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-   -   yanmar 3gm30f 1 cylinder bad condition (http://www.sailnet.com/forums/diesel/77833-yanmar-3gm30f-1-cylinder-bad-condition.html)

yjchun 08-22-2011 09:38 PM

yanmar 3gm30f 1 cylinder bad condition
 
Hello.

My new (first) boat has a 10 years old yanmar 3gm30f.
Engine works fine but not good sound and vibration (especially in low RPM) and feels like underpowered.
I am planning to bring the boat to my home next month and do not want it stop in the middle of the ocean.
I do know next to nothing about the engine but here (in japan) engine repair/overhaul is very expensive and don't want to hire anyone unless very required.


Symptom:
1. Engine stops at lower than 1100 idle rpm
2. for 1 minute after engine start, white smoke, a little lower rpm, worse sound and vibration than later.
3. bad vibration and sound at idle or low rpm gets a lot better when I engage engine to >2000rpm for a while (10~20 seconds is enough).


Analysis:
1. When I turn the decompression lever ON of cylinder 1, RPM goes up with better sound. So I guess it is problem with cylinder 1
2. Checked fuel is coming out from high compression fuel line (by manually rotating the crankshaft). No knowledge if the fuel amount and timing is OK or not but fuel line is not blocked and fuel pump is working at least.
3. I replaced the injector with cylinder 1's. No change. So injector seemed OK.


This is all I could do myself so far. What are your suggestions from now?

Thanks

fryewe 08-22-2011 11:22 PM

If you have the tools (hand tools, only the required torque wrench is a bit exotic) and experience (or mechanical skills and can read a technical manual), I would first pull the valve cover and make sure the valves/springs/rockers/push rods are all doing there jobs and look good. I would then take the head off it and inspect the pistons, rings and cylinders. If it all looks okay, you can pull the oil pan to check for wear products, and inspect the bottom end of the engine. Neither expensive nor difficult to do these inspections. Don't know about your engine arrangement in your boat, but perhaps you can do the top end inspections without pulling the engine.

Good luck.

HPLou 08-23-2011 12:13 AM

Another possibility could be a blown head gasket. Check the engine oil for signs of any water contamination. Also, check compression for each cylinder and note any variations.

yjchun 08-23-2011 03:01 AM

fryewe: Well, All I have is a socket wrench and spanners. I am reading the workshop manual right now and will try it as you suggested. will be a good study.

HPLou: I replaced engine oil and oil filter but did not check if there was water in the engine oil. I will see how I can test the compression of cylinders.

Thanks. Chun.

NCboatrx 08-23-2011 08:29 AM

Chun,
I suggest that you check the valve clearances (tappets). There will be a section in the workshop manual on the cylinder head and valves. Work carefully and check with a feeler gauge if the clearances are correct. If they are too tight on one cylinder, you will experience loss of power on that cylinder.
Stanley

fryewe 08-23-2011 09:46 PM

Chun, you can tell a lot about your engine by pulling the valve cover off and looking at the valve train, rockers, springs and push rods. Usually, only one or two nuts on the top of the engine hold the valve cover on. When you pull the cover, you need to keep things clean.

If things look okay, operate the compression release and slowly jack the engine over. Observe the valve train operation carefully while you do this. Check the valves and valve seats closely. Check the valve clearances as noted above and in your manual.

If I would you, I would do this step and then evaluate what to do next.

If you can take video and post it, why not do that, and perhaps some experts or experienced do it yourselfers could look at it and give you advice at that point?

yjchun 08-26-2011 11:01 AM

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.

arf145 08-27-2011 02:55 PM

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.

dabnis 08-27-2011 06:09 PM

Quote:

Originally Posted by arf145 (Post 766718)
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

fryewe 08-27-2011 09:50 PM

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?


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