Diesel workings...

[Allure2sail]

Did a compression check Sunday on the M12 in my 27 and was really surprised at the results. The two cylinders had 460 to 480 pounds of compression !!!! I did not believe it so I check it three time, and it repeated it self over and over. Motor was at operating temperature and I tested by way of the glow plug hole with an adaptor that came with the tester. Shut the fuel feed off so as to not fill the gage with any diesel fuel. Motor has 1,300 hours on it and appears to be in pretty good shape after all. Today I set the tappets and was pleased at how much it quieted the motor down. Setting from the factory was .006 to .007 thousants warm. Set them cold to .008, they were out to about .015-.016 on the intakes and .020-.022 on the exhausts. I am going to take the boat out for a spin tomorrow to check on the engine performance before it gets pulled on Weds. The only glitch was the rubber valve cover gasket broke when I lifted it off the cylinder head. Made a mad dash to company near by that services pumps and we found an o'ring that fit just right. A light coating of Permatex (the red stuff in a tube) in the gasket groove to hold the o'ring in place. I placed it on a plat surface with a weight on top of the valve cover to give the permatex a chance to cure and hold the gasket in the groove. After about thirty minutes I took off the weight and reinstalled the valve cover, tightened down the two hex nuts and started it up. Twenty seconds of glow plug heat and it fired right up.....so much quieter. The o'ring cost me a dollar, the gasket from the marine part suppliers was $19.95.....what a score. Needless to say, I'm a happy sailor !!

[Bob23]

Allure:
   Sounds like you are a promising diesel mechanic. Most people misunderstand diesel engines but they are quite a wonder running on the principle that if an air/fuel mixture is compressed ehough, it will ignite.
   I have a background (long ago) in air-cooled VW's which were quite prone to swallowing exhaust valves when the clearance was set too small. It seems that the short time the valve sits on the valve seat is neccesary to disapate the heat built up at the valve head. We always set the #4 exhaust valve a bit more because that cylinder always ran a little hotter than the others.
   I'd be a little leary of setting the clearance cold if the specs call for setting it hot. True, it might be quieter and rightfully so considering the clearances you found, bit too quiet might mean not enough clearance. Just my 2 cents and it sounds like you have a good understanding of the engine.
   Me, I have an outboard on my 23...wish I had a diesel but that'll have to wait for the next boat.
   Where do you sail? I'm in NJ where we are pulling the boats out...fall is here, water is colder and I'm afraid it's time.
Bob23

[Allure2sail]

Hi Bob:
No intention of becoming a diesel mechanic, but they do really interest me. My background is in mechanical engineering and my engine experience is from building and campaining two race cars a number of years back (or should I say in another lifetime). Those engines always had solid lifters and setting the valves was a weekly ritual. I use to think race cars were expensive! The hot setting for the M12 was .006, the .008 I set them at was to allow for heat expansion once the engine came up to operating temperature. I set the valve lash after checking the compression and the motor had cooled down to pretty much ambient temperature. Still trying to figure out why this motor never gets above 145 degrees. It starts blowing black smoke (unburnt diesel after 2100 to 2200 rpm. I have replaced everthing you could think of, from the thermostat (three times), both injectors (brand new and tested), raw water pump (now the preferred Orberdorfer) & strainer, air cleaner, glow plugs, & lift pump. The only two things left on the list to check is the injector pump timing and the prop. The boat has a 12 X 9 pitch on it, the "parts" boat has a 12 X 8 pitch on it. Hard to believe one degree pitch on the prop would make it react the way it does. I'll do some reading up on the injector pump and look into the timing on that as well. The motor appears to have never been messed with so I find it hard to believe someone messed around with the shim pack under the injector pump which is how you adjust the timing of it. Perhaps there is wear on the cam lodes or followers for it and it has the effect of retarding it. I'll get into that once the boat is on the hard or perhaps wait until the spring. My season is over as well, the boats being pulled tomorrow, and stored at where I sail out of which is in Swansea, MA.

[Tim Gardner]

That "1 degree of pitch" represents a change of 11% more (or less) of travel through the water  - quite a change of load when pushing aside 3000 pounds of water.

tg

[BobK]

Black smoke from a diesel engine is most often caused by a propeller with too much pitch.  The easiest way to determine if your prop is over pitched is to look at the maximum RPM your propeller can reach while in gear.  The maximum RPM of the M12 engine is 3600.  A good rule of thumb is for every inch of pitch you decrease the prop the engine will increase 200 RPM.  If your engine does not max out at least 3300 RPM it is lugging too much and the engine is being fed more fuel than it can burn.  Not only will the engine smoke the oil will be contaminated by the fuel which will shorten the potential life of the engine.  Do you have any idea what your max rpm's are?
BobK   

[Allure2sail]

Hi BobK;
I had the boat out today for the last time this season. I pushed it as fast and as high as it would rev and I got up to a smokey 2800-2900 rpm. It did run better and quieter with the valve lash set. I was able to get up to around 2300-2400 rpm before the black smoke started. By the time I got to the 2800-2900 rpm's it was nasty looking. Also I could not get the motor temp above 145 degrees at the 2300-2400 rpm range. I ran it at this rpm for a good 20 minutes. with no increase in temp. When I pushed it to the max rpm it would go (2800-2900 rpm) the temperature did go up to perhaps 170 degrees. The way it was smoking I did not want to run it for very long because I just knew that the oil was getting contaminated big time. First thing I did when I got the boat back to the dock was change the oil and filter for the winter storage. I know these motors run best at the 185 degree level.
Thank you for your reply.....

[BobK]

I would try your 8" pitch prop next year.  If the motor does not reach at least 3400 rpm I would take it to a prop shop and have the pitch lowered even more.
BobK

[Allure2sail]

Hi Bobk (again):
I agree, it is worth a try and I have a prop puller (from Craig's list). Next spring I'll swap it off. I have to do some reading up on checking the injector pump timing as well, I'll do that come springtime.. Got some stuff sold from the parts boat and I really got to get those items boxed up and shipped out, no more playing diesel mechanic for awhile !!
Thanks again
Bruce

[Bob23]

   I wonder if part of the reason for the low operating temperatures is due to the fact of too much unburnt fuel being present. I remember reading somewhere many moons ago how (and this is pertaining to gasoline motorcyle engines) the air-fuel mixture plays a part in the cooling of the engine. I don't know if that's true for diesels but maybe a conversation with a diesel mechanic might be helpful. If it does pertain, that might explain at least in part, the reason for the  low operating temperatures.
  It'll be interesting to see how this problem gets solved so keep us posted.
Bob23, the incurable motorhead

[Tim Gardner]

Check for restriction on intake or exhaust, both of which can cause black smoke (un-burnt fuel). I had a fouled up exhaust manifold on my 20 yr old diesel and had it removed & chemically cleaned at a rad shop. No more smoke!

tg

[Allure2sail]

Hi:
What was carboned up causing the exhaust restriction? The mixer elbow or the exhaust manifold itself? I took the mixer elbow off of the engine in the parts boat, cleaned it all out and purchased new insulation wrap. When I went to install it on allure I found that the previous owner had replaced the mixer elbow already, It looked almost new and the insulation wrap around the pipe was pristine. Must have been replaced just before I purchased the boat. Thanks for the input, good idea but it had been pretty much crossed off the list. The injector pump timing and the 1 degree pitch issue with the prop is all that's left to look into.
Thanks again
Bruce