Yanmar 2GM20 - smoking exhaust

[Polarsailor]

Advice would be very appreciated.

I have a Yanmar 2GM20, raw water cooled and it has run 2700 hours.

I've had the boat 10 years and the engine has generally been totally fine. A few weeks ago it suddenly started putting out lots of white smoke. I limped back to my mooring and systematically checked the engine. The water injection exhaust elbow had failed, the weld had failed on the inner tube. Unfortunately I snapped off one of the bolts removing the elbow. After a few attempt had to take the head to an engineers to get the bolt drilled out and helicoiled.

As I had the head off I reground the valves, cleaned out the waterways and generally serviced the head although did not remove the injectors. The valves were reground. The inlet were really good but the exhaust vales were slightly pitted even after grinding Put the head back together and ran the engine. New gaskets used throughout. The bores looked fine, no scores and minimal lipping at the top of the bores.

It started easily and ran really well in fact better than before, as I had done the tappets which needed doing. At low speed up to about quarter power the engine produces little smoke. However under load the engine produces increasingly more white smoke. More than before.

If I carefully remove the rocker cover oil filler I get some white smoke coming out. This would suggest to me that the exhaust valves are not sealing too well ( I did not replace the valves, seals or guides)?

1. What is likely to be causing the white smoke - poor valve seals?
2. Could poor valve seals be lowering the compression leading to unburnt fuel being exhausted?
3. The engine has only been run for 2h after re-building is it likely to improve as it is run in?

If I hold my hand over the exhaust it smells oily but no really that much of diesel.

I have a siphon fitted between the thermostat and water injection elbow. At the top of the siphon is a very small tube that I had not noticed before I rebuilt the engine. This small pipe may be a tell-tale? I don't think any water use to flow through the small pipe but I now have a steady stream, is this correct? Are these siphon fitted with a non -return valve? The volume of water is running into my bilge and is quite substantial... has anyone seen one of these units before?

Any thoughts gratefully received!

Keiron

 

[black mercury]

The anti siphon valve must be stuck open. It will either be a bronze fitting or a plastic one, either way you should be able to dismantle and clean it up, or route the small pipe to outside the boat and use it as a telltale.
Smoke from the oil filler is usually from the bores, not the valves. But a small amount of smoke wouldn't be unusual from the filler cap, depends on how much smoke there is?
Yes, the infamous yanmar exhaust elbow! What can happen is the head can actually rot just inside the exhaust port and corrode through, was yours ok there? Also water can enter the cylinders and cause a hydraulic lock, bending the con rod. But in that case they are usually hard to start and any white smoke usually clears at higher engine speeds and load. Unless one cylinder is carrying the other. Next time what you could try is isolate one cylinder either with decompressor lever or cracking open one injector. (this is with engine cold). Now try to start on the one cylinder, it should fire but will be slow to build up the revs. The engine doesn't need to start. Now try the cylinders the other way round. What you are doing is comparing the two cylinders. Either that or buy/borrow a compression gauge. They should be similar.
Another possibility is that dirt has entered the injectors while the work was being carried out, where the injectors capped where the pipes screw on? May be worth getting them tested.
Was the two hours running under load? It may just need a good run.

 

[earlybird]

Not much to add, but white smoke usually denotes unburnt fuel. A faulty injector is a common cause. Poor exhaust valve seating or stem seals is an unlikely cause. Injector removal for testing is straightforward on a GM.
Anti-syphon valves may be either spring loaded air inlet, in which case yours is leaking, or, perhaps less common, a permament water bleed, in which case yours needs an overboard discharge point. The pipe for this should not have any loops or U-bends.

 

[ghostlymoron]

White smoke is usually steam from water entering the cylinders somehow - head gasket? Did you renew it when reassembling? Black smoke is associated with fuel problems. This unfortunately is as far as my knowledge extends.

 

[rotrax]

White smoke on old tech diesels with mechanical injectors is invariably leaking injector nozzles.

As ghostlymoron suggests it can also be steam, but I would describe that as white vapour, not smoke.

In my experience, steam dissipates far quicker than white smoke.

When I had a diagnostic to do on my Bukh DV 20-which are notorious for steam in the exhaust-I joined a length of hose to the manifold water feed and fed it overboard, then I started the already warm engine. White smoke aplenty, no steam as there was no water injected into the exhaust.

New injector nozzles affected a complete cure.

 

[Polarsailor]

Thanks all. I'll work my way through the suggestions above. According to the manual it sounds like removing the injectors on a 2GM20 is relatively straightforward. However, looking at some of the forums it sounds like getting the injectors out of the head can in practice be very difficult. Has anyone removed these injectors previously?

 

[Spyro]

Thanks all. I'll work my way through the suggestions above. According to the manual it sounds like removing the injectors on a 2GM20 is relatively straightforward. However, looking at some of the forums it sounds like getting the injectors out of the head can in practice be very difficult. Has anyone removed these injectors previously?

Yes, Both mine came out very easily. After removing the hold down plate and bolts a small knock released them. Took them to a local diesel specialist who refurbed for £12 for the pair. I've got the popping pressure written somewhere if you need it but I think It's mentioned on a post here somewhere as well.

 

[david_bagshaw]

have you rechecked the valve clearances, after re torque the head bolts after the appropriate settling down period.