Yanmar YSM 12 - Troubleshooting Help

[Compass790]

Man that's a sorry state of affairs! You could buy a good used YSM12 for much less than parts prices I imagine but you need time & if you have schedule pressure it's difficult. Try posting a request. I got an injection pump that way off a guy on CF that was going to crush his engine. Good luck with parts hunt & keep posting please

[Wotname]

Originally Posted by wheatfieldcrows

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Looking closely at the diagrams of the PC Chamber it would seem there is some sort of pins in it. I wonder if they might have tried pushing the precombustion chamber up and the pin sheared off the wall?

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Don't worry about that pin too much, it is just an alignment pin so the section of the PCC closest to the piston aligns correctly when it is inserted into the injector hole. The is a groove in the head that the pin slides down. Of course in your case it may have rusted into place.

[Wotname]

Originally Posted by wheatfieldcrows

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The upper (rear) precombustion chamber is largely intact but looks like it might have part of the injector attached to it! .........

Most likely this is a piece of the heat insulating packing that goes between the injector nozzle face and the rear section of the PCC. It's dark and when old, looks like metal and is brittle(ish).

But given your recent run of luck, I might wrong .

[Wotname]

Originally Posted by wheatfieldcrows

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It is about $1000 in new parts here in the US to fix the head (including $590 for a new head) and then I can finally find out if the piston rings are any good.

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Being as you have the head off, you might as well take the piston out and then measure the ring gap, ring grooves, piston and bore.

The piston removal is quite simple and only requires you to remove the plate on the crankcase opposite the head. This might be a way of giving you some data to see if you want to continue with chasing down a used head or whatever.

I'm told there are many of these engines in the south west part of the UK, they were popular with small fishing boats there so this might be another source of used parts.

There is also Minards in Australia and they sell used Yanmar parts worldwide. They aren't always the cheapest but they know their stuff and only supply used parts that they have fully inspected. Minards Diesel

Still I'm sure you should be able to find stuff locally.

[Wotname]

Originally Posted by wheatfieldcrows

I have a Yanmar YSM 12 in a 1979 Hunter 30. It is a 1 cylinder 12 hp diesel. We are getting ready to sell her because we have our eyes on a bigger boat but the engine wont start. I'll admit that we have been traveling to look at boats lately so haven't had her out in a few months. She ran fine last time but was a bit hard to start. It was a cooler day (thats how long it was ago) and the engine doesn't have glow plugs so not that unusual.
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Maybe compression was getting lower due to the head fracture you have just found and this finally let go giving even lower compression - enough to not start.

If so, this might be an indication that the piston / rings / bore are OK.

[wheatfieldcrows]

Ok... so it has been awhile but finally got a used head in hand and cleaned it up. Didn’t lap the valves which I already regret but threw the head on and with my brand spakin’ new injector the spray pattern was flawless. I couldn’t test compression numbers because my tester didn’t come with the right adapter. I figure fortune favors the bold so... in went the injector and after a good fuel system bleed she definitely is starting to fire. In the long weeks it has been I somehow forgot to buy new bolts to hook up the exhaust so I couldn’t let her run as the admiral frowns on carbon monoxide poisoning and/or soot in the cabin. That being said she seemed to spew pretty dirty in the few strokes she fired on. Wish I would have lapped the valves so I could just chalk it up to not having an exhaust manifold. Anyway, Wednesday I’ll have time to hook up the exhaust and see what it does with the reins loose.

I also realized I might have overtightened on of the fuel system bolts such that the hole in the bolt wasn’t lining up with the supply pipe. It would be funny if that was the root cause but obviously there was plenty on its way to going wrong to warrant some replacement parts.

[Wotname]

OK, sounds like progress, good to hear and let's hope it will run just fine when you get the exhaust hooked up.

I don't understand your concern with due system bolt though...

Originally Posted by wheatfieldcrows

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I also realized I might have overtightened on of the fuel system bolts such that the hole in the bolt wasn’t lining up with the supply pipe. It would be funny if that was the root cause but obviously there was plenty on its way to going wrong to warrant some replacement parts.

These are banjo bolts and the hole doesn't need to "line up" with anything. There is a recessed area in the banjo section so that fuel flows around in the fitting and then into the hole in the bolt.

More detail https://en.wikipedia.org/wiki/Banjo_fitting

[wheatfieldcrows]

Originally Posted by Wotname

OK, sounds like progress, good to hear and let's hope it will run just fine when you get the exhaust hooked up.



I don't understand your concern with due system bolt though...



These are banjo bolts and the hole doesn't need to "line up" with anything. There is a recessed area in the banjo section so that fuel flows around in the fitting and then into the hole in the bolt.



More detail https://en.wikipedia.org/wiki/Banjo_fitting

Well that’s good to know, maybe I did breath too much exhaust after all. Well mine are all perfectly aligned now for that high performance YSM-12 feeling.