[TSOJOURNER]

I have a Yanmar 3YM20. The engine was just reinstalled following a piston repair. Now the engine stinks up the cabin when running. While trying to track down the source of the smell, I noticed that the air intake silencer was expelling air as if it were an exhaust. Is it supposed to do this?

 

[bubb2]

It sounds like you have a intake valve hanging up (Not closing)! Then on the compression stroke the piston just pushes the air/fuel mixure past the open intake valve and out the breather!

 

[JohnRPollard]

I have a Yanmar 3YM20. The engine was just reinstalled following a piston repair. Now the engine stinks up the cabin when running. While trying to track down the source of the smell, I noticed that the air intake silencer was expelling air as if it were an exhaust. Is it supposed to do this?

Definitely not. That's potentially dangerous, too. Diesel exhaust only has a small fraction the CO content of gasoline exhaust, but if it's discharging into your cabin for long durations it could eventually build up to poisonous levels.

Who did the piston repair work?

 

[timebandit]

Intake valves adjusted to tight
Rings on new piston not seated yet
Crankcase vent hose not attached properly

 

[TSOJOURNER]

Definitely not. That's potentially dangerous, too. Diesel exhaust only has a small fraction the CO content of gasoline exhaust, but if it's discharging into your cabin for long durations it could eventually build up to poisonous levels.

Who did the piston repair work?

Another mechainc looked at it today. Turns out what felt like air coming out of the silencer was actually air going in (confirmed by smoke test). The smell is reported to be "new engine" smell.