Turbo - Is this OK?

[markpj23]

Yanmar 4JH2-DTE turbo. Problem with black smoke. Check the turbo to see if it's turning.

I took off the intake screen and stuck my finger in to turn the vanes. They turn OK, and I feel no binding. However, they do not spin freely like a pinwheel or a top. When I turn them and take my finger off the vanes, they stop. I expected them to keep spinning a bit before stopping.

Should they spin more freely? It's kinda tight to get my finger in there so maybe I don't have the right angle or something.

[David M]

The turbine only gets lubricated when there is oil pressure from the engine. It should be able to freewheel a couple turns or so. If there is any metallic noise when you turn it by hand then you have problems. Black smoke is an indication of a rich mixture or fuel which is not being completely burned.

Do you hear any turbine whine while the engine is under a load at higher RPM's? If the turbine is not spinning up at higher RPM's then that would cause a rich mixture. Is your engine still able to reach its maximum rated RPM with its normal load?

[Alan Wheeler]

I got to the "stick my finger in the" and damn near screamed. Then I realised it wasn't running. It's one very quick way to trim your fingernails.
No you won't get it to free spin. The turbo shaft is floating on oil and the oil viscosity stops it from turning freely.
David has the right question, can the engine reach it's full RPM or/and have you noticed lack of power???

[David M]

Alan...of course with the engine off! (smacking my forehead) And then, if normal, it will spin a few times if you take your finger and give it a spin. It certainly won't freewheel like a top.

[Ex-Calif]

When did the trouble start - When troubleshooting a problem it's always a good idea to start at the beginning.

If you can identifiy what has changed you can often zero in on what has failed or is not working right.

If it has been a gradual change over time, it could be that the engine is old and ready for overhaul. Lot's of stuff between a and b.

In simple terms black smoke will usually indicate the engine is under excessive load for the speed. i.e. the throttle is open to a point where there is too much fuel being dumped in for the air flow (rpm) and unburned fuel is coming out the exhaust. With a lower load the engine would speed up and "balance" the fuel air mixture. Hnece the question does it smoke in neutral at any RPM and does it make "full" rpm?

Blocked inlet, increased resistance in the drive train - shaft/prop bearings, fouling, too high a pitch etc - are all candidates.

A failed turbo could possibly do it but that would be low down my list of things to suspect.

Is there a reason you suspect the turbo?

[markpj23]

All valid questions...

Yes I hear the normal turbo "whistle" while running. The engine sounds about the same.

I cannot reach full RPM as before. I am investigating shafting / cutlas bearing as we speak (gonna pull the shaft).

This appeared rather gradually. Smoking gradually worse, now heavy and lots of black soot floating in the wake. I am pulling the exhaust elbow also. The PO carried a spare exhaust elbow, so this tells me a lot.

Sounds like it may not be the turbo - at least I can hope eh?

[Ex-Calif]

The shaft problem could hide itself. Does it smoke from initial start up? If it smokes after a while running in gear I might zero in on the shaft. Heat can change dimensions and cause binding at temperature that may not be there when cold.

However if it is binding in the shaft you should be able to check it out without pulling the shaft. i.e. does it rotate freely in neutral.

It sounds like you have checked a lot of the easy stuff first, inlet filters, exhaust blockages etc.

I am assuming from your last post that it doesn't smoke in neutral through the entire rpm range and that you can get max rpm?

[markpj23]

Does not smoke at startup / idle, only under load. I cannot get max RPM - not even close. Should get 3200, my max is 1600 in gear.

That's why I really suspect shafting / cutlas bearing issue.

[Ex-Calif]

Good call - I am sure you dove on the prop and checked for fouling, rope snags, nets etc...

[Alan Wheeler]

I cannot reach full RPM as before. I am investigating shafting / cutlas bearing as we speak (gonna pull the shaft).

I know this is obvious, but have you ensured the prop and hull are clean??? :-) Because that is often a very easily ovelooked problem. Honestly you wouldn't believe the number of people that simply miss that.

[markpj23]

Originally Posted by Alan Wheeler

I know this is obvious, but have you ensured the prop and hull are clean??? :-) Because that is often a very easily ovelooked problem. Honestly you wouldn't believe the number of people that simply miss that.

Agreed. Yes we had some growth on the prop and it's time to re-do the bottom. Boat is already scraped, sanded and waiting for paint. I'm going to do the boot stripe first, then paint the bottom.

I've got something else going on though... it's hard for me to turn the shaft by hand unless I grab the prop to do so.

[Alan Wheeler]

I am not sure if I would expect the turning of the shaft easy, but certainly should be no effort grabing the prop. Does it feel stiff??
Another question or two with the motor, are there any telltail signs of smoke that you never saw before?? A failed turbo results in little air getting into the motor. Because the fuel is wound up on the injector pump to compensate for more air, the amount of raw unburnt fuel is huge. So they smoke like an old Steam Locomotive.
Does the engine rev to normal max RPM out of gear??

[David M]

I hate to say it, but I would hire a professional at this point. Only so much can be diagnosed on a forum. There are just too many variables without any of us being able to see anything.

[Alan Wheeler]

Totaly agree David. But it's till fun trying ain't it.

[markpj23]

I did not try to go too far above 1500 rpm in nuetral. Seemed fine, spun up as usual.

I'll be back there this weekend and am pulling the exhaust elbow - my main suspect at this point.