Yanmar YSM 12 - Troubleshooting Help

[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.

The engine has never burned much oil but we've had trouble with contaminated fuel in the past. My first reaction was that it must be the fuel so we removed the tank, cut an access port, cleaned it back to a mirror polish inside and re-assembled the fuel system with fresh filters, fuel and lots of bleeding. No dice.I yanked the air intake off and noticed some oil residue from blow by. I don't know how much blow by is too much but it seems like there is a lot.

Another oddity is that I decided to pull the valve cover and have a look and noticed the exhaust valve rocker has probably a good 1/2" play side to side. It is to the point where the rocker tip is almost off the valve stem. Maybe with the cover in place this play is reduced but curious if this is normal?

I'm left thinking it is either:

1. Excessive piston blow by leading to low compression.
2. A bad injector
3. Bad timing

I popped open the raw water cooling jacket and didn't notice anything strange there besides how awful raw water cooling is in general. The engine oil seems normal but is about due for a change according to the log.

I want to test the compression to see if the rings are bad but I'm wondering if there is anything special about buying a compression gauge? There are a few on amazon that look like they include dummy injectors but just wondering if anyone has any advice before going down that route? Is it possible to buy something off the digital shelf and go straight to testing compression on a 1979 yanmar with no glow plugs?

I'll probably reach out to a mechanic soon but always try to DIY as much as I can because that is the point of being a sailor to me so wondering what the hive mind has to say...

[wheatfieldcrows]

And now with video evidence for the side to side play of the exhaust valve rocker...


Also here because not sure uploading the video to CF worked... https://youtu.be/avWK16wpTzA?t=5

[Compass790]

I have a YSM8 so the sister engine. Yes you can slide the rocker arm to one side quite a bit but it shouldnt sit like that. The only thing that holds them there is the pushrods. I would suspect fuel delivery problem or lack of compression before timing. Have you ever checked yr v/v lash/ tappet clearance? First thing to do is check that high pressure fuel line is squirting. Loosen pump end & then take it off where it goes in injector & swivel around till it points up. Then operate starter with decompression engaged & see if it squirts. If it does take injector out & bolt that on & check it's spray pattern, should be an even narrow cone shape ( 5o to 10o).
If it doesnt you have to check that lift pump is working. If you want to try a quick start trick if you have access to shore power a hair dryer blowing in the air intake & some WD40 sprayed in can work wonders. Also I used to squirt a little bit of engine oil in air-intake when we had real bad compression before I reco'd the engine. BUT BEWARE you can bend the pushrods squirting oil in. Ask me how I know? About 1/2 teaspoon is about right.
I borrowed a compression tester & it was straightforward with the right dummy injector. Hope sumthing in here helps. Let us know what u find.

[Wotname]

Good advice from Compass79 and I would try his ideas.

Does your YSM12 have a little cap near the base of the inlet tube just near where it bolts onto the head. If so, pour a teaspoon full of petrol (5ml) (gasoline) into it and then try a start. Not all Y series engines have this port but it's function (if fitted) is to assist in cold weather starting.

Originally Posted by Compass790

I have a YSM8 so the sister engine. Yes you can slide the rocker arm to one side quite a bit but it shouldnt sit like that. The only thing that holds them there is the pushrods............

This is not entirely correct. Have a look inside the valve cover (rocker cover) and you will see a cast web that prevents the rockers sliding along the rocker shaft when the cover is fitted.

[Wotname]

Originally Posted by wheatfieldcrows

And now with video evidence for the side to side play of the exhaust valve rocker...


Also here because not sure uploading the video to CF worked... https://youtu.be/avWK16wpTzA?t=5

I think you will find the inlet rocker will also side a bit once the camshaft is moved so the valve is fully closed. As posted above, a web inside the valve cover prevents the rocker from sliding once the cover is refitted.

It seems like you have way too much valve lash on that exhaust valve but maybe it is just how it looks on the video clip. It should be (IIRC) 8 thou (0.2mm).

[wheatfieldcrows]

Thanks for the advice. From memory the exhaust valve rocker had way more clearance than 0.2 mm so that definitely needs to be adjusted. I guess I should have read the manual first! Sometimes I just need the moral support of knowing other people have unscrewed that nut before without the whole engine falling apart.


I'll be down there tonight to adjust the valve lash and see if that does the trick. I got my compression gauge on the way and will be pulling the injector to inspect / test compression even if she starts with properly adjusted valve rockers.



I don't think it has a starting fluid cup but I'll investigate.

[Matsubob]

If the engine was running fine the last time, "timing" is not the culprit. Timing is constant unless something drastic has happened to change the engine mechanically on the inside.
Diesels only need air and fuel for combustion, but the compression must be good because heat generated from compression is what causes the fuel to ignite.
I would guess that fuel is not reaching the cylinder, for some reason. So loosening the fitting at the injector pump and observing whether or not fuel is reaching that point is the first step. The next is to check at the injector.
If it is determined that the injector is clogged, they are very easy to disassemble and clean. The tiny pieces are delicate and need to be handled with care but you first split the top from the bottom by unscrewing them, then carefully lifting out each piece, keeping track of how each piece is installed. Clean the pieces in clean diesel fuel and reassemble.

