Yanmar 2gm20 valve clearance issue

[Oldyanmarguy]

Thanks for the replies.

Yes I have heard about the tractor engines and mini excavators but I think the gm20 is mostly used as a marine inboard.

I will try again to get my injectors apart and clean them myself, if not I will have to pay an injector shop.

I looked at the injector pump today to either add or remove shims, there were no shims at all so I tried adding some, for a minute this stopped the unburmt fuel then the problem came back again. This could mean a very worn cam lobe.

It could also be an issue with the governer, I could not fully remove the pump so maybe a problem with the governer fork assembly.
I'm also fitting a new thermostat as the engine seems to be running really cool, the exhaust water is barely even warm and today it was the same temp as the Raw water feed.

I have spent way too much on this "tired" engine, so need to try and solve this myself if possible.

 

[Charles Erwin]

Take a break and frustration will subside. One thing at a time else you cannot get to the root of it.

As to the injector pump:
Adding shims make the fuel timing later. Subtracting causes the opposite. 0 - shims means fuel timing is probably not right - ie too early. In any case - shim such that the pump opens when the flywheel mark is at the reference. The fork will not interfere with pump removal. Just slide the rack forward or aft until it passes upward through the groove. It will withdraw very easy. Do not pry on the pump or you will bend the rack - not good.

As to the injectors:
One cannot cure a leaking injector by assembly/disassembly. They must activate at no less than 2350 psi.
Any earlier and you will have over fueling. My guess is the diesel shop will test for nothing.

This is all in the service manual. Remember they took the time to write extensively so you should take the time to read the relevant parts.

Pretty sure I can't help further from over here in the colonies.

Charles

 

[Oldyanmarguy]

Hello charles and all, today is a good day !!

My engine is now way better and happily gives me 3.5 knots at its "quiet sweet spot" which I think is around 2750 - 3000
Rpm (no tachometer gauge but I do have a sender on the bellhousing). I still had some black smoke and trace residue from the exhaust though. So I looked at the crankcase breather and it was putting a constant puff of smoke into the air filter housing, i disconnected it from the housing and just let it point towards the drip tray and then no smoke or residue out of the exhaust.

I can only assume the breather is releasing burnt oil, unburnt oil or unburned fuel ?

I have not over - filled the sump, at the moment it has 1.5 ltrs of 15w 40 in it, deliberately under filled because of the issue, just in case the oil relief valve was not working.

If I continue to have it disconnected I will have to put some sort of filter on it, unless someone here advises me not to and re-connect it to the air filter housing ?

I suppose what I need to do is somehow determine what the crankcase breather is breathing out and why is it doing it.

I have my own oil pressure gauge installed and I get between 48 and 57 psi, the oil relief valve appears to kick in at 57 - 58 psi, idle oil pressure never lower than 35 psi

Also my own temp gauge, but with the sender cable tied to the outside of the cylinder head block, I didn't have the tools to tap into the thermostat housing, it reads a max of 40 c and also shows my old thermostat was way too cold, getting stuck 15 % open.

If anyone can offer advice on the crank breather smoke, I would really appreciate it, it's not solid black smoke, more black / grey smoke.

I fitted new piston rings a couple of months ago, could not find over size rings so they were standard yanmar size and the cylinder bores measured up within yanmar tolerance spec.

Last but not least, I've pop tested my injectors again and they do not appear to be leaking, I filmed them popping on my mobile phone and then played back in slow motion and could not see leaks between pops. However I'm still prepared to get them tested / calibrated and now have a marina workshop recommended to me, which is much better than a car / truck diesel workshop.

Happy days though, my engine is way better and happier.

 

[Charles Erwin]

There is a hole drilled in the bottom of the breather chamber. This drains liquid to the crankcase and so prevents any accumulation of condensed vapor in the chamber. There is a risk that accumulated liquid will be drawn into the intake - not good. So check this drain and keep it clear.

No filter in the breather assembly because there needs to be a clear breathing path crankcase to intake. A filter is not so good an idea because it can foul and so reduce the limited intake vacuum path which keeps the crankcase pressure low and the crankcase clean.

 

[Oldyanmarguy]

Thanks for the reply.

The breather is working fine and not blocked. I checked the video of my injectors popping again and im now pretty sure they are not always popping, number 1 looks to be missing popping erratically. So it looks like it's either injectors, pump or governer rack. New injectors are £180 each or £60 each for New nozzles, which is the complete lower half of the injector.

