Engine Woes. Again.

[Balbas]

I bought an old Longbow earlier in the year. It's been re-engine with a 33hp Vetus lump, which to be fair to it, seems to be a decent engine.

The trouble I've had is starting it. Sometimes it goes, sometimes it doesn't. I've had a couple of people look at it and diagnose poor connections to the starter / solenoid, so they've all been cleaned up and it's been playing nicely. Until this weekend. It started first time to get us off the mooring and ran like clockwork for an hour or so (getting out of the river and putting some charge back into the batteries), but then later on, when I decided to motor sail in order to make up time, it just wouldn't play.

We had very slow cranking and then a very nasty smell of electrical burning. Opening the engine cover allowed a lot of smoke to escape (forum users with classic cars will instantly recognise the smell and be reminded of 'Joe Lucas, the Prince of Darkness'), so obviously it wasn't going to play.

The fantastic Sea Start guys did their thing. We sailed back towards the mooring, but as the wind dropped and the light faded away, they came and found us and towed us the final 4 miles home and got us safely moored up. If you're on the south coast and you haven't got sea start membership then you're missing a trick in my opinion, I can't commend them to you highly enough!

The Sea Start guy is coming out to the boat in the week in his 'normal' capacity as a marine engineer to hopefully diagnose my problem, and with a bit of luck fix it once and for all. In the meantime what's the likely culprit do we think? Personally I think the starter may be goosed, but I can't work out why it would still crank slowly if that was the case. But if it isn't the case..... then why would so much load be going through the cabling that something got hot enough to try catching fire? It's obviously not the lump itself which is seized, because it's turning over (albeit very slowly). Maybe the cabling is poor quality (although it looks to be decent stuff and is a respectable size), or I've got a short circuit in the starting system somewhere?

Wish I had an old fashioned decompression lever and a hand crank...

 

[NickRobinson]

Did you not see where the smoke emanated from?
I think you're right about the starter motor, but i'd check to see if any starter cable +ves had rubbed through onto earth.
You could use a jump lead to discoubnt earthing by bridging between the block and battery -ve but a bad earth is unlikely to make copious smoke.

 

[Contest1]

How old is the starter battery?
Slow cranking could be down to a poor battery.

 

[TQA]

Start by checking two things.

1 battery voltage at the starter motor main lead while cranking. As a rough guide it should be 10.5 volts or better. If below this clean and check every connection in the starter motor circuit ESPECIALLY THE EARTH LEAD.

2 Cold cranking rpm. There will be a minimum figure given in the workshop manual. Achieving this is CRITICAL Do not rely on any old tachometer but get an optical tachometer and measure off the front pulley by adding a blob of white paint. They are not expensive just make sure it covers low rpm

Only look deeper after you know you are achieving minimum cranking rpm.

 

[vyv_cox]

The means by which power is transferred to the motor by the solenoid is very crude. Two brass or copper contacts around 10 mm diameter are bridged by a short length of the same metal that is pushed in by the action of the solenoid. Over time these contacts become pitted and corroded. Assuming you can separate the two parts, usually possible on older models but increasingly less so, file the contacts with a fine file and order will be restored. I have had just your symptoms on old VW vans and fixed them by this method.

 

[neil_s]

Second vyv's reply above. The way to stop it happening is to protect your starter motor from condensation. Take it home over Winter!