Clunking, not starting

[nicksharpe]

Just back from a trip round Loch Lomond, lovely as ever.

We did almost need a tow though. Engine (60hp Mariner EFI) running great. Stopped at an island for an hour, went to restart and just got a really solid "clunk" from under the cowling. Electrics all good, but it felt like something was stopping the engine turning over.

After about 10 "clunks", it started normally, but not before we'd radioed a nearby yacht for help (apologies and thanks duly dispensed).

Once back at the slipway I started the engine 5 times, all fine.

Would be grateful for any ideas about what might have been going on, and whether it'll happen again.

[Fenlander]

Do you reckon it was a solenoid type click or the starter trying to spin and something stopping it? Maybe the in-gear interlock slightly out of adjustment?

[Peter_C]

Visually inspect the ring gear for any damage too. My first thing to do though would be to test the battery, then the voltage at the starter, both resting and while cranking. Knowing the cranking amps of the starter would help diagnose it. Any corrosion noticeable?

After not starting, how did it start? Was there smoke or any rough running?

[smallribber]

Flick the bendix on the starter and give it a squirt of lube. Also check your battery connections. If corroded this can happen. Then if not this move onto the starter solenoid

[spartacus]

Get yourself a cheap multimeter to see what the battery is doing. Do you have the battery on a trickle charge before an outing?

If that all works out, run power direct to the starter bypassing solenoids. It should flick into action straight away. One thing to watch, if before this the engine was difficult to start (I don’t mean clunking), then continual or long bursts on the starter can burn them out.

[nicksharpe]

Thanks everyone. Unfortunately many of your knowledgeable answers are beyond me, but I do get the feeling it was caused by something not been lined up correctly... Hopefully it never recurs!

[spartacus]

Originally Posted by nicksharpe

Hopefully it never recurs!

Sod's law say it will and generally when you least expect it. You need to get to the bottom of it as to determine why it's happened. A marine engineer will follow exactly the same process of elimination as we're suggesting. If you're not confident, book it in, but the benefit of doing it yourself is invaluable.

A multi-meter is straight forward and you can pick up on Ebay for less than £10.

Check the battery from cold. You adjust the multi-meter to 20v setting and put red to positive and black to negative or earth on the terminal. A healthy battery should display around 12.6 to 12.7 volts (that's not with the engine running).

You can pick up a battery trickle charger from Halfords. Again, expect to pay £30-40 and it's good practice to put battery on charge before an outing just so you know everything is topped up power-wise.

Back to the battery. You get lead or AGM batteries. Modern boat batteries, ideally (AGM). The technical specification that comes with your engine engine will determine cold-cranking amps, etc.

Back to the starter motor. The first thing I would do is check the physical connections on the battery, and then the connections on the starter motor. You can get oxidisation on the battery terminal spades which stops continuity and hypothetically you don't get 12+ volt at the engine. Remove, and using a emery board or light 3M paper, sand until you can see the copper. Reconnect everything. You can get issues with wiring. Boat manufacturers don't use tinned wiring, so not unusual to get a lack of continuity due to corrosion and again a multi-meter comes with continuity setting.

If you remove the starter from the remote throttle, then the starter should fire into action with 12v supplied direct to it. That doesn't just mean the starter just spins, the bendex gear on the end rises and engages with the flywheel which starts your engine. This bypasses any fuses on the engine and any starter solenoid. Connect the earth, place starter on a block of wood with your foot on the starter connect the positive to the battery. A short burst to see what happens. If the starter doesn't spin up properly - then there's your root cause, assuming battery is putting out the required voltage too.

If all that checks out - then I would move onto the starter solenoid/relay. You can search for the manufacturer part number on Mercury Marine here. For the £20-30 for the part, it may just make sense to replace and keep the old one as a starter. https://www.boats.net/catalog/mercury/outboard/60hp