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New cylinder head 11/02/03

A week ago, on the 3rd February, the crew drove to Brightlingsea with the old cylinder head and the Jenter credit card to obtain some new parts from French Marine Motors.  We purchased a new cylinder head, the exhaust elbow and a new flexible exhaust pipe.

The head came with new valves and springs but the combustion chambers had to be transferred from the old head, along with an oil pipe, temperature sensor and lifting ring.  We had already obtained, by post, a new head gasket and exhaust manifold gasket.

We were away for a week but then, on the 11th February, Peter started to put things back together again.

The new head gasket was markedly different from the old, in that only two channels for cooling water now exist, the other four having been blocked!  Hurried telephone calls confirmed that this is correct and it represents a change in design by Yanmar.

The head was soon installed and tightened down to the correct torque settings and attention turned to the exhaust.  The flexible exhaust pipe was far from flexible and had to be cut to length with a hacksaw.  The reinforcing helical wire  proved difficult to cut because the flexibility allow it to move but eventually the job was done.  Reaching over and alongside the engine and back to the watertrap was not as difficult as first feared.

Other parts previously removed were re-installed including:  braided fuel pipe from the diesel lift pump to filter; the diesel filter itself; the air filter back plate and air filter itself.  The next job will be to replace the rocker gear, set the valve clearances, fit rocker box housing and decompression lever, fit injector, re-connect high pressure diesel line and return line, fit thermostat and water plumbing, fit generator and re-wire.

Since the London Boat Show, I have spoken to Michael French, of French Marine Motors at Brightlingsea, several times and his advice has been absolutely spot-on each time.  His advice that a partially blocked exhaust would cause grey smoke containing unburnt diesel and a lack of power prompted me to remove the exhaust manifold.  The build-up of carbon in the exhaust port almost blocked the port and would not have been removable in situ.  With some reluctance, the decision was made to remove the cylinder head and this job was tackled on Saturday, 25th January.

The reluctance on my part was understandable for there is very little room to work on the engine and I was also fearful of what I might discover for I knew the difficulties of removing the engine from the boat.  As it happened, the various auxiliary components were removed one after another without any real problem at all.  Even the 'head itself offered only token resistance.

Although the picture looks a little messy, the piston and bore appear to be in quite reasonable condition.  It would have been nice to have had the bore re-honed to remove the glaze but that would have meant removing the engine and stripping it down completely.  Given that the engine starts readily, I think it will be good enough for another couple of years.

Removal of the carbon from the piston and general cleaning of the surface of the block required no more than a light brushing with a wire brush.  The water channels were generally clear and I have temporarily covered the top of the block with polythene to keep out any moisture.

There is now more room for me to reach over the engine and get to some less accessible parts.  The exhaust elbow and pipe back to the water trap have been removed as well.  I will replace a braided flexible diesel pipe between the lift pump and the filter that may be leaking.  I also hope to clean oil, diesel and dirt from the outside of the engine before re-assembly.

The exhaust elbow is virtually blocked with carbon and it is difficult to see how the cooling water was ever able to enter via the side tube.  I am advised that this part of the exhaust can corrode easily.  The high temperatures and sea water probably have something to do with it!  Unfortunately, it costs something over £100 but will have to be replaced.  The flexible hose back to the water trap will also be replaced.

The exhaust port of the 'head after some effort had been made to clean it up!  Initially it would have been impossible to get a pencil through the opening.  The head is really in a very poor state.  Slithers of metal came away as we were cleaning and much of the metal has 'wasted' away.  A straight edge across the flange shows about 1mm missing in places.  The face could be machined but inside the port itself the metal surface is in a real mess.

After a further telephone call to French Marine, I have ordered a new head costing £270.  Some parts from the old head will need to be transferred to the new but not the valves, surprisingly enough.

I have decided to drive to Brightlingsea this coming Friday and hope to return with all the goodies necessary to rebuild the engine.  It will be a considerable relief to put this problem behind us, since it has been causing us grief for the best part of a year now.

I hope to be able to post a picture of a newly re-built engine and to be able to tell you how it starts and runs...

Speed log 25/01/03

Jenter is fitted with the Autohelm ST50 series of sailing instruments.  Autohelm are now part of Raymarine and their current range of equipment can be seen on www.raymarine.com.

The instrument head gets information from a 'paddle wheel' transducer mounted just to the port side of the keel.  It gives the speed of the boat through the water and from this calculates the number of miles travelled.  As the paddle wheel rotates, magnets enclosed in the spokes pass a coil and the change in flux linkage produces a measurable voltage.  The faster the boat, the higher the voltage.

According to the Raymarine man at the London Boat Show, our problem is almost certainly due to losing one, or more, of the little magnets from the paddle wheel.

Throughout 2002 we have experienced ever increasing amounts of exhaust smoke and, most recently, engine overheating as well.

Early enquiries to the importers, E.P. Barrus Limited, resulted in them suggesting we check carefully the colour of the smoke.  Was it black, blue or white?  Well, it was black off of Beachy Head when we used full power to escape from a fisherman's buoy that we had fouled.  But then, sometimes in the twilight, it appeared tinged with blue.  Most of the time, though, it was just plain white.  Maybe then it wasn't smoke, but steam!

Our final sail of the season from Lymington to Eastbourne, documented elsewhere in these pages, proved difficult because we could use the engine for no more than 10 minutes at a time without it overheating.

Blocked pipes and channel into cylinder cooling jacket

Leaving the pink paint behind the water comes up to a 'T' piece and either enters the cylinder cooling jacket or continues up the pipe shown, or both, or neither when the pipes are blocked!

Michael French, of French Marine Motors, was on the Yanmar stand at the London Boat Show and he suggested that this might be the case.  He also told us that the engine had a thermostat but it was not mentioned once in a 34 page Operating Manual!  He was correct.  Both the pre-formed pipe from the water pump and the bypass pipe and the 'T' connector were all blocked with what looked like limescale.  The thermostat was also wedged in the open position and faulty.

The water flow through the system is now much improved and the overheating problem cured.
 

The thermostat housing

The picture shows the thermostat housing, on the cylinder head, at the top of the bypass pipe.  When the thermostat is closed water goes straight up the bypass pipe and on to the exhaust and when it is open the water goes through the cooling jacket and the bypass pipe is closed off.

To access the various pipes and thermostat, I had to disconnect and remove the alternator and also the high pressure pipe from the distributor pump to the injector, seen in this view.

The final result, then.  The flow of water is much improved and the engine no longer overheats, but, we still have smoke.  It is dirty white in colour and there is unburnt diesel even when the engine has been warmed up.  Back on the 'phone to Michael French, he suggests that the exhaust manifold could well be obstructed.  When I told him that the engine was also down on power and slow to accelerate, he said that the obstructed exhaust would also give these symptoms.

We will let you know what we discover...