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.

 

[Gregted]

Thanks for all your replies.

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.

The exhaust valve seat was badly corroded, and the engine rebuilders said they have welded in new seats many times, and it looks brand new.
I have disassembled the injector and cleaned it as good as I could, and it seems to operate as it should. Aka it squirts a fine spray.

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

Yes. I tried multiple times to bleed the fuel system, but I know that can be tricky, so I will try that again.

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.

RE the smoke from the exhaust.. When we blow hot air into the inlet, we get black smoke from the exhaust. Without the hot air, only white smoke.
Fuel is fresh.
It will not start or run on Start Y Bastard.
Timing is something I will have to read up on for this motor.

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 !!

I did disassemble the injector pump, and it seems to supply fuel to the injector.

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.

Have squirted some easystart into the inlet port but no dice. I completely disassembled the engine and cleaned out all water lines. They were completely blocked, but coolant isn't the problem as I can't even get it to run to get hot, but thanks for the suggestion.

I will take the side cover off this weekend and have another look at the governor and check what I can in there.

The only thing I remember from 2 years ago when I started this journey was I was unsure of how to check and set the timing, so any info on that would be appreciated.

 

[Tranona]

May be worth giving John here a call https://www.yanmar.com/global/dealerlocator/gb/213046 His Yanmar experience goes back to the older engines.

 

[LittleSister]

Fuel injection timing adjustment is described on page 3.11 (Chapter 3, Section 2, paras 2.7.2) onwards of the Service Manual which can be found at the following link:
https://nhmr.nl/wp-content/uploads/2022/03/YANMAR-WORKSHOP-MANUAL-YSM.pdf

It states correct timing is 25 degrees, plus or minus 1 degree, before top dead centre on the compression stroke. Fine adjustment is done by shims and by reference to a mark on the flywheel (viewed through an inspection hole - p.s. I now think this is viewed through the aperture created by removing the starter motor).

Injection is triggered by a separate cam ring mounted on the cam shaft, which is located in relation to the valve timing by a key in the shaft. (Note that seemingly you can't have the fuel timing completely out relative to the valve timing, but you could have both out relative to the crankshaft & pistons.)

Re-reading your original post I am suspicious that the fuel governor doesn't move much, but i suspect there is something more fundamental amiss as it won't start with Easy Start.

 

[LittleSister]

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. . .


It seems slow to turn over . . .

Hmmm.

Could it be something binding/sticking rather than compression that's making it so hard to turn? What happens when you use the decompressor lever?

And are you using the decompressor to get the engine up to a good speed before you try to start?

 

[Boater Sam]

Black smoke is partially burnt fuel, like when you overload the engine and it struggles to rev up.
White smoke is totally unburnt fuel, not enough compression to get the cylinder temperature up........unless of course it is steam not smoke.

I reckon, despite your remark about it being hard to turn, that you do not have enough compression to get it to run.

Checked the valve clearances?

Last shot, ensure a full charged battery.
Put 5ccs, no more, of engine oil into the engine inlet directly as it is cranking over with the decompressor lever set to decompress. So the engine spins over freely. This will assist the rings in sealing to the bore.
Then try it immediately on easy start, dropping the decompressor lever only when the engine is spinning as fast as it will go.
If you can get a compression tester and find out what figure it should get to, it may save you a lot of time and messing.

 

[Beneteau381]

Thanks for all your replies.

The exhaust valve seat was badly corroded, and the engine rebuilders said they have welded in new seats many times, and it looks brand new.
I have disassembled the injector and cleaned it as good as I could, and it seems to operate as it should. Aka it squirts a fine spray.


Yes. I tried multiple times to bleed the fuel system, but I know that can be tricky, so I will try that again.



RE the smoke from the exhaust.. When we blow hot air into the inlet, we get black smoke from the exhaust. Without the hot air, only white smoke.
Fuel is fresh.
It will not start or run on Start Y Bastard.
Timing is something I will have to read up on for this motor.



I did disassemble the injector pump, and it seems to supply fuel to the injector.



Have squirted some easystart into the inlet port but no dice. I completely disassembled the engine and cleaned out all water lines. They were completely blocked, but coolant isn't the problem as I can't even get it to run to get hot, but thanks for the suggestion.

I will take the side cover off this weekend and have another look at the governor and check what I can in there.

The only thing I remember from 2 years ago when I started this journey was I was unsure of how to check and set the timing, so any info on that would be appreciated.

Go to the basics and ignore the scattergun approach. If it has compression good enough to fire then giving it easy start should make it fire. Thats it. Timing, no diesel at the injectors, doesn’t matter, compression and easy start equal BANG! One other thing, is it turning over briskly! If it isn’t then the previous doesn’t apply! I had it once with crappy starter cables and bad connections, it wasn’t turning over fast enough. Once it fires on easy start then do the rest of the trouble shooting.
EDIT, I read your op again, you said it’s turns over slowly, there is your problem. Check your cables etc to the starter, get it turning over properly, then easy start, if it fires then trouble shoot the fuel system.

