Yanmar 3GM 30F stopped while motoring, won’t re start.

[Cheechako]

-The engine ran an hour.... likely a fuel issue. Check the filters , especially if it has a Racor type, an air gap in a filter will sometimes not go away. Fill the bowls completely. Racor plastic bowls can look full but the top 1.5" can be just air. They are often before the lift pump and the vacuum wont fill the filter from the tank.

-How long was the boat out of commission before this? Is the fuel vent clogged at the hull exit by insects?

-The mechanic should have tested for fuel spray at the injectors long before removing the injection pump or doing a compression test....? This also would confirm the lift pump is functional. I gotta believe this was done?

-Manually move the stop lever to the "run " position and try it.

[Lepke]

When a diesel just stops it's usually the stop solenoid. When you run out of fuel or suddenly get air in the lines there's usually a few minutes or seconds of erratic engine performance.

Verify you do or don't have fuel to the injectors before changing filters, etc., and induce new issues. Check that the injector pump is in the run position. Some engines allow you to hold open the stop solenoid. Verify you have power to the stop solenoid.

[skipperpete]

Well, the 3GM-30 is still alive but it took 5 hours to resuscitate. First off, thanks for all the thoughtful suggestions, all were considered and nearly all were followed but the actual reason the engine stopped was far more interesting than I expected.
The exhaust hose was removed from the mixer elbow to make sure there was no back pressure then an external fuel supply connected to the primary filter and the old fuel was purged up to the injector pump and eventually to the injectors. water pump">Raw water pump belt was removed in anticipation of extended cranking. The stop cable and speed control cable were both disconnected from their respective engine arms. The heat gun was used to warm up the intake manifold and a few precautions were taken to manage a possible runaway in the happy event that it might actually start, so far so good and now ready to crank it over.
Short periods of cranking and heat gunning produced a fair bit of smoke and a sort of half hearted effort by the engine to start. This went on for quite a while but no start so now the timing was checked with the delivery valve in situ and the whole problem changed from a fuel issue to a major mechanical issue. To locate the timing mark the engine needs to be turned over manually with a breaker bar on the crankshaft pulley nut but it was really hard to turn, like REALLY hard which was totally confusing. The starter would spin the engine as would normally be expected and it should have started, injectors buzzing, lube oil pressure up. I initially suspected a mild piston seizure and then maybe a gentle crank shaft seizure but the real reason remains a bit of a mystery. Noting an earlier suggestion to review the last work done, in this case the saildrive and damper plate it was decided to slacken off the flywheel housing bolts to see if that made any difference....... and it did. The saildrive gap popped open by 3mm as the bolts were loosened and the crank could be turned much more easily so it was decided to put the exhaust hose back on and give it a spin. After a bit of turning it finally fired up and blew out a cloud of smoke and it ran for about 1/2 minute at varying speeds quite happily but refused to idle and once the saildrive was tightened, it again refused to start so I’m guessing that either the thrust bearing is toast or the unexplained pressure on the input shaft has caused the saildrive to bind up , but whatever happened was enough to stop the engine at 1500 rpm.

[Wotname]

Yikes!
Truth is stranger than fiction .

Thanks for the update, very interesting.

[skipperpete]

Originally Posted by Wotname

Yikes!
Truth is stranger than fiction .

Thanks for the update, very interesting.

Yeah, one more “I never saw that coming” moment to store in the already overloaded memory bank. I’ll be interested to hear what the damage is when the engine is out and the drive plate is accessible.
One more thing I’d not seen on a 3GM30 before was what seemed to be a fuel return system pressure maintaining valve or metering orifice bolted to the square inspection cover aft of the injection pump, just a square block with a line in from the little secondary filter and a return to the tank with a tee in for the injector leakoff pipe.... nothing in my service manual shows this and it seems to be an OEM part.

[Wotname]

Yep, if you do get any feedback about the fundamental failure, please post.

Also if you get the opportunity to see the engine again, a picture of the thingy in the fuel return line would be appreciated.

[skipperpete]

I’m far away from that engine now but I found a very poor [ATTACH]269592 pic of the fitting in google images. The injector pipes are different too, the two rear injectors have the HP connection close to the valve cover and the front injector faces away from the cover. Maybe its an EU engine???
I’ll post an update when I hear from the owner about the progress on the repair. The cause could be as simple as the drive plate being installed back to front but the repair could be quite complicated.

