Yamar 3GM30F Rebuilt Gloopy Exhaust

[robbieg]

I have a rebuilt 3GM30F on the bench and I am testing it prior to putting in the boat. Rebuilt means new bearings, rebore with new piston and rings, serviced injectors, reconditioned head with new valve seals, all new gaskets etc.. The engine starts and seems to run fine with good oil pressure. However, I cannot run under load and so have just run here for an hour or so at 12-1500 rpm to check all joints, fluid levels etc-all look good.

However, on taking off the temporary exhaust I noticed “gloopy” residue in the exhaust flange. Removing it showed no 2 and particulary no 3 exhaust port was producing an oily deposit and not dry carbon. Hard to tell whether this is oil or diesel mixing with the soot to produce this gloopy mixture.

I suspect (am hoping!) that this is either the engine overfueling after being run at low speed on light load and/or some oil being burned whilst the new rings bed in. Acccordingly once the engine is under load and gets some work I am working on the assumption this will clear up.

However, I don’t want to get the engine in the boat and find I have a problem so any thoughts from anyone else who has had this sort of deposit or has any idea about the cause would be most welcome. Additionally if there are any further tests I can do with the engine on the bench do shout.

Thanks.

 

[rotrax]

Hi, As a 45 year small engine mechanic I can offer the following: 1. If the engine is quiet, has good oil pressure and runs at a normal tempreture with no significant exhaust smoke all is probably well. 2.If you were water cooling the exhaust the tempreture at this point would be low because of the lack of load.This can cause deposits in the areas you mention. Even without water cooling a low load situation with give this. 3.After spending on an expensive rebuild you are always aprehensive about over reving or overloading too soon. Dont be-use up to half the avaialable RPM range freely.If the rebuild has been done right all will be well. The oft mentioned bore glazing will not happen in the relitivly short space of time you will be testing out of the boat. 4.When you are happy all is well,put it back in and gradualy increase the loads applied against warps at the dock.Always keep a good eye on the engine temp. and oil pressure untill you are sure of the reliability.Hope this helps,Good Luck.

 

[steve28]

having just done the same on 2gm20 i think you will find its just the overfueling.

I bet your pocket is feeling the same as mine, although i only have 2 pots.



regards

Steve

ps dont run it above 3/4 throttle for 50 hours

 

[oldharry]

I have a rebuilt 3GM30F on the bench and I am testing it prior to putting in the boat. Rebuilt means new bearings, rebore with new piston and rings, serviced injectors, reconditioned head with new valve seals, all new gaskets etc.. The engine starts and seems to run fine with good oil pressure. However, I cannot run under load and so have just run here for an hour or so at 12-1500 rpm to check all joints, fluid levels etc-all look good.

However, on taking off the temporary exhaust I noticed “gloopy” residue in the exhaust flange. Removing it showed no 2 and particulary no 3 exhaust port was producing an oily deposit and not dry carbon. Hard to tell whether this is oil or diesel mixing with the soot to produce this gloopy mixture.

I suspect (am hoping!) that this is either the engine overfueling after being run at low speed on light load and/or some oil being burned whilst the new rings bed in. Acccordingly once the engine is under load and gets some work I am working on the assumption this will clear up.

However, I don’t want to get the engine in the boat and find I have a problem so any thoughts from anyone else who has had this sort of deposit or has any idea about the cause would be most welcome. Additionally if there are any further tests I can do with the engine on the bench do shout.

Thanks.

The rings will not have bedded in properly after the rebore yet. Running on light load it will not be hot enough to burn off carbon/oil deposits. As Rotrax says, resist the temptation to cosset it after spending all that money, and let it run at a good speed. Much better for something to break or leak now, than when its back in the boat!

 

[robbieg]

Thanks

Yes it was expensive but hopefully worth it. Right off to the garage to run it hard and anoy the neighbours!