Intermittent CLUNK (not click) from new starter

[fishnfiend]

1986 Mercruiser 3.0 140 MR Alpha One.<br /><br />Installed new marine starter (one long bolt, one short bolt) this spring. Boat is new to me, so thought slow revs of starter were starter problem. Turns out corroded connections, cable ends, etc. were stealing juice. Replaced slave solenoid. Have excellent voltage at starter when key is turned.<br /><br />Starter has good power and fires engine up most of the time. Motor runs excellent at all rpms. Has good power. Plugs were a little sooty from too rich idle mixture most likely (possibly too rich jets, but runs great at all speeds). No evidence of water in cylinders. Just serviced the manifold assembly (problem existed prior).<br /><br />About every 5th try, the starter "clunks" and moves the crankshaft about an inch. Typically, on the second try then, the motor fires up instantly. Bendix gear is new, shows no wear pattern yet. Ring gear on flywheel looks fine - no missing teeth that I can see.<br /><br />Have read posts addressing shims to better postion bendix/ring gear. Tried a thin shim under engine side of starter. SEEMED to reduce frequency of no spin at start. Then tried a thicker shim, and it "clunked" on nearly every try (still always started second time).<br /><br />My best guess is either bendix/ring gear binding or internal starter problem. How can I best nail this one down? <br /><br />I'm forunate to have easy access - when I rebuilt the boat, I made sure I can get easily to engine from any angle.<br /><br />Thanks for any information, gentlemen.

 

[bigbrownbuku]

Re: Intermittent CLUNK (not click) from new starter

what is the CCA rating of your battery?<br />do a volt drop test from battery post to starter post(use a remote starter or get someone on the key to perform this test) you should get <.5 volts

 

[fishnfiend]

Re: Intermittent CLUNK (not click) from new starter

Hey, thanks. The battery is a fresh charged 575 CCA marine deep cycle. see post below for drop info.

 

[fishnfiend]

Re: Intermittent CLUNK (not click) from new starter

Ben, After getting a better understanding of "voltage drop", I measured the volts at the starter before starting (13 volts) and during starting (fluctuating but drops to 9.76 volts at one point). I take it a 25% voltage drop is not good. <br /><br />I read in a Mercruiser Tech bulletin that the starter requires a minimum of 9.5 volts to operate - definitely too close for comfort here. The starter does feel pretty warm after brief cranking, but I don't know how warm is normal.<br /><br />The battery cables are 2 guage, appx 4 foot run. There was some rust on the terminals that I polished off, but I'm also wondering now about rust/corrosion on the terminal crimp to the wire. Going out now to remove the terminals, clean up the insides and solder them back on.<br /><br />Going skiing this afternoon. Will have a good real-life test. The lake will be busy with plenty of tows, but hope not to need one!!

 

[fishnfiend]

Re: Intermittent CLUNK (not click) from new starter

OK, back from the lake. Prior to going, replaced both battery cables with new 2 guage. The negative cable had rust in the terminal (below exhaust riser). Voltage drop showed about 10.2 volts at the starter when engaged, which is within Merc specs.<br /><br />Still had intermittent "clunk" after which motor turned an inch or so. Usually would then spin and start right up on second try. Typically about every 3rd or 4th start. Still stumped.

 

[bigbrownbuku]

Re: Intermittent CLUNK (not click) from new starter

voltage drop isnt measured like that. voltage drop is the potential difference between 2 points in a circuit. measure the drop through the positive cable from battery post to starter post and the same from engine ground to battery negative post while cranking.<br /><br />take the key switch out of the equation. use a remote starter at the starter solenoid and see if anything is different.<br /><br />if your drop is excessive shorten the test area to determine the problem.

 

[Mischief Managed]

Re: Intermittent CLUNK (not click) from new starter

I suspect it's not the starter or voltage.<br /><br />You may want to see if your carb is leaking fuel into the intake manifold and into one of the cylinders at rest. It's possible you are hydrolocking the engine with fuel now and then. This can bend a connecting rod so it is something that needs to be checked. Next time it happens, pull the spark plugs, disable the ignition, have some rags ready, and crank the engine over. If fuel comes out one of the spark plug holes, you'll have your answer.<br /><br />Could also be an ignition timing problem. Check your ignition advance and dwell.

 

[fishnfiend]

Re: Intermittent CLUNK (not click) from new starter

Thanks for the opinions. I hope to get a chance to work on it again late this afternoon - will post update on this thread. Gotta get this baby right - it's skiing season!!!

 

[jlinder]

Re: Intermittent CLUNK (not click) from new starter

If you are getting about 10 volts to the starter and you have the motor just rotate a little bit the problem is not voltage. Your battery is 12.6 volts with no load. Try starting and you can easily drop by what you are seeing.<br /><br />Normally I would question the starter, solonoid, or engine.<br /><br />1. If it turns the bendix is engaging.<br />2. If you have a solonoid that lets you measure voltage on the starer side and you have good voltage the solonoid is not the problem.<br />3. Could be starter, but you replaced that. Could it be defective?<br />4. Good point about hydrolock. That sounds most likely. If you remove the plugs and try cranking a number of times does the problem go away? If it cranks slowly (just rotates a little bit) and you pull the plugs are they wet?

 

[fishnfiend]

Re: Intermittent CLUNK (not click) from new starter

Thanks for the ideas, gents. Wanted to post more information after trying some of your ideas.<br /><br />Timing was at 8 degreees, adjusted to 6 per manual.<br /><br />Starter is getting 11.3 volts to crank with on average. Interesting, as its cranking for 10 seconds or so, the multimeter does flash by 9.6 volts a few times. 11.3 most of the time, though.<br /><br />Starter moves the engine well after it breaks inertia.<br /><br />Starter did "clunk" a couple times. Pulled plugs - all were same color and dry - #2 cylinder was slightly damp with gas. Cranked engine with #2 plug out - got the same "clunk" once. Engaged it again and no gas expelled into a towel.<br /><br />Removed all plugs but could not get problem to show.<br /><br />The "clunk" is completely intermittent. Seems random. I'm suspecting a defect in the starter -somehow a "flat spot" in which power is less than optimum.<br /><br />I'm going to have the old starter rebuilt. Once it's finished and installed, I'll be able to rule in/out the starter as the problem.<br /><br />Thanks so much for all of the excellent leads in chasing this one down!!