[skipperpete]

This is a better picture of the valve and it was partly involved in the failure to restart, all the fuel at lift pump pressure delivered to the injector pump was being dumped into the return line because the relief valve was stuck open. Clamping/blocking the return line fixed the problem temporarily. [ATTACH]

[skipperpete]

Here’s a bit more on the “ it just stopped” incident. Yes it was indeed the drive plate that caused the shutdown. The mechanics took out the new plate, it was different to the original plate thickness by about 5mm and the pressure on the thrust bearing was enough to cause it to heat up and seize the crankshaft. This might have been a relatively easy fix on most engines, just drop off the main bearing cap and, assuming the damage is not too severe, slip in new thrust washers and it should be good to go.
But the 3GM30 has an “all in one” thrust and main bearing so when the thrust seized to the crank, there’s now the possibility that it also spun the whole bearing shell in the carrier and the only way to verify that is to remove the crank. The clue to support this theory is that if the engine is spun over decompressed with the valve cover off, jets of oil squirt out from the rocker gear.....that’s a lot of oil pressure. Has anyone here run a 3GM with the valve cover off? or seen oil squirting energetically from the holes in the rocker arms?

[phantomracer]

Did you replace the bypass valve on the side of the motor, if you have that year motor? The valve often fails with no start hard start symptoms.

In the pic, it is to the right of the fuel filter

[skipperpete]

Hi Phantomracer, that valve was a bit of a surprise, most 3GM’s don’t have one and my service manual makes no mention of it ..... a real trap for the uninitiated ...which on this occasion was me. The goal at the time was simply to get the engine started and there was almost zero lift pump pressure at the injector pump bleed screw so I just clamped off the return line after the tee where the injector leak off line joins that extra return line. The engine showed more enthusiasm towards starting after that...and produced more smoke but it was only when the flywheel housing bolts were released by 2-5 mm that it actually fired up and ran.

[Wotname]

Originally Posted by skipperpete

....... but it was only when the flywheel housing bolts were released by 2-5 mm that it actually fired up and ran.

Truth is stranger than fiction!

[phantomracer]

Originally Posted by skipperpete

Hi Phantomracer, that valve was a bit of a surprise, most 3GM’s don’t have one and my service manual makes no mention of it ..... a real trap for the uninitiated ...which on this occasion was me. The goal at the time was simply to get the engine started and there was almost zero lift pump pressure at the injector pump bleed screw so I just clamped off the return line after the tee where the injector leak off line joins that extra return line. The engine showed more enthusiasm towards starting after that...and produced more smoke but it was only when the flywheel housing bolts were released by 2-5 mm that it actually fired up and ran.

yup my manual and parts manual do not mention it either. I found a reference to it on toadmarine.com . did some research and did find a parts manual to MY serial number motor, which shows the valve.

replacing it was like magic on my boat! cheap and easy fix! Hard to find if you do not know about it!

[phantomracer]

Originally Posted by skipperpete

Hi Phantomracer, that valve was a bit of a surprise, most 3GM’s don’t have one and my service manual makes no mention of it ..... a real trap for the uninitiated ...which on this occasion was me. The goal at the time was simply to get the engine started and there was almost zero lift pump pressure at the injector pump bleed screw so I just clamped off the return line after the tee where the injector leak off line joins that extra return line. The engine showed more enthusiasm towards starting after that...and produced more smoke but it was only when the flywheel housing bolts were released by 2-5 mm that it actually fired up and ran.

I found this pdf catalog is accurate for my motor, possibly yours too. it shows the check valve and block and piping in figure 45

https://dieselpartseurope.com/media/...-M46001_en.pdf

[skipperpete]

Here’s an update on the 3GM. The engine just did an 8 hour run after the new OEM drive plate was installed with seemingly no dramatic problems or seizures. It’s now possible to rotate the engine by getting a good hand grip on the front pulley with the decomp levers engaged.
Now there’s a new problem...The engine barely idles and cuts out when returning to idle in gear ( which made docking a bit problematic). I found out that the alternator is part of the problem because at startup the panel light stayed on while the engine idled happily in the normal way but as soon as the revs were increased in neutral to make the light go out , a slight belt squeal could be heard and when returned to idle the revs dropped to an unhappy 500rpm. In gear there was a lot of dead lever travel till the revs started to pick up and once past 1500 all seemed ok, with no belt squeal. The journey proceeded uneventfully from there on at 2,500 rpm using both engines but with noticeably different lever positions.
After docking I took the belt off the alternator then ran the engine and ALL the symptoms totally disappeared so it’s definitely related to the alternator and here’s where I’m a bit puzzled........ is it totally an alternator problem or is it a combination of low engine power and the alternator drag?
Has anyone else on the forum had these problems with a 3GM30?
Pete J