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Old 16-02-2017, 15:17   #1
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Yanmar 2GM lift pump failing

Hello all,
My Yanmar 2GM has an issue where the mechanical lift pump fails. Inside the lift pump there's a plate that retains the 2 valves. This plate has bent on 2 different pumps as if the outbound valve is pushing against it. On one occasion a piece of the plate broke, punctured the diaphragm and caused a runaway but that's a separate story. It seems to me the only possible way this plate could break is from a pulsing back pressure coming in the solid steel line between the lift pump and the injector pump. I spoke to Yanmar and an injector shop and both say this is impossible. I've searched the net quite a bit and can't find anyone complaining of this issue. Has anyone ever seen or heard of this? Any thoughts on how I should proceed? It takes a lot of hours for the plate to bend but I don't like having a critical failure waiting to happen again.

Thanks
Steve
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Old 16-02-2017, 15:54   #2
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Re: Yanmar 2GM lift pump failing

Have you replaced the pump or did you rebuild the original? Could be a fault there??
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Old 16-02-2017, 16:17   #3
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Re: Yanmar 2GM lift pump failing

I wish it was my work. The first pump it happened to was a new in the box spare that came with the boat. I assumed it was a freak defect from the factory but then found the identical issue with a more recently purchased pump.

Steve
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Old 16-02-2017, 19:36   #4
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Re: Yanmar 2GM lift pump failing

Is the engine a 2GM or a 2GM20?
What brand is the pump - I believe (but don't know) that Yanmar has used a couple of different pumps over the years and in different countries at POS?
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Old 17-02-2017, 04:53   #5
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Re: Yanmar 2GM lift pump failing

Wrong part or cam problem ?
You could remove the pump, cover the mounting hole and just use an electric fuel pump instead.
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Old 17-02-2017, 05:17   #6
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Re: Yanmar 2GM lift pump failing

It's a 2GM engine. I don't recall the actual manufacturer or country of origin of either of the failed pumps but I do know they had slightly different part numbers. Both were correct but one had superceded the other. The first time it happened I assumed it was a factory defect in the assembly of the pump but I can't accept both pumps produced in different years had the same defect.

As for wrong part or cam, the pumps were definitely the correct part. I can't see how anything could bend that plate except the lifting and vibrating of the valve it retains. I've considered abandoning the mechanical pump, I actually have an electric pump in line but my big concern it the root cause. I also strongly suspect if I replace the steel line between the lift pump and the Yanmar fuel bowl with a flexible hose, that hose would absorb whatever pulse is causing this. I've learned that Yanmar replaced the steel line with a braided hose but I believe they did that because the banjo bolts worked loose from vibration on the solid line. Hmmm...saying that out loud I realize there's other steel lines attached to the engine they didn't replace....
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Old 17-02-2017, 05:27   #7
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Re: Yanmar 2GM lift pump failing

Here's a picture of the failed pump. You can see the broken retaining plate and the slightly displaced valve in the lower half. The piece that broke off is laying on the diaphragm in the upper part of the photo. It had been lodged in the diaphragm, caused a puncture and a runaway. I was alone, motoring in no wind a couple miles offshore the coast of Florida. Scared the crap out of me.
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Old 17-02-2017, 05:49   #8
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Re: Yanmar 2GM lift pump failing

"You could remove the pump, cover the mounting hole and just use an electric fuel pump instead."

If you've a persistent problem with the fuel pump(s) this is good advice, Im guessing that a new mechanical lift pump will be several hundred dollars, but to cap the opening and wire/install an inline electrical pump is an easy afternoon's job that will cost under $100 for suitable parts; just wire the pump back to the ignition switch.

