YSM12 Oil Pressure Problem

[sailaway78]

From what you have posted

so far, I am beginning to lean towards some excessive bearing clearances. There just isn't a lot of different things that can cause this problem. You don't have a regular filter, so a bad filter is kind of ruled out, you have replaced the oil pump gears, and the pressure control device. Not much left. It only takes a couple of thousands excess clearance on a bearing to lose oil pressure. Don't sound good.

 

[Rob19574]

Bearings Clearance

Guys - I am curious...can someone explain to me why a worn bearing would cause a loss of oil-pressure? I am stumped on this on and love to learn all I can about Diesels. I also have a YSM-12.

Thanks - Rob

 

[Ross]

Your oil pump is a positive displacement gear pump.

if it is pumping against an open line the oil pressure will be very nearly zero. If it is pumping against a completely closed line the pressure may be hundreds of psi. If you made a pin hole in the closed oil line the pressure would be relieved a little. A larger hole equals more relief. Nice new, tight bearing represent a very small hole in the oil line. worn bearings are just a bigger hole.

 

[porsche]

as to scott

yes a crank shaft can be reground to except an over sized bearing but of course there are limits as to how far but the machine shop will know. Ross is spot on with the bearing clearence, think of taking your garden hose and let the water run out of the end, now put your finger in the hole and watch the press build up, same idea with bearings on your crank. Alan

 

[Hermit Scott]

Diesel cut off

OK this is going to sound really elementary. What is the kill mechanism on a diesel? It seems the only thing you could do is shut the gas off or the air intake. Redidculously simple things like this and the glow plug being absent are so obvious to anyone with any expierence that they don't even mention them in the manuals. I just don't want to get it running and then not be able to stop it if I need to immediately.

 

[sailaway78]

Diesel cut off

You are quite right Hermit, in the ways to shut off a diesel engine. Shut off the air, or the fuel. The best way if the fuel shut off cable is broken or not functioning is to hold your hand over the intake and choke it down. In a pinch you can open the compression release and kill it that way but that is not recommended. The kill cable on the Yanmars basically shuts off the fuel. Lots of folks want to make a diesel engine much more complicated than it is. Basically they are very simple engines.

 

[J Page]

thanks a ton to this forum and this topic

I have learned more in reading these respondes than in three years on the water. Now that said I haven't had to do anymore to my motor than change oil and drain water for the filter. My motor is original and is still running like a top. Starts in less than 3 sec.( longer when its colder) and I will use the water shut off idea when colder temps set in. My motor is in fresh water so that takes some deamons away, and the rest I have a good friend in Brian Torresen to help if needed.

Again, thank you so much for the great info.
Lugeman

 

[Hermit Scott]

compression

Before I take the head off to replace the valve guides and lap or replace the valves/seats I would like to check the compression just to see where it stands now.
Does any one know where I can rent a diesel compression tester that will fit in the injector port on the head? IS that some type of standard sized port that all compression testers will have an adapter for?
I know someone here knows because there is nothing I could think to ask about boats that would stump these guys.
I have to say, I am truely impressed with few things in life. But using the archives and the fact that there are people here so knowledgeable and are willing to answer my amature questions with patients, is amazing.

 

[Rob19574]

Bearing Clearance

Ah - thanks guys...that makes sense.

- Rob

 

[sailaway78]

If thicker oil helped

your oil pressure, you more than likely have a clearance problem somewhere. As for replacing a one lunger with a three cylinder, measure carefully. That three cylinder is going to be quite a bit longer, and clearance might be problem.