In this installment of our maintenance series, we diagnose low engine power output on a Northern Lights 12kW generator. This engine is unable to produce more than 7kw of power, but can reliably deliver that, and otherwise is running fairly well. We walk through the diagnostic procedure checking for intake blockage, fuel system problems, exhaust restriction, exhaust design problems, and valve adjustment.
Thanks for the feedback on the video.
James, Could their be a relationship between the cylinder head problem at the rear cylinder (valve seat failure) and the rear oil seal? It would seem to me that with the rear piston not driving at the same pressure and power as the other two pistons. Might that not cause an increase strain on the crankshaft and the rear seal?
That’s a pretty interesting question. My general rule is that it’s (almost) never the case that two completely isolated problems show up at exactly the same time. We all know that the rare does happen and it actually happens frequently at scale. But, it’s an excellent policy to relentlessly search for correlation when two seemingly unrelated problems show up at the same time.
I can’t rule out two uncorrelated problems showing up at the same time but in thinking through all the possible issues that could relate the engine suddenly starting to leak oil profusely when the valve seat failed and there are some possibilities. One that I find super interesting is the there is a crank case pressure vent into the intake manifold fairly close to the valves. If the intake valves were leaking there would be pressure spikes in the intake manifold which would cause pressure spikes in the crankcase which could cause the rear main oil seal to leak. When I vented the crankcase to atmosphere directly, the problem was still there but it appears to be much less serious.
When I took the old cylinder head off there is evidence that both the exhaust and intake valves are not sealing well with the valve sealing surface not polished where they contact the seat. It’s possible that we had pressure spikes in the intake manifold and I’m sufficiently interested in this theory that, even though we have both the parts and time to change the rear main oil seal, I’m planning to let the generator run for 20 to 50 hours to see if the oil leak is diminished by having a new head with properly sealing valves.
I suspect we’ll still need to change that rear main oil seal but it’ll be an interesting experiment to see if it’s actually leaking less with properly sealing valves.