Yanmar YSB Govenor Setup/ Engine Runaway

[Seastar]

Apologies for the lengthy dissertation
I have recently installed a second hand Yanmar YSB12 Engine. Initially all was well and the engine appeared to run well without any adjustment. Prior to re launching I gave the engine a run to check out the installation for electrics and cooling. Whilst looking for leaks and any loose items the engine for no apparent reason went into self destruct mode. The Governor appeared to be demanding idle yet the engine was at full overspeed and only responded to the fuel being cut off. Being a little puzzled by this I checked over the Governor area to make sure everything was free and correctly secured. All appeared to be OK, the engine was restarted and behaved normally. I repeated this process several times and the engine behaved normally. The boat was then launched. Needless to say on the first sea trial I experienced the same engine run away to what appeared to be self destruct RPM again the condition was controlled by shutting down the fuel. After consulting Yanmar dealers I replaced the needle valve and again the first impression was that the problem was fixed (I did not note any damage or problem on the old needle valve) Now the problem is that the engine still gives sporadically give uncommanded acceleration thought much more gentle than before (+200/300 RPM) and this is controlled by resetting the throttle position and the engines responds normally after a few seconds. The change in the way the fault manifests has lead me to believe that part of the problem is with the Governor Set up, and this is where the real issues begin. I can not make head nor tail of the Yanmar Manual (copy attached) The initial adjustment appears to be turning a cam to a specific position. (Presumably the author assumes the engine was set up correctly) The second adjustment is a little more detailed but posse’s questions. The manual states to put the throttle to the full power position, this is great but all it appears to do is to load the governor feedback spring. What is full power on these engines as the as needle valve is infinite in its operating range. The manual appears to be requiring that the throttle lever attached to the needle valve be set in a particular position and that the cam is adjusted to allow precise governor control.
The problem is I can’t figure out how to accomplish this adjustment iaw with the Yanmar Manaul, has anyone out there successfully completed this task and would be willing to comment.
Off more concern is to find the reason for the engine run away problem, as I shall not be comfortable with this engine until I have understanding as to the cause, any ideas appreciated. (Its not crank case vapours or high oil level)
Thanks and again sorry for being so long winded.

 

[oldharry]

Scarey when they do this! Is there a lot of white smoke when it runs away? If so, it could be that the engine is running on lubricating oil. Two possible ways it could be getting there, both as a result of either worn bore or damaged rings: if the sump is pressurising, then oil gets blown through the crancase breather inbto the inlet manifold. Once enough oil gets there, the engine sucks it in and runs away on it at high speed until the manifold is clear - usually about the time it takes to start trying to cut off fuel supply etc. i.e. about 30 seconds. Any badly worn diesel suffering excessive 'blowby' on the rings is likely to do this, particualrly when it is run at high throttle settings.

The other, which is more specific to the YS engines with their horizontal configuration is that excess lube is being splashed up in to the bore, particularly when the boat heels over and getting past the rings, allowing the engine to run on it. Either way it is a rings/bore job!

Checking for crankcase compression is easy. Close off the breather pipe, run the engine at fast tickover for 10 seconds, then release the breather pipe. If there is a puff of gasses from it, the engine is suffering blowby. Also the inlet manifold will be coated in engine oil.

 

[Heckler]

Apologies for the lengthy dissertation
I have recently installed a second hand Yanmar YSB12 Engine. Initially all was well and the engine appeared to run well without any adjustment. Prior to re launching I gave the engine a run to check out the installation for electrics and cooling. Whilst looking for leaks and any loose items the engine for no apparent reason went into self destruct mode. The Governor appeared to be demanding idle yet the engine was at full overspeed and only responded to the fuel being cut off. Being a little puzzled by this I checked over the Governor area to make sure everything was free and correctly secured. All appeared to be OK, the engine was restarted and behaved normally. I repeated this process several times and the engine behaved normally. The boat was then launched. Needless to say on the first sea trial I experienced the same engine run away to what appeared to be self destruct RPM again the condition was controlled by shutting down the fuel. After consulting Yanmar dealers I replaced the needle valve and again the first impression was that the problem was fixed (I did not note any damage or problem on the old needle valve) Now the problem is that the engine still gives sporadically give uncommanded acceleration thought much more gentle than before (+200/300 RPM) and this is controlled by resetting the throttle position and the engines responds normally after a few seconds. The change in the way the fault manifests has lead me to believe that part of the problem is with the Governor Set up, and this is where the real issues begin. I can not make head nor tail of the Yanmar Manual (copy attached) The initial adjustment appears to be turning a cam to a specific position. (Presumably the author assumes the engine was set up correctly) The second adjustment is a little more detailed but posse’s questions. The manual states to put the throttle to the full power position, this is great but all it appears to do is to load the governor feedback spring. What is full power on these engines as the as needle valve is infinite in its operating range. The manual appears to be requiring that the throttle lever attached to the needle valve be set in a particular position and that the cam is adjusted to allow precise governor control.
The problem is I can’t figure out how to accomplish this adjustment iaw with the Yanmar Manaul, has anyone out there successfully completed this task and would be willing to comment.
Off more concern is to find the reason for the engine run away problem, as I shall not be comfortable with this engine until I have understanding as to the cause, any ideas appreciated. (Its not crank case vapours or high oil level)
Thanks and again sorry for being so long winded.

