Completely seized alternator!

[Sailing Amok]

Out for a pleasant sail back from our weekend anchorage on Sunday, when the wind shut down and we had to fire up the Iron Genny. Over the course of a couple hours of motoring the intermittent hissing that I'd been attributing for the past two seasons to a slight leak at a fuel injector (a stitch in time...) gradually grew louder and more constant. Slowly the hiss started to sound less like a hiss, and more like grinding. Kristina went below deck to grab a beverage, and yelled up "It smells really weird down here". I went to check things out, and it sure smelt like burning rubber. I opened up the engine cover and just at that moment, the engine let out the most horrible squeal. Kristina quickly pulled the kill switch and we unfurled the headsail. Once back at the dock (thanks to a tow in from our slip neighbours) I pulled off the belt to try giving things a spin. The alternator is so frozen I couldn't even turn it with a wrench. Anyway, time for a new alternator, but I've got a few questions I want to run by you knowledgeable folks.

I'll give some info regarding usage and power needs, because I know it's important:
Our typical sailing is 3 weekends (Friday night to Monday morning) per month mid May to early Oct, with one 10 day trip during August. We have a house bank of 4 Trojan batteries wired for 12 volts and 460ish amp hours, installed by PO 2015. Solar = 123w rigid solar panel and 2 50w flexible solar panels, all over 10 years old, and the flexibles are questionable at best. We sail as much as we can, and keep motoring to a minimum. With North Western Ontario's long days, we're typically down 5-10 amp hours when we go to bed, and 30-50 when we wake up, depending how full the fridge is I guess. The alternator that failed is a 50 amp Mando, which seems likely to be original. The engine has 1360 hours on it.

Given the age of our batteries and panels, as well as our plans for longer cruising in a few years, I suspect a major electrical overhaul is in our future. That is not something I want to do now, in the middle of our short sailing season. So, while I know a large output, externally regulated alternator is the way to go, I'm thinking for now I'll go with a more simple swap, to get through the next season or two before everything else gets changed. So, I'm thinking an internally regulated unit with more amperage to run cooler, but still small enough that I don't need to start changing all my pullies. If I understand correctly, I should be able to get away with the current belt size on something up to about 75amps? Or, if I were to go for something around 100 amps, how much of a job is it to go up in belt size? I suspect I'd need to start changing wiring as well, to handle the increased current. Would that be the case with a 75ish amp alternator as well, and am I correct in thinking it is only the B+ cable that would need to be upgraded, or would all of the wires be carrying additional current? If so, it may make sense to stick with 50amps for now, though I suspect the undersized alternator relative to battery bank may have expedited this unit's demise.

Before installing the new alternator, are there any red flags I should look for in the rest of the system that may have caused the failure? I suppose I should check the batteries in case an issue with one of them could be to blame. Perhaps the belt has been too tight, in which case is there a way to determine if damage has been done to the water pump bearing? Anything thing else to check before I fry a new alternator?

Lastly, my understanding is that the B series engines have a bit of odd wiring, related to the oil pressure and ignition switch (if I recall). What do I need to look for in selecting a replacement alternator that will work here. The wiring on the old alternator includes two wires going to the exciter post, a wire going to an "S" post which I gather is battery voltage sense, but appears to be spliced to the (unmarked but I'm guessing) B+ post, and another wire going to the "P" post which seems to have something to do with the tach, though I don't understand what an alternator has to do with the tach, or what changing alternators will mean for my tach accuracy.

Thoughts and wisdom appreciated!

[Breakin Away]

I've never had an alternator problem, so not speaking from experience. But in reading others' stories here and elsewhere, I'd suggest looking into a rebuild of your existing alternator. Every time I read about someone replacing something, whether alternator, transmission, engine, windlass, water heater, etc., the shiny new replacement is just different enough that you invariably go down a rabbit hole of new fittings, belts, connectors, shafts, stuffing boxes, adjustment brackets, etc.

Maybe it's too fried to fix, but I'd at least have it diagnosed for possible rebuild.

