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Old 26-11-2011, 16:12   #1
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Another 2GM20F Question

I am still looking for a Yanmar 2GM20F to repower my trusty Atomic 4. I posted on another thread a near new raw water cooled Yanmar 2GM20 that I am looking at. I want to have another one to look at for comparison purpose and found a fresh water cooled one that is in a pretty good condition but with a few issues that I will detail below:

1. The head gasket is blown. The owner resurfaced the head and did a valve job in addition to replacing the gasket. The surface around the valves are slightly pitted.

2. The top of the cylinders have some sticky carbon build-up (approximately 3/8" wide rim around the top of the cylinder). The very top of the cylinders are slightly pitted. Probably the result of the blown gasket.

3. The old injectors are worn. The owner is putting in a pair of new injectors.

4. The engine mounts are old and tired. The owner will replace those with newer (not brand new) R&D mounts.

The engine was not running when I saw it but the owner said that he will put everything together. My main concern are the pits around the valves and at the top of the cylinder. Are these acceptable flaws in diesel engines?

Thanks very much for your insights.
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Old 26-11-2011, 17:06   #2
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Re: Another 2GM20F question

I would have to see the pits as you describe them.

The carbon buildup aroung the top of the cylinders is not a major concern....you will see that on any engine.

Where are you located?
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Old 26-11-2011, 18:04   #3
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Re: Another 2GM20F question

Thanks Chief Engineer!

I am kicking myself for not bring a camera with me this morning. The pitting in the valve area are very minor and very shallow. The pittings around the top of the cylinder wall are limited to the very tip of the cylinder wall and are even less severe than the pitting in the head around the valves. I found another picture from this Forum that shows the pitting on the head of a Volvo that the owner rebuilt. Compared with is picture I would say that the pitting on the Yanmar is nothing.



I also read from a Ford diesel truck forum that said that as long as the pitting is above the piston rings's top most travel range they should not impact engine performance. I looked at the Yanmar pistons and suspect that the reason that the carbon build up on the cylinder walls are limited to the top 3/8" is because that is above the piston rings' travel range. I think that makes sense but want to see if others agree with that view.
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Old 26-11-2011, 19:20   #4
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Re: Another 2GM20F question

Why are you looking at junk engines ?
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Old 26-11-2011, 19:31   #5
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Re: Another 2GM20F question

That picture looks familiar. Did the owner of that engine previously post that picture on the forum? Perhaps you could ask the seller of the engine and find out what thread he posted on (if he did so).

You need to be very, very careful when buying a used engine.
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Old 27-11-2011, 18:10   #6
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Re: Another 2GM20F Question

DeepFrz, the owner of the engine has not posted on this forum before. The engine just came of another boat because of the blown head gasket. I will see if I can get the owner to take a couple of pictures.
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Old 30-11-2011, 19:45   #7
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Re: Another 2GM20F Question

Well, as it turned out I missed the opportunity to get the pictures of the pitting around the valve and the cylinder top. The owner wrote back to me -

Quote:
I have assembled the motor, so we are a little late on the photo op. I did a little research with regards to cylinder condition, my concern was with some of the discoloration. After consulting my machine shop, they said not to worry if you can’t feel any roughness. I cleaned the bores with solvent, and inspected for scoring. I think the motor quite serviceable with the restored head, and price point. Once the bottom is opened you will replace bearings pistons, and rings and re bore. We then get close to the crossover for a new motor.
As stated before I am not too concerned with the pitting. However, I have not noticed nor heard the discoloration that the owner mentioned in the mail. Does anyone know what he maybe referring to and is it something to be concerned?
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Old 30-11-2011, 20:04   #8
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Quote:
Originally Posted by Triton106
I am still looking for a Yanmar 2GM20F to repower my trusty Atomic 4. I posted on another thread a near new raw water cooled Yanmar 2GM20 Buying Used Yanmar 2GM20 that I am looking at. I want to have another one to look at for comparison purpose and found a fresh water cooled one that is in a pretty good condition but with a few issues that I will detail below:

1. The head gasket is blown. The owner resurfaced the head and did a valve job in addition to replacing the gasket. The surface around the valves are slightly pitted.

