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Old 13-08-2011, 21:39   #91
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Re: Engine Diagnosis

.........And now...the moment we've been all waiting for...



I knew I would not sleep tonight. Even thought the shop was 95 degrees, I spent a few hours and pulled the plumbing and head. Sat the head on some rags and it looked ok...hmmm...



So lets try rotating the crank...hmmm...it spins all the way threw now...

BUT... piles of carbon on top. You can see from the one picture of a sole cylinder, I piled the carbon to show the amount. I believe the 2 center cylinders dropped carbon from the combustion chamber preventing TDC in each cylinder. Personally I was running out of options and thought I was going to find Jimmy Hoffa in a cylinder
Obviously the engine will need to be bored. There was a sizable vertical scratch in bore #2. So Monday, I will price out a piston set and gasket kit for Mitsubishi. I think I might be out $2K but that's not too bad. So if I'm not mistaken...we were all wrong, but hey it was fun...more to come
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Old 14-08-2011, 06:51   #92
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Re: Engine Diagnosis

At least you'll know you have a good motor when your done with it, still cheaper than a unkown replacement .
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Old 14-08-2011, 08:15   #93
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Re: Engine Diagnosis

If it's re-sleevable, it might be worth going that way rather than boring/re-ringing way over. Also, was the engine salt water cooled? If so, make sure the block has not become porous.
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Old 14-08-2011, 09:06   #94
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Re: Engine Diagnosis

OK, I was close. You beat me taking it apart. Had a last tip for you to avoid taking the head of.
Tip was to undo all main bearings and remove crankshaft with all pistons...

Are you sure you need a new piston. Some careful grinding and re polishing (maybe new rings) might be all it needs. Cylinders and pistons are not rocket science and can stand some abuse.

I can remember we had a valve broken off once (easy to diagnose because of the noise it made). The liner had hundreds of dents in it since the valve bounced around in it for some time (kept the remains of the valve). The head (lucky each cylinder had it s own head) was totalled. The piston also didn't like it (made a nice ashtray out of that) and was torn off at the pin for 270 degrees (just in time to sop the engine). We tidied up the cylinder (we could have replaced the sleeve) with an grinder and sandpaper and put in a new piston and cylinder head. It consumed more oil than normal after a while; after 1000 hours (little over a month) we gave it new rings and that was it. The cylinder looked really good there.

Eric
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Old 14-08-2011, 09:07   #95
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Re: Engine Diagnosis

Okay, of than the pile of carbon on top of piston what else? Are any of the valves seized in their guides? If you have that much carbon in the cylinders your valve stems may have a lot more. Let us know how the valves and valve seats look when you get the head disassembled. It looked like the valves were seated in the head which is a good sign. Possible seized valve guide(s) locking the rotation of the engine.
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Old 14-08-2011, 09:24   #96
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Re: Engine Diagnosis

I see some carbon true but really is enough to cause an engine to stop and cause a thunking? I think the mystery is still deeper in there. I hope not but ...
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Old 14-08-2011, 10:33   #97
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Re: Engine Diagnosis

When you get 'er done be sure to check your prop for the right pitch... dont know why you would have that much carbon unless all the PO ever did was idle the engine.... and yes resleeve it if possible!
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Old 14-08-2011, 10:54   #98
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Re: Engine Diagnosis

Quote:
Originally Posted by Wishinforwind View Post
I see some carbon true but really is enough to cause an engine to stop and cause a thunking? I think the mystery is still deeper in there. I hope not but ...
Interestingly enough, the combustion chamber is very tiny. Essentially a small recess in the center of the piston with the piston is only a few thousands of an inch from the top of the cylinder. So .010" would probably do it. I'm not a motorhead per say, although I seem to be tearing into engines lately. Although I have a machine shop, it is not geared to engine work and i am smart enough (just barely) to let a professional machine and put things back together. I will also insist on a bench test with me there to assure no leaks or problems.
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Old 14-08-2011, 10:58   #99
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Re: Engine Diagnosis

Quote:
Originally Posted by Cheechako View Post
When you get 'er done be sure to check your prop for the right pitch... dont know why you would have that much carbon unless all the PO ever did was idle the engine.... and yes resleeve it if possible!
The previous owner had passed away, so no telling. But I think you are right...idling in the slip for 1/2 hour once a week for a few years.
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Old 14-08-2011, 11:53   #100
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Re: Engine Diagnosis

