Yanmar - eccentric & fuel pump

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May 8, 2008
5
Hunter 30_74-83 Norwalk
Greetings. I have a 1979 Hunter 30 with a Yanmar YSM-12-R inboard diesel. When we went to commission it for the season this year, the manual fuel pump stopped working. It would pump if we manually worked the lever but otherwise, the engine would start and die or not start at all. The yard's theory is that the eccentric shaft has worn to the point that it won't drive the pump anymore. It'd be a huge job to replace and they're suggesting that they bypass the manual pump and install an electric one.

Has anyone run into this kind of wear on an engine? Does it seem plausible? The yard swears that there's no down-side to the electric pump and that in fact it will work better.

I'm hoping someone has experience or opinions on this.

Thanks,

Mark Berns
 

Ed A

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Sep 27, 2008
333
Hunter 37c Tampa
i dont know if i agree, you mayjust have abad pump. replacing it its good.
The electric route works pretty well too but why not have them both.
i would remove the pump and check it out.
 
May 8, 2008
5
Hunter 30_74-83 Norwalk
i dont know if i agree, you mayjust have abad pump. replacing it its good.
The electric route works pretty well too but why not have them both.
i would remove the pump and check it out.
Thanks, Ed. I probably should have mentioned that they did install a new one and had the same result. It wouldn't actually pump unless they pushed the lever manually -- kind of tricky with the belts running past there. If they bled the line and pumped it manually, the engine would start but then die within a minute or two. The fuel lines also have been replaced, so we're sure it's not an air/fuel issue.
 
May 11, 2005
3,431
Seidelman S37 Slidell, La.
First check your fuel

Helped a friend recently with a very similar problem. His ended up being water in the fuel. If you are not using off road fuel with the dye in it, is almost impossible to tell there is water in the seperator bowl, as the undyed fuel is nearly as clear as water. As for the electric fuel pump, I have had one on a 3GM Yanmar for a few years, and love it. This would certainly be a much less expensive repair than having to replace the cam for the manual pump. Not sure but I think it is part of the engine cam shaft. Check for the water, and then go electric.
 
Mar 2, 2008
406
Cal 25 mk II T-Bird Marina, West Vancouver
I also have a 1979 Yanmar YSM-12R. This very simple and robust diesel is extremely reliable. I very much doubt that your problem is with a worn fuel feed pump cam on the PTO shaft. That would put a lot of steel into the oil that would probably cause problems with your oil pump, compression and bearings. If it work properly last year and now doesn’t work, ask you self, what has changed from when it worked last year.

To trouble shoot anything, start by asking a series of questions:
- Was there any work performed on the motor since it last work properly?
- Is the fuel tank clean?
- Is the fuel in the tank clean?
- Do you have a screen on the tank pickup tube? If yes, remove the screen.
- Is the fuel tank valve fully open?
- Is the infeed “Racor” fuel filter clean?
- Is your oil level going up? If so, then you probably have a leaking pump.

Do you have the shop manual for the Yanmar YSM 8/12 motors? The fuel feed pump is detailed in chapter 3 starting at page 21. The trouble-shooting guide is in chapter 13 starting at page 12.

A worn cam or broken pump lever would exhibit the symptoms you describe but the problem may also be due to other causes. Have you removed your oil filter screen (be careful it is easy to strip the treads in the aluminium housing) to look for steel filings? Are you sure that you get proper operation when you use the external manual lever. Remove and inspect the fuel feed pump on the port side of the motor. Possibly the nuts on the two mounting studs are loose or you may be able to adjust the pump stroke by lowering it a bit on the mounting studs.

That said it may still be easiest / cheaper to replace the mechanical pump with an electric pump.
 
May 8, 2008
5
Hunter 30_74-83 Norwalk
Re: First check your fuel

Thanks for the detailed response.

The only work that's been done was my replacing the rubber fuel hoses late last season because they seemed to be sucking air, and the yard did the commissioning and then replaced the rest of the fuel hoses - the mesh-covered ones - this week as part of their trouble-shooting. They did install a new fuel pump during trouble-shooting, and got the same results - worked as long as they manually worked the lever but died within a minute or so after they stopped pumping.

The fact that it worked while they pumped by hand seems to me to point away from it being a fuel or fuel-line issue.

I guess at this point I'm OK with the electric pump but my biggest concern is that there might be something else going on in the shaft or cam that could be worse. But that seems like it'd be a pretty big job to disassemble enough of the engine to find out - and while it's running it's not making any unusual noises, which presumably it would.

I can't think of anything other than the cam at this point that would explain the fact that it works manually but not mechanically.
 
May 11, 2005
3,431
Seidelman S37 Slidell, La.
If in fact

If in fact the cam for the lift pump is bad, for whatever reason, I would certainly remove the lift pump and just block off that hole. An arm that is rubbing on the cam enough to damage it, is still rubbing on that cam, even if the pump is not pumping or being used. While anything is possible, I have never heard of a lift pump cam going bad. The lift pump cam is the same as the cam lobes for the valves, just a different profile, and they valve lifters take much more load than that little lift pump.
 
Sep 15, 2009
6,243
S2 9.2a Fairhope Al
Thanks for the detailed response.

The only work that's been done was my replacing the rubber fuel hoses late last season because they seemed to be sucking air, and the yard did the commissioning and then replaced the rest of the fuel hoses - the mesh-covered ones - this week as part of their trouble-shooting. They did install a new fuel pump during trouble-shooting, and got the same results - worked as long as they manually worked the lever but died within a minute or so after they stopped pumping.

The fact that it worked while they pumped by hand seems to me to point away from it being a fuel or fuel-line issue.

I guess at this point I'm OK with the electric pump but my biggest concern is that there might be something else going on in the shaft or cam that could be worse. But that seems like it'd be a pretty big job to disassemble enough of the engine to find out - and while it's running it's not making any unusual noises, which presumably it would.

I can't think of anything other than the cam at this point that would explain the fact that it works manually but not mechanically.
there is one thing that it might be....yanmar makes different lift pump arms for different models example....a 2qm15 lift pump is different from a 2gm20...but on the out side they look the same....this may not be the problem but i would sure check it out and make sure they have the correct pump....

regads

woody
 
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