Engine failure, 2300 hours use.

 Whilst on a routine 50km run Medium loading, calm sea, 3200 rpm, I noticed a sudden jump in the engine operating temp from the usual just above 80c to just below 100c.  I initially thought a water blockage and over the next two months whilst continuing to work the boat systematicaly went through both salt and fresh water systems, replacing impellors, thermostats, cleaning heat exchangers, intercoolers, etc.  Below 3200 rpm the engine would run at about 90c all the time but would heat up if ran any faster. The only pump that I had not checked was the engine water pump as removal of timing gear required for this but I had got to the point where I thought this could now be the only problem.

The oil drain from the intercooler began to intermittently dump a lot more oil than usual and I began to think one of the turbo oil seals was effected also.

As this is peak season with bookings every day for the next two months I was hoping to nurse the unit through to the winter layoff for a thorough check.

This was not to be the case.

On a short run the engine suddenly died down to 1000 rpm with clouds of smoke from the exhaust. Opening the engine bay revealed oil pouring out of the air filter, my initial thought that the turbo oil seal was gone but this was soon dispelled when I removed the oil filler cap and was confronted with about 10 p.s.i. back pressure and black oil being sprayed everywhere.

We managed to idle home under our own steam where removal of the engine head revealed pistons 2 and 5 cracked right through.

Possible reasons for failure.

(1) Initial engine overheating due to partially blocked exhaust watermixer. I have found that these need replacing every 2 years if boat left in the water. Internaly the cast iron water jacket rusts and flakes off blocking the water flow. A quick way to check is to squeeze the rubber hose feeding the salt water into the mixer at about 3000 rpm, if the hose is hard and under pressure the mixer is probably blocked. I now have access to S/S water mixers which I can supply.

See Picture.

(2) Piston design, I have recieved at least 50 reports of cracking in the same position on these OEM Yamaha Pistons. It appears as though the piston has been redesigned for the engines 2006 release.

This is no consolation for owners who have found out the hard way.

(3) Fuel quality and injector servicing. It appears that during this time Caltex NZ were obtaining diesel fuel through China, My injectors in some instances were jetting. I now service injectors at 1000 hours.

(4) Other cooling water restictions. The Intermediate housing was found to be corroded where raw water hose passes through. This causes narrowing of hose (See photo). The raw water hose through the intermediate housing at both ends, is a huge source of problems for many people who contact me. Many including myself have sought a separate 'Through hull' solution to the problem. The water which now passes through the leg by way of elaborate hoseing I now pipe into the plastic cover on the upper drive to assist in cooling it.

2nd Rebuild 3450 hours

Near the end of my 2005 summer season I began to notice an increase in exhaust smoke all the time and an increase in running temperature when the engine was again pushed over 3200 RPM, I decided that this was a good opportunity to remove the engine and inspect.

When the head was removed it was found that the inlet valves were carboned up and in one instance the buildup allowed the valve to make contact with the top of the piston. As some of the valves had become distorted it was neccesary to replace them all. Several cracked pistons were again replaced.

Probable reason for carbon buildup, Oil

Since the first rebuild a visit to my Caltex oil merchant suggested that Caltex Delo 400 would be a suitable oil for my engine. Unfortunatly this was wrong. This oil is an extremely good diesel engine oil but not for Japanese diesels which require different additives, sulphur levels etc. The Oil which I should have been running is Caltex CXJ, J stands for Japanese. Now Jan 2008, I have been advised that a better oil for the engine is Caltex Super Tractor.

Main pully balance wheel loose.

Not long after my first rebuild the main pully came loose on several occassions and it took a fair amount of loctite and torque to secure it properly. During this rebuild it was noted that the crankshaft, main pully and timing gear had all been damaged and required replacement as a result of the loose pully. There is  design fault here as only one little woodruff key holds all this together. I now use plenty of locktite and bearing retainer compound on all mating surfaces.

 Do not be tempted to use the main engine pully to drive additional components, pumps, refridgeration what have you, as this pully is not up to it.

Replacements of those damaged parts does not come cheap

 Inspection also found the Fuel pump was not working, however the injector pump was able to draw fuel through the bypass system without any noticable difference. If you do not have a bypass system fitted, you should do so.(See Photo)

TRP Sterndrive

I am the owner of 5 TRP  and 1 single prop sterndrives.

Unfortunatly unless underpropped it appears as though some parts in these drives are not able to handle the torque of the ME420STI engine they are attached to.

Legs usually operate for about 300 -500 hours before they fail.

The impending failure of these legs is usually indicated by stiff gear changing and smelly black oil which is caused by metal particals usually from damaged  bearings and broken oil seal rings becoming trapped in the gear selector valve, if left unchecked some of these particals will  find there way into the oil pressure relief valve eventually jamming it open resulting in no oil pressure and lost drive. The black oil is caused by clutchplate wear and overheating as a result of the above.

The other type of failure is usually more  sudden. And involves the breaking off of pinion gear teeth, usually the top,  this results in sudden lockup and in one instance also resulted in the destruction in the 2 stage rate coupling on the engine by sheering the rubber bobbins.

Post Mortems and analysis of some of my leg failures.

Leg 1, 1500 hrs

Failure of lower case driveshaft uppermost bearing,  Yamaha Part no; 93332-OOOUA

Failure of uppercase pinion bearing set

Failure of inner/outer propshaft bearing, Yamaha Part no; 93332-OOOUB

Fractured tooth lower case driveshaft pinion gear, Yamaha Part no; 6U4-45551-00

The metal fragments from the above parts caused extensive damage to the gear selector valve and jammed the oil pressure relief valve.

Leg 2, 300 hrs

Sudden failure and tooth loss of Gear 2, upper pinion gear, Yamaha Part no; 6U4-4588E-00

Attributed to a 'Momentary impact' with some sort of object.

Failure of lower case driveshaft uppermost bearing,  Yamaha Part no; 93332-OOOUA

Failure of 2 oil seal rings, Broken teeth

The metal fragments from the above parts caused some damage to the gear selector valve and jammed the oil pressure relief valve.

Leg 4, 500 hrs

Failure of lower case upper driveshaft bearing,

Breakage of 2 steel oil seal rings on clutch carrier shaft.

Probable cause

(1) Design, The lower case upper driveshaft bearing is insufficient for the job. I now replace this bearing with SKF equivalent and replace at 150 hours, I have also reduced preload on this bearing (Newsflash) 2006 I hear Yamaha have upgraded this bearing.

(2) Better standard of oil must be used only one specific oil is now recommended for this sterndrive and should be used; Castrol SAF XO 75w.

(3)Steel oil seal rings on clutch carrier wear and small teeth lugs break off. I actually suspect that this may be the cause of subsequent bearing failure.

Intermediate housing

Loose steering arm, replaced both arm and shaft, several of the factory bushes are unobtainable. Basically if main upper bush becomes worn, then seal becomes worn, sea water is able to creep up shaft. Shaft and steering arm are different metals so electrolysis/corrosion sets in between  the two and they begin to wear and move quickly.

2 Stage rate coupling

 I have replaced the main bobbins twice now and have replaced the old damper plate setup with the new solid rubber one.