Visit our Popular Forums

Compass790 · 11-10-2018, 02:26

Quote:

Originally Posted by a64pilot

I don’t understand the reluctance to remove the engine?
Remove it, then you can do a proper overhaul clean and paint it etc, and while you can hone the cylinder, if you replace it and maybe a piston, and have the head done, you have essentially a brand new engine, and will likely never have to do anything serious to it again.

Yea agree with a64 but dunno how big u r. I managed to pull our YSM8 by hand but know that yr motor is bigger. U can strip a lot off 1st. I did remove head & starter before I dragged engine & gbox out. U can figure out a way to jack it & slide it & then take gearbox off in cabin.It's the best way to do it ( out of boat)if you can manage it

Homer Shannon · 11-10-2018, 12:24

Let me comment on maintenance first. I run the engine an average of 50 hours a season. I change the oil annually and I check the primary fuel filter annually. I check the secondary filter whenever I'm working on the diesel side and it has never been dirty, though I've replaced it at least three times in my ownership. I do inspect the anode and replaced it at least once. I look the engine over and inspect for issues regularly. I carry spares, including the secondary filter and an anode, and keep a pretty good watch on the motor's behavior.

I used the bad weather today to clean up the head and a few other parts. When cleaning the head I noticed dent marks right by the injector precombustion chamber. Associated with this is a "lumpy" area by the adjoining water jacket port that looks like a possible crack. I went and got the head gasket from the boat and you can see that these marks match marks on the head gasket in the same area. The head gasket looks to be in poor shape in this area, though I don't know how much of the damage came from the life of the engine and how much came from disassembly.

Should get the head machined to remove this damaged area and get a perfectly flat surface again? I don't think this engine has ever been apart before, so it's a bit of a mystery as to how these imperfections were created.

I also removed the valves, which seem ok. Some crud and build up on them, but otherwise they look good (to my untrained eye). I will give them a light lapping on re-assembly. The valves are very tight in the guides with no lateral play at all. I'm assuming the guides do not need replacement.
Photos are posted at (Note, the photos are full 16MP resolution, they will take a moment to load.) https://1drv.ms/f/s!AiR9KzpBmPls1jA4sX7lMEUkrMwM

**Wotname** · 11-10-2018, 15:00

^^ interesting "dents and lumpy bits". It may be a crack or it may be some erosion but I am no expert in this field so I will leave to wiser heads to make more informed comment.

I would certainly investigate further!

And yes, the valves sound OK, lap and check for tightness when re-assembled. They should hold alcohol for 24 hours.

Homer Shannon · 11-10-2018, 15:12

I'm leaning towards the result of minor gasket blow by over a long period of time. I will need to get the head machined. Now I need to figure out how to remove the precombustion chamber. There isn't a word about it in the workshop manual. The parts list shows an "pin" of some sort that aligns or locks it in place. Hopefully someone knows the answer to how the thing is removed. Otherwise, I'll have to mill the head with chamber in place and it sits only about 0.020" below the current head surface.

I'll try the alcohol trick once I get things reassembled. Wish I could hold alcohol for 24 hours :-)

**a64pilot** · 11-10-2018, 15:32

It’s erosion, maybe even what is called flame cutting from a dirty injector.
However I would not ever surface a Diesel head unless there was no other way, there just isn’t any extra meat on a Diesel Head and often the valves have to be recessed and pre combustion chambers are an issue as well if there are any.

**Wotname** · 11-10-2018, 17:51

Quote:

Originally Posted by Homer Shannon

I'm leaning towards the result of minor gasket blow by over a long period of time. I will need to get the head machined. Now I need to figure out how to remove the precombustion chamber. There isn't a word about it in the workshop manual. The parts list shows an "pin" of some sort that aligns or locks it in place. Hopefully someone knows the answer to how the thing is removed. Otherwise, I'll have to mill the head with chamber in place and it sits only about 0.020" below the current head surface.

I'll try the alcohol trick once I get things reassembled. Wish I could hold alcohol for 24 hours :-)

The head shop will get it out but here is some pictures showing the one part of the pre-combustion camber (the part with the pin). The pin is just a guide / locating pin and slides in the groove in the head. The other part sits above the the shown bit and there is a copper sealing washer between the two parts.

One apart, they slide in and out easily; presumably a gentle tap will remove it

Homer Shannon · 11-10-2018, 18:14

That's great information, wotname. Right now, the injector is still installed in the head. If I take off the two stud nuts and backing plate on the top of the injector, will the injector come right out? Once the injector is out, I assume you tap on the precombustion chamber to back it out of the head. Correct? (Nothing on this in the workshop manual at all!)

I found this article https://www.pbo.co.uk/expert-advice/...der-head-20467 that covers injector removal pretty well, along with other good information. I'll take a crack at this.

One of the things I've picked up on, is the fact that Yanmar diesels, for the most part, operate on the same principals. If you find a good article on a 2GM or something, chances are the processes are about the same for SB12.

Compass790 · 11-10-2018, 18:27

Quote:

Originally Posted by a64pilot

It’s erosion, maybe even what is called flame cutting from a dirty injector.
However I would not ever surface a Diesel head unless there was no other way, there just isn’t any extra meat on a Diesel Head and often the valves have to be recessed and pre combustion chambers are an issue as well if there are any.

I agree with A64, avoid skimming the head. Looking at yr pics just noticed little marks where steel flame ring sits. Dont know if they are oil or leakage marks. I would put Loctite 518 flange sealant on the new head gasket & torque it up IF any marks on head are less than 0.15 mm deep. It works. Nobody believes me when I tell them to do this but I'll continue to piss into the wind.

