Hi all, i did the annual fuel filter x2 change today and bled system before startup. Started as normal but after 5 secs there was a bang and it stopped. Checked everything and all looked ok. Restarted and has ran fine since. Just curious as to what happened ? Yanmar 3ym30 with 450 hours. Cheers

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5knotsisbest said..
Hi all, i did the annual fuel filter x2 change today and bled system before startup. Started as normal but after 5 secs there was a bang and it stopped. Checked everything and all looked ok. Restarted and has ran fine since. Just curious as to what happened ? Yanmar 3ym30 with 450 hours. Cheers

You didn't leave a spanner or something near the V belt or any other moving parts did you??

Nah.... it was more if a" bang within". Stopped it dead .

how often do you use this engine,yanmar,s have issues with the exhaust mixing elbow where the internal and external welds crack and allow water back into the exhaust valves and the bang is often a sticky valve . check for rust on the back starter side of the engine and also release the 4 bolts holding the mixer and push the mixer back and look for water or white powder.it is very hard to see the cracks by eye.both my engines cracked before 400 hrs.i replaced my mixers with cast stainless mixers that seem ok so far.The cracking is due to the weld process of stainless steel and re welding will only warp and delay the problem .

Yeah, the elbow mixer on my Yanmar cracked at around the 400 hrs too. It appeared to me that when the elbow was fabricated, the weld at the flange joint was machined off leaving very little metal holding it together. I re welded mine and have been without further issues.

thanks all. pretty sure elbow was replaced by previous owner. its just the coincidence of it occuring directly after bleeding fuel and repriming. prior to fuel filters change and bleeding i drained raw water , changed impeller and restarted without issue. water exhaust all ok. after fuel reprime it strarted and ran for a few seconds, long enough for me to think it there was no air in the system, then bang stoppd dead

What are the possibilities that it started up and ran the wrong way for a few seconds?
Just asking.

gary