Yanamar Scare

[jfkal]

My Yanmar had trouble starting. After some cranking the engine came alive and thick greyish blackish smoke out of the engine compartment. I rushed down, shut off, got the fire extinguisher ready. But nothing wrong and the smoke cleared. Thought the exhaust pipe might havbe come off. Found nothing wrong, started the engine again and everything was fine. Where did the mistery smoke come from??

 

[billskip]

I give in... tell me

Bill
www.aegeansailing.co.uk

 

[oldharry]

Possibly a sticking inlet valve blowing unburnt fuel/air mix back through the air intake? This assumes the engine is multi cylinder, and when it did fire ran roughly until the problem cleared.

 

[brian_neale]

My Yanmar 1GM appeared to have started running backwards once - I was trying to start it on the handle and it bounced back from compression and seemed to fire a few times going the wrong way. Lots of smoke from the air filter inlet until I stopped it with a quick lunge at the stop control. Never done it since, but my starting technique has improved since then!

 

[pete]

Usefull web site /forum for Yanmar owners www.marinedieseldirect.com/yanmar/

 

[ccscott49]

Almost definitely started momentarilly backwards. happens with diesels, even known to happen with petrol engines when switched off.

 

[jfkal]

That sounds like a plausible explanation. Lucky I did not draw water though. After that incident the waterpump started making squeaking sounds. Indicates that the impeller has been run "backwards". Better change it soon.
Thanks

Joerg

 

[brian_neale]

Why does reverse running hurt impeller?

Not sure that running an impeller backwards for a short time will do any harm. The books always talk about putting new impellers in place with the vanes going the right way, but have you ever looked at what happens if you do not? When replacing my 1GM impeller once, I greased the vanes as per usual but had more trouble than usual getting the vanes to point the right way. So I put it in anyway, and slowly turned the engine over with the handle before putting the lid on the pump. The vanes had flipped within a single revolution. Since then, I have not worried about it. Impellers parting company from the bronze bush are more common on my boat (done it twice now).

 

[ccscott49]

Re: Why does reverse running hurt impeller?

Normally, when the impellor has been run for a while, it takes up the shape of the direction of rotation, when you run it backwards for a while after that, it often self destructs, especially if its been in there a while. Had the bronze bush seperation a few times, but only on small impellors, genny etc and on a few small yanmars.

 

[brian_neale]

Re: Why does reverse running hurt impeller?

Good point about old impellers. Certainly take on a permanent set if left in the pump over winter! However, if the impeller is getting that brittle, probably time to change it anyway?

How often should you change an impeller?