I doesn't look to me like there's enough carbon to prevent the engine from moving more that 140 degrees. I can agree it might be enough to prevent it from going past TDC, but I would think that it would rotate at least 170 degrees if the problem was that bad in two cylinders and about 340-350 if it was only one cylinder. I'm wondering if it's not something more than the carbon. Is the scratch in Cylinder 2 aligned with the wrist pin? A "thunk" is usually caused by excessive play in something. If there was not excessive play it would have just come to a stop as you turned it by hand. I'm wondering if a wrist pin bushing is worn to the point that when it encountered compression it caused the piston to jam in the cylinder. Removing the head removed any resistance to the movement of the cylinder allowing it to move without the thunk. In any case if you replace the pistons that should solve the problem. I take it that you'll be replacing all the bushings and bearings in the block while you have it apart. I agree with previous posters that resleeving the engine would be better than boring it out if that's an option for you.
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Old 14-08-2011, 13:07   #101
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Re: Engine Diagnosis

Wow! Never thought that'd be it.
Glad you found the culprit and the major mystery is solved.
later,
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Old 14-08-2011, 13:26   #102
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Re: Engine Diagnosis

Quote:
Originally Posted by Captain Bill View Post
I doesn't look to me like there's enough carbon to prevent the engine from moving more that 140 degrees. I can agree it might be enough to prevent it from going past TDC, but I would think that it would rotate at least 170 degrees if the problem was that bad in two cylinders and about 340-350 if it was only one cylinder. I'm wondering if it's not something more than the carbon. Is the scratch in Cylinder 2 aligned with the wrist pin? A "thunk" is usually caused by excessive play in something. If there was not excessive play it would have just come to a stop as you turned it by hand. I'm wondering if a wrist pin bushing is worn to the point that when it encountered compression it caused the piston to jam in the cylinder. Removing the head removed any resistance to the movement of the cylinder allowing it to move without the thunk. In any case if you replace the pistons that should solve the problem. I take it that you'll be replacing all the bushings and bearings in the block while you have it apart. I agree with previous posters that resleeving the engine would be better than boring it out if that's an option for you.
I know its hard to understand unless you can look at it. Remember, as the piston nears TDC the crank has to rotate more degrees for less movement as opposed to when the crank is at a 3 o'clock position
Example: Crank from 4 o'clock to 3 o'clock might move 1". The same would be true 3 o'clock to 2 o'clock. From 2 o'clock to 1 o'clock maybe 1/3" and from 1 o'clock to TDC 1/16". As I stated earlier the Piston is only a few thousands of an inch to the top of the bore with a small channel on top of the piston for a combustion chamber. There was a pile of carbon in each cylinder. I am assuming moisture caused it to swell and dislodge. I have put the head back on and it rotates fine now....proof is in the pudding.
However...what can we all take away from this? Lets here it. I have my answers.
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Old 14-08-2011, 14:06   #103
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Re: Engine Diagnosis

Run your engines at 75% for at least long enough to thoroughly heat up your engine and blow out small amounts of carbon.

Make sure you are not over propped.

Make sure your injectors are serviced regularly.

Make sure your thermostat is working correctly.

Those things (along with your regular maintenance items) should help alleviate carbon build up and make for a healthy engine.

What have I missed?
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Old 14-08-2011, 14:37   #104
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Re: Engine Diagnosis

+1 on the above about running the engine >= 3/4 throttle on a regular basis. I did a lot of research on this before deciding to re-ring my engine (Yanmar 3GM30F) which had only 70 hours on it when I got it. It was getting a lot of blow-by, smoking, and burning about a qt. in an 8 hr motoring day. Previous owners must not have run it up to speed because the rings never set: no ridge at all but badly glazed cylinder walls. Once the walls were cross hatched and re-ringed, now this year she burns no oil, usually starts before the starter knows it's in gear, and purrs right along at 2800 rpm. These little marine/industrial diesels are designed to be run at peak rpm.
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Old 14-08-2011, 16:35   #105
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Re: Engine Diagnosis

I almost hate to add this but I was once told and tried it myself to rid carbon build up was to spray from a spray bottle water into the intake about a spray every 30 seconds for about 4-5 times. Under pressure and heat the Oxygen and Hydrogen separate and cause the loosening of the carbon. The few times I did it I got horrendous amounts of black smoke. Having said that, I am not endorsing anyone else try it...
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