Yanmar sb8 runaway

[Wotname]

It is the perfect motor to learn on - a single cylinder, very simple, very easy to pull down and put back together again, good manuals available - very bullet proof.

Number one rule - if it was made by man, it can be repaired by man. This engine is simple design so the repairs are mostly simple.

As for the runaway, you first have to determine where the engine is getting the "fuel" from. The fuel is can anything that burns but usually is either diesel or oil.

It is sort of rare an engine of this age has enough compression left to start on the first crank unless the rings and/or sleeve has been replaced in the last 500 hours. Assuming the rings and sleeve is old, the fact is wanted to start on the first crank suggests to me there was oil in the cylinder which helps to seal the rings and raises the compression. Then once it fired, it kept sucking oil / oil+diesel from the crankcase passed the worn rings.

What is the oil level in the crankcase?

I would drain the oil cold, refill to just below the min mark. Turn the engine over decompressed (with the throttle closed) until you have some oil pressure. Then let it sit for say an hour and try a normal start.

If it runs away again, remove the injector and test as described upthread.

Report back

[Withinreason]

Originally Posted by Wotname

It is the perfect motor to learn on - a single cylinder, very simple, very easy to pull down and put back together again, good manuals available - very bullet proof.

Number one rule - if it was made by man, it can be repaired by man. This engine is simple design so the repairs are mostly simple.

As for the runaway, you first have to determine where the engine is getting the "fuel" from. The fuel is can anything that burns but usually is either diesel or oil.

It is sort of rare an engine of this age has enough compression left to start on the first crank unless the rings and/or sleeve has been replaced in the last 500 hours. Assuming the rings and sleeve is old, the fact is wanted to start on the first crank suggests to me there was oil in the cylinder which helps to seal the rings and raises the compression. Then once it fired, it kept sucking oil / oil+diesel from the crankcase passed the worn rings.

What is the oil level in the crankcase?

I would drain the oil cold, refill to just below the min mark. Turn the engine over decompressed (with the throttle closed) until you have some oil pressure. Then let it sit for say an hour and try a normal start.

If it runs away again, remove the injector and test as described upthread.

Report back

You are giving me the courage to keep going, Wot.

I figured I’d share a video I took of the engine with the mechanic- you can see it is running away here and there- he’s throttling it with the air box again.

Water is indeed running through it. After this video we found the block zinc had deteriorated in the cooling channel, blocking it substantially.

Impeller is fine- I just changed it. Anywhere else to check for water blocks?

How does the smoke look? My hair, after this video, smelled really bad. It could be because the rubber exhaust hose was getting hot.

I may have exaggerated it turns over first crank. Alas, it does start quite easily. The oil level is right at the standard mark. Your oil hypothesis has been concerned though. The test you are proposing- if making oil level that low, it can’t get sucked into cylinder is the idea?

Forgive me for partially hashed thoughts here. I am working a weekday 9-6 desk job so I’m working on half a brain on the forum at end of day.

Running away:
https://youtu.be/9Md9g0mUoAA

Post initial runaway after overheat etc (this was the first runaway where I didn’t understand how to use the decomp lever, so I just yanked the fuel tank out and it ran for about a minute past WOT):
https://youtube.com/shorts/PgGW6zkQgso?feature=share
https://youtube.com/shorts/iVkcP0Mc2rc?feature=share

Pre runaway running (no water, don’t worry, impeller has since been replaced)
https://youtu.be/MlJUSaghOwo

[Wotname]

The smoke looks sort of normal to me, especially the amount of smoke when the throttle is opened. The IP is such a simple design, they over fuel initially when throttle is advanced. There is good reason this IP went the way of the dinosaur.

It is hard to tell from a couple of short videos but it doesn't seem too be an oil problem.

So if it due to fuel, then the IP could be root cause after all. Ignoring the governor linkage (spring), the engine should slow down and stop when the IP regulator spindle is rotated counterclockwise. As the spindle is rotated CCW, the regulator needle should open which reduces the fuel delivered. Perhaps needle valve is badly gunked up or somehow blocked but this is unusual as the valve is on the high pressure side of the pump. Or somehow the regulator needle is disconnected from the spindle.

