Rebuilt YSM-12 will not start after rebuild.

[Gregted]

Hey all,

So a couple of years ago my son bought a Roberts 25 with a Yanmar ysm-12 inboard motor.
The previous owner told us the motor hadn't run for years, and we removed it to my shed to do a rebuild.
I found the exhaust valve and seat completely rusted from sitting salt water so had the exhaust seat ground out and a new seat welded in stainless.
I then installed a new exhaust valve and reground and lapped in both valves.

I also replaced the rings which were a nightmare to remove.
I honed the bore which was in reasonable shape.
The piston isn't great, but the motor has great compression to the point where I can't crank it by hand so we went with it.
I cleaned up every part of the engine, and we attempted to get it to run.

I bled the system at all points from the fuel pump to the injector multiple times, and we spent many nights trying to get it to start on the starter to no avail.
I have tried a heat gun at the inlet port, motor oil and kerosene squirted down the inlet port and even some aero start, but it will not fire.

It seems slow to turn over and when we apply some hot air into the inlet port, some exhaust smoke seems to be coming out the exhaust pipe, but it will not kick over.

I have noticed that the governor lever doesn't seem to move much in any direction but not sure if that would make much difference if we are injecting oil and diesel directly into the inlet port.

I have worked on petrol engines my whole life but know little of marine diesel engines but have been told that if the diesel engine has compression and fuel, it should start.

We would like to get out on this yacht at some point so would appreciate any help to get this motor to run.

Thanks in advance.

Greg

 

[david_bagshaw]

Replacing rings without a re bore can be a nightmare, as bore usually can have a size change due to wear at the top due to wear, causing the new rings to break. welded in valve seat, sounds very unusual... suspect you might need a new head..

would suggest best move to have the injector serviced.

pouring diesel directly into manifold wont get it going.

 

[peteK]

Do you get fuel at the injectors when you slacken the the nuts?

 

[Boater Sam]

A diesel needs only 3 things to run.
1 Good compression to get the fuel injected into the cylinder hot enough to ignite.
2 Air.
3 Fuel. Injected at high pressure at the correct time so that it atomises. Have you checked the timing?

To achieve 1 you need the mechanical part to actually pump air which will involve the engine turning over fast enough. It should suck you hand hard when spun over with your hand over the air inlet.
2 is easier, just unrestricted inlet. And valves opening and closing at the right time.
3 can be just about anything that will burn but clean fresh diesel is what it is designed to burn.

When you spin it over is there any smoke from the exhaust if so what colour is it?
?
Is the fuel clean? Not years old and full of water?

Is there fuel spraying out of the injector when you spin it over? At the union first, then with the injector out. Beware of high pressure injecting fuel into your eyes or even skin.

Will it start and run on" Start Y'Bastard " spray? "Easy start" in UK, ether, similar to brake cleaner too. Don't over do it and hydro lock the engine.

Feeding it hot air is good but if the fuel injection is not right or at the wrong time it will not run.

 

[Refueler]

Pal of mine rebuilt his 12 .... and it failed to even fire let alone start ....

It was the little injection pump ... I cannot tell you exactly because he only showed me once while I was busy with other stuff ... as I understood - its one of those items DIY people should NEVER take apart !! Maybe 4yrs ago - I asked on YBW if anyone had solution ....

Thread 'Anyone have an injection pump - YSE12'

14 Aug 2022

Pal of mine - the injection pump on his Yanmar YSE12 has failed ... he's followed all the service / repair videos / instructions - but still engine will not start. The fuel pump is basically not pumping when assembled. If the output ball valve is removed - it pumps, replace ball valve - its near stopped. We think its the stroke bore worn out.

Looking for a 2nd hand unit.

• Refueler
• Replies: 0
• Forum: Practical Boat Owner's Reader to Reader

Probably not reason for OP's engine not starting .. but it certainly stopped my mates !!

 

[vyv_cox]

I would also try Easy-start. If it won't run on that there is something fundamentally wrong. As said above, don't overdo it as it tends to wash lubricant off the bores.

One other suggestion, although this will not prevent it from starting. There is a small coolant passage in the cylinder head. It is not obvious as it can become blocked with salt and carbon. My engine would not run when hot due to blockage of this passage. It is straight and can be cleaned out with a drill.