Wierd Diesel Generator Cylinder Damage.

Messages
28
Location
oxfordshire United KIngdom
I picked up a broken diesel generator for free(10hp Chinese yanmar clone 6kw unit), i didn't know the history of it, all i knew is it was faulty in some way. Anyway the initial inspection was good, it appeared to have decent compression (at least i thought it did) and the injector was spraying evenly and making the distinctive chirping sound when it injects. I tried to start it, which was very hard with out the starter motor (Dead battery), but when it ran it could not get up to full speed and made the most awful noise imaginable (at the time it sounded like heavy pinging) and it created a huge cloud of black diesel smoke. This was odd as at first it looked like an injector issue, but they checked fine so i thought i might take the rocker cover off to change the valve clearance to see if that made a difference. They where a bit loose but i have seen a lot worse before! After that i started it up with the rocker cover off, just to see if anything unusual was happening. It turned out that my previously diagnosed pinging sound was actually the noise of the combustion gas escaping in to the crankcase, presumably from blow by . Sounded kind of like a blown head gasket but 10x louder, i suppose when the engine is sealed the noise sounds more like a knocking sound which is what i previously thought. So my next course of action was to remove the head, a 10 minute job on these yanamr / yanmar clone engines. Upon inspection i noticed everything looked normal, but when i turned the engine over there was a huge dent in the cylinder wall at both ends, literally 1/8" of metal was gone on both sides! This is obviously what was causing the excessive blow by. It looks like i will have to replace the block but what could cause this in the first place? No metal had impacted the valves or the cylinder head. [img:left]https://flic.kr/p/oxYjQe[/img] [img:left]https://flic.kr/p/oeHRT9[/img]
 

JTK

Messages
13,432
Location
Buffalo, NY
WOW that is weird! The piston would be all banged-up if it ingested something 'non-combustible'. I wonder if it could be fixed with a sleeve?
 

Lewis

Thread starter
Messages
28
Location
oxfordshire United KIngdom
That's what i thought,the piston appears to be perfect! The sleeve is cast in to the engine block, and you can get a new block for next to nothing. I was thinking it could have been due over advanced injection timing causing detonation.
 
Messages
13,088
Location
North Carolina
Looks like something went wrong( tool failure?) when the cyl was being bored initially. Then they just said screw it and put it together anyway.
 
Messages
2,008
Location
grande prairie AB
If it was only one side I would say the Rings were not spaced opposite to each other. is it steel or alum? If it was sleeved you could get a new sleeve. But why did that happen in the first place?
 
Messages
11,656
Location
Illinois
It would be interesting to see what the side of the piston looks like. My vote is for a failure in the wrist pin or the circlips holding them in place.
 
Messages
1,429
Location
quebec canada
Originally Posted By: loneryder
Lousy Chinese steel?
sound like bad quLity coolant !we (trucking industry)had ton of cylinder liner pitting issue caused by coolant being not pure enough.
 
Messages
750
Location
MN
Detonation usually isn't an issue with a diesel because they always run lean and the fuel isn't part of the equation till right around TDC if the injection timing is set right. I'm guessing that it was a very thin spot in the casting that blew through. Was there any debris in the crank case? If no debris then it likely happened before or during assembly and the QC department was not on the payroll that day which is often the case with clone engines.
 
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