Normally the issue is the other way around, the regulator needle wears so it remains partly open thus preventing a full fuel load getting delivered to the injector.

Another wild guess, the injector pressure setting is too low (worn injector spring). This could mess up the IP metering as the IP metering is achieved by bleeding off fuel from the high side of the pump back to the low side. If the injector pressure is low, the high side of the IP is low and affecting the metering - but this is semi educated guess.

If it was me, I would remove the injector and look at the spray as I manually operated the regulator spindle. After that, either pull the IP apart and clean everything, there are no critical adjustments involved OR send it (and the injector) to a diesel injection shop.

[Bilgediver]

Originally Posted by Withinreason

Yanmar 1 cylinder ran away on the dry. Mechanic is working through it with me.

Have narrowed it down to the high pressure fuel pump. Injector and everything else appears fine- pump just won’t back off no matter what. Also got a worn governor spring.

Mechanic wants to just buy a new pump - like $400+. I’m wondering what can be done to rebuild the one on it. Is it possible something isn’t seating right?

Welcoming any advice

Some of the early Yanmar engines had a constant delivery injector pump and between the pump and injector was a spill needle valve controlled by the governor operating a lever arm lever arm on the spill valve . If this was not set correctly the engine could do what you describe. I have tried to find details of your fuel system but not managed so far. You may have this system . The spill valve is on the centre of the front of the engine and low down if this is what you have and is adjusted by rotating the spindle in the arm bush and then locking it in position. The top of the spindle has a line marked into it for reference. When the valve is closed you get full power.

[Wotname]

Originally Posted by Bilgediver

Some of the early Yanmar engines had a constant delivery injector pump and between the pump and injector was a spill needle valve controlled by the governor operating a lever arm lever arm on the spill valve . If this was not set correctly the engine could do what you describe. I have tried to find details of your fuel system but not managed so far. You may have this system . The spill valve is on the centre of the front of the engine and low down if this is what you have and is adjusted by rotating the spindle in the arm bush and then locking it in position. The top of the spindle has a line marked into it for reference. When the valve is closed you get full power.

This is EXACTLY what is fitted to the OP's SB8. What you call a 'spill needle valve', Yanmar calls a 'regulator needle' but it is the same function. See attached parts breakdown in post #4 upthread.

From my limited experience, incorrect adjustment causes the opposite problem (i.e. lack of power) as any movement of spindle opens the 'spill' (regulator) valve thus decreasing the fuel delivery. However if the governor arm is not moving the spindle, then all bets are off. I have posted the correct adjustment procedure elsewhere.

I have marked up the OP's picture for reference.

[Wotname]

More info on adjusting the governor / IP regulator spindle.

[Wotname]

FWIW, the regulator assembly (spill needle valve) as fitted to the OP's IP.

[Bilgediver]

Originally Posted by Wotname

This surprises me, are you 100% sure the injection pump (IP) is the cause of the runaway. It would be a rare thing for this style of IP to be at fault, usually they are the problem of low power. The only way to get full fuel is when the regulator spindle is fully clockwise, any movement of the spindle (counterclockwise) reduces the amount of fuel being injected. Usually the regulator needle wears thus causing less fuel being injected.

How did the mechanic determine the IP was the problem?

FWIW, IME, not many mechanics actually know how to adjust this style of IP unless they have had previous experience of YSE and SB Yanmars.

Does the governor arm rotate the regulator spindle?

I think you are spot on here that the problem is to do with the regulator. If this has remained closed then the engine WILL run away. I had no manual when I encountered one of these on a friends Contessa 32. I discovered the top of the Regulator spindle had a deeply marked slot and so put the spindle in the closed position by turning the spindle. It is I am pretty sure R.H. threaded and closed can be felt. I then opened it no more than about 1/4 turn and locked the clamp on the operating lever. The engine started for the first time in a while however I had to make MINOR adjustments of the spindle in the clamp. This valve hardly moves when the engine is running and from memory I think the slot on the top of the spindle on that model was fore and aft however I think the regulator on the OP's engine is side mounted so the slot could be port/starb.

