Thursday, 3 May 2012

Servicing the Yanmar GM10 marine diesel engine

Not to run an engine will be bad for it, not to service it will be even worse!  Running the engine allows the oil to heat up and rid itself of any moisture that may have collected in the cranckcase, the same with the motor in general, a hot engine cleans itself of many of the problems that can cause sludge and rust inside an engine. Run your engine under load, not just on tick over or a fast idle, that will do little good for the engine and its liable to start using oil, blue smoke from the exhaust may be the first warning?

You should see this amount of raw cooling water escape from the exhaust pipe, it will wax and wane some. Note the lack of blue smoke, the engine is running at around 3000 rpm and is powering a 220 volt generator, the load on it is around 16 amps 220v and 20amps 12 v, enough to see that the load makes the engine work well.

Note: spots of black oil on the water as the exhaust exits can just be the black foam air strainer in the air box breaking down. the result is it is then going into the engine combustion chamber and then part burning, when it hit's the water outside it looks just like oil!

With an assumption that both the pump and injector is in good condition, what else is there to do after changing the oil and oil filter? Well even to do the oil change your in with a bit of a problem, most boat engines have their oil sumps so low that the oil drain plug can not be accessed? In this case we need a suction pump, the ones with the solid brass bodies seem to leak less than the plastic ones? Heat the engine right up by running it, then using the suction tube, it will reach the oil sump through the plastic oil filler screw on cap, remove the hot oil. Beware its messy stuff and the use of rubber gloves may be a good idea? You will need an empty container to take the old oil away in, dispose of that and the old filter in a responsable manner please.

Next remove the filter, the new one should be inspected to see it matches the one that came off it, is the canister the same diameter, does the thread hole match? then smear clean oil onto the rubber O ring seal, it will be flat, fit the new filter so that it is hand tight, there is no need for more than that if you ever want to remove it again.

Read the link for some inforamtion on filters.;postID=4108350423016376000

 The oil filter is the grey canister seen low down and on the left side of the picture.

 There is also a tiny thermostadt, thats to be found where that yellowing braided clear hose is. Remove the fitting, its bronze and check that the thermostadt is clean with no silt or salt stopping it from working. Test it by lowering it into some hot water from a kettle.

Oil? not all oils are the same, simply put, a standard engine oil will probably have a life of 50 hours or one year before it has to be changed, which ever is the sooner, check the owners User Manual. Check also to see if it gives the optional running time with Diesel Grade oils, it will probably say 100 hours or one year, which ever is the sooner. Yes thats double the hours you can run the engine, so assuming we use the engine enough in a year, its a simple cost  and labour saving job to buy the better oil each time.

See below on a blog I did on oils some while back.

All companies will have a name for this grade of engine diesel oil, Shell calls theirs Rotella, thats a fine oil. Castrol call theirs GTX Diesel, which is simple enough to remember.

Valvoline imported diesel oil, you can see what we paid here around one year ago, plus the tax!
Setting the engine Tappets is quite easy on this motor, as the engine has both a decompression lever and a hand start handle, so by using both we can turn the engine over untill the valve in question is closed and the tappet gap can be set to the manufacturers setting, which my manual states as 0.20mm . This is important, that gap affects the engines timing, plus if its too tight we can maybe burn a valve, too loose and we have a very noisy engine. The cork gasket under the tappet cover should be reusable, try a little clear silicone if you feel the need, wipe any excess off with a clean cloth so things stay neat and clean.

The tappets can be found under the silver dome cover on the top of the engine.

The engine has a small anode on the side of the block and on the alternator side, its is held captive on a small plate with two M10 bolts, that anode protects the cast iron block, they are not expensive, get a new paper gasket when you buy one, try the clear silicone again, its cheap, cleans up easiliy and works well. Turn off the sea water supply before you remove the anode plate!

This is the correct Yanmar anode part number, the small stainless parts are what an anode was connected to, in this case the zinc has vanished!

This is what the Yanmar 1GM10 looks like when new, best to replace it when its half gone, as they will last a shorter time from then on.

The owners manual says the anode must be changed every 500 hours, thats assuming we run the engine a lot I assume? The anode above has done about 135 hours and was last fitted 28 months back, as we can see its finished, so  I think it needs changing every 15 to 18 months?

The parts ready to refit, note the black rubber washer, that is the seal to the raw sea water, apply jointing paste. I used clear silicone, then make it into a good joint by screwing into the stainless mount plate, its threaded. Do not over tighten, as the rubber will deform, once the rubber is making a decent seal, lock the stub thread off on the outside of the mount plate with the lock nut. In this case I made my own cork mount gasket with an offcut of thin gasket cork, I had used the correct Flexoid paper gasket in the past.

The anode and mount plate back where it belongs, I have sprayed the area with Fluid Film to prevent surface rust, click on any picture for a larger view. Later I will wash off the engine with water soluable degreasing fluid, then apply two coats of Hammerite smooth silver rust convertor paint.

Note, the space here to emove the two 10mm bolts holding the mount plate is very tight, some recomend you remove the starter motor and I agree!  You will need a short 10mm ring spanner here, an open ended one can be used but its very difficult to work with.

The fan belt to the Alternator is really good on this motor as the belt really does wrap itself around the alloy pully and I have noticed no wear worth its mention, check it anyway, not too tight and not too loose.

The fan belt tension is given as 10mm play either way when you push it with one finger, if you make it too tight, its possible a bearing can go in the Alternator.

The cooling system is run from a lower sea water pump, its driven off the inside of the engine, at least once a year the rubber impellor needs an inspection, keep a spare on the boat just in case yours breaks. To remove the impellor on its own is asking for tears, the screws or bolts holding the inspection plate are behind ( unbelievable) the lower main crank pully, who thought of that bright idea?

I find the easy way is to remove the entire water pump as one unit, then on a bench or table we can inspect the pump more closely, check to see is salt has built up under the lower end of the rubber impellor? This can happen due to a lack of use, another very good reason for running the engine more often. Your hoping to find the rubber impellor all in one piece, re using a faulty one just makes no sense given the work involved, you may need a new paper gasket and again the use of clear silicone works well in this application.

WARNING: Do not turn the motor over or move the pumps impellor shaft while you have the water pump off the motor, there may be a problem in relocating the drive peg when you refit it. I have done this job many times and have never had any problems.

Check all the hose and fuel line clamps, look for tell tale leaks, the exhaust header may have started to corrode, they are not easy to re weld, so if that is the case buy a new one.

Finally, wash the engine down with water soluable cleaner, then rinse with fresh water, next clean the bilge!

How hard can this be?