Join Date: Mar 2009
Location: Boston, MA
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Starter motor running backwards?
I've got a diesel Yanmar 3QM30. Recently I've been having trouble starting; there have been a few issues that have come up and been resolved.
About two weeks ago, I was having trouble with the starter... the solenoid wasn't kicking the Bendix forward, and the interior connections seemed unreliable... had to jump it to get the motor firing. Pulled it, brought it into the shop my company uses regularly. Get it back a few days later, all good to go.
Still no dice starting, but no reason to suspect the starter at this point; it was spinning fine with no compression on the engine.
I bled the lines, there's a steady stream of diesel on all three injectors.
Pulled apart the lift pump, cleaned a bit of gunk, and achieved some more fuel pressure to the injectors. Bled the lines again.
Finally it seemed like the battery bank just didn't have the cranking amps needed. I swapped in a high-cranking starter battery, isolated it, and the engine now cranks like a champ, so there's certainly plenty of power going to where it needs to be. However: the crankshaft is spinning in the wrong direction.
It was baffling for a little while, because the engine would show all signs of being able to turn over, and in fact did on one cylinder (which I've read 1-cylinder diesels can run backwards), but the other 2 never fired, presumably because nothing was spinning along with the shaft, and when they hit the compression cycle, they prevented the shaft from spinning any further.
I've checked the wiring and the battery itself. Nothing seems to have reverse polarity. I swapped the connections leading into the starter; it wouldn't fire at all, so I swapped them back. The house bank doesn't have the amps to crank the engine, so I can't tell which direction the crankshaft would spin powered off them. I could swap the house bank and the starter battery and see what happens, but I figured I'd ask around here and see if what I'm worried about may be the case:
Is it possible that, when my starter got rebuilt, it was rebuilt to spin in reverse? Maybe the shop thought it was a starter for a second engine in a twin-screw, going the other way, or an automotive setup. Is there something obvious I may have missed? Everything else about the engine seems fine... muffler isn't backed up, no signs of water or blockage, plenty of diesel running through the system, plenty of power. It's got air, compression on at least the 1st cylinder is happening, it's got fuel.
Just when I crank, it attempts to run backwards, which is amusing but frustrating.