As in a previous post here, in all my years overhauling, maintaining fixing diesel engines I have never seen a runaway 4 stroke diesel engine. I know that Detroit Diesel 2 stroke engines have a shutdown intake flap in case the seals go in the supercharger. I have never seen one of these run away either. I have repaired both 2 and four stroke diesel engines that had such badly worn bores that it was difficult to start them. Again they didnt run away by burning their lube oil. I can confidently say that any one talking about your case is due to the engine burning its lube oil is far off the mark.
From your description and also because messing with the governor seems to fix the prob temporarily, I would be concentrating on that area of the engine, especialy given that shutting the fuel off stops it.
I would be looking for a broken spring or sticking plunger.
Stu

 

[sailorman]

As in a previous post here, in all my years overhauling, maintaining fixing diesel engines I have never seen a runaway 4 stroke diesel engine. I know that Detroit Diesel 2 stroke engines have a shutdown intake flap in case the seals go in the supercharger. I have never seen one of these run away either. I have repaired both 2 and four stroke diesel engines that had such badly worn bores that it was difficult to start them. Again they didn't run away by burning their lube oil. I can confidently say that any one talking about your case is due to the engine burning its lube oil is far off the mark.
From your description and also because messing with the governor seems to fix the prob temporarily, I would be concentrating on that area of the engine, especially given that shutting the fuel off stops it.
I would be looking for a broken spring or sticking plunger.
Stu

the Governor linkage on this engine is a very "Odd" set-up & i have adjusted the YSE 12 in my previous boat. yes the engine will "race" & is disconcerting @ the time. i am sorry but i cant actually remember how i adjusted it

 

[davidbfox]

Got to disagree with Skipper Stu. It happens. I have experienced this. My YSM12 ran away when overfilled the oil. This is very easy to do because the engine is usually mounted on a bit of a slope, so what the dipstick shows as slight overfilling is actually quite significant.

If the rings are worn, as on mine, the engine burns the oil in addition to the diesel. The governor only controls the diesel supply.

The forum advised how to stop it in emergency - cover air intake with a hard board, not a rag or your hand.

I now have a lump of ply at the ready. However not had it happen again since being very careful not to overfill the oil.

It's terrifying when it happens, and not reassuring to know that the inventor of the diesel engine is said to have been killed by his invention.

 

[oldharry]

"I have repaired both 2 and four stroke diesel engines that had such badly worn bores that it was difficult to start them. Again they didnt run away by burning their lube oil. I can confidently say that any one talking about your case is due to the engine burning its lube oil is far off the mark".

Then you are lucky not to have come across it happening - it does the blood pressure no good at all!

I was fairly certain what was happening but obtained three independent opinions: 1st from the local garage diesel mechanic. 2 was Confirmed by major Portsmouth Diesel specialist. 3rd confirmation from Adams Morey the LDV/Rover specialists who had a look at it. 3 opinions sought because of the substantial cost of repairs. All 3 quite definite in their recommendation and diagnosis. The diesel mechanic at my boatyard did not see the engine, but was first to suggest this as the likely cause, seeing it regularly on high mileage taxi engines which he also deals with.

The engine concerned - a Perkins Prima with around 200k on the clock in a Sherpa van - had well worn bores, and the rings gapped at nearly twice the recommended limit. As a result, when run at more than around half throttle, oil was being forced up the breather pipe, which fed directly into the inlet manifold. We put the breather in to an oil can, and found it was pushing nearly out half a litre of oil in 50 miles at 50 - 55mph (fast for a Sherpa!). Interestingly even with such bad wear, starting was never ever a problem.

On 3 seperate occasions on load - usually climbing a hill, the engine would start to knock, and emit dense blue/white smoke. As soon as the clutch was disengaged, the engine would race to around 5000rpm +, even with fuel supply cut off at the ignition switch. This condition lasted between 10 and 20 seconds, the engine would then stop. It could be started again and ran entirely normally - until it was worked hard again.

