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Old 23-05-2006, 07:12   #1
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Yanmar fuel leak in primer pump

On my Yanmar 2-GM there is a small hand primer pump where the fuel enters the engine. It is used when bleeding the fuel system. The pump diaphram is also a gasket for the 2 halves of the unit. There is fuel leaking out around this gasket. Does this diaphram/gasket need to be replaced or is ther some type of sealer that could be used. Has anyone replaced one of these?


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Old 23-05-2006, 07:21   #2
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I'm certainly no expert, but...

Rebuild the pump.

At least replace the diaphram.

And while you're at it - install a "squeeze bulb pump" (like on your outboard) on the fuel line. Locate the pump in a position where you can reach both the pump and bleed nuts comfortably at the same time (one hand on the pump and the other on the wrench). This will help greatly when it comes time to bleed the fuel system.

Note - the rubber hand pump will eventually harden and fail after a few years of diesel service - but they're cheap enough and greatly improve the fuel system


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Old 23-05-2006, 11:49   #3
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I'm not a Yanmar type, but on my Volvos the pump you describe sounds like the lift pump, which also has a small lever to aid in priming. If yours is the lift pump as well, you certainly need to rebuild or replace it. You will lose fuel from the system and if fuel can get out, air can get in. Not a good thing on a diesel.

I have a squeeze bulb as described by Gallivanters but an alternative to that is an electric fuel pump. Wow what an easy way to bleed the system. I have one additional advantage, the way the two fuel tanks are mounted, one higher than the other, I can open the feed valve on the upper tank and the return valve on the lower and actually gravity bleed my system. Not fast but very low hassle.

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Old 23-05-2006, 12:18   #4
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Thats your mechanical LIFT pump thats leaking. The 'lever' actuates the diaphragm of the LIFT pump when the engine is at rest ... used for priming and bleeding air.
So, before you have 'some difficulty' get a new diaphragm for this pump.

Incidentallly, the cause of such diaphragm breakage is typically running too small a retention rating filter ... or not increasing the surface area of a smaller retention fuel filter to compensate for the 'work'. The reduction in retention size puts a greater load on the lift pump diaphragm - a 2uM filter takes about 5X the 'work' of a 10uM filter to get the same flow rate; otherwise, the lift pump diaphragm has to work much harder to overcome the resistance to flow from the small retention rated filter.

Its usually best to keep a spare lift pump diaphragm as these can 'fatigue', etc. just from 'normal' wear and tear.
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Old 23-05-2006, 12:47   #5
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Great reply Richhh.

Firstly, NEVER NEVER EVER, use sealants ANYWHERE in fuel systems.
Second, check the little screws around the base are all tight.
If the diaphragm has failed as Richhh has said, maybe due to fatigue of sucking through a fine filter, then a good course of action IS to do as Sunspot said, and that is to use a small electric pump on the upstream side of the filter. Force the fuel into the filter with this pump and it aids the small engine pump. I would not bypass the engine pump, all though you could, I still recomend you keep it in line. Inside that pump, you may (or may not) find a small gauze screen. Make sure you clean that.
I have a large Racor filter/water seperater and then the mechanical pump and then twin CAV filters and then into the injector pump. I removed the screen in the mechanical pump because it it so hard to get to, plus it is hardly fine enough to worry about filtering anything after the Racor.

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Old 23-05-2006, 18:44   #6
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The Yanmar lift pump is only available as an assembly the are about $70.00 US. I go thru about 8 a year here.
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Old 25-05-2006, 14:22   #7

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The problem with using sealants, etc. in the fuel system (past the filters) is that anything which works free, is now free to get to your injectors and make an expensive problem. Even if the diaphragm is made of Unattainalon (similar to Unattainiam<G>) it will eventually wear, so I side with the chorus that says REBUILD THE PUMP. New diaphragm, clean the seats and it will seat right, and not let you down.

If the diaphragm actually tears or pinholes from old age, it can also let fuel into your lube oil since the rocker arm usually is open to the cam in the engine. And that, in turn, could cause all sorts of grief. If your engine oil level never seems to go down but actually INcreases? that can be the cause. Worth fixing ASAP.

I'd be in favor of installing an auxiliary electric pump, if for no other reason than most boaters use the starter in order to work the mechanical lift pump when they are bleeding the fuel lines. And using the starter for more than 30 seconds per ten minutes (will vary with the maker, etc.) *will* cause overheat damage and eventually kill the starter. Which will be more expensive than an electric pump.

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