Black smoke on yanmar diesel

[Compass790]

Did you do a compression check when you did that work 3 years ago? I would clean the tank too if possible as you say it gets worse when fuel is stirred up. How many hours on the engine? i can't see any link to the vid fyi

[Craighershoff]

Thank you for the response
I haven’t figured out how to post the video directly, so here is a link :
https://www.dropbox.com/s/wwe2hebe44....TRIM.MOV?dl=0


I have approximately 2500 hours on the Yanmar. It’s a 1991 model year. I never did a compression test before. I assume the Manual will show me how, and I suppose the appropriate compression Gage can be found or maybe rented.
Regards
Craig

[ed2068]

Hi:
I have had the same problem with my Weterbeke 38 b 1993 engine. Went thru the same issues of the black smoke, low rpms etc. that you state. I was down in Marathon and wanted to get a second opinion on it, a great the mechanic by the name of Diesel Don looked at what you have looked at mixing elbow, exhaust hose etc. nothing. Then he took off the valve cover and it was a broken rocker arm. Easy to detect, take off the valve cover and look. Let me know if this helps.

Regards

[Copacabana]

Start with the easy things:
- Is the bottom and prop clean?
- Remove the air filter and see if the smoke stops and revs go back to normal.
- Mixing elbow (remove and clean- and also the manifold).

I had the same problem with my Yanmar 3GM30F. Over time, I couldn't get up to higher revs and it began smoking at cruising revs (black smoke). I went through the obvious things and then got to the mixing elbow. I removed the elbow and manifold- both were partially blocked. I put on a new elbow and- most importantly- had the manifold cleaned by a local Yanmar shop. Problem solved.

[Craighershoff]

Thanks, I will try looking at the Rocker arm.
I did try all the easy steps first, that were mentioned.
I replaced the elbow two years ago, I checked it recently and it’s OK. Forgive my ignorance but does a one cylinder yanmar have an exhaust manifold?

[Copacabana]

Originally Posted by Craighershoff

Thanks, I will try looking at the Rocker arm.
I did try all the easy steps first, that were mentioned.
I replaced the elbow two years ago, I checked it recently and it’s OK. Forgive my ignorance but does a one cylinder yanmar have an exhaust manifold?

The elbow should be bolted onto the manifold. It's the collector for exhaust gasses. I imagine yours will be small with only one cylinder. It can't hurt to remove the elbow and manifold to have them cleaned. It doesn't take much crud to affect engine performance.

Check your air filter as well. An easy test is to just run the engine without it to see if things improve.

[Craighershoff]

In the 1 GM 10, the elbow is bolted directly to the cylinder exhaust port. I did not really inspect the port when I took off the elbow, so I will do that. I did run it without the air filter, with the same results. I am going to try to find a compression tester to rule out that issue.

[Compass790]

After viewing yr vid I'm wondering if you have enuff water flow, it's steaming & smoking. Unless its very cold where you are you need to check water intake strainer & raw water pump impeller. Is it using oil?
I'd check tappet clearance when you have rocker cover off but you wont have a broken rocker arm as a single wont run with that problem. Check your workshop manual trouble-shooting section but given that you did up the fuel system recently I'd check the compression. It should tell you in the w/shop manual but I imagine it wud be similar to our Yanmar ysm8 which is 397-454 psi @ 200rpm & the minimum is 355psi
if you are in the US I believe you can rent a compression tester from auto parts places

[Craighershoff]

Thanks for the input. I just put in a new water pump, and I’m pretty sure the inflow is not blocked. The water output seems to be normal, and the engine is not overheating. I spoke with my Yanmar dealer, and he said that on a one cylinder, if it starts, there is no compression problem. He suggested I change the primary filter, which I had previously inspected and it looked good so I reused. I did that today, it sounds better. FOT is 3600 RPM in neutral, with no smoke. I’ll know when I try it in gear tomorrow.

[Compass790]

Ok good that it's not a cooling issue then. Agree with Yanmar dealer if it starts EASILY, however if hard to start that's another story.
Maybe you need to check secondary filter too. Have you cleaned tank? Does it burn oil? Maybe injector needs a clean if dirt/water been getting in.
Let us know what you find.

[Craighershoff]

I changed the primary filter, even though it looked good, and that seems to have stopped the smoke issue. I still can’t get beyond 3050 Rpm in gear, even with a clean prop and bottom. Also I may have an oil issue since the level was way down. I’ll have to keep an eye on that. The engine starts easily, and tops out at 3600 RPM no load.