Yam are engine problems

[mikew320]

Hi all,
Having recently purchased a Hunter 326 I'm gradually working my way through it sorting out age related issues.
One of them is the Yanmar 2GM20F engine. It starts and idles well and will run in neutral up to 3,500 rpm reasonably smoothly. However when in gear and out cruising it's not so good. Up to 2000 rpm it's fine. But if I try and quickly apply full throttle it bogs down, shakes a lot and gives off a lot of white smoke in the exhaust. Equally if I slowly apply the throttle to achieve greater rpm it still bogs down and won't accelerate.
At first I wondered if it was a rope around the prop so took a dive under the boat. No rope and the prop was clean but the prop shaft was covered in barnacles. The reason for the vibration?
Any thoughts on what should be causing it? Also under normal operations how much should the engine vibrate?
Thanks in advance for your advice.
Regards and fair winds.
Mike

 

[mikew320]

Thanks auto spell on my ipad. The thread should of course read Yanmar Engine Problems. Sorry!

 

[kloudie1]

Runs OK without load, bogs under load.. for a diesel, that is probably a fuel delivery problem.. dirty fuel, dirty fuel filters, bad lift pump, fuel pickup tube tip screen fouled, very small air leak at a fitting or hose crack between the tank and the lift pump.. If one of those doesn't correct it, then things start to get a little more expensive..
These symptoms are not usually caused by a clogged exhaust elbow or clogged intake filter
Vibration may be a mis-aligned prop shaft at the engine coupling, or bad engine mounts..

 

[justsomeguy]

Definitely clean the prop. A one-inch putty knife will take care of the worst barnacles and should help reduce vibration.
Agree with Claude regarding bogging down because of fuel issues.

Edit: sorry for misspelling your name Claude!

 

[py26129]

Absolutely, check the easy stuff first, but white smoke is typically a symptom of water entering the combustion chamber due to a bad head gasket or worse.

Matt

 

[Don Crowther]

You could also check the prop pitch. One blade maybe twisted a little from hitting something or you might be over/under pitched.
Just my 2 cents

 

[Roland5048]

Agree with the fouled shaft and possible fuel problem. I know when my running gear needs a good cleaning because I can't get up to 3600 rpm and vibrates. This happened recently. Could barely make 3400 rpm. Cleaned the prop and shaft and now running almost 3600 rpm with little to no vibration. Fuel filters are next when I do an oil change.

 

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[Ken Cross]

Chronic problem with the 2GM20F, the exhaust elbow clogs up just past where the water is injected into it.
Some have cleaned them out, some just replace them. They aren't cheap. The stainless fitting between the exhaust manifold and the elbow has a LH and A RH thread. So to disassemble it you just rotate the shiny silver hex piece between them.

When I took ours apart the opening was about the size of a #2 pencil or smaller and we could still get 3,000 rpm. It runs way better with a larger exhaust passage. Still, clean the prop shaft as others have said which gives you a chance to check the Zincs.

A dirty fuel filter is another possibility.

Ken

 

[mikew320]

Hi all and thanks for the great thoughts and ideas.
I spent some time down on the boat the other day and thoroughly cleaned the prop shaft. Then I ran the engine in the slip with doubled lines and the vibration appears to have gone so hopefully we've cured that problem. I was also able to get 3600rpm by slowly increasing the power. However if I gave it instant full throttle it again bogged down, white smoke and refused to go above 2000 rpm. It's nice to know that with a gentle throttle hand all seems to be ok but if I need a sudden burst of reverse when coming into the slip that may not be available.
Any thoughts?
Mike

 

[Benny17441]

Yes, for us "shade tree mechanics" the process of elimination works best. We start at the cheapest and easiest and work up to the more labor intensive and expensive with the hope that we find the problem and the fix somewhere along the way. You have identified a possible fouled prop so definitely clean it up before moving on. Check your tachometer and speed readings to make sure the RPM readings are within reason and the engine is truly underperforming. Next I would replace the filters and drain the water separator. Gauge the condition of the fuel; you want a clean and fresh fuel with little water. Check the valve lash. If still problems then remove, inspect or replace the mixing elbow. I have not addressed vibration as it is usually a by- product of the problem. After you get the engine back to normal operation and still have a vibration you may check the motor mounts for undue wear. A visual inspection is worthless. A fouled prop can lead to overfueling which usually results in black smoke. Bogging down when increasing throttle usually points to clogged fuel filters. Old or contaminated fuel causes many of the symptoms you are experiencing. If the prop has barnacles I would imagine the hull does too so cleaning the bottom will help.