Yanmar YSM12 fuel injection pump

[mjberns]

I have a 1979 Hunter 30 with a Yanmar YSM12 engine. The engine ran fine all last season but died en route to winter storage and won't start. We believe the problem is the fuel injection pump. I've contacted a few dealers who say the pump itself (part 704571-51700) isn't available.

I'm wondering if anyone has a line on either a rebuilt pump (or new) or a rebuild kit for a YSM12 fuel injection pump. Or any info on an alternate injector pump that might work with this engine.

If I can't find anything the engine is essentially toast and I'm reluctant to repower the boat, so there's that.

Appreciate any help or suggestions.

Thanks
Mark

 

[Ralph Johnstone]

The engine ran fine all last season but died en route to winter storage and won't start. We believe the problem is the fuel injection pump.

Before you even BEGIN to look for another injection pump, I would suggest you determine EXACTLY why your engine won't start. It's highly unlikely that your pump "ran fine all last season" and then just up and died without any warning. What leads you to a pump failure as the cause of the no start ?

Rather that me writing up a long check list of things to check for an engine which won't start, why don't you list everything you've tested so far and your results.

OR

Continue your search for the non-existent PN 704571-51700 injector pump.

 

[mjberns]

What EXACTLY is happening that fuel is getting to the fuel injection pump, which we can see is being activated by the cam in the engine but fuel is not coming out of the pump other than a drip or two. Not the stream that should be coming out.

Other things we've checked:
* The entire fuel supply up to the injection pump is fine. I had added an electric fuel pump a few years ago when the internal mechanical pump stopped working. The electric pump is pumping fine.
* Mixing elbow is fine
* Fuel injector had some carbonization but was cleaned (doesn't really apply since the pump isn't putting out anyway)

First mechanic who looked at it believes there's a compression problem but neither he nor a second mechanic was able to come up with a correct fitting to run a compression test. Mechanic One jury-rigged something with a rubber stopper and still believes it's a compression issue. But he didn't want to go further into pulling the valve cover or looking at the pistons, etc., because his marina got super busy with spring launching and he was concerned about getting parts; he recommended repowering.

Mechanic Two says that when he cranks the engine he's getting some pressure and the pistons sound like they're working OK so doesn't think it's the issue - and he and some other people I've talked to believe that a compression failure wouldn't have been sudden and symptoms would have been noticeable before we got to dying and not starting at all. Plus, again, nothing's coming out of the pump.

Mechanic Two took the pump to his go-to on fuel system issues who took it apart and will rebuild it if possible. He believes that's where the problem lies. He's apparently found most of the gaskets and o-rings but thinks the issue is the nozzle inside, hence my search for the pump or a rebuild kit or a source of parts.

Not my first rodeo, or the first thing we checked. If you think there's something we missed short of pulling the head, happy to hear about it.

Regards,
Mark

 

[Ralph Johnstone]

What EXACTLY is happening that fuel is getting to the fuel injection pump, which we can see is being activated by the cam in the engine but fuel is not coming out of the pump other than a drip or two.

You've certainly done your homework here. Yes, if the injector pump is not putting out, nothing is going to work until that problem is corrected, for whatever the reason is for failure.

Mechanic Two took the pump to his go-to on fuel system issues who took it apart and will rebuild it if possible.

Unfortunately, it sounds as if your pump is not longer on the engine until its rebuild is completed, so the rest of this conversation is only applicable after the pump is reinstalled. I'm gob smacked at Mechanic #1 as he shouldn't even be allowed out on a day pass. #2 Mechanic, I don't know. If there's a certified diesel shop near you, stay away from the amateurs.

The one thing that doesn't sound as if it was done when the pump was attached is to back off the fuel connection, at the injector, on the engine, and look for the high pressure micro spray issued as the starter cranks over. This is a high pressure spray as the result of the injector spring back pressure. I know, sounds goofy if there's no fuel coming out of the pump itself but best to get everything up to pressure (if possible) and see what issues right at the injector. The other big caution here the with all this tubing being disconnected, you may very well have an air lock in the pump. Try opening a fitting on the fuel return to your tank and see what issues. I don't have a manual for your Yanmar YSM12 engine and it may well be different from the recirc system on a Yanmar 2GM20F. Please forward a copy if you have one or you may well be able to find one here on the site. Only requires time to find it.

Sorry, but there's really not a lot of further checking you can do until the pump is back in place.

Please keep in contact with this site when your pump is back and let's solve this problem. I do not think a $10K repower is required IF the pump is properly overhauled.

This is all future work but if your engine still won't run after the rebuild, the above will be worth looking at.

 

[mjberns]

Ralph, thanks for that. We'll give it a try when we can. Mechanic #2 actually is a professional diesel mechanic.

Someone sent me a link to an aftermarket pump on alibaba.com, but I'm hesitant because the picture doesn't look like my pump.
I've attached the engine manual.

If the pump works, hooray. If it doesn't I don't know that I can justify a $10K repower on a boat that I've seen listed for $12K. It may mean doing a donation or selling for other parts, assuming there's interest. Then shopping for a replacement.

Fingers crossed.

 

[Ralph Johnstone]

Thanks for the manual. I'll dig into the fuel pump and injector.

 

[mjberns]

Just circling back - we found that the injection pump wasn’t putting out fuel. That’s been rebuilt and installed, and now is putting out fuel, but still not starting. We’ve pulled the cylinder head and are rebuilding that - there was buildup around the valves so there wasn’t compression. Everything else on the head looked good. So cleaning and reassembling and hoping that by this time next week running.

 

[Ralph Johnstone]

The one thing that doesn't sound as if it was done when the pump was attached is to back off the fuel connection, at the injector, on the engine, and look for the high pressure micro spray issued as the starter cranks over. This is a high pressure spray as the result of the injector spring back pressure.

Did you prove this out ?

 

[Charles Erwin]

Don't know if this helps but the high-pressure pump internal components are almost certainly the same as the (preceding) GM series. That means pump parts are easy to get. Any diesel injector service company (skip the Yanmar dealers by the way) can rebuild and deliver an as-new pump using your present one for a reasonable price. No need to look for a replacement.

 

[mjberns]

Thanks, Charles, good to know. We were able to rebuild the pump and now we're about to replace the valves and clean up the cylinder head. Fortunately we were able to find those parts.
Mark