soot

[jstoesz]

The M25XP on my 88 has a lot of black (although that is probably given) soot on and near the alternator, and I am not sure why.  Is soot always from an exhaust leak?  There does not seem to be soot by the exhaust manifold gasket, with no soot on the wrap but hard to tell.  In addition, there is no noticeable/unusual odor.  It seems to be originating inside the alternator windings, but it still provides 13.5 volts or so.  This would indicate the the alternator insulation is not burning up.  I would guess my first diagnostic step would be to clean the area thoroughly and find out where the soot is originating...assuming it deposits first at the sight of the cause.  Has anyone had this issue, my 10 minute search did not find any close matches. I am hoping for a smoking gun, before I spend time diagnosing.  Diagnosing is the most time consuming part usually. 

Any thoughts?
Jake

[Stu Jackson]

black soot = alternator belt

Is it properly tensioned, not over tight, and lined up?

[jstoesz]

I considered that, but the belt looks good.  I have owned the boat for 1year or so (50hrs tops), and I have not changed the belt.  It still looks good.  So this may be the culprit, but it seems like the belt should be wearing more for this amount of soot.  But that is my purely qualitative analysis.  How much soot can a belt produce? a lot?

[RV61]

I found that the belt can produce quite a bit of "soot"  really dust especially when not properlytensioned and aligned as Stu mentions. On my boat when I first owned the engine compartment door in the head which is near the alternator was completely black.
The inside door looked at first glance it was charred however it cleaned up fine. The heavy dust was also found on the sound proofing on the inside of removable bottom steps on the side where the alternator is. You may want to take a  look at and smell the "soot" to determine if it dust from the belt.
The belt looked fine even after producing much "soot" or dust. I believe this is your smoking gun .
   

[Ted Pounds]

The belt can look good and still be too loose or out of alignment.  If you have the stock alternator set-up then it's likely that your belt is too loose as opposed to out of alignment.  It should deflect about 1/2 an inch in the middle.  

[Ted Pounds]

Rick,
Once again I see that "great minds think alike"... 

[Ken Juul]

Jake,
You said the belt looks fairly new, perhaps a lot of the dust came from the previous belt that failed.  I personally don't like the 1/2" deflection check, requires a finding a straight edge to do accurately.  I prefer to twist the belt mid point on the longest span.  It should turn 90 degrees but not much more.  This also stresses the belt, any rotting or cracking should be obvious.

While your sorting this out, make sure you have the alternator bracket upgrade.  See the critical upgrade thread for more information.

[Stu Jackson]

He's got the M25XP which came with the upgraded alternator bracket.  What he needs is a belt tensioner:  http://c34.org/bbs/index.php/topic,3667.0.html

[Tom Soko]

Jake,
I think that if you look at the belt and pulleys carefully, you will find that they are not in perfect alignment.  If the belt is loose, you will create the black dust.  If the pulleys are not in perfect alignment, you will create dust.  Even with the alternator bracket upgrade, your pulleys might off.  As little as 1/32" will create dust.  Best way to check is to get a yardstick and hold it up against the main pulley on the engine. You can then measure the amount the alternator pulley is off (it's the most likely one to be off).  To fix, you can put spacers at the mounting bolt, or spacers at the pulley.  Either way, the alternator pulley has to be EXACTLY aligned with the engine pulley.

[dave davis]

You might want to try this simple test to verify the soot is coming from the belt or some other place. Take a piece of paper and pin it to the inside of the door. Run the engine for about 10-15 minutes and look at the shape and location of the soot, if any. Don't leave the paper there, it gets too hot for it. If you decide you want to leave it there for longer perion of time. replace it with a sheet of aluminum paper.
Good luck, Dave

[Ron Hill]

Jake : What you are experiencing is "belt dust" (aka belt wear).  As Tom and Stu mentioned, I'll guess that your pulleys are not aligned properly!!
Take a straight edge and place it on the lower (drive) pulley and angle it up to the alternator pulley.  That straight edge should just touch the outer edge of the alternator pulley.  You might have to add or take out some washers in the upper bracket that holds the alternator to the engine- to get proper alignment.  Good Luck - A thought