Yanmar SB12 won't start

[rockin411]

Ran fine weekend before on both days and then fine getting in and back the other Saturday and then wouldn't crank Sunday morning.

Here's what I've tried:

1. New diesel
2. Replace both fuel filters
3. Bled the air
4. Pulled the injector and installed upside down - seems to spray fine
5. Sprayed WD40 in intake - bad idea but it did run - VERY high rpms
6. Adjusted valve clearance
7. Removed exhaust to check for blockage
8. Replaced battery
9. Started with compression lever engaged and then released (don't think it's starter)

Not so much as a knock from all of that.
The last thing I've tried was heat gun in the intake and I got a few knocks from it but that's it.

I should add that I had another thread where the governor arm was stuck but Wotname helped me resolve that - maybe there's a lingering issue from that?

What now? Compression?

[Compass790]

Yep I'd try a compression test maybe but look around the head joint & see if there are any salt crystals around it first. I'm assuming its still raw water cooled & the boat is in salt water. If you have salt crystals around the joint its leaking. A bad leak you will see steam & water spraying when its running.
It makes me suspicious it does have still a fuel problem still tho if it runs when you spray WD40 in it because it might struggle to run even with WD 40 when the compression is real low.Not sure how that can be if injector is spraying properly
A crude trick I used to use to get a very low compression diesel to run was squirt a little, say a few ml engine oil in the air intake whilst cranking. BUT its risky, you can bend the pushrods if you use too much.
It can be a way of determining if compression is the issue.

[Compass790]

Rockin411 a gud idea would be to go thru yr 2020 thread on this subject too & see if anything jumps out. Bit of reading there but saves waiting for the same advice.
Good luck with diagnosis

[Lepke]

Sounds like low compression/heat problem. The speed the engine cranks can be an issue, but if you got knocks from a heat gun, then you need more heat. Diesel needs a temp above 500°F to ignite. The piston compressing the air is usually enough, but as the weather cools it may not be enough in an older engine in colder weather.

Try leaving a heater or heat lamp pointing at the engine block overnight. If that works, install a pan or block heater. Block heater works best. Another method is to drain the oil into a pan and heat it on a stove to hot. And put it back in.
If the engine started a few days earlier, then it's not fuel, filters, valves, or exhaust. And doing all that introduces the possibility of other problems like air in the system. The speed the engine cranks can be an issue, but if it cranks like in the past, it's not the battery or starter.

Eventually in an engine's long life, starting fluid may be required in cold weather. But only a minimal amount. Just touch the spray button briefly. If it knocks but doesn't start, try a few times using minimal amounts. Don't be tempted to run the engine on ether. It creates much higher than normal pressures and can crack rings.

[rockin411]

I tried the heat gun one more time and left it on a little longer and it fired up and ran for about 10 seconds and cut off. Ran the heat gun again and it's running fine now. Does that indicate a compression problem? That's the only way it will start. It's also a little warmer today.

[Wotname]

Yes...low compression for sure.

Could be rings or valves or head gasket or any combination.

[Wotname]

Step 1. Pull the head off and have look at the head gasket and valve seats.

[4Dorchesters]

Wow, a 40 year old Yanmar single cylinder diesel, great engines!

I'd boroscope the nozzle hole looking for a polished or gauged cylinder wall for worn or broken rings; or can it be compression tested, assembled?

[rockin411]

Right before I tried this one more time, I had gone ahead and ordered rings, valves, and a sleeve at lunch. I'll be rebuilding or "overhauling" next weekend - I'll keep you posted and I plan to record the process so as to help someone else down the road. Thanks!

[Wotname]

Originally Posted by 4Dorchesters

Wow, a 40 year old Yanmar single cylinder diesel, great engines!

I'd boroscope the nozzle hole looking for a polished or gauged cylinder wall for worn or broken rings; or can it be compression tested, assembled?

Not possible with the pre-combustion chamber in place and it is almost impossible to remove the pre combustion chamber with the head on.

[Compass790]

Originally Posted by 4Dorchesters

Wow, a 40 year old Yanmar single cylinder diesel, great engines!

I'd boroscope the nozzle hole looking for a polished or gauged cylinder wall for worn or broken rings; or can it be compression tested, assembled?

Yes they certainly can be compression tested, just need to remove injector.

Great engine?? well depends on what you desire. Very strongly built & long lasting with proper maintenance but noisy shakey beasts. Personally I'd rather have one than a modern Yanmar but thats just a reflection of preferring the ruggedness & ease of repair if you can get the parts.

[Compass790]

Originally Posted by rockin411

Right before I tried this one more time, I had gone ahead and ordered rings, valves, and a sleeve at lunch. I'll be rebuilding or "overhauling" next weekend - I'll keep you posted and I plan to record the process so as to help someone else down the road. Thanks!

Be interested to know what your bore wear is like if you have the measuring tools. A rough estimate can be made by measuring piston dia. with a vernier & then inserting piston in bore & jamming a feeler gauge in.
could check used rings gap as well.
Also do you know engine hrs? If your engine has never been rebuilt before your parts purchase wont be wasted dollars entirely anyway.
After you rebuild it leave it on the compression stroke when you leave boat as it shuts off the bore from the salt air in the exhaust.
Another tip is to use head gasket cement on gasket when you reassemble. It proves to have a much lower failure rate if you do. My experience is with Loctite 518 but there are others. I sell parts for them locally so I know a bit about these engines.
Be interesting to see if there is a smoking gun when you remove head.
I recently sold a head gasket & rings to a yse12 owner who complained of slow starting but the evidence pointed more to a fuel problem & I told him that its more likely fuel related but he insisted on buying the parts without doing a compression test. The new parts didnt fix the problem so now he is getting the injector serviced.
I'll be following with interest.