How should a rebuilt Yanmar behave?

May 15, 2015
131
Marlow-Hunter 31 Everett, WA
I just had a mechanic do a major rebuild of my Yanmar 2GM20F including new bearings, seals, oil pump, rod bearing, piston & rings, cylinders rebored, etc. Re-installation was completed yesterday and I took her out for a trial run today. I noticed a fair amount of fuel in the water when first starting up and at RPMs > 1400, blue smoke from the exhaust. I was mindful of the need for a break-in period and only ran her up to ~2000 RPM, but blue smoke increased with higher RPMs from 1400 to 2000.

I’ve read that the rings need to seat and that blue smoke is to be expected until that happens... But on the internet there are widely divergent opinions about this, as well as the best strategies for breaking in a rebuilt diesel marine engine.

Is it in fact “normal” for a rebuilt engine to temporarily burn oil? About how many hours will it take for the rings to seat in a 2GM20F? Any suggestions for the best methods of breaking the engine in?

Thanks,

Matt
 

Mikem

.
Dec 20, 2009
820
Hunter 466 Bremerton
My son had a 2gm completely rebuilt in a previous H306 that he owned. It started fine, no smoke, no metallic sounds, no fuel in the water...it ran smooth and like a swiss watch. I don't remember any issues at all. If the symptoms you mentioned persist you have problems.
 
May 29, 2018
457
Canel 25 foot Shiogama, japan
A properly rebuilt engine should, look, sound and perform like a new engine.

I noticed a fair amount of fuel in the water when first starting up
Is that fuel that has been ejected out of the exhaust (into the water) on start up?
If it took a bit of cranking to get it started the first time that is not a problem.
How was the start up the second or third time?


Is it in fact “normal” for a rebuilt engine to temporarily burn oil?
If the mechanic has sprayed oil liberally in the bores on reassembly, there will be some smoke. That should be gone in a few minutes though.

About how many hours will it take for the rings to seat in a 2GM20F?
The rings should seal pretty quickly. I would guess in an hour of running, but that is just a guess.

Any suggestions for the best methods of breaking the engine in?
Did you mechanic give you any guidelines to break in the engine?
I would not run it slowly.
Let her idle at higher revs or take her out for and hour or two and gradually increase the revs/ load should do it.


Go back to your mechanic with your concerns.
Keep him in the picture as to what is happening and what you expect.

gary


gary
 
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dLj

.
Mar 23, 2017
3,373
Belliure 41 Sailing back to the Chesapeake
On a major rebuild as you describe, the engine should run like a brand new engine.

dj
 

dhjay

.
Jan 8, 2021
7
Hunter 31 Saylorville Lake
I rebuilt our 2GM20F over the winter. Starts immediately with no drama. Runs beautifully. No smoke or other symptoms described above.
 

RoyS

.
Jun 3, 2012
1,739
Hunter 33 Steamboat Wharf, Hull, MA
I rebuilt my 2QM15 about seven years ago. Never had smoke like you describe. Something is clearly wrong.
 
May 15, 2015
131
Marlow-Hunter 31 Everett, WA
Thanks guys....I was hoping to hear a different story, but suspected a problem.

Gary: it did take me a while to start it up and that could account for the fuel in the water. Right now, there's only about a half-hour on the engine, so I’ll run it again today for a good hour to see if things improve. In terms of breaking it in, he only told me to not to run it above 2000 RPMs initially, but it sounds like I should push it a little more today, slowly working up to cruising RPM.

I’ll report back in a few days. Talking to my mechanic tomorrow.

Matt
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
Matt, Diesels do not like to be run in neutral for long periods. You need to run them in gear with a load. Even if you tie yourself to the dock. Securely.
 

dLj

.
Mar 23, 2017
3,373
Belliure 41 Sailing back to the Chesapeake
One other piece of advice I've gotten in the past for breaking in a diesel is to vary the RPM's as you are breaking it in. Don't just set the RPM at one speed and let it run, change it up every few minutes. Don't know if it really matters but the last brand new diesel I broke in is still running beautifully after 21 years and very hard usage. But that was a diesel car, not a boat. Don't think it matters though.

dj
 
May 15, 2015
131
Marlow-Hunter 31 Everett, WA
Thanks for the break-in instructions---they are both informative and a little funny (how many 30-minute intervals can one keep track of?).....and I can certainly use a little humor right now.

Question: The manual says: "During the first 10 hours of operation, the engine should be operated at maximum rpm minus 400 to 500 rpm (approximately 60 to 70% of load) most of the time.” Don’t know that I've ever tested the max RPM on my engine....what should that be on a 2GM20....3200-3300 RPM..higher?

Matt
 
Nov 22, 2011
1,192
Ericson 26-2 San Pedro, CA
Thanks for the break-in instructions---they are both informative and a little funny (how many 30-minute intervals can one keep track of?).....and I can certainly use a little humor right now.

Question: The manual says: "During the first 10 hours of operation, the engine should be operated at maximum rpm minus 400 to 500 rpm (approximately 60 to 70% of load) most of the time.” Don’t know that I've ever tested the max RPM on my engine....what should that be on a 2GM20....3200-3300 RPM..higher?

Matt
Max RPM for the 2GM20F is 3600.
 
May 15, 2015
131
Marlow-Hunter 31 Everett, WA
Update: As everyone on this thread expected, putting another 2-3 hrs on the rebuilt engine did nothing to reduce the exhaust smoke. But it did help me resolve the color of the smoke—it’s more white than blue (I sent a video to a couple mechanics to confirm). Very discouraging…. white smoke was the problem last summer that eventually led to the engine rebuild, after having the exhaust elbow replaced and the injectors and injector pump rebuilt—with no improvement.

So, 9 months and several thousand $$ later, I’m back where I started. I had the injectors pulled again last week and sent them back to the diesel shop where they were rebuilt last summer. The guy there told me he thinks bad fuel (i.e., low lubricity) “scored” the injectors (sticky nozzles) and he overhauled them again. Next week I’m going to drain & refill the fuel tank, replace the fuel filters, have the injectors re-installed, and take her back out for another run.

Wish me luck.

Matt
 
Jan 30, 2012
1,123
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
Good luck. Hard to help from a distance but -

Assuming the assembly was carefully done and all the parts met wear limits --

White is unburnt fuel or water. Careful reassembly probably eliminates water and this one is an F so if it was water your coolant reservoir would be drawing down. If fuel it smells sweet. If the injector reinstall does not solve the problem consider rechecking injector pump timing. You need to remove the starter, or if the flywheel marks are clear on the aft side of the flywheel you can look through the bell housing window from the rear. In any case fuel timing in this motor is exclusively dependent upon shims under the pump at the front housing joint.

Think back to when the problem started. Did anyone remove the pump? You said the rebuild include taking the pump to the diesel shop. Did the most recent builder physically verify pump timing with a drip tube at final assembly?

This is just a guess but maybe worth the effort.

Charles
 
Jan 4, 2006
6,444
Hunter 310 West Vancouver, B.C.
The chances of all that crap continuing on at this stage in the game are 0% . Pick up a lottery ticket as well, you're on a roll.
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May 29, 2018
457
Canel 25 foot Shiogama, japan
I just had a mechanic do a major rebuild of my Yanmar 2GM20

Luck won't cut it.
Where is the mechanic through all of this?

gary
 
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RoyS

.
Jun 3, 2012
1,739
Hunter 33 Steamboat Wharf, Hull, MA
You can get white smoke from water in your fuel. You will know soon after you replace the fuel in the tank. Was your boat covered over the winter so as to prevent snow build up on top of your fuel fill port?