I will try again to get the pump out, feels like it's jammed tight on the governer fork, then if successful get the gearcase cover off to have a look at the governer rack.

Engine also sometimes sounds imbalanced, like sometimes only firing fully on 1 cylinder, this may explain the awful state of my old cylinder head with 1 combustion chamber more cooked than the other.

It's taken me ages to get to this conclusion but at least I now know.

If the lower half of the injectors are available separately, then I'm wondering if the top half rarely fails ?

 

[RoyS]

Removing the injector pump takes courage. Purchasing the lower parts of the injector nozzles will do you no good unless you have a bench pop tester to adjust the pop setting. This is usually done with shims above the spring.

 

[Oldyanmarguy]

Many thanks Roy, I managed to remove the pump. I discovered there is an inspection plate on the rear side of the gearcase case cover, this allowed me to get a screwdriver in to the pump fork and gently tweak it to release the pump. The fork looks fine and inside the gearcase looks really clean, well lubed and completely free from corrosion or rust.

The pump looks ok and I found it did have 1 shim still on, I removed the shim and the fuel timing now looks good at tdc on both cylinders, i have pumped some penetrating fluid through both injectors and will leave them over night, may not do anything but certainly won't harm them.

I took the cylinder head off and there's a lot of black carbon, the exhaust port which was clean a few days ago was black with wet oil.

I also realised I did not hone / crosshatch the bores, which I have now just done but it may be too late. Silly mistake as the bores were well glazed.

I will pop test the injectors again tomorrow and if they look uneven or mis firing then I will get them looked at by someone who has been recommended.

I now think the issue is, fuel timing was late and hopefully now fixed, so maybe just 1 or both injectors needing service.

 

[Charles Erwin]

You are trying to do too many things all at once and so crippling the likelihood of success.

If you did not hone the bores you will probably never get the rings to seat even if the clearances are OK. And - honing needs to be done with stone - no diamond no plateau. These motors use chrome rings so you need to have that initial sharp cross-hatched scratch (45 degree intersections) to retain oil and obtain a decent ring sealing. Also wash the block with hot soap and water after honing. This is a job for the machine and it is very cheap to do.

As to fuel delivery timing - it is virtually impossible for these Yanmar motors to go out of time. Removing the shims has changed fuel delivery timing. Moreover fuel timing is not TDC. The 2GM20 is 15 degrees before TDC. The flywheel is clearly marked. Anyway you better re-verify timing. (See manual 3-20)

Head gaskets are a one time deal which means you now will need a new head gasket.

Charles

 

[Oldyanmarguy]

Many thanks Charles. I forgot to.mention that fuel timing is now at the correct Mark, 15 degrees just before the tdc Mark, after removing the 1 shim that was on the pump. I've extensively tested and the lift pump, injector pump and injectors now all seem to be fine. No drips, no miss firing, equal spray patterns, and I can hear the injectors opening and closing with the little click from the spring and plunger etc.

I filmed the injectors on my phone whilst the head was off, then played it back in slow motion and it clearly showed injector pulses just before each piston reached tdc, so I'm happy with fuel timing now.

My cylinders are slightly oversize from wear (maybe 0.2 to 0.35mm) my digital calipers only just reach past the bore ridge, so difficult to get accurate reading of bore further down, I tried to find over size piston rings before ending up buying standard yanmar rings. So maybe they will never bed in anyway, a re-bore and sleeve of this block will not be happening.

Engine now starts really quick and runs well but still some fuel or oil in exhaust, much less than before. More concerning is the amount of carbon build-up I found on the combustion area of cylinder head directly under the injectors, only in that exact area, which I'm not sure how is happening when the entire fuel system seems ok. Could the injectors be leaking when the engine has warmed up to temp ? I fitted new heat shields, washers etc.

I know that carbon build-up is very common, especially in old diesel engines but this was a lot of carbon in a short space of time, maybe just 2 days sailing.

With regards to tractor engines, it appears that the John Deere 650 / 750 had a 1gm, 2gm or 3 cylinder yanmar. I've found injectors for sale that look identical with very slightly different yanmar part numbers, really low prices but none in the u.k

Could a moderator change the title of this thread to something like yanmar 2gm20 rebuild so that other people can find it, I will try and post everything I have learned here.

Thanks again for the help in this thread, much appreciated.

