Possible leaking Cylinder Head Gasket

[SEADANCE]

Hi guys...need some help with this one

This season we noticed another loss of power in our engine a Yanmar 2QM15,
about One knot of power.Mixing elbow was replaced last spring, and fresh fuel and filters just replaced.

While working on the engine we noticed a small leak of oil and a place where air or exhaust was escaping from the back of the engine. We think that it could be the cylinder head gasket.

The Engine is working fine and we do not want to miss out on our sailing season..
My two questions are:
1. Is it possible that this is causing the loss in power
and
2.could this cause damage to the engine running it in this condition?
The amount of oil is very minimal and not noticeable when the level is checked.

 

[RichH]

With exhaust coming out the of head.... 99% a blown head gasket.
At what location do you feel the air/exhaust? The exhaust manifold on a QM doesnt use gaskets and is sometimes subject to coming loose ... and if you feel such 'gases' on the starboard side of the engine near the valve cover, it may simply be a loosened exhaust manifold. You usually see 'soot streaks' on the engine surface near the manifold indicating that the manifold has started to come loose. Check the bolting of the exh. manifold.

What your really have to watch for (until and if you replace the head gasket) is for water leaks that 'communicate' into the cylinders. If you want to risk running the engine with a possible blown head gasket:
1. re-torque the head - it may 'lessen' the 'leak' and will help prevent the head from warping !!!!!
2. Religiously watch the quality and quantity of water in the fresh water side. If the water level is dropping, you may be sucking water from FW side into one or more of the cylinders ... usually this will happen AFTER you shut down the engine, so inspect the water level BEFORE starting the engine. Be watchful for the Fresh Water to become 'blackish' or 'murky' as a result of soot (from exhaust gases) being forced through breached gasket.

When a head gasket blows its usually a symptom that the head is beginning to change shape (warping) and/or some of the head bolts are elongating. Best is to replace the gasket as soon as possible.
To prevent a blown head gasket, the headbolts, etc. should be lubricated and re-torqued every few years.

 

[Joseph Shirley]

I agree with Rich completely but feel you should replace your Gasket immediately. If you wait you will most likely warp the head and have to get it ground flat as part of the process. If you do it right away you may be able to get away with only changing the gasket. If you don't change it right away install a CO detector. Carbon monoxide is truly a silent killer.

Sail safe

Joe S

 

[seadaddler]

Agree

I agree if the head gasket has developed a leak it will do more damage using it so it's better to repair now when it could cost a lot less to repair.
Check all already mention like said just might need some miner repair,how many cylinders is it,if two you could start it and release one at a time compression release valve one at a time and see if it will run with one cylinder at a time to narrow down where or which cylinder is leaking causing the problem.
Nick

 

[Bob J.]

I'd also keep an eye on my oil level. If it seems to be unusually full, stop using the engine.

Bob

 

[Hermit Scott]

Does the engine have to be pulled to replace the head gasket? If not this could be done in a day. I wouldn't run that thing another minute with a partially leaking head gasket. There could be a sudden breach in the gasket and dump water into your oil.
What rich said could be possible with the exaust leak. At least do a compression check to assess what's going on. On my engine, a compression test or replacing the head gasket would probably take about the same amount of time. But mine's very accessable and a simple enigne anyway. But I know how it can be, if you replace the head gasket you might as well go through the head and get a valve job etc etc.
I wouldn't run it until I knew what was going on.

 

[kloudie1]

It would be good to get a mechanic familiar with this engine to look it over.. This is a raw water cooled engine so there is no header tank or places where you could see gasses evolving if there were a head gasket leak.. If you have and can feel gas moving out of the engine, it probably is an exhaust manifold or manifold-to-elbow leak.. but, an honest mechanic, familiar with the engine, could probably tell you really quickly what it is .The stuff that looks like oil could be soot and a little water from the manifold. If the head has a crack big enough for you to feel gas coming out, it would not fire on that cylinder because the compression would be too low.. In any case, it is best to have it looked at now.

 

[SEADANCE]

Thank you for all the input. As always, the excellent advice here helps us make the right decision and a new gasket arrived yesterday. We will be going today to begin dismanteling. The Shop manual we have for the engine describes total disassembly however, we would like to take as little as possible off to get to the problem. We know we have to remove the exhaust valve and mixing elbow, high pressure fuel lines, and valve cover. Is it possible to replace that gasket without removing the injectors, push rods, and rocker valves by leaving them attached to the head?
thank you for all the help

 

[Rick Webb]

While the Head is Off

I am no diesel mechanic but was half a motorhead before I bought a boat. It seems to me you should at least lap the valves and have a machine shop check it for being warped.

As far as the rockers and push rods go the push rods are going to come out and the rocker arms are going to have to be loosened to torque the head. It probably mentions it in your manual but make sure you put the push rods back in the same place they came out. they are typically all the same but it is easier to keep them straight than to try and figure it out afterward. A piece of carboard labled with which is which then stick a screwdriver in to punch a hole and insert the push rod. Works well with valves too.