 

[Tranona]

Turning it over with the decompressor up will also help , then drop when spinning over well. The original would have had a hand start and have memories of actually being able to start one in that way.

 

[Beneteau381]

Turning it over with the decompressor up will also help , then drop when spinning over well. The original would have had a hand start and have memories of actually being able to start one in that way.

Just had a pacemaker fitted! Your words about hand starting bring back memories of listers and ball breaking swinging on handles, it makes my chest twitch!

 

[Tranona]

We had Listers in our club workboats. Never really got thr knack but fortunately my rescue boat mate did. In the winter we used to leave them running all the time as the warm air came out of the engine box at just the right height.

Hope the pacemaker works for you.

 

[earlybird]

A feature of these old YS engines that I recall is that the injector should audibly squeak at the point of injection when the engine is turned over. Hand turning on the decompressor is best to keep the noise down. No squeak means almost certainly no start. Also it can aid an approximate check on timing. That said, in this case not firing on easy-start is a puzzle.

 

[LittleSister]

A feature of these old YS engines that I recall is that the injector should audibly squeak at the point of injection when the engine is turned over. Hand turning on the decompressor is best to keep the noise down. No squeak means almost certainly no start. Also it can aid an approximate check on timing. . .

The YSM engines have different fuel injection pumps (a Bosch type) to those used on the YSE engines. I believe it is the YSE injector that squeaks.

I read that according to the Yanmar manuals YSE injection timing is done by adjusting shims to get the audible squeak to coincide with the flywheel timing mark, whereas the YSM is also done by adjusting shims, but to get the ejection of fuel (viewed by using a 'measuring pipe' temporarily fitted to the injection pump) to coincide with the timing mark. (The timing degrees and, I believe, the shims are also different between the two engine series.)

. . . That said, in this case not firing on easy-start is a puzzle.

. . . If it has compression good enough to fire then giving it easy start should make it fire. Thats it. Timing, no diesel at the injectors, doesn’t matter, compression and easy start equal BANG! . . .

I agree that is a puzzle. More than that, I think it is a red flag. If the engine is spun at a decent speed it should start with Easy Start. If it doesn't there is either very little compression or something else very fundamentally wrong.

First job is to sort out why the engine is not spinning fast enough. Use decompressor, replace battery, cables, clean connections, or whatever is required. If the engine is still not spinning fast, perhaps the engine is partially seized or binding in some way.

 

[Beneteau381]

The YSM engines have different fuel injection pumps (a Bosch type) to those used on the YSE engines. I believe it is the YSE injector that squeaks.

I read that according to the Yanmar manuals YSE injection timing is done by adjusting shims to get the audible squeak to coincide with the flywheel timing mark, whereas the YSM is also done by adjusting shims, but to get the ejection of fuel (viewed by using a 'measuring pipe' temporarily fitted to the injection pump) to coincide with the timing mark. (The timing degrees and, I believe, the shims are also different between the two engine series.)





I agree that is a puzzle. More than that, I think it is a red flag. If the engine is spun at a decent speed it should start with Easy Start. If it doesn't there is either very little compression or something else very fundamentally wrong.

First job is to sort out why the engine is not spinning fast enough. Use decompressor, replace battery, cables, clean connections, or whatever is required. If the engine is still not spinning fast, perhaps the engine is partially seized or binding in some way.

Exactly. Until it spins fast enough to start on easy start all the advice on here is just noise!

 

[jamie N]

Is the decompressor fully disengaging? Personal experience, where even with Easy Start the engine wouldn't fire, but sort of 1/2 tried. The decompressor was part of the valve/rocker cover, which was sealed with a very old gasket. The gasket had compressed to the point where the decompressor was fractionally in contact with the valve and thus lowered the compression enough.
I removed the rocker cover to view the valves and check they were actually functioning, and (of course) the engine immediately started now that the valve was able to fully seat. Ahhh, a "now I get it" moment.
I hope that your issue is so simple.

 

[Beneteau381]

Is the decompressor fully disengaging? Personal experience, where even with Easy Start the engine wouldn't fire, but sort of 1/2 tried. The decompressor was part of the valve/rocker cover, which was sealed with a very old gasket. The gasket had compressed to the point where the decompressor was fractionally in contact with the valve and thus lowered the compression enough.
I removed the rocker cover to view the valves and check they were actually functioning, and (of course) the engine immediately started now that the valve was able to fully seat. Ahhh, a "now I get it" moment.
I hope that your issue is so simple.

But he says it is difficult to turn over compression?