It's possible both starters are bad, but I'm thinking main bearing trouble. For heavens sake try another starter before tearing into it.
Jeff
Jeff,
That's an interesting comment you made about being into another engine with similar problems and bad mains. In looking at the pieces here. He said it ran good a week ago. That speaks of recent lubricant and motion to the mains. Not conducive to rust buildup in my mind. I guess they are SS needles like the rod bearings? With that said, wouldn't you discount rust as a culprit?
I think he could pull the plugs, shifter in N, grasp the flywheel with a crank rope and pull it through by hand to determine internal resistance. If he can easily pull it through I wouldn't look for engine resistance as the problem; opinion! I started an 85 hp once with a crank rope (plugs intact). In my early years I only had a cranking battery and my trolling motor ran it down. It didn't take all that much effort to start it. Actually I was amazed it didn't, being 85 hp.
I want him to measure the voltage at the starter copper + terminal on the starter and starter ground....metallic end cap of the starter, metallic band around it, black battery - lead to engine block, but measure the stud not the lug attached, when cranking, plugs installed. I want to know what voltage is present. If 10v or more why not take the starter(s) to Autozone and have them tested like they do for automotive starters? If less than 10v clean up the wiring or take the battery to Autozone and have it load tested. It should have at least 11v at 200 amperes across the terminals with the tester.
Something about batteries. When lead acid batteries age the sulfuric acid reacting with the lead plates forms a sulfate scale that winds up in the bottom of the battery. When bad enough it piles up andshorts out the plates and can render a cell dead. 6 cells in a 12v battery so you lost 1/6 (17%) of your cranking power besides the series resistance (you don't want) in the high current path. With no current draw a bad cell may have enough static voltage left to make you think you have a good battery when you put a voltmeter to it.
One way of telling something is wrong is when you have a battery that you think is run down and put it on a charger only to find that it charges at a very slow rate and prematurely shows charged. You are expecting 12a on a 10a charger initially and it only runs out to 6 for example. Putting the battery under load forces each cell to contribute and if it's not functional it will show up in reduced voltage across the terminals.
Seems odd, but nothing says you don't have 2 bad starters. Where'd you get the second one?
HTH,
Mark