[Wotname]

^^ Agree.
Full marks for getting it adjusted without reference to the set up procedure

As you say, in operation the spindle hardly moves (maybe a degree or less) but unless it is set right, the engine will hardly run or will run away; there is no near enough is good enough. Get it right and all is good, even if noisy, shaky and smoky.

[sailormed]

Witinreason, it looks like CF saved you $400 and many unnessary diesel mecanic hours .

[Withinreason]

I am very grateful for all of this information, gentlemen. Wotname- you are a real hero. After a lot of work- some me- some my mechanic- we got this engine running again. However, the runaway clearly blew the head gasket. My question now- can I remove the head (take off the 4 head bolts and change the gasket) without removing/touching the rocker assembly? Again, Wotname, thank you so much for this…

[aminto]

Hello,
I have just removed and replaced the cylinder head on my Yanmar yse8 - it was taken off to have the leaky valves replaced and the valve seats refaced. In my experience there is no way to remove the head without removing the rockers for i could not remove one of the head bolts without removing the rockers and pushrods (not enough space in a narrow hull to swing a cat).
BUT be careful not to lose the valve head rings!!!
When i put the engine back together it started to runaway only to be stopped by closing off the fuel (perhaps not the best of methods!). The runaway was a result of a loose spindle on top of the injection pump - the clamp bolt i had neglected to firm up, d'oh! - after a degree of cursing - i shall return to it when calmer...
btw during runaway cooling water spurted out of the junction between the exhaust manifold and its attachment to the mixing elbow??? I presume that under normal conditions the exhaust pressure pushes cooling water towards the exhaust hose and muffler and out but am perplexed by this development!
Any thoughts on the matter would be appreciated.
Best regards,

[Bilgediver]

The diagram showing the fuel system makes me think you may be looking in the wrong place. If your engine is as that drawing then check out the regulating valve. This system is unusual in that the pump delivers full volume all the time. Between the HP fuel pump and the injector is a spill valve.
The spill valve is controlled by a lever from the governor.
If the spill valve is not controlled and or set up incorrectly then the engine will run away.
The spill valve has a slot on the end of the shaft and the lever is clamped on the spindle.
A friend had one of these engines that defeated everyone. I adjusted it by setting the spindle in the clamp at the optimum position. . The spindle is threaded into the valve body so turning it anti clockwise a little at a time the correct position is soon found the valve should be just closed to start with. And with enough movement that it can open as the engine fires up. If Too firmly closed then a runaway is likely.

Your photo does not show this arrangement however your parts list does?

[Compass790]

Originally Posted by aminto

Hello,
I have just removed and replaced the cylinder head on my Yanmar yse8 - it was taken off to have the leaky valves replaced and the valve seats refaced. In my experience there is no way to remove the head without removing the rockers for i could not remove one of the head bolts without removing the rockers and pushrods (not enough space in a narrow hull to swing a cat).
BUT be careful not to lose the valve head rings!!!
When i put the engine back together it started to runaway only to be stopped by closing off the fuel (perhaps not the best of methods!). The runaway was a result of a loose spindle on top of the injection pump - the clamp bolt i had neglected to firm up, d'oh! - after a degree of cursing - i shall return to it when calmer...
btw during runaway cooling water spurted out of the junction between the exhaust manifold and its attachment to the mixing elbow??? I presume that under normal conditions the exhaust pressure pushes cooling water towards the exhaust hose and muffler and out but am perplexed by this development!
Any thoughts on the matter would be appreciated.
Best regards,

It probably means the nipple or pipe & elbow is rusted out. Best if you attach a pic of the problem area. You probably need to replace exhaust elbow. It will have to be removed & inspected.Search on the forum for yse8, ysb8 or ysm8 exhaust & you mite find more info. If you have trouble finding it ask & I will see if I can find it for you. I posted a fair bit on them some time ago