Diesel backfiring.

[ccscott49]

I have a small generator, aircooled with a Lombardini single cylinder engine. It backfires?? I have never heard a diesel engine backfire in all my years and I've worked on many. Any ideas? Injector is fine, just serviced, the fuel is clean and new although the engine has not been run for a couple of years, could it be sticking valves? It doesnt reach full revs, just tries to, then backfires and slows again. Any help would be appreciated, thanks.

 

[boatmike]

Unusual to get a backfire on a diesel unless the valve timing has slipped. I think these little lombos have a cambelt rather than chain (not sure of my facts here) so it's possibly slipped a notch. If you know how it's easy enough to check.
It could also be a burnt, or as you say sticking, valve allowing unburnt fuel into the exhaust that then ignites. best to have the lid off and check......

 

[coromar]

I have a G&M genny powered by a single cylinder Lombardini diesel. I also have had a problem with smooth running.

After lots of "experts" had given their opinions, I found that the wire conector to the circuit board had iffy conections. With a resolder running was perfect.

If this helps I have photos of the area in question.

Best wishes,

Paul

 

[Manuel]

Could be pre-ignition due to some carbon build-up. Or maybe some rust that has become carboned. If you like taking things apart I would take the head off and have a look but you will need new gaskets. Ideally try running it for ten or twelve hours at the highest power you can before 'backfiring' starts. That might burn it off. But this is a generator with servo control of the engine speed, I presume, driving an alternator? The problem is that if the alternator is run significantly below speed the laminations might overheat and burn out your coils so you would need to run at zero electrical load. Can you find the worm drive (or whatever) that controls the speed, and turn that manually with a spanner after disconnecting the servo? You probably have to disconnect the servo physically or you will strip its gears using the spanner on the worm. This way you should be able to gradually run the engine speed up using the spanner as a manual throttle. If you have a contact-less tacho find out the correct shaft speed and aim to get to the appropriate revs for 50Hz. I would also find the 12V charging output to the battery and remove that as you want zero electrical load on the alternator while playing these games and the charging circuit might not be tolerant to wide frequency swings.

I hope that makes sense? If not of if the engine looks very unlike that, ignore this post.

 

[Bilgediver]

I have a small generator, aircooled with a Lombardini single cylinder engine. It backfires?? I have never heard a diesel engine backfire in all my years and I've worked on many. Any ideas? Injector is fine, just serviced, the fuel is clean and new although the engine has not been run for a couple of years, could it be sticking valves? It doesnt reach full revs, just tries to, then backfires and slows again. Any help would be appreciated, thanks.

Sounds like a gummed up inlet valve......Mix 50/50 oil and kerosene or just thin oil , remove the rocker cover or whatever gives access and squirt the mixture over the valve stem while working the engine by hand to rock the valve up and down. Have seen this with small Volvo's and 1 GM valves from time to time.

If this doesn t free it then the head might have to come off.

 

[pappaecho]

Agree either a timing issue or a stuck valve, or a very outside chance - crankcase breather blocked?

 

[Mrnotming]

Backfiring Diesel

Are there black fumes from the air intake.? If so suspect valve spring fracture, or as another poster said, sticky valves.Sometimes the valve stems have little hats, so these will maybe prevent your kerosene cleansing mixture getting down the stems. Removing said little hat seals may involve spring removal.Unless valves are perpendicular to piston crown to assist with support of released valve, head removal is neccessary to avoid valves going down cylinder. Collets which hold springs in place need to be carefully managed.
Plug all aperatures with rag.
Hope all posters hints help, collectively.
That's the great thing about these forae!(forums then!),
Good sailing n boating to all.