[Noah]

You should be able to successfully run up to a 105A small case alternator with a 3/8 in. V-belt. I would recommend using an external regulator with temp sense snd set the alternator output derated downward approx. 10-25% for cooling efficiency.

[Sailing Amok]

Thanks guys. I'm going to bring the alternator over to a local shop today, but I have strong suspicion it is beyond a rebuild. But, it would be nice, as Breakin said, to avoid all those potential downstream issues that always crop up when changing out any part.

You should be able to successfully run up to a 105A small case alternator with a 3/8 in. V-belt. I would recommend using an external regulator with temp sense snd set the alternator output derated downward approx. 10-25% for cooling efficiency.

I had seen in one of Main Sail's articles that the industry recommended maximum for 3/8 belts was 80A, but a more realistic recommendation accounting for imperfections in installation was 70A. Is it the derating done in the external regulator that allows the extra amperage with a smaller belt? I guess my biggest concern right now is trying to figure out a wiring diagram, to determine how all the various charging sources, and controllers interact on the boat. A lot was done by the PO, and I need to figure it out, to determine where I need to run larger whites for a larger alternator.

[Sailing Amok]

Another question with regards to working on my wiring diagram. I'm thinking the simplest way to determine if the alternator has been run directly to the battery rather than the 1,2,B switch would be to put a DMM between the AO wire and engine ground, turn the switch off and check again? If it's run to the switch I should see similar voltage as at the switch selected battery bank, and with it off no voltage. If it's run straight to the house bank, I'll see no change with use of the switch. Is this correct and safe? I'm assuming the DMM provides sufficient resistance to do this. Currently with the alternator removed from the boat, I've got many wraps of 3M electrical tape around each cable terminal, but the thought of a dead short to the engine with these wires sitting loose as they are now is horrifying. I keep telling myself the electrical tape will do its job, but would feel better knowing the wires are either switched, or if direct to the battery, fused.

[Breakin Away]

Thanks guys. I'm going to bring the alternator over to a local shop today, but I have strong suspicion it is beyond a rebuild.

It's worth a try. If rebuild it possible, it will buy you time for a more carefully thought out upgrade/replacement.

[Catalina007]

On our last alternator change I found ZERO shops that made sense to do a rebuild. At $100/hour labor cost and $150 for a new one makes no sense. 
Don't bother looking to repair.   
I would be careful going bigger than 75 amp until you do a bigger upgrade due to the origina brackets that have been known to fail. 
Throw a cheapie in there for the rest of this season.   

[Jim Hardesty]

Another question with regards to working on my wiring diagram. I'm thinking the simplest way to determine if the alternator has been run directly to the battery rather than the 1,2,B switch would be to put a DMM between the AO wire and engine ground, turn the switch off and check again? If it's run to the switch I should see similar voltage as at the switch selected battery bank, and with it off no voltage. If it's run straight to the house bank, I'll see no change with use of the switch. Is this correct and safe?

You answered your question correctly.  On Shamrock a 2001 OEM wiring with the selector switch set on 1 the engine running (shortly after starting) the voltmeter on the electric panel set to 1 will read much higher than 2 (about the same as on the engine panel).  Set the selector switch to both and will read same on 1 and 2.  The factory wired to only charge bank 1 to charge bank 2 need to set the switch to both.  I think it's in the manual.
Jim
 

[Breakin Away]

I would be careful going bigger than 75 amp until you do a bigger upgrade due to the origina brackets that have been known to fail. 

I'm almost sure his MkII has an improved bracket vs  the older motors.

[Noah]

https://marinehowto.com/marine-alternator-installation-tips-tricks/

Above is (I believe) the article that was reference from Mainesail. Lots of good info there. However, I have been successfully running a smal frame case Leece/Prestolight 8MR, 90A, externally regulated alternator for 6 years with a 3/8 belt. Never had any issue. There are also many in are group that are running 105A models with no issues. It is important to have temp sense and down-rate the output. Some use "small engine" mode setting/switch as well. All are still using a 3/8 in. V-belt.

[Ron Hill]

aAaron : I'd still take it to an alternator shop and see if they will repair it. I had a shop install new windings and a new stator. I say that so you can reinstall the same case!!  They also might be able to rewire so you can purchase a new (smart) external Voltage regulator.

