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#1
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Mercruiser Chevy starter: unusual diagnosis and repair
The 20-year-old Four Winns Liberator 211 with Chevy 5.7L Mercruiser I/O
left us stranded when it wouldn't crank after anchoring in the ICW. My initial thoughts were battery or connections, or (yikes) a hydrostatic lock since we had been stopped in some chop for a while. So after towing back home I took out the sparkplugs and she would crank. However I could not find any water coming out the sparkplug ports after some cranking. I did compression tests one cylinder at a time with all the sparkplugs removed, and it would hardly crank whichever cylinder was compressing, as I tried each of the eight in turn. Up to this point I hadn't considered a bad starter, since they usually just quit altogether, but I decided to test it anyway. I put an ammeter on the cable and found it was drawing 400 amps (!). I took the starter off and ran it in a vise and found the same draw while it ran freely. The engine manual said 60 or 90 amps was about right for a free=running starter. I disassembled the starter and found two of the four permanent magnets inside had come unbonded from the case, and shifted around in position, and were rubbing on the rotor. I glued them back in place with epoxy, reassembled everything, and now it cranks and starts like new. In retrospect, I should have caught that the engine had always cranked weakly during the month I've had it, despite having a freshly charged battery and good connections. The 2-gauge battery cables always got warm when starting. I should have known better than to overlook and ignore such warnings. I don't think this starter was the original. It has a cast aluminum body and zinc chromate housing, with a sticker that says MAS over an anchor. Apparently nearly all GM marine engines use the same starter, which appears to match the Sierra 18-5913 type with permanent magnets. Sierra 18-5905 and 18-5910 were also listed as replacements, but I couldn't find what the differences were. |
#2
posted to rec.boats
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Mercruiser Chevy starter: unusual diagnosis and repair
I'd get another starter, that epoxy will probably let go when it gets
hot. |
#3
posted to rec.boats
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Mercruiser Chevy starter: unusual diagnosis and repair
Capt John writes:
I'd get another starter, that epoxy will probably let go when it gets hot. For some value of "hot". For now I'll just try to keep it cool. I wonder what they're bonded with originally. Didn't appear to be much of anything there. Phenolic resin, perhaps? |
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