1.7 failure insight

[Arlon]

I've spent some time on the phone with several cummins techs and gotten some interesting feedback from folks on the baotdiesel forum. This is what I have learned so far. Basically, throw the mercruiser manual away. I was told the manual was being revised. Cummins techs told me to prop the engine to run 4600-4800 wot with a max load then never run it there again. Biggest problem for this engine is to over prop (over stress) it.

My boat came with a 15x19" pitch prop that will just pull 4100rpm. That's just fine according to the manual where it states the engine should turn 4000-4400rpm WOT. Where the problem comes in is that the engines rated "high idle" (zero load on the engine) is 5000rpm +-50. Mercruiser manual has us proping the engine to turn 80-90% of it's rated rpm. Cummins says that's too low and can seriously over stress the engine. I went to a 17" prop that now turns 4400 with a decent load. That is still on the ragged edge according to cummins and they recommended having it repitched to 15 or 16". They really want me to see at least 4600 rpm and preferably 4800.

Where the real problem comes in is when we are running an over stressed (over propped) engine that has to bleed off some boost and then has a sticky wastegate. Engine over boosts and breaks. Having the engine propped to turn 4600-4800 then never exceeding 4400 will keep the engine from reaching the overboost condition in the first place and should really never see the wastegate open. Pay close attention to the wastegate hinge pin. If it rusts and sticks you may blow an engine. Just about every engine failure I've been able to track down has been directly related to a failure of the wastegate to function properly. Best solution is to keep boost (stress level to the engine) down to the point where it doesn't even try to open the wastegate. I have not found this part (wastegate) on my engine yet but plan to do some looking SOON. Second is to get a boost/egt gauge and watch it closely when under a heavy load. Boost/egt are the blood pressure and pulse rate of a diesel engine. We keep those under control and we're less likely to give the engine a heart attack. Best gauge would have an alarm for over boost.

Problem is apparently worse for lighter boats like RIBS who may have propped the boat for speed empty then add a load of people and dive gear that may add 50% to the load in the boat. The large % change in load possible in smaller craft is definately something to consider when selecting a prop. Best solution is to have at least two props. One for speed when you are running a light load and one with a lot less pitch for those days you load it down to the gunnels!

This is all just my opinion/observations and I'm not recommending anyone do anything different than the manual suggests. I am just passing on what I have been told. I do suggesting you contact cummins by phone or email at wave.master@Cummins.com for their recommendations. If you own one of these engines I strongly recommend you contact a cummins tech who has a clue about these engines. Be sure to get his name and number or better yet get an email reply for reference in case anything goes wrong. Beware of Cummins too, they have very few techs with any REAL experience with these engines.

Hopefully I can relate some meaningful numbers as soon as I get the gauges installed and try some different props. Arlon

[Dave B]

I have the 1.7 Mercruiser in a 6.5 Mt rib

And it has just failed due to a known fault on the heat exchanger. Also I have had to replace the starter motor due to a small amount of water in the bilge, show me a diesel that does not have some water in the bilge. This is also a known problem.

My Engine failed in a heavy sea that resulted in the rib taking a large wave over it and filling the rib up to the top of the tubes, the only saving grace was that the engine kept on running but only at 1400 rpm, enough for us to hold head up and await the lifeboat.

The heat exchanger has allowed water into the engine and blown all the seals allowing the engine to dump it now emulsified oil in to the bilge.

I hope that Cummings are going to try to clear up the faults that they know about, If the engine had stopped we would have been dumped in to the sea and the rib lost. If the new engine fails at the same age then the warranty will have run out or will Cummings honour a new two year warranty and recall the units as a permanent remedy becomes available, or just say hard luck, remains to be seen. May be a Cummings tech could post here to explain how the new owners of Mercruiser are going to sort the problems?

Could any 1.7 Mercruiser owners with problems post here so we can all benefit from our hard luck and experiences?

Dave B

[jwalker]

Originally Posted by Dave B

...show me a diesel that does not have some water in the bilge. ...

[Arlon]

Can you elaborate on how or where the water entered the heat exchanger? I can see it being sucked into the intake but not sure I understand how it gets into the heat exchanger? I also had a cummins tech tell me their number one failure on the 1.7 was the starteer. Apparently it gets salt water into it rather easily from the bilge and corrodes from the inside out with nothing you can really do to stop the problem.. They suggested a good spraying with things like corrosionX, etc. Thanks, Arlon.

[keelhauled]

The problem with starters mounted too low on inboard engines comes from the fact that these engines probably have another function e.g in an industrial machine/ generator, in a car or in an agricultural machine and the position of the starter is not as serious as in the bilge of a boat. In a previous boat I had I went to the extreme of buying a spare starter and getting my local butcher to vacumn pack it and kept it on board. I also changed all the starter connections to good quality push fit connections and removed the nut that was difficult to get at. Essentially the starter was held on by two bolts(not a problem) and if i was leaving the boat for a week unattended 5 minutes and I would whip it off. This was the bane of my life before I done the above as invariably the starter decided to pack up every time salt water got near it. Also during the winter hang up your cleaned and degreased starter and spray 5 coats of lacquer to inhibit rust.
Regards
Mick