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Old 08-01-2015, 06:03   #16
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

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Originally Posted by dtlx11 View Post
Thanks Zai

I have been considering doing this all along but I'm worried that low compression is a death sentence for the engine and a new one is big bucks.

Is it possible to get an engine with low compression back to a good standard?
Not a death sentence. As you may know the 3GM30 do not have cylinder sleeves but you (Machine shop) can rebore the cylinders oversized. Yanmar sell oversized pistons and oversized rings. I have done my 3GM three years ago this way and it has been running A-OK since . However, you can only do this procedure once because they (Yanmar) only have one oversized ring/piston set available.
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Old 08-01-2015, 06:13   #17
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

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Originally Posted by a64pilot View Post
Ether is fine as long as they are no glow plugs, if there are glow plugs and you still want to use ether, be sure to dis-able the plugs.
WD-40 is sort of a low grade starting fluid, it works some what, but not nearly as well as ether. It is possible to get a small fire in the intake manifold with ether if you use a lot, if that happens usually best thing to do is continue to spin the motor as the motor will ingest the fire.
I like to spray ether directly into the intake manifold when the engine is turning over.
I've used ether most of my life on farm and Earth moving equipment, never a boat yet.
Ether may be heavier than air also, if so another reason to shoot it directly in the intake with the engine spinning.
BTW just use a short shot of ether if any. don't over doit.
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Old 08-01-2015, 12:25   #18
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

good point to by pass raw water if not starting, if it starts, run engine and crack each fuel line at each injector one at a time,then close after you get fuel. if rpm does NOT drop on the injector line you opened that is the cyl that is not firing. possible that had air in that line.
worth a try...
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Old 08-01-2015, 12:38   #19
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

Another way to tell which clyinder isn't firing is to lift the decompression levers one clyinder at a time and note when the RPM / sound doesn't change.
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Old 08-01-2015, 12:51   #20
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

That engine is famous for a cracked piston. Often the lower piston land. The engine will start reluctantly, but run pretty good... at least at anything above idle. From what I can tell the 90's ones were the ones that have this problem... but that's anecdotal...


SailorChic had this problem and so did I. Mine was '92 engine.
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Old 08-01-2015, 21:15   #21
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

To avoid all the guessing around and lotīs of time do a compression test.
This will narrow down the posibilities to what might be the cause of the problem.
I agree with Pierre....there is still a long way to the death sentence
Pistons can be changed, cylinders can be honed for to bigger size and Yanmar supplies piston rings for over size.
As to starting a diesel engine U need
1. Fuel
2. Air
3. Enough Power from Ur starter engine/crank amps Batterie
4. INJECTERS...they can be pressure checked and recovered with ultrasound treatment
5. Very important !!!PROPERLY FUNCTIONING GLOW PLUGS...to check take out...they should be dry....if wet / covered with oil.... means Ur engine is not new anymore but still a long way to go to the graveyard. Usually a new set of glow plugs and U are all good....when have U changed the last time if ever ?

Checking the Glow plugs would be my first test
2.Injectors DO THEY get fuel from the pump...unplug fuel lines from pump at the injectors > start engine to give a few turns and check for proper fuel supply
Have U performed those tests ....?
After that the compression test defenitly will be Ur best choice and next step of diagnosis
BEFORE U TAKE EXPENSIVE DECISIONS

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Old 09-01-2015, 15:40   #22
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

head gasket correctly in.....?, right torque?
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Old 09-01-2015, 21:36   #23
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

all bolts MUST be torqued to specs. I know of other rebuilds that weren't and then re-torqued then they ran fine. good luck
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