Vibrations and stalling at idle

[Bigjim]

I just bough a boat with a Yanmar 1GM10. At first it didn't start due to a sticky fuel pump. The mechanic disassembled it and got it running.

I've been using it for nearly three months now. Until recently, it started and ran fine.

In the last few uses, the motor is not starting as easy. At low idle it runs really rough, even when warm.

Yesterday it nearly stalled when we were coming into the pier.

I've never worked on diesels before so I don't know what to look for.

At higher RPMs it seems to run smoothly

Any suggestions?

[Wotname]

Let's hope the regular diesel gurus chime in soon but in the meantime, here are some questions, comments and ideas.

First up, how old is the engine (the 1GM10 has been around a long time...), how many hours (if known)?

These engines are well known to vibrate at idle at the best of times - due in part to being a single cylinder and soft mounts. However if you engine is running slower than normal at idle, the vibrations will be worse. BTW, the idle adjustment is pretty straightforward - plenty of youtube info out there.

Assuming there is some problem as indicated by the poor starting, the usual culprit is blocked exhaust elbow, decreasing compression or injector issues.

So always start with the simple.

A simple diesel engine like the 1GM10 only needs three things to start and run - fuel, air and compression

Ensure battery is good and all terminations between battery and starter motor are clean and tight (including the negative side). A good starter motor helps with the compression aspects.

Has the ambient air temperature decreased noticeably - poor starting in cooler temperatures suggest a compression issue.

Air - check there is no obstruction in the air filter - usually there isn't but it's an easy check so do it . Check there is no obstruction in the exhaust elbow - this is important as these engines are known to get carbon build up in the exhaust elbow. Pull it off and inspect.

Check valve clearance (lash in USA parlance). This can affect air or compression. Again easy to do.

Check injector spray pattern. This tells you if the fuel is being delivered into the cylinder properly. A little harder to do but certainly still a DIY for the mechanically apt. Youtube is your friend.

Check compression - either with a diesel compression tester (not a gas engine type), you will be wanting about 400 psi or a "leak down" test. This is starting to get beyond many DIYer's but a there are other ways of checking the valves and rings. Take the head off and see if the valves seal using alcohol and if the rings seal using oil. But this is the last thing to do, not the first .

[Sailmonkey]

What is your idle speed? I'm may be that it's just idling too slowly.

When you start do you advance the throttle? If not , coupled with a low idle you're going to have starting problems

[Bigjim]

Originally Posted by Wotname

Let's hope the regular diesel gurus chime in soon but in the meantime, here are some questions, comments and ideas.

First up, how old is the engine (the 1GM10 has been around a long time...), how many hours (if known)?

These engines are well known to vibrate at idle at the best of times - due in part to being a single cylinder and soft mounts. However if you engine is running slower than normal at idle, the vibrations will be worse. BTW, the idle adjustment is pretty straightforward - plenty of youtube info out there.

Assuming there is some problem as indicated by the poor starting, the usual culprit is blocked exhaust elbow, decreasing compression or injector issues.

So always start with the simple.

A simple diesel engine like the 1GM10 only needs three things to start and run - fuel, air and compression

Ensure battery is good and all terminations between battery and starter motor are clean and tight (including the negative side). A good starter motor helps with the compression aspects.

Has the ambient air temperature decreased noticeably - poor starting in cooler temperatures suggest a compression issue.

Air - check there is no obstruction in the air filter - usually there isn't but it's an easy check so do it . Check there is no obstruction in the exhaust elbow - this is important as these engines are known to get carbon build up in the exhaust elbow. Pull it off and inspect.

Check valve clearance (lash in USA parlance). This can affect air or compression. Again easy to do.

Check injector spray pattern. This tells you if the fuel is being delivered into the cylinder properly. A little harder to do but certainly still a DIY for the mechanically apt. Youtube is your friend.

Check compression - either with a diesel compression tester (not a gas engine type), you will be wanting about 400 psi or a "leak down" test. This is starting to get beyond many DIYer's but a there are other ways of checking the valves and rings. Take the head off and see if the valves seal using alcohol and if the rings seal using oil. But this is the last thing to do, not the first .

Great reply. One of the reasons I avoided boats with gas engines is the simpler functionality of the diesel. I will check the air intake and exhaust as soon as I can. The engine ran nicely at idle previously, so something has changed.

As far as I know, the engine is original with the boat (1984) with unknown hours. It is very clean, so someone kept it maintained nicely, or it was rebuilt or replaced recently. I've only owned the boat since March and only run the engine maybe 10 times. So, either the throttle linkage slipped a bit lowering the idle, or it's one of the other items you mentioned.

Thanks

[Bigjim]

Originally Posted by Sailmonkey

What is your idle speed? I'm may be that it's just idling too slowly.

When you start do you advance the throttle? If not , coupled with a low idle you're going to have starting problems

I have not checked the idle speed yet. But as I wrote earlier, the engine was running fine until the last couple times I took the boat out.

I've only used it about 10 times. 8 times it ran fine, the last two it started running rough at low idle. So, to me, the first culprit sounds like the throttle cable slipped. The engine runs better at higher RPMs. But I obviously don't want really high idle when I'm shifting gears. Low idle is safer coming and going from the pier. I simply slip into forward or reverse to nudge the boat one way or the other.

I was just looking for items to check, since this is my first diesel.

Thanks

[puffcard]

Fuel pump is my bet, same happen to me. Soon it will die after running and you pull back to idle. The warmer weather is not your friend with a weak pump. Check the easy stuff first.

[DeepFrz]

Check that the fuel tank is clean and your filters are also clean with no water accumulation. Even if you changed the filters when you first got the boat they may now be partially clogged. If you haven't opened and cleaned your fuel tank then you have an unknown item that could cause you a lot of grief.

[Compass790]

I would suggest buying a workshop manual or finding one online ( You might find a free copy) if you want to work on it yourself.All good posts here, I'd just add make sure all your fuel line fittings are not leaking. Be careful not to overtighten where they go into aluminium alloy tho as they are easy to strip like on the fuel filter. If air leaks in you get dodgy idle too. We have a YSM8 which is the forerunner to your 1gm10 & it's a noisy shakey beast but thats endemic in 1 cylinder diesels. Idles well tho but we did up everything in the fuel system. Agree with cleaning tank checking fuel filters as well. Our P.O. had no o-ring on the deck fuel filler cap & I even found leaves in the tank! not to mention masses of water, algae,dirt etc.

[Wotname]

Good points by others suggesting checking that fuel source is clean etc.

I forget that some (many?) older boats have less than clean fuel tanks, lines, filters etc especially when they have been recently sold

Originally Posted by Bigjim

I just bough a boat with a Yanmar 1GM10. At first it didn't start due to a sticky fuel pump. The mechanic disassembled it and got it running.
........

Originally Posted by Bigjim

....... So, either the throttle linkage slipped a bit lowering the idle, or it's one of the other items you mentioned.

Thanks

This maybe a language / terminology thing but which fuel pump are you referring to.

Is it the low pressure (or lift) pump that gets the fuel from the tank to the engine mounted fuel filter or is it the high pressure (or injector) pump that gets the fuel from the fuel filter to the injector.

I have assumed it was the later and that the mechanic did the job properly but it is possible that he did not properly tighten the idle adjustment screw screw that is part of the governor / injector pump. There two connections at this point that partly interact with each other and both can affect idle speed. One is the idle stop screw and the other is the throttle (morse) cable end float.

[Mithril Bham]

Lots of great suggestions many which should be done for basic maintenance. A shot in the dark would be after checking idle speed to check fuel pump. You should have a spare anyway. You did have a problem with it before.