45 psi.

on the flip side of that argument, a worn N engine has a hard time making relief pressures anyway.

pull the plunger and reseat and see what you get.

What do you mean by reseat? Just unscrew and pull out the spring and plunger and reassemble? I recall that the spring was roughly 3" long.

We were assuming we didn't have any vacuum in the oil pump since the pressure initially was at 0psi. To gain pressure at all I had to add 6-7oz of oil in the cavity that the plunger and spring fit into. Could this have anything to do with it? We let it run for maybe 20seconds with the high pressure and then I noticed oil leaking from the connecting at the pressure gauge.

 

[Eyecatcher]

You said the op went to 80 and did not go down. Is it still @ 80 not running? If so the gauge is plugged. I also don't think an N oil pump will push 80 psi unless something is plugged solid. I had to prime my pump to get pressure, and I used gear oil. It never went over mid range on the gauge. Have you changed the oil filter? don't know if a plugged filter would cause this or not.

 

[Rockfootball47]

You said the op went to 80 and did not go down. Is it still @ 80 not running? If so the gauge is plugged. I also don't think an N oil pump will push 80 psi unless something is plugged solid. I had to prime my pump to get pressure, and I used gear oil. It never went over mid range on the gauge. Have you changed the oil filter? don't know if a plugged filter would cause this or not.

Let me rephrase. While the engine was running it read 80psi (Max). Come to think of it, the needle may have been trying to go beyond 80psi but couldn't. When I turned the engine off the gauge dropped to 0psi. This happened the last two times that I ran the tractor. I also noticed oil leaking from the pressure gauge threads and the 3 way splitter valve that screws into the block.

I did apply about 1oz of gear oil to the pump when I was reassembling the engine. It sat for about 3-4 weeks after I did that until I tried to start it so I also added about 3-4oz's of car oil 5W-30 into where the oil relief spring and plunger go to attempt to prime the pump just incase. When this didn't work as I got it started and the oil pressure gauge read 0psi we tried adding more (4-6ozs) of oil into the same location. From this on the gauge has read 80psi.

 

[doxford jim]

A shot in the dark but have you tried to verify that the current gauge is reading correctly ? If it is a mechanical gauge with a tube supplying oil to the gauge, it would be a simple and easy job to connect another known (new) pressure gauge to see if the old gauge pressure readings are repeated. If the new gauge gives different readings then I would suspect the old gauge is shot (borden tube failing). Anyway, it wouldn't cost very much to buy a replacement gauge and install - that would be my next step if it were me.

 

[Rockfootball47]

A shot in the dark but have you tried to verify that the current gauge is reading correctly ? If it is a mechanical gauge with a tube supplying oil to the gauge, it would be a simple and easy job to connect another known (new) pressure gauge to see if the old gauge pressure readings are repeated. If the new gauge gives different readings then I would suspect the old gauge is shot (borden tube failing). Anyway, it wouldn't cost very much to buy a replacement gauge and install - that would be my next step if it were me.

No I haven't. The main reason I don't want to buy a new gauge is because of the oil leaking from the threaded connections which I confirmed are pretty tight. I didn't want to over-tighten them so I left them along for now, but when I installed the lines I made sure they were reasonably tight.

I do have the original gauge but the background is rusted so I can just make out that the needle is all the way to the left when not hooked up. I will try it tonight.

 

[Soundguy]

Those fitting are all taper, so just go back with some tape

 

[Eyecatcher]

I would certainly put the old gauge back on there and see what it indicates. My gauge face was so dark I couldn't read it, but it indicated about mid face. Got a new one when I re-assemble the tractor. You have completely rebuilt this engine. Figure FO-27 in the IT service manual shows the oil path. It's not a very good representation, but it appears that there is an oil galley down the side of the engine, and the op gauge comes off the rear of that galley. It's difficult to tell from that drawing what happens to the oil that is bypassed by the pressure relief valve, but I would say that it sprays down over the timing gears. That being a rebuilt engine, all tolerances should be tight, and if the oil pump is in good shape or replaced, it's making maximum pressure. The only thing I can think of is that there must be something plugged tight, and the relief valve is stuck shut. Can't imagine what could cause that, unless someone in the past has used a much heavier spring, trying to up the op to over come wear. I think if the old gauge registers full scale, I'd pull the oil relief valve, disconnect power to the ignition coil, roll the engine over with the starter, and see what comes out where the pressure relief is supposed to be. It's just possible someone has installed the wrong spring.

 

[doxford jim]

Until you know for sure that the oil pressure gauge you are using is good, you are really chasing a problem that may not exist. The threaded section for the pressure gauge should be tapered and either pipe thread dope or PTFE tape should fix that. If the pressure is proven good, it might pay to try a different (weaker spring) in the relief valve and see what happens. I am guessing here, but would think around 30 psi. or better might be the oil pressure for the newly built engine.

 

[Soundguy]

Oil relief was designed to open fully by 45, so I'd call that closer to new engine spec.

However if I owned an n that held 30 psi hot idle, I,d celebrate.