Yanmar 2QM1. Head gasket leaking

[O32]

Originally Posted by Perna

Looking at the last picture of the head, the problem doesn't seem to be so much a bad gasket as the fact that there is a misalignment with the cast coolant hole in the head. That together with a bit of corrosion,

The original problem was very clear once I removed head. The fire ring delaminated and had leaked combustion gases. These found their way out in the exact area that we see the erosion of the head. No doubt vaporizing water along the way. No kind of sealant would have helped. 518 Loctite is only good for service at 150C. The copper spray-a-gasket is good up to 260C and is recommended for cylinder heads. I now have some, but waiting on machine shop to get back to me once they have had a closer look before taking next step.

To me, key is to get as perfect a sealing surface as possible all over the head, but in particular on the fire rings. I believe the cylinder liners are flush with the block. They would have to be for the gasket to work.

[O32]

Originally Posted by Perna

Don't know about the rust/paint. As for the mixing elbow if the original worked and it is made from pipe fittings can you not just take it to a plumber or remake it yourself?

My plumbing contractor friend made up a new exhaust for me using malleable iron fittings. He had more fire power than I do and said pipe came out of flange once he used enough heat/leverage.

Anyway, one less job for me!

[Wotname]

Originally Posted by O32

......

To me, key is to get as perfect a sealing surface as possible all over the head, but in particular on the fire rings.

Yes to having a good seal on the fire rings.

I believe the cylinder liners are flush with the block.

Maybe to the liners being flush but unlikely.

They would have to be for the gasket to work.

No, this is incorrect.

Liners are more often proud of the block deck, this ensures a better fire ring seal and saves having to take additional measures to ensure a good liner to block seal. The crush in the head gasket provides a proper seal for the water galleries etc providing the liner protrusion is within the specs.

[Perna]

Originally Posted by O32

In looking at the block today, I noticed that the pistons come all the way up flush with top of cylinder liners. What this indicates to me, is that the total combustion chamber volume is made up of pre-combustion chamber+cylinder head depression + volume at TDC between the top of the piston and the underside of the head. That last volume is determined by the thickness of the gasket which is ~1mm (measured off old compressed gasket).

Taking a skim of the cylinder head hardly changes combustion chamber volume. It does bring the valves slightly closer to the piston head. I talked to shop about that. They said that if it is a concern, the just move the valve seats higher.

Firstly, glad you could get the mixing elbow made up.

Secondly, if a fire ring failed and allowed the passage of combustion gasses, these would pass straight out around the multi-layer-steel (MLS) gasket and would be unlikely to result in the water leak. There is also no sign on the head of the combustion leak, although you have cleaned it! Was the water leak evident on the side of the engine coming from that slightly offset/ corroded water passage? I mean do you think the leak came from that water passage? If so probably you are better to reassemble with a good sealant etc.


Skimming the head and "just" sinking the valve seats is not particularly minor work for me. You have to re-cut and grind the valve seats for one thing and it will probably not improve the water hole sealing.

What do you think?

[a64pilot]

Before I had the head surfaced, I’d see how hard and how much a new one cost. I’ve seen several heads ruined by too much taken off.
If you proceed with having it surfaced, be sure to find out how much is allowed to be removed, and have it in writing on the work order to not remove over the allowed amount.

[O32]

Originally Posted by Perna

Firstly, glad you could get the mixing elbow made up.

Secondly, if a fire ring failed and allowed the passage of combustion gasses, these would pass straight out around the multi-layer-steel (MLS) gasket and would be unlikely to result in the water leak. There is also no sign on the head of the combustion leak, although you have cleaned it! Was the water leak evident on the side of the engine coming from that slightly offset/ corroded water passage? I mean do you think the leak came from that water passage? If so probably you are better to reassemble with a good sealant etc.

Skimming the head and "just" sinking the valve seats is not particularly minor work for me. You have to re-cut and grind the valve seats for one thing and it will probably not improve the water hole sealing.

What do you think?

Pictures don't tell a lot, but if you are interested, I could post pics of the block and the top and bottom of the old gasket that show where the problem was. The fire ring failed first and then it seems destroyed the water seals and the gasket! Right now, I am more interested in moving on to next step than re-analyzing failure!

I discussed skimming the block with the guy that was Yanmar's technical rep in Canada in the heyday of Canada's sailboat industry. I had dealings with him from when I had my first one-lunger back in mid 70s. He is retired now, but still very helpful. His recommendation was to skim the block to remove all imperfections. He knew of no number for max skim. Only that head should not be out of flat by more than about 3 thou.

I visited the shop again and spoke to owner this time. He measured head surface to valve clearance. It was in in 50-95 thou range. Exhaust valves have no doubt been lapped before. He said they would remove valves, take a minimum cut off head (~3 thou) and see if that was all it needed. Take more if need be. Then grind or lap valves to get back to at least spec clearance ( approx 50 thou).

I have attached specs that apply to all QM models

By the way, the head work will be in the $150 range. Not that bad for some peace of mind. But lets see what it looks like once done!

[O32]

They don't give us long to edit posts! I said skim block when I meant skim head.

Well, seeing I am here, here are some pics of new exhaust.

[Wotname]

^^ exhaust is looking good
Question - what is the water injection arrangement?
Does the tube / nipple / barb extend into the pipe? If so, how far and at what angle?
Any internal collar at this point?

[Wotname]

While I'm in the question asking mode - what does the manual say about liner height above the block deck?

Asking for my own future reference!

[O32]

Originally Posted by Wotname

^^ exhaust is looking good
Question - what is the water injection arrangement?
Does the tube / nipple / barb extend into the pipe? If so, how far and at what angle?
Any internal collar at this point?

The old exhaust injection nipple was flush on inside. The new one just projects though a 1/2" at most. Exhaust has already passed through a water jacketed manifold, so isn't that hot. Might not mix that great, but the muffler is metal, so by time gases get there they are cooled.

By the way, the original Yanmar mixing elbow had quite a restriction. I have a pic here, but not sure I can post it (sent to me by DMI)

[O32]

Originally Posted by Wotname

While I'm in the question asking mode - what does the manual say about liner height above the block deck?

Asking for my own future reference!

If you mean the height of the cylinder sleeve above the block deck, it is in the pdf I attached in earlier post - last item under cylinder block. approx 1 to 3 thou.

[Wotname]

Originally Posted by O32

If you mean the height of the cylinder sleeve above the block deck, it is in the pdf I attached in earlier post - last item under cylinder block. approx 1 to 3 thou.

Thanks, I missed it the first time - my bad; off to get new glasses now...

[Wotname]

Originally Posted by O32

The old exhaust injection nipple was flush on inside. The new one just projects though a 1/2" at most. Exhaust has already passed through a water jacketed manifold, so isn't that hot. Might not mix that great, but the muffler is metal, so by time gases get there they are cooled.

By the way, the original Yanmar mixing elbow had quite a restriction. I have a pic here, but not sure I can post it (sent to me by DMI)

[Perna]

Hi,

Nice job on the exhaust!

I agree the problem is not to re-analyse the failure, just to understand it.

When it comes to reassembly you could place the new gasket on the clean head and make sure that the suspect water channel will lie within the gasket sealing bead for that hole. That is the over-riding requirement for sealing the water. If it is marginal then it will need extra sealant.

Best of luck

[O32]

For anyone who does not have it, this is a link to the Yanmar 2QM15 Service Manual. Just saw this on-line:

http://j30.us/files/2qm15_servicemanual.pdf

I already have paper & file versions, but this is a convenient place to download from for those who don't.