The Yanmar single cylinder is a reliable engine. Provide it with adequate fuel and air and it will start. Good luck!

[grantmc]

A common cause for old Yanmars like YSx12s and YSx8s to not start, when they've been left for a few months is a failed head gasket. It's common given the cylinder is sideways mounted and that raw sea water is flowing through. When the motor is turned off there's still sea water in the jacket.
It's a simple repair and relatively cheap.

[High Pointer]

I went through an endless number of work hours re fuel and air supply, the most
important is that air has been purged from the fuel lines.After all of my problems
it was spider s%&t in the line that lets air into the fuel tank to replace the fuel use.
My Yanmar ran for 5/10min and quit.I mean hours of running through every possible
adjustment and even a new fuel pump..If your pump works and no air in the fuel to
the injector,maybe the injector clogged and will not spray as it should and needs cleaning

[Wotname]

Originally Posted by wheatfieldcrows

..... Sometimes I just need the moral support of knowing other people have unscrewed that nut before without the whole engine falling apart.

.............

Be careful with that nut, one thing can lead to another and before you know it, your engine will look like this

[Compass790]

Originally Posted by wheatfieldcrows

Thanks for the advice. From memory the exhaust valve rocker had way more clearance than 0.2 mm so that definitely needs to be adjusted. I guess I should have read the manual first! Sometimes I just need the moral support of knowing other people have unscrewed that nut before without the whole engine falling apart.


I'll be down there tonight to adjust the valve lash and see if that does the trick. I got my compression gauge on the way and will be pulling the injector to inspect / test compression even if she starts with properly adjusted valve rockers.



I don't think it has a starting fluid cup but I'll investigate.

There is a Yanmar injector cleaning video on youtube. Make sure, when you get your engine to TDC to adjust tappets, it's on the compression stroke. Thats when the valves are closed for the longest period before & after TDC. Well spotted by Wotname that I didn't add "when the cover is off" when I said the only thing holding the rocker arms on was the pushrods. Dont be frightened to maintain it, if in doubt follow the manuals instructions. Good luck

[wheatfieldcrows]

Well a day later than I thought but made it down to the boat tonight. Adjusted the valves which was easy but no start. Bled the fuel again and cracked the injector fuel lines and saw pressure there.. on to the injector removal!

Well, the darn injector is stuck. Got it down to just the bottom holder and the thing just wont budge. Penetrating oils, wrenches trying to turn with cheater pipes, hammering, prying against whatever, ect... that thing don't want to move. Almost got out the blow torch but given everything was covered in diesel decided against. Going to build an extractor that will pull it out against the cylinder head with a 1.25 ID pipe and a bolt that will fit into the injector. Number 3, I'll never forget you. https://imgur.com/a/JColA75

Try again tomorrow. Excited to see if its the fuel/injector or compression at this point!

Thanks everyone for the input so far, I'll provide celebratory pictures eventually.

[wheatfieldcrows]

Originally Posted by grantmc

A common cause for old Yanmars like YSx12s and YSx8s to not start, when they've been left for a few months is a failed head gasket. It's common given the cylinder is sideways mounted and that raw sea water is flowing through. When the motor is turned off there's still sea water in the jacket.
It's a simple repair and relatively cheap.

In poking my head way around back there does seem to be a good bit of surface rust on the aft side of the head. If compression shows low I may try swapping head gaskets before pulling the whole thing out and changing rings. Thanks!

[wheatfieldcrows]

Well a day later than I thought but made it down to the boat tonight. Adjusted the valves which was easy but no start. Bled the fuel again and cracked the injector fuel lines and saw pressure there.. on to the injector removal!

Well, the darn injector is stuck. Got it down to just the bottom holder and the thing just wont budge. Penetrating oils, wrenches trying to turn with cheater pipes, hammering, prying against whatever, ect... that thing don't want to move. Almost got out the blow torch but given everything was covered in diesel decided against. Going to build an extractor that will pull it out against the cylinder head with a 1.25 ID pipe and a bolt that will fit into the injector. Number 3, I'll never forget you. https://imgur.com/a/JColA75

Try again tomorrow. Excited to see if its the fuel/injector or compression at this point!

Thanks everyone for the input so far, I'll provide celebratory pictures eventually.

[Compass790]

Yea the injectors can be a PITA to remove alright as you've discovered. The overnight soak with the penetrating oil can help. Also can use the engine compression to blow it out but wire it on. The puller sounds like a plan. Forgot to say there is a vent line coming from the sump that goes into your air intake tube that oil mist vents out of which is where some of the oil comes from. Another thing to consider is your piston rings mite be a bit sticky if the engine has been left unrun for long. A little WD40 or penetrating oil sprayed in intake & left overnite would help with that.
Be careful about the spray from the injector when testing as at about 2400 psi it can easily penetrate yr skin .Ask me how I know