2. The top of the cylinders have some sticky carbon build-up (approximately 3/8" wide rim around the top of the cylinder). The very top of the cylinders are slightly pitted. Probably the result of the blown gasket.

3. The old injectors are worn. The owner is putting in a pair of new injectors.

4. The engine mounts are old and tired. The owner will replace those with newer (not brand new) R&D mounts.

The engine was not running when I saw it but the owner said that he will put everything together. My main concern are the pits around the valves and at the top of the cylinder. Are these acceptable flaws in diesel engines?

Thanks very much for your insights.
Just 2 cents here... The pitting at top of cylinder is not a result of blown head gasket but could be a cause of it. Unless you are talking about pitting on the block deck, which would be a mirror of the pitting in the picture of the head you posted. As you know the head seals against the block deck. Overhauling the head is good especially if all the pitting is milled away. This reduces deck height slightly and may increase compression and at extremes reduce valve/piston clearance unacceptably. Any increased compression is going to put increased stresses on piston rings, piston domes and crank bearings.

In this case what was the condition of the block deck and was it milled? Putting a nice new overhauled head against a crappy block may be throwing good oney after bad. Especially as you indicate that the engine mounts and injectors are old and tired - i.e. How old is this engine since last bottom end overhaul?

If I were trying to get my engine to go another couple of seasons I would consider a top end overhaul. But if I were going to do the job right, especially if I am repowering from something else (your atomic 4) I would be looking for a complete rebuild.

Repowering is expensive and not something I would like to cheap out on. I missed your other thread so what's wrong with rebuilding the A4?
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Old 30-11-2011, 23:13   #9
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Re: Another 2GM20F Question

Thanks Dan for your comments. BTW, your boat name is pretty funny for people who have been to Singapore. Seems like every sentence in Singapore ends with Lah... I digress there.

Let me clarify the picture in my previous post is not from mine engine but someone else's picture I used to illustrate the location of pitting near the valve (I did not bring my camera on the day I checked out the engine.) The pitting on the cylinder wall are not on the block deck. However, the pitting around the tip of the cylinder wall does surround the pitting in the head (around the valve). In both locations the pitting problem on the engine I am checking out is far better than the picture.

The owner resurfaced the head and did a valve job. I am not sure how much material was taken off the head. Hopefully not enough to cause excessive compression. The owner did not resurface the block deck. It appears to be in very good condition when I inspected it visually. I don't know the year of the engine but it appears to be in very good condition. I think the Yanmar 2GM20F were manufactured in mid 1990's.

The owner did suggest a bottom end overhaul. I will decide on my next step after I make my decision to buy it (or not).

My Atomic 4 is in a very good condition. I have always babied it. Previous maintenance and upgrade work include -

1. Valve job (including new springs)
2. Resurfaced the head
3. New head gasket
4. Rebuilt mechanical fuel pump
5. Rebuilt carburetor (2 times)
6. Changed oil every year
7. Acid flushed it every 3~5 years
8. Electronic ignition
9. New alternator
10. New spark plugs and wires every 2 years
11. New primary and secondary fuel filter and filter element every two years
12. New distributor cap every 3 years
13. New coil
14. New water pump impeller every 2 years
15. New water temperature sender
16. New water lift muffler

I am considering repowering because I am planning to do some coastal cruising in the not too distant future. I also recently added a propane stove. Having two different types of volatile fuel on my small Pearson Triton makes it a little uncomfortable for me.
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Old 01-12-2011, 02:11   #10
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Re: Another 2GM20F Question

I figured it was for the fuel concern.

Take my comments with plenty of salt but if it were me, whatever repowered engine I put in would be fully overhauled. If the price point on this engine with a top overhaul makes sense considering another teardown to finish the job right (bottom end + accessories) then I'd consider it.

Minor cylinder pitting and discoloration would not worry me as these would be taken care of when I finished the overhaul.
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Old 02-12-2011, 22:54   #11
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Re: Another 2GM20F Question

Thanks Dan, I appreciate your comments. The owner actually suggested an overhaul on another 2GM20F that came off his own boat. But that engine was sold before I got there. This "new" 2GM20F in question is in much better shape than his own. So he has not done an bottom end overhaul. I think I will make that decision after I have a chance to see how well it runs first.
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