The problem with the "B" engine bracket is that the stud "ears" (one with a clean hole and the other with a threaded hole) is made out of an aluminum alloy. If you tighten the bolt and there is space between - you can crack or break of both of the ears.  Any space must be filled with a washer/shim. -- so be careful tightening !!!
If you want to check your bracket just try putting a magnet on it!!!

The rebuild will get you through the season and the external regulator can be used with a new alternator!!

A few thoughts

[Breakin Away]

The problem with the "B" engine bracket is that the stud "ears" (one with a clean hole and the other with a threaded hole) is made out of an aluminum alloy. If you tighten the bolt and there is space between - you can crack or break of both of the ears.  Any space must be filled with a washer/shim. -- so be careful tightening !!!
If you want to check your bracket just try putting a magnet on it!!!

Thanks for pointing this out. I want to be sure I understand you. Is the part I highlighted below (#17) the one that B-engine owners should check out with a magnet?

It's interesting, I've never attempted to tighten the studs before. I move my alternator 2-3 times a season to keep my V-belt taut, but I've never loosened/tightened the pivot studs, since I figured the rotation of the alternator is only a couple of degrees. Maybe it's a good thing I've never tried to tighten it. It almost looks like the studs are not meant to be too tight in anticipation that V-belt adjustments would require some limited rotation. Maybe just snug enough to compress the lock washers.

Here's something really odd: The two adjacent studs are different - #11 is metric and #14 is 3/8". WTF is the reason for that?

[Ron Hill]

Breakin : Yup!!  #17 is the critter to be careful of.  I also believe that the engine bracket that #17 fits into on the engine!! is also an Al alloy - check with a magnet!!

Good Catch - as I had forgotten that the 2 capscrews in #17 are of a different diameter and one was metric and one ASE!!  I believe that smaller #11 capscrew is metric because of the hole on the OEM alternator case bracket.  When I adapted my Balmar I had to install a sleeve in my alternator case!!

Also - Later I had #11 capscrew break at the threaded end and I replaced it with a Fastenal "made in the USA" capscrew!!

A few thoughts

[KWKloeber]

Perhaps the belt has been too tight, in which case is there a way to determine if damage has been done to the water pump bearing?

Lastly, my understanding is that the B series engines have a bit of odd wiring, related to the oil pressure and ignition switch (if I recall). What do I need to look for in selecting a replacement alternator that will work here. The wiring on the old alternator includes two wires going to the exciter post, a wire going to an "S" post which I gather is battery voltage sense, but appears to be spliced to the (unmarked but I'm guessing) B+ post, and another wire going to the "P" post which seems to have something to do with the tach, though I don't understand what an alternator has to do with the tach, or what changing alternators will mean for my tach accuracy.

The Alt per se has nothing to do with the oddball wiring scheme on the "B" and "A" engines.  The posts on the Alt are merely connection points for the circuit to the oil pressure switch and fuel pump.  So long as the new alt has the identical posts it will not affect the harness/oil pressure wiring.

On a gas engine, the Tach uses the spark at the distributor cap to determine engine RPM.  On our diesels there is no spark so the alternator produces a low voltage alternating current (A/C) output to the Tach, which the Tach "reads" and converts to engine RPM.  The RPM reading on the Tach is proportional to the frequency (hertz) of the A/C signal -- which is proportional to how fast the Alt spins -- which is proportional to the engine RPM.

Both the number of poles on the Alt stator and the diameter of the pulley affect the frequency of the A/C signal.  So if either of those two is different than your current Alt, the Tach RPM reading can be off and the Tach would need to be adjusted to match to the new alternator.  If the replacement Alt is a one-for-one to the current Alt, there would be no effect on the A/C signal or Tach reading. 

[Ron Hill]

Guys : Look in the Mainsheet tech notes !! 

I wrote a couple of articles one of which covers some of what Ken has mentioned.  There is a formula of how and what to set the dip switch setting at on your Teleflex engine tach instrument.  This formula compensates for a different number of stator poles and a different size pulley!!

A few thoughts