Even if you repair/replace the mechanical pump, you can still install an electrical one (just leave the power-feed wire disconnected - a two minute task) in the system too ready to deal with any future failure; it makes bleeding the fuel system easier as a bonus.
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Old 17-02-2017, 08:40   #9
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Re: Yanmar 2GM lift pump failing

It's possible, but unlikely, that back pressure caused this.
Closer examination of the picture of failed part indicates that the plate was not evenly bearing against the check valve, causing it to be under a bending stress. If that's the case, it would be an assembly error. Get a magnifier and take a very close look at it.
I know it seems difficult to believe that two pumps could have the same fault but, that's possible too. The part number on the package is not necessarily indicative of the manufacturing lot number.
I've seen a lot of these engines around, and no mention of similar problems .
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Old 17-02-2017, 09:27   #10
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Re: Yanmar 2GM lift pump failing

I dont know what caused your problem, but i am replacing my pump with a walbro fra 2 17616, uscc approved, from summit racing equipement for$99.97. mine worked then quit then worked and was very warm to the touch. hope this helps.
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Old 17-02-2017, 09:52   #11
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Re: Yanmar 2GM lift pump failing

My initial thought is that it looks like a high cycle fatigue failure. I can't tell how much bending was in the separated piece but the plate retained in the pump doesn't look very bent, which means it was not very ductile. I'm wondering if the plate had a bad heat treat, was relatively brittle and fatigue failed due to either the valve or the diaphram movement. If there is clearance a potential fix would be to install two plates, friction between them would dampen the vibration and of course increase the strength of the retention. Looks like either a design or manufacturing defect to me, try the manufacturer again!
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Old 17-02-2017, 13:29   #12
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Re: Yanmar 2GM lift pump failing

Replace it, but don't over think it. Yanmar lift pumps are usually pretty reliable so I'd be surprised if a new one fails any time soon.
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Old 17-02-2017, 17:56   #13
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Re: Yanmar 2GM lift pump failing

Quote:
Originally Posted by Steveschr View Post
Hello all,
My Yanmar 2GM has an issue where the mechanical lift pump fails. Inside the lift pump there's a plate that retains the 2 valves. This plate has bent on 2 different pumps as if the outbound valve is pushing against it. On one occasion a piece of the plate broke, punctured the diaphragm and caused a runaway but that's a separate story. It seems to me the only possible way this plate could break is from a pulsing back pressure coming in the solid steel line between the lift pump and the injector pump. I spoke to Yanmar and an injector shop and both say this is impossible. I've searched the net quite a bit and can't find anyone complaining of this issue. Has anyone ever seen or heard of this? Any thoughts on how I should proceed? It takes a lot of hours for the plate to bend but I don't like having a critical failure waiting to happen again.

Thanks
Steve
I think we have the same lift pump on our Yanmar YSM8 and it has a braided line between the lift pump & the injector pump that works fine. You could try it instead of the steel line. We have a backup electric pump as it was way cheaper than a Yanmar mechanical as others said.I would be a little worried about the injection pump if it's leaking pressure back on the fuel feed side & you are sure that's the problem.
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Old 17-02-2017, 18:03   #14
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Re: Yanmar 2GM lift pump failing

The pumps could be fixed by making your own retaining plate. All it does is hold the valves in place. If you switch to an electric pump, get a high volume. Diesels usually pump many more gallons of fuel per hour than they burn. This helps keep the fuel clean and extracts water by going thru the filters several times. Also the additional flow cools the injector pump. In cold climates it preheats the fuel.
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Old 17-02-2017, 21:25   #15
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Re: Yanmar 2GM lift pump failing

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<snip> Diesels usually pump many more gallons of fuel per hour than they burn. This helps keep the fuel clean and extracts water by going thru the filters several times. <snip>.
Not to be contrary, but to get other's experience or knowledge: I've heard that that is true for older diesel designs, especially Detroit Diesels, but not so much for newer designs. That they just don't return that much fuel.

I think an observation I've had is relevant. I have an electric fuel pump that runs at a certain rate when my 2 Yanmar 3GM30s are not running (or even while they are running), but when I open the normally turned off valve on the line to the not-running 1 cylinder Faryman (1950 design?) genset, the fuel pump really pumps fast. If I need to purge air after changing the Racor, I open the genset valve.

Who out there knows?
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