Yanmar sb8 runaway

[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

[cal40john]

Never dealt with it myself, but 99% of what I've read is that even diesel mechanics won't rebuild an injector pump, they send it to a shop that specializes in that.

1 person on this site said he went ahead and rebuilt his on his own and claims it turned out fine.

[ItDepends]

At $400 for a new pump, I’m guessing it would be hard to get a professional rebuild and save much.

However… before I plunked down the $400 I’d get that pump to an injection pump/injector shop and have them put it through a proper bench test, just to be sure it is the actual source of the problem. Lots of these guys around. Your mechanic SHOULD know a good local one.

If you can find documentation on how to do a rebuild, you could try it… if you can source the parts cheap. Its not easy, and special measurement tools are usually required.

[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.

The IP is simple enough to repair as long as you are clean and careful. Last time I checked (a couple of years ago), parts were still available. There are only 3 parts that are replaceable. The barrel and plunger paired assembly, the regulator needle and the delivery valve assembly. Wear in any of these parts would not cause a run away.

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?

[Wotname]

FWIW, the injection pump fitted to OP's engine is nothing like any injection pump fitted to any later Yanmar engine.

It is an incredibly simple pump and easily adjusted although the adjustment procedure must be followed exactly . Adjustment is detailed in the operators manual and Yanmar suggests adjusting every 500 hours or earlier if excess wear occurs.

The service manual has the details for rebuilding the pump and no specialised test equipment is required. The only tooling required is a couple of metric spanners (wrenches).

[Withinreason]

Basically one crank into cranking the engine it takes off and flies away so the troubleshooting was as follows basically the only way to control the engine speed is by choking the air intake - adjusting the throttle or the governor spindle itself near the fuel pump does nothing whatsoever - only way to affect the speed is by choking it. a conclusion from the mechanic is that it doesn’t make sense that it would be the injectors fault because otherwise the engine would have a hard time starting it wouldn’t takeoff so easily. Also removing the fuel fitting and cranking the engine shows that the fuel pump is constantly dumping a lot of fuel.

[capt jgw]

I had the injection pump on my Universal M15 (5411) rebuilt for $200, ($100 per cylinder) at the local Diesel Injection Service. Checked with the local Kubota shop (it's really a Kubota engine), they said they don't touch them and send them out. That was several years ago, but probably not a lot more now. I did have to remove and reinstall myself but that was not hard. Kubota pump looks a lot like the Yanmar pump, in fact it might be the same make. I don't think either engine company makes thier own. I would think that if the factory authorized repair center won't service the pump, you probably shouldn't try it either. Every engine manual I've read said in effect "don't even think about it. "

[Wotname]

Originally Posted by capt jgw

I had the injection pump on my Universal M15 (5411) rebuilt for $200, ($100 per cylinder) at the local Diesel Injection Service. Checked with the local Kubota shop (it's really a Kubota engine), they said they don't touch them and send them out. That was several years ago, but probably not a lot more now. I did have to remove and reinstall myself but that was not hard. Kubota pump looks a lot like the Yanmar pump, in fact it might be the same make. I don't think either engine company makes thier own. I would think that if the factory authorized repair center won't service the pump, you probably shouldn't try it either. Every engine manual I've read said in effect "don't even think about it. "

I am sorry to say this is incorrect. The M15 uses a Bosch style pump ('Mini K type'). The OP's pump is nothing like a Bosch style pump.

Yanmar started using the Bosch style pump first on the YSM engine. The YSE, YSB and SB engines use the pump I have described upthread.

[Withinreason]

Wot, any suggestions for the regulator spring? Part no 105282-66010. Spring is petty worn. Replacement OEM is like $130… for a spring..

[Wotname]

Originally Posted by Withinreason

Basically one crank into cranking the engine it takes off and flies away so the troubleshooting was as follows basically the only way to control the engine speed is by choking the air intake - adjusting the throttle or the governor spindle itself near the fuel pump does nothing whatsoever - only way to affect the speed is by choking it. a conclusion from the mechanic is that it doesn’t make sense that it would be the injectors fault because otherwise the engine would have a hard time starting it wouldn’t takeoff so easily. Also removing the fuel fitting and cranking the engine shows that the fuel pump is constantly dumping a lot of fuel.

Pull the injector out, reconnect it to the IP, turn the engine over and observe the spray when the regulator needle is closed (fully clockwise). Now rotate the regulator spindle anticlockwise a degree or so. The amount of spray should decrease markedly. Further rotation anticlockwise should completely stop the spray. If so, the run away is NOT from the IP.

Be careful and make sure the spray is directed away from body and eyes.

When everything is adjusted correctly, you can hear the IP and injector squeak when it delivers a full fuel load.

[Compass790]

My advice is listen to Wotname, he has actually repaired the same pump O.P. is talking about. They are as simple in construction as you will find, as Wotname shows.

[Wotname]

Originally Posted by Withinreason

Wot, any suggestions for the regulator spring? Part no 105282-66010. Spring is petty worn. Replacement OEM is like $130… for a spring..

No sorry, I would just experiment with after market springs until you get something that works. It is important but not critical.

Fix the runaway first - very unlikely to be spring.

[Wotname]

Originally Posted by Withinreason

Basically one crank into cranking the engine it takes off and flies away so the troubleshooting was as follows basically the only way to control the engine speed is by choking the air intake - adjusting the throttle or the governor spindle itself near the fuel pump does nothing whatsoever - only way to affect the speed is by choking it. .........

Presumably the decompression lever would have stopped the engine but I dunno if you tired that. Using the decompression lever in this manner is not ideal but should not cause any long term damage assuming the exhaust valve seat and assembly etc is within specs.

[capt jgw]

Originally Posted by Wotname

I am sorry to say this is incorrect. The M15 uses a Bosch style pump ('Mini K type'). The OP's pump is nothing like a Bosch style pump.

Yanmar started using the Bosch style pump first on the YSM engine. The YSE, YSB and SB engines use the pump I have described upthread.

Ok, mine was a Bosch and I was remembering the pump on my old 2GM which looked similar. Maybe also a Bosch. Either way the local injection shop can fix it.

[Withinreason]

Originally Posted by Wotname

Presumably the decompression lever would have stopped the engine but I dunno if you tired that. Using the decompression lever in this manner is not ideal but should not cause any long term damage assuming the exhaust valve seat and assembly etc is within specs.

Yeah, I saw a different thread Wot where I think you suggested this. When the mechanic started the engine it flew off and he stared at me. I pulled the lever, and it really fought back hard - so much so it sort of hurt my finger. But it did kill it.

I am in Brooklyn, NY. Most people run outboards or IOs. Few diesels.

I bought this Bristol 1972 15' launch to learn diesel - and boy am I learning.

I redid the whole drive shaft, had the prop reconditioned, and installed a new cutlass.

Went to warm up the oil for an oil change before launching it for the first time and the engine ran off.

Has been very frustrating. I've never hired a mechanic before - so we're seeing how this one will do.

He has had some good insights on a few things.

I'm considering trying to pull the injector and do the test myself, or I will ask him to confirm to me that he checked the injector.

Again, this has all been rather demoralizing.