 

[Oldyanmarguy]

Cannot believe I did not think of trying this......I have just separated the water flow from the exhaust and sent it out over the other side of the boat, the water is clean and there is no residue from the exhaust , so it's all been due to the water mixing with carbon deposits in the exhaust and forming it into a floating liquid that looks like fuel or oil ! Happy days, my boat is not dumping oil or fuel as I have thought for ages : ))

The exhaust smoke may also be getting less so maybe I might be lucky and the piston rings are starting to bed in a bit.

However, the excess carbon build up will continue until I find out why and if I can solve it at all.

So very pleased my boat is not dumping fuel or oil, it's been worrying me a lot

 

[mz4wheeler]

Have you checked your exhaust elbow? A clogged elbow will cause smoke, slow starts and wasting fuel. They require cleaning every 3-5 years. Replaced mine a couple of years ago and made an amazing difference.

 

[Oldyanmarguy]

Hello, yes I cleaned it when I fitted the new cylinder head and the exhaust port was cleaned and checked for cracks or holes. The carbon build up in the combustion area is directly under the imjectors, maybe it's unburnt fuel when I stop the engine and the injectors fire 1 or 2 times after combustion has stopped, meaning there is a pool of fuel in a hot cylinder head = carbon build up.

I checked the valve and fuel timing again today and it's all good, the fuel starts to pulse at exactly on the fuel timing mark before Tdc and stops at the right time too.

I wish I had a diy compression tester, I may see what a boatyard will charge for a test.

 

[jibes138]

You can probably rent one (compression tester) at an auto parts store. Try NAPA, AutoZone, etc.

 

[Charles Erwin]

I made one - but here is the idea. Hoye probably won't be able to
help much in the UK.

 

[Oldyanmarguy]

That looks very well made. I will have to find a way because I now have to know. I checked the fuel return today and there is only a tiny amount of fuel getting expelled from the top of the injectors back to the tank, I have just been searching Google and what I'm reading is that it should be a lot more, so does this say that my injectors are indeed spraying way too much fuel / leaking etc ? If so I will definitely get them looked at.

My engine temp is now approx 40 to 45 Celsius at cruising speed , measured on the outside surface of the head with the probe touching it. One day I will get it tapped into the stat housing.

I don't have a fuel gauge but do have a measuring stick for the tank, I will try and calculate litres per hour.

 

[heritage]

That looks very well made. I will have to find a way because I now have to know. I checked the fuel return today and there is only a tiny amount of fuel getting expelled from the top of the injectors back to the tank, I have just been searching Google and what I'm reading is that it should be a lot more, so does this say that my injectors are indeed spraying way too much fuel / leaking etc ? If so I will definitely get them looked at.

My engine temp is now approx 40 to 45 Celsius at cruising speed , measured on the outside surface of the head with the probe touching it. One day I will get it tapped into the stat housing.

I don't have a fuel gauge but do have a measuring stick for the tank, I will try and calculate litres per hour.

I also found very little fuel returning to the fuel tank on my yanmar 2gm20f. After a little research, I read that most diesels do have a substantial overflow of fuel through the injectors for cooling purposes. But for some reason the GM yanmars don't seem to need the extra cooling so most of the fuel is shot into the compression chamber.

 

[RoyS]

Regarding measuring liters per hour; My 2QM15 gets two hours of operation at 2750 RPM per gallon or about two liters per hour. This Yanmar also has very little return line flow.

 

[Oldyanmarguy]

Thanks for the info, mine seems to be 1.2 litres under medium load with the prop, and 0.8 litres on idle stationery and just running the alternator. I had some problems today with the engine under load, speed not increasing after a certain rpm and some hesitation / sluggishness. I know most of the causes of this so will check tomorrow, but I'm a bit confused right now about the mixed exhaust system - my 2gm20 was setup with the normal yanmar mixing elbow going to an exhaust pipe running down to a container / bottle then running back up and out through the side plate. My concern has always always been that the water runs down to this bottle and fills it up before it travels back up and out, so surely this temporarily blocks the exhaust gasses until they build up and literally blow the water out, meaning the engine is constantly struggling to breathe properly ? Or am I mistaken and this is exactly how a mixed exhaust system works ?

 

[Ken13559]

My 2GM20F started off with 1.5L/hr @2800rpm 15years ago. Now after 2200+ running hours she clocks in at 2.1L/hr @2800rpm.

 

[Oldyanmarguy]

Oh well, glad I decided to take the cylinder head off again, this is what it looks like after a couple of days use - not good....

I'm not sure if that's oil or fuel or both.