Yanmar L48N diesel single cylinder running waterpump black exhaust smoke

   / Yanmar L48N diesel single cylinder running waterpump black exhaust smoke #1  

FordnMassey

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ford 3000 and MF35
Hi,

I have an L48N single cyl air cooled diesel engine running a water pump that has become very smokey. The smoke is black and sooty, making soot on anything nearby. It was mild when I bought it second hand (unknown hours) around 100 hours ago, and suddenly became very heavy recently. It produces it at idle, light load and heavy load. I am trying to find the cause of the smoking. It sounds like it is producing less power and not quite reaching full rpm - I can't put a tachometer on it.

I pulled the injector and hand cranked the motor and produced 4 neat jets of diesel spray at 90deg to each other with no dribble before or after. I think this is fine. Following that I ran injector cleaner thru it and no change.

I pulled the oil fill cap while running and eased it clear for around 1 second. Large amounts of blow by are present - enough to think I was looking at an exhaust outlet.

I am figuring the smoke is sump oil being burnt, likely thru the rings, which are also the source of the blow by.

Questions:

1). Am I right in thinking rings?

2). can anyone suggest a tool set or brand/item number for compression testing this? Looking online at kits I see a variety of inserts but none appear to match the injector on the Yanmar.

3). Could a valve issue cause sufficient oil burn to give this appearance?

Thanks in advance for your help.

FordnMassey
 
   / Yanmar L48N diesel single cylinder running waterpump black exhaust smoke #2  
There is a purposed thread for your Yanmar engine located here. It's rather extensive. On several pages, one can even find the manuals posted.


Seafoam is a great product to clean up the inside of the single piston motor without tearing it apart piece-by-piece.
 
   / Yanmar L48N diesel single cylinder running waterpump black exhaust smoke #3  
If you've not done so, check the air filter and the air path from there to the manifold. Perhaps you'll get lucky and that's all it is. (Perhaps not.)
 
   / Yanmar L48N diesel single cylinder running waterpump black exhaust smoke
  • Thread Starter
#4  
Hi,
I should have said, I changed out the air filter, and ran it briefly without one and there was no improvement. I haven't inspected the air intake pathway fully tho, so will do. Nothing lost by looking there.
It wouldn't explain the blow by tho, unless I'm missing something.
Thanks for your reply.
FordnMassey
 
   / Yanmar L48N diesel single cylinder running waterpump black exhaust smoke #5  
I think that if you are getting significant crankcase blow by, my bet would be on rings. You might take the valve cover off to check there, just in case a valve seal has gone.

All the best,

Peter
 
Last edited:
   / Yanmar L48N diesel single cylinder running waterpump black exhaust smoke
  • Thread Starter
#6  
Hi,
Thanks for the replies. I'll pull the head and the piston and see what I find.
Thanks
FordnMassey
 
   / Yanmar L48N diesel single cylinder running waterpump black exhaust smoke
  • Thread Starter
#7  
Hi,
ring 1 found to be 2.30mm thick, where normal is 3.00-3.20mm and service limit is 2.77mm (from bore contact surface of ring to the inner surface which faces the centre of the piston). So I'm calling that bad rings. Correct me if I am wrong.
Never did compression gtest it as I could not find a kit that would provide the right fitting for the injector hole.
Planning to hone, re-ring and run it.
Anyone see an issue with this as a plan?
Thanks,
FordnMassey
 
   / Yanmar L48N diesel single cylinder running waterpump black exhaust smoke
  • Thread Starter
#8  
Hi,
Thought I'd give the results of the next step, for reference for others.

Re ringing and honing reduced the smoking to very mild, which could be normal for a diesel. I'll watch sump oil level and see if it's consuming oil.

Thanks for the help.

FordnMassey
 
   / Yanmar L48N diesel single cylinder running waterpump black exhaust smoke #9  
Good news. What are you running for oil in that engine? Regardless, Might be good to do a couple of short 50hour oil changes due to soot contamination…
 
   / Yanmar L48N diesel single cylinder running waterpump black exhaust smoke
  • Thread Starter
#10  
Hi,
Apologies for the delay.
30W mineral oil by Penrite, a well regarded Australian brand. Temperature range here 10-30C or 50-90F.
Good tip on the early oil change. It wasn't visibly sooty inside, but I'm sure there's much more in there than would be normal.
I should add to help others who find this later that compression ring one measured well below tolerance, so it's an easy one to tell once the engine is disassembled.
 
 
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