Yanmar SB8 injection regulator

[copaco]

To set up my stopper cable I had to drill two holes in the lever to have it pull forward.Not much room.On the cockpit panel there was a pull button with wires but apparently the engine cannot be stopped electrily.Yanmar says not to stop on decompression as many do.

[rockin411]

Wotname, I tried to get a pic of it but there was no way to get my camera in the tight space. After looking at it I was wrong about the cable attaching somewhere else. The Pull cable(stop) and the throttle cable are separate but they both attach to the regulator arm. So the pull cable moves the regulator arm all the way towards the engine so that it opens the needle and stops the engine and the throttle moves the arm very slowly to increase/decrease the speed.

The decompression lever is not attached but looks like it may have been attached to the panel at some point but was disconnected.

I (somewhat) regret having to learn more about the regulator/fuel pump than I wanted but knowledge is power right? Hopefully I can return the favor.

[Wotname]

Originally Posted by rockin411

Wotname, I tried to get a pic of it but there was no way to get my camera in the tight space. After looking at it I was wrong about the cable attaching somewhere else. The Pull cable(stop) and the throttle cable are separate but they both attach to the regulator arm. So the pull cable moves the regulator arm all the way towards the engine so that it opens the needle and stops the engine and the throttle moves the arm very slowly to increase/decrease the speed.

The decompression lever is not attached but looks like it may have been attached to the panel at some point but was disconnected.

I (somewhat) regret having to learn more about the regulator/fuel pump than I wanted but knowledge is power right? Hopefully I can return the favor.

OK thanks, that cable arrangement makes sense.

I'm sure the extra knowledge you gained will prove useful to you (or somehow you know) one day.

And for me it's good to be able to make a deposit into the Karma bank when I can!

[Withinreason]

Hello thank you so much for this forum post.

I experienced an uncontrolled runaway on my SB8. Please read my below post and advise on the exact order of steps I should pursue to rectify my issue.

Today my one cylinder, 8 hp power Yanmar ran away on me. Brief backstory: I bought a Bristol 19 7215 foot launch boat which originally had a small Atomic gas engine in it but has since been swapped out with Yanmar aforementioned (YS8) Even though the Bristol is rated to accept upwards of 20 hp motors Yanmar barely fits in the engine bay. When I bought the boat I found that it needed more work than the seller advertised. The boat ship very hard a bit past idle which I initially attributed to a bad Cutlass bearing. I have since fully addressed the drivetrain with new componentry and have been running the motor in the yard with water plugged in. I’ve come to the conclusion that the engine resonates with the boat all a bit above idle and then smoothed out above that. I tried to show a friend this when suddenly the engine ran away as a past the resonant rpm zone. I initially panicked and tried to jiggle but I believe is the governor at the top of the engine I pulled it back quickly but didn’t notice a difference so I went and yanked the fuel line out of the fuel tank. The runaway event probably lasted a bit over a minute until fuel ran out. I could not block the airbox as the intake is positioned directly next to the alternator belt which I deem to be too much of a risk to attempt to reach. The engine eventually ran out of fuel and temperature readings taken on the block with the temperature gun read over 260°F. After the incident I crank the engine and confirm that it could turnover although I did not attempt to start it again. Some water appear to be leaking out of the head gasket area of the no other visible damage can be observed on the engine. The ground behind the boat was very dark and initially it was believe that the engine may have been leaking oil are blown some sort of seal. We’re not able to confirm this though as it’s believed that the wet exhaust tube was burning rubber exhaust out behind the boat. My driveshaft was not connected to the engine during any of this.

This is my first diesel boat and although I wish that I would not have experienced this event I definitely will accept it as a learning experience. When working with diesel you have to have a solid plan in the event of a runaway. I welcome advice on how I could have responded to this event faster and how I might be able to troubleshoot the cause.

Please see videos below and help me identify parts of the boat which are relevant here in either stopping a run away and what and where I might want to look in determining what caused the runaway. Thanks all and be safe.
You Tube

https://youtube.com/shorts/PgGW6zkQgso

[Compass790]

Welcome to the forum withinreason.
I suggest you start another thread titled SB8 engine runaway as it will probably attract more responses. I dont have time to respond in depth at the moment but I'll try to post a reply later today or 2mrw.
Quick answer is that its fine to use decompression lever pictured in yr vid to stop engine in emergency.

[Compass790]

Ok withinreason, I’ll try to help but not entirely sure where to start.
First off I guess is how to stop a runaway. You say you cant block off the air safely & I can see your point. Next thing to try is decompression lever which you were fiddling with in yr utube vid mistakenly calling it a fuel control lever but not sure as my hearing is not good. As stated in earlier post that is the decompression lever & it should kill the engine dead as it lifts the exhaust valve & releases compression making it impossible for combustion to occur.
But you say that didn’t work. Not sure why, maybe u pressed it the wrong way? It takes a bit of force to overcome the valve spring pressure to lift the valve off its seat..

Next is cause of runaway.
Did the motor noise sound any different frm usual max revs?
If the answer is no maybe stuck open injection pump.
If it reached higher than normal max revs its possibly a governor problem(extremely rare ) or some how engine oil getting into combustion chamber ( much more common ) Or fuel mixing with the lube oil & overfilling the crankcase possibly the most common cause of runaway on engines with a block mounted fuel lift pump.
Overfilling with oil & worn rings/bore can cause a runaway too.
Another possible cause is blocked crankcase vent or installed upside down.
Does that engine have a block mounted fuel lift pump or is it gravity fed?
Has any work been done on the engine recently?

If you can answer all the questions I may be able to help.
Best tip I can give you is get the service manual if you can as you need diesel tuition.
I can supply yse8 & YSM 8 workshop manuals they, share some parts with the SB8 but maybe someone on CF has the SB8 manual.
You will have to pull the head off & replace the head gasket anyway if water is leaking at the joint. Its common for them to blow head gaskets if overheated, the block should not get above 60oC ( 140oF ).
Good that you can turn it over, you may have dodged a bullet.

If you answer all my questions it makes it easier to narrow down what caused the runaway but check the oil level for a start.
Still think its better if you start a thread saying its a runaway Yanmar SB8 but hope this helps

[Withinreason]

Thanks so much for the help here. I had someone come and help me and we have determined it is indeed the injector pump which is stuck open.

What is the protocol for rebuilding it? Otherwise I am just going to buy a new one. Part number appears to be 704500-51700. Thanks!