78buckshot
I work on a handful of 7kw/8kw HSB, recently I found two units that eat oil at a high rate and foul the spark plug, the most recent one has 151 hours on it. Both of these machines were not our installs and the maintenance history is spotty. I'm hoping to glean some insight from those with a more broad example of the single cylinder models. I'm leaning towards poor maintenance, any thoughts?
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Peddler
I have never been a fan of the single cylinder units but I have not seen any high oil consumption and never oil fouling of the plug.  Coils and airbox issues are our only pattern of trouble.  I put a slightly used 8 KW Nexis unit in for my daughter and it ran 8 days straight shortly after install, did not burn an ounce of oil.
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78buckshot
I'm also not impressed with the single, the eight or so that I work on have been problematic, so far only the two with oil control trouble.
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Cobranut
Check the crankcase breather system closely.  Anything that causes pressure to build up in the crankcase can unseat the oil rings and cause high oil consumption.  It also can blow oil vapor into the intake. 
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78buckshot
The breather system on these is very simple, valve cover with reed valve mounted in the cover, rubber hose about 3/4 inch dia. from valve cover to air box, all of which are clear.
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78buckshot
For those interested: follow-up on the 8kw with 151 hours. I suspected the piston rings were trashed and I was going to swap engines, I re-thought the issue and didn't want to take a chance on a used engine. I rebuilt the original engine and found what I believe was the main cause of the oil consumption - the head gasket was leaking due to the two lower headbolts being loose. The head gasket not only seals the combustion chamber but also seals between the push rod cavity and cylinder so it was sucking oil into the cylinder on the intake stroke and over pressurizing the crankcase on the compression and power strokes. I replaced the rings, honed the cylinder to break the glaze, replaced all gaskets and seals. Re-installed the engine and put everything back together today. It starts and runs with no smoking and no blow-by. As a side note, I was very happy to find that Generac uses NO plastic parts for the oil pump on this model -  the only internal use being a plastic/brass pick-up screen.
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ohmslaw
Common issue. With the valve cover off and a start you can hear and see the leak most of the time.
Tim
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in2hockey
I have a 10 year old 13kw.
Just curious should you and/or can you re-torque the heads as part of your PM?
Also, what, if any, oil consumption is considered normal? Prior to my inheritance (so to speak) of this unit we had a 10 day outage and I did have to add oil to this unit during that time.
It ran 24/7 during that outage and toward the tail end the low oil light came on, so we shut it down and added oil. How much I don't remember as we were dealing with record snow (for our part of the country) and major outages.
Thanks.
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78buckshot
I have not consulted an engine manual for these, it probably would not hurt to put a torque wrench on the head bolts during maintenance but the twins are not as easy due to shrouding. As far as oil consumption on your machine - if you only had to add oil once during a ten day outage I'd say you are lucky.
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in2hockey
Thanks 78buckshot! So it's not unusual for these units to consume that much then. I was a little concerned but i take it that these units aren't designed to run continuously for that length of time then. 
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78buckshot
The long run time is not a problem, it is recommended to shut it down every 24 hours and check the oil level, also depending on which model change oil and filter every 100 - 200 run hours or one year which ever comes first.
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in2hockey
The Model # is 52530 and the serial # 4904677. It's good to know about the 24 hour continuous oil check. I couldn't find where it stated that anywhere in the manual. I did see where they recommended oil & oil filter every 100 hours. Is it safe to assume that the bigger water cooled units are designed to run continuously for longer lengths of time? I replaced this unit with a 45kw that has a Mitsubishi motor and an additional oil reservoir so I'd think it's is safe to say that it could run hypothetically indefinitely, correct? Thanks!
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78buckshot
For the most part the liquid cooled aren't as hard on oil both in terms of consumption and condensation, the Mitsubishi has been a good engine. I would still keep an eye on any unit that is running a long outage.
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in2hockey
Thanks 78buckshot!
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Geoff Z
It's good to know about the 24 hour continuous oil check. I couldn't find where it stated that anywhere in the manual.

You won’t find that in print anywhere. As 78buckshot recommends, it is simply a good practice. 
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