**Wotname** · 11-10-2018, 19:54

Quote:

Originally Posted by Homer Shannon

That's great information, wotname. Right now, the injector is still installed in the head. If I take off the two stud nuts and backing plate on the top of the injector, will the injector come right out? Once the injector is out, I assume you tap on the precombustion chamber to back it out of the head. Correct? (Nothing on this in the workshop manual at all!)

Yes, correct BUT the injector might not just come out easily - some do and some are rusted in a bit. If rusted, let some diesel or some ATF/acetone (50/50) sit around the injector overnight. The thread at the top of the injector is a M8 and you can put a bolt in here to help pull the injector out or if necessary, a slide hammer.

I found this article https://www.pbo.co.uk/expert-advice/...der-head-20467 that covers injector removal pretty well, along with other good information. I'll take a crack at this.

Looks like a good resource

One of the things I've picked up on, is the fact that Yanmar diesels, for the most part, operate on the same principals. If you find a good article on a 2GM or something, chances are the processes are about the same for SB12.

This is true!

Homer Shannon · 12-10-2018, 03:16

Wotname: Thanks again. I may not know exactly what I am doing, but I'm learning every day. I just need to keep my education ahead of my blunders!

Homer Shannon · 12-10-2018, 12:38

The mystery of the oil consumption deepens.

I took the piston out today. It was not overly difficult though I can see that reassembly will be a hassle. That was the good news. The bad news is that nothing is wrong. It was immediately obvious that there were no broken rings or significant wear that would cause high oil consumption.

All of the parts were clean and well oiled. There is negligible carbon build up anywhere other than on the top of the piston. Even that is not too bad. The wrist pin is nice and tight and the rod bearing looks fine.

I spent the better part of the afternoon going over all the parts, checking them with a micrometer and a caliper to determine their wear state. Nothing is beyond spec requiring replacement. Most notably, the oiler ring had less wear on it than any of the other rings and its perfectly clean. But all of the rings are within tolerance for breadth and thickness. The piston diameter is OK and all the ring landings are within spec - except the compression ring landing. That is at maximum spec (+0.15mm) but not over spec. I’m not sure about the ring gaps. I measured the gap on the compression and oiler rings and it is about 1.10mm. I don’t have a spec for this but this seems reasonable (and shouldn’t be out of spec unless there was as significant loss in the ring thickness and or an increase in the bore diameter).

I also checked the valves. The valve shaft diameters are well within maximum tolerance and the spring heights are within limit.

So, now I’m in a bit of a quandary. I have a list of parts I’ll be replacing, including the rings and the rod bearings, I’ll hone the cylinder and I’m getting the head worked on to fix the damage near the precombustion chamber. I also plan to pull out the injector and clean the injection pin. I have no doubt that my work is going to prevent a head gasket failure that was probably going to happen next season and the engine may run a bit better, but I have no reason to believe that I will have done anything that would reduce the oil consumption. What next?

Compass790 · 12-10-2018, 15:06

Quote:

Originally Posted by Homer Shannon

The mystery of the oil consumption deepens.

I took the piston out today. It was not overly difficult though I can see that reassembly will be a hassle. That was the good news. The bad news is that nothing is wrong. It was immediately obvious that there were no broken rings or significant wear that would cause high oil consumption.

All of the parts were clean and well oiled. There is negligible carbon build up anywhere other than on the top of the piston. Even that is not too bad. The wrist pin is nice and tight and the rod bearing looks fine.

I spent the better part of the afternoon going over all the parts, checking them with a micrometer and a caliper to determine their wear state. Nothing is beyond spec requiring replacement. Most notably, the oiler ring had less wear on it than any of the other rings and its perfectly clean. But all of the rings are within tolerance for breadth and thickness. The piston diameter is OK and all the ring landings are within spec - except the compression ring landing. That is at maximum spec (+0.15mm) but not over spec. I’m not sure about the ring gaps. I measured the gap on the compression and oiler rings and it is about 1.10mm. I don’t have a spec for this but this seems reasonable (and shouldn’t be out of spec unless there was as significant loss in the ring thickness and or an increase in the bore diameter).

I also checked the valves. The valve shaft diameters are well within maximum tolerance and the spring heights are within limit.

So, now I’m in a bit of a quandary. I have a list of parts I’ll be replacing, including the rings and the rod bearings, I’ll hone the cylinder and I’m getting the head worked on to fix the damage near the precombustion chamber. I also plan to pull out the injector and clean the injection pin. I have no doubt that my work is going to prevent a head gasket failure that was probably going to happen next season and the engine may run a bit better, but I have no reason to believe that I will have done anything that would reduce the oil consumption. What next?

Yes your problem getting in the hard basket now but a thought just struck me.Does the SB12 have an aircleaner? Had a case on a motor-sailer I was sailing master on with a 75hp CAT diesel that the oil consumption skyrocketed & it was due to a dirty aircleaner. It caused it to pull such a vaccuum that it was sucking oil into the combustion chamber thru the v/v guides & rings You can try removing yours ( if you have one) when you get it back together. Otherwise check the head very carefully for cracks near the intake valve as that could pull oil in from the rocker chamber or pushrod holes. Or it could be yr head gasket leaking near the pushrod hole on the suction side. Just some random thoughts for you to consider.
Yea your bore sounds ok but would still do rings & hone now you've pulled it.

**Wotname** · 12-10-2018, 15:12

Quote:

Originally Posted by Homer Shannon

............ I’m not sure about the ring gaps. I measured the gap on the compression and oiler rings and it is about 1.10mm. I don’t have a spec for this but this seems reasonable (and shouldn’t be out of spec unless there was as significant loss in the ring thickness and or an increase in the bore diameter).
............

The YSE12 manual gives ring end gap measurements as 0.4mm new with 1.5mm as the wear limit.

The YSE12 and SB12 use the same piston (same part number) so I would assume the end gap would be the same.