Forum for air cooled diesel engines and clones

[90cummins]

I repaired a 6500 watt set like yours last year the owner was using it to power his job site carpentry tools and charge the cordless batteries.
Ran fine for 2 weeks being very lightly loaded in the summer then suddenly started running rough, smoking and skipping.
When I cranked it over trying to start it also had low compression.
When I tore it down I found a large burned mouse nest in the exhaust side of machine.
Having seen these symptome before I tore the engine down expecting to see the cam bearing damaged, not the case.
Found carbon on the piston rings and rust patches in the cylinder.
Removed the valves and saw they had bad seats.
Honed the cylinder to clean it up and soaked the piston and head to remove carbon.
Cut new seats with my Neway seat cutter and ordered new rings, bearing & gaskets.
Reassembled and ran it at 75% load for an hour or so with no issues.
Problems I've seen in the past is a failed bearing on the camshafts small end which will afffect the injection timing.
You can check the bearing condition if you remove the injection pump and pull the injection tappet out.
It the bottom of the tappet that rides on the injector cam lobe is worn that's a sign the cam bearing is bad.
In your case I'd check valve clearances first then the injector tappet, if no problems are found pull thhe head and check the valves for proper seal.
Injectors rarely go bad unless bad fuel was used.
Running these with a light load will create running issues (wet stacking) which I've seen on 2 used military Yanmar L70's
removed from generators that were purchased on Ebay.
Wet stacking is a real problem with these if are operated in cold temps with a light load.
90cummins

 

[90cummins]

I was sitting here thinking about your air filter being burned up & missing.
These generators have a cat in the exhaust and it may be plugged. I would remove the pipe and check to see if it’s restricted.
90cummins

 

[xp190]

Thanks 90cummins

The cat was plugged up. I took the exhaust apart and the baffles in the cat were sideways blocking the outlet. I have a picture of this, I will try to post it up here shortly.
I gutted the cat and removed everything out of it until the path was clear. I will have to double check this in case something broke loose again. Once I verify this, I will proceed with your suggestions and continue troubleshooting. I hope the piston is fine, but I suspect the valves might have an issue as well, hence the backfire and burnt up air filter.

Thank you for all your help, once I have a chance to take it apart, I will post my findings, but doing this in an uninsulated garage is a bit difficult.

xp

 

[90cummins]

I would reattach the pipe and give it a run without the sheet metal on before you tear into the engine maybe that was the problem.
90cummins

 

[xp190]

Here are some photos of what I found after the exhaust started glowing:

Current hour count, not even 120 yet...


What was left of the air filter



And what I found the Cat like, it all came apart.




xp

 

[Industrial Toys]

Typical story about the cheap Silent Diesel gensets in a box. A one time, no parts, type thing.

Friends of mine have a 6000 Watt or so Northern Generator, open frame, with the proper Yanmar Motor. The Generator end was fried and the air filter was also melted. I thought this was due to high temperature in the dog house where the generator lives, as the poorly installed exhaust extension had come loose, causing exhaust to blow inside the dog house.

Maybe, this is in fact not the cause of the melted filter. When I replaced the genend, the motor ran nicely.

 

[90cummins]

Typical story about the cheap Silent Diesel gensets in a box. A one time, no parts, type thing.

Friends of mine have a 6000 Watt or so Northern Generator, open frame, with the proper Yanmar Motor. The Generator end was fried and the air filter was also melted. I thought this was due to high temperature in the dog house where the generator lives, as the poorly installed exhaust extension had come loose, causing exhaust to blow inside the dog house.

Maybe, this is in fact not the cause of the melted filter. When I replaced the genend, the motor ran nicely.

It would be interesting to find out why/how the air filters are getting damaged.
90cummins

 

[Kyle_in_Tex]

It would be interesting to find out why/how the air filters are getting damaged.
90cummins

Me too. Burned intake valve?

 

[bennyboy95]

I have two yanmar L90 engines with 4800 generators on them that were removed from a fire truck. The one engine got water in it and ruined the cylinder wall. Does anyone know if I can have this bored out to fit a L100 piston? L90 seems to be a rare one and impossible to find a piston with rings. Thanks Ben

 

[hr3]

I too have one of the China clones. So far good but it only has 8 hours on it. I bought here in the Philippines at a local big box store. Question is I have a slight fuel leak at the fuel shutoff I think it's coming from the small plastic nut on the bottom. In order to get at it properly I'm going to have to take the enclosure off. The question is can I leave it off for easy servicing later ?