Burnt Piston 37C

[JHoward]

After last falls massive overheat, from a failed impeller, that caused my dipstick to blow out and evacuate the oil from my engine, which, after a clean up and an oil change, we seemed to recover from and after a lot of initial smoke (which mostly cleared up) ran pretty rough, but it ran, to the crane dock for seasonal haul out.

Now, this spring launch I asked my local Yanmar dealer to look it over. His (the) local certified Yanmar tech, after examining my 3gm motor (which smoked a lot until it really warmed up), said that it had a burnt piston, probably caused by either used to help it start faster. We (he) are now looking for a new piston and/or rebuild kit.
This after determining that the 3 new injectors we DID install for the previous smoking condition caused the smoke to change colors from gray to a more white(ish) shade.

This marina really is a Yanmar dealer.

(Still the same neglected 1980 Hunter Cherubini Cutter that just got the toilet fix.)

Are new pistons difficult to come by or are we really looking at a rebuilt motor? The burnt piston has a small hole in it, which I've seen my own self.

 

[ALNims]

I would suggest that you get estimates for both. I would also ask what the warrantee is for both. Based on your description it is possible that a rebuilt engine maybe cheaper and with a better warrantee than with a repair.

 

[JHoward]

Appreciated.

 

[Jim Legere]

Ether is a diesel's worst enemy. A diesel may be hard to start for many reasons, but if its old and 'burns blue' it may be worn rings and poor compression. An old trick to starting a diesel with poor compression is to put a squirt of motor oil in each cylinder. This can be accomplshed by removeing the air cleaner and using a pump oilcan with a long flex spout. Crank it over - it should start. The oil helps seal the rings and boost compression. Relatively harmless to the engine as long as you use no more than a couple of squirts per cylinder (too much oil could cause a hydraulic lock of the piston).
YMMV

 

[JHoward]

YMMV?

 

[Bill Roosa]

Well the small hole explains lots of stuff, the oil evacuation, engine oil getting into the combustion chamber and making a smoky mess out the exhaust ....
An engine rebuild of this nature will require one of two methods both of which require you to drop the oil pan. if you can't do that with the engine in the boat then you will have to pull it.
If you can get the pan out of the way (all the way out that is) you can disconnect the connecting rod at the crank and, after pulling the cylinder head off pull the piston out that way. Plan on new bearings and sizing them for the connecting rod/crank.
if you have to pull the engine then plan on all new crank and connecting rod bearings for all the cylinders. You can't reuse them with any success once you remove the crank.
If you have never done "bottom end" work on an engine I'd recommend getting some help or letting a pro do it. There are several not so obvious things you HAVE to get right like ring alignment, bearing sizing (with the plastigage stuff), crank bolt torque ....... oil seals installed the right way out.....

 

[JHoward]

Hey Bill - I am probably having my local Yanmar certified tech do the work, especially after he pretty much explained what you just said when he spoke with me yesterday. We have a crane lined up to hoist the engine for the work, etc. He also works in a high visibility location and a lot of knowledgeable boaters use him. Thanks for your comments, it'll help me to keep tabs on the work.

 

[Johnb]

Oy vay, this must be getting to the point where you have made a comparison with the cost of a new engine. Reason I am curious is because I have the original 3QM30 in my '83 HC37 and just wonder what I would do in the same circumstance.

 

[Jim Legere]

YMMV?

Your Mileage May Vary - a sort of disclaimer to indicate that not everyone may agree with your statements and that's OK - no point in picking a fight.

 

[JHoward]

No fight, just a question. Sheesh

 

[Jim Legere]

No fight, just a question. Sheesh

Exactly. YMMV means I am not taking a stand or getting scrappy over what I posted.

Very sorry to hear about the demise of your engine. The sticker shock of the repair will likely get you thinking about the merits of replace versus repair, but if your mechanic is as good as he seems, rebuilding will be fine.

 

[Blaise]

I just had my 3GM30 overhauled. Parts are readily available. I don't understand how it got so hot unless the alarm wasn't working. NEVER use ether to start any engine. Besides burning the pistons, it will also stretch the head bolts. 3GM's are hard to start in the winter. Something that works is removing the air cleaner and blowing hot air from a blow dryer or heat gun directly into the intake.

When you overhaul this little engine, make sure you replace all the external oil lines.

 

[JHoward]

Thanks, the local diesel expert is getting at it this coming week and will tear it down and inspect everything. He is very good. It seems the overheat happened because a impeller failed, don't know which one. The techs at that marina cleaned it up, replaced the impeller and put a lot of Seafoam in the crank case and let it sit like that for the winter. In the spring it was launched with the seafoam still in it and we motored about 30 minutes away to our new marina where we had the oil changed and the motor inspected.
Question: could the Seafoam in the crank case be the culprit of the burnt piston?