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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel > yanmar 3gm30f 1 cylinder bad condition
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Thread: yanmar 3gm30f 1 cylinder bad condition Reply to Thread
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Topic Review (Newest First)
09-05-2011 11:59 PM
MitchM one can check for a bent con rod using a test with a piece of solder bent at a right angle to see whether the solder compresses evenly when each piston is (manually) raised, details of how to do this test are in the service manual..(not the owners manual..) if the piston travel (and smash pattern on the solder pieces for each cylinder) is different between the 3 cylinders, that suggests a bent con rod as dabnis points out. if it's a bent con rod that would be important to know from a $$$ standpoint.
09-03-2011 04:55 PM
dabnis
Quote:
Originally Posted by dabnis View Post
Not even close to being an expert on anything but do have some years working on gas and diesel engines. The crank being hard to turn when only the #1 valve train operates is interesting, perhaps an out of tolerance camshaft, bent valve stem, seized valve guide, galled cam lobe or rocker arm? For starters a compression test on all cylinders should be done.
When things settle down when operating the de- compression lever on #1 leads me to think of the above valve issue(s) or perhaps a blown head gasket in the #1 area. Let us know what you find.

Dabnis
Bandaid,

A compression test has been suggested a couple of times. Don't know if one was done, but it sounds like the head has already been taken off. If #1 piston doesn't come all the way up it is likely to be a bent rod.

Dabnis
09-03-2011 04:34 PM
bandaidmd I just want to say to anyone that's having these sort of issues, do a compression check before you start monkeying around. At the very least you'll have a baseline to refer back too. Your dealing with some high pressures in a compression ignition engine(diesel) so your normal gas powered automotive tester is not going to work. Harbor freight has a rather inexpensive compression tester kit for diesels some will use the glow plug hole and some you'll have to pull the injector.
09-03-2011 11:19 AM
fryewe Water can also get into the exhaust if you crank and crank and crank and the engine doesn't start. Exhaust pressure expels the cooling water, and if there is no exhaust pressure, and the engine is being spun for a long time by the starter (with the cooling water pump pumping as a result of that), water can flood into the engine.
09-03-2011 11:07 AM
dabnis Sounds like a badly bent connecting rod? Perhaps water got into the combustion chamber either through the exhaust manifold or a large leak from the head gasket or a cracked block or head? You might want to get a detailed estimate from the mechanic before attempting to re-use the existing engine. Don't know if Yanmar offers "short blocks", just the block and internal moving parts, but you might explore that possibility. Also while the engine is out you might want to inspect or remove the fuel tank or anything else that is hard to get at with the engine in place.

Dabnis
09-03-2011 09:00 AM
yjchun As you suggested, I did adjust valve clearances but did not see much difference. I did ask an engineer here to take a look after all. After careful examination (He pointed my valve adjustment was all bad), we found out that one piston head was a lot lower than others. We are planning to take the engine out to pontoon for further examination and repair. So this is becoming a semi-overhaul.

Because cost is major concern to me now, the engineer will fix the main problem and take care of parts in very bad condition (injector rebuild and replace oil pipe, mixing elbow and thermostat).
I will do minor maintenance, cleaning and have the engine repainted (in red).

My heart is hurt for the extra expenses and time, I am learning a lot at least and happy to finally be able to clean my engine room.
If there is anything I should know before the engine rebuild, please let me know.
Thanks.
08-27-2011 10:50 PM
fryewe yj, the advice to check your valve clearances and adjust if needed is a good start. You already have the cover off, so you are ready to go. Do you have the Yanmar manual for your engine? Is your engine access on top of the engine enough to allow doing the clearance check and adjustment?
08-27-2011 07:09 PM
dabnis
Quote:
Originally Posted by arf145 View Post
I was hoping a real diesel person would be weighing in with more here. But have you actually checked your valve clearances, as someone else suggested? All you need is the right thickness feeler gauge, a spanner, and a screwdriver. I think all does usually look beautiful under the valve cover, but that doesn't tell you if they're adjusted correctly.
Not even close to being an expert on anything but do have some years working on gas and diesel engines. The crank being hard to turn when only the #1 valve train operates is interesting, perhaps an out of tolerance camshaft, bent valve stem, seized valve guide, galled cam lobe or rocker arm? For starters a compression test on all cylinders should be done.
When things settle down when operating the de- compression lever on #1 leads me to think of the above valve issue(s) or perhaps a blown head gasket in the #1 area. Let us know what you find.

Dabnis
08-27-2011 03:55 PM
arf145 I was hoping a real diesel person would be weighing in with more here. But have you actually checked your valve clearances, as someone else suggested? All you need is the right thickness feeler gauge, a spanner, and a screwdriver. I think all does usually look beautiful under the valve cover, but that doesn't tell you if they're adjusted correctly.
08-26-2011 12:01 PM
yjchun Today on the way back from a nice sailing, I felt a slight vibration when I raised engine rpm, I ignored. When I lowered RPM to approach the slip, engine stopped.

I opened valve cover, all just looked fine and beautiful to me. But when I rotate crank, it is extremely hard to rotate crankshaft only when cylinder 1 valves are moving. This hard to move crankshaft at some point has been always like this since I first tried it. Now I see it is related to cylinder 1.

This seems some kind of clue to me. I am not starting engine since then and can't now 'cause valve cover gasket is not reusable anymore.

Would anyone tell me where the problem seems to be? I'm praying problem can be solved by a simple parts replacement.
Thanks. Chun.

PS: one more thing, I once before tried to rotate crankshaft when I removed injectors from cylinder 1 and 2 and was same as above.
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