View Full Version : Yanmar 2GM20 Exhaust Problem

04-07-2010, 12:08 PM
I have a 2GM20 in my yacht. It is raw salt water cooled . It was installed in 1997 by the previous owner.
He told me with great pride he only ran it at 2200 rpm. I has been running close to full throttle since I purchased the boat in 2007, and it has run progressively better over time. It starts immediately and up until recently would pull 3200rpm OK. It would smokes at full throttle.
I did get the prop re-pitched which increased the revs by 200 to 300 rpm.
I ran the engine continuously for 8hrs, at 3000 rpm, 6 month ago and after that the performance has progressively reduced.
It will now only pull 2100 rpm.
Yesterday I pulled off the inlet manifold and all is clear here.
I then pulled off the exhaust manifold and found the the internal tube had come away and dropped down the bend.
Question 1 - Can this be re-welded or is it best to buy a new one.

The motor is very confined space wise, and I stuck my finger into the exhaust ports to find that they are really blocked up. I would say less that 3/8" dia on each port.
I jammed a screw driver in the port and managed to open up the outer part of the port to about 5/8". I pulled out chunks of metallic/black (carbon?) as I crunched away.
I am now very concerned some of this has fallen into the engine.
Question 2 - Do I need to pull the head off to fix this up or will it blow out when the engine is started.
My concern is the chunks will score the bore and my problems will magnify.
Cheers Steve