After the block had been rebored, it ran perfectly, and never produced these symptoms again - and has done some 30k miles since without trouble.

I also had a Montego with the Turbo Prima. This had about 140k on the clock when a turbo seal failed. This caused similarly high levels of crankcase pressure, and the first indication of a problem other than slight power loss was the same: the engine would start to run roughly and knock, and as soon as taken off load, raced with the fuel solenoid 'off', for 10 - 20 seconds, after which it would start and run normally.

This again was diagnosed as being caused high crank case pressure, by the local Rover dealer, because of the failed turbo seal. Replaced turbo - ran perfectly until the body fell apart with rust soon after! In each case the evidence was that the inlet manifolds were heavily contaminated with lube oil from the breather tube.

So not my diagnosis, but that of several experienced diesel mechanics, including two
trained on the specific engine concerned. I have also heard of a couple of other older diesels that have behaved like this for the same reason, including a Yanmar YSB, scaring the pants off their owners, but without seeing them at first hand.

So perhaps not quite so uncommon as suggested?

 

[Heckler]

"I have repaired both 2 and four stroke diesel engines that had such badly worn bores that it was difficult to start them. Again they didnt run away by burning their lube oil. I can confidently say that any one talking about your case is due to the engine burning its lube oil is far off the mark".

Then you are lucky not to have come across it happening - it does the blood pressure no good at all!

I was fairly certain what was happening but obtained three independent opinions: 1st from the local garage diesel mechanic. 2 was Confirmed by major Portsmouth Diesel specialist. 3rd confirmation from Adams Morey the LDV/Rover specialists who had a look at it. 3 opinions sought because of the substantial cost of repairs. All 3 quite definite in their recommendation and diagnosis. The diesel mechanic at my boatyard did not see the engine, but was first to suggest this as the likely cause, seeing it regularly on high mileage taxi engines which he also deals with.

The engine concerned - a Perkins Prima with around 200k on the clock in a Sherpa van - had well worn bores, and the rings gapped at nearly twice the recommended limit. As a result, when run at more than around half throttle, oil was being forced up the breather pipe, which fed directly into the inlet manifold. We put the breather in to an oil can, and found it was pushing nearly out half a litre of oil in 50 miles at 50 - 55mph (fast for a Sherpa!). Interestingly even with such bad wear, starting was never ever a problem.

On 3 seperate occasions on load - usually climbing a hill, the engine would start to knock, and emit dense blue/white smoke. As soon as the clutch was disengaged, the engine would race to around 5000rpm +, even with fuel supply cut off at the ignition switch. This condition lasted between 10 and 20 seconds, the engine would then stop. It could be started again and ran entirely normally - until it was worked hard again.

After the block had been rebored, it ran perfectly, and never produced these symptoms again - and has done some 30k miles since without trouble.

I also had a Montego with the Turbo Prima. This had about 140k on the clock when a turbo seal failed. This caused similarly high levels of crankcase pressure, and the first indication of a problem other than slight power loss was the same: the engine would start to run roughly and knock, and as soon as taken off load, raced with the fuel solenoid 'off', for 10 - 20 seconds, after which it would start and run normally.

This again was diagnosed as being caused high crank case pressure, by the local Rover dealer, because of the failed turbo seal. Replaced turbo - ran perfectly until the body fell apart with rust soon after! In each case the evidence was that the inlet manifolds were heavily contaminated with lube oil from the breather tube.

So not my diagnosis, but that of several experienced diesel mechanics, including two
trained on the specific engine concerned. I have also heard of a couple of other older diesels that have behaved like this for the same reason, including a Yanmar YSB, scaring the pants off their owners, but without seeing them at first hand.

So perhaps not quite so uncommon as suggested?

My long story about my experiences was to illustrate that it is very unusual to come aross such cases and given the symptoms presented by the OP, it would be unlikely that the engine was burning its own lube.
Anyway what on earth is a highly experienced chap like yourself doing driving around with a shagged engine and then having to get second opinions as to what has gone wrong?

 

[Seastar]

Just put it down to insanity and a silly determination!

 

[oldharry]

My long story about my experiences was to illustrate that it is very unusual to come aross such cases and given the symptoms presented by the OP, it would be unlikely that the engine was burning its own lube.
Anyway what on earth is a highly experienced chap like yourself doing driving around with a shagged engine and then having to get second opinions as to what has gone wrong?

Lots of diesel gone through the filters since then and I dont drive shagged engines any more - spot the troubles before they let me down, nowadays!



Er... usually!

 

[Manuel]

I hope not but you have not got a gas leak? Diesels run away if there is LPG around but you would smell it.