Log SplitterDear Ole Mechanic;

When I went to start my log splitter the other day, it wouldn’t start.  When I pulled on the starter rope, there was almost no resistance--even though the engine was turning over.  It didn’t knock, clank or make any other expensive noises and it ran fine a week ago when I split a small pickup-load of wood.  The mechanic I took it to said that it had no compression but he couldn’t work on it right away.  The splitter is about ten years old and has never been worked on except for oil changes, a few spark plugs and cleaning the air cleaner. 

Oh, it has a five-horse Briggs & Stratton engine and it has always used a little oil, so I keep an eye on the oil level.  What happened?   Thanks

Not Splitting Wood

 

Dear Not Splitting;

A ten-year-old Briggs & Scrap-Iron engine?  You sure got your money's worth out of that one, didn’t you.  Actually, it may be salvageable--at least for a little while longer.  Since it was running OK when you shut it down a week ago, you probably have a valve stuck open. 

How expensive it will be to fix it will depend on what is holding the valve or valves open.  I will start with the least expensive problem and work my way up.  If it is just a chunk of carbon holding the valve off its seat, then all that will be required is to pull the head to do an old-fashioned carbon scraping and cleaning job.  If a valve a being held open because of carbon buildup on the valve stem and in the valve guide, then the head, carburetor, muffler and tappet access-cover will all need to come off so that the valve spring keepers can be removed and the valves pulled out.  That will allow the carbon to be cleaned off of the valve stems and out of the valve guides.  The same procedure would be used if a valve spring is broken and is not pulling the valve shut.  That would just cost a little more because of the cost of the new valve spring.

If the camshaft has broken or the camshaft drive-gear teeth are stripped and the camshaft is holding a valve open because it is not turning, then you are getting into a situation that will be expensive enough to consider a replacement engine, because the engine will need a complete tear-down and rebuild after the broken chunks are cleaned out.  The labor and parts for a complete rebuild would probably cost more than a replacement engine.

Why would any of the above items occur?  A log-splitter engine only has a load on it when actually splitting logs.  During the time while the ram is being retracted and while you are grabbing another piece of wood to split, the engine is running fast but with little load.  This causes a high vacuum condition much like a car going down a hill and maintaining its speed even though the throttle is closed.  That will tend to suck oil up past the piston rings and also cause it to go up through the valve guides.  Since air-cooled engines like the Briggs tend to run hot, extra clearance is needed to keep them from locking up when working hard.  This extra clearance also helps oil get into the really hot areas of the engine like the valves and combustion chamber.  Since oil does not burn cleanly like gasoline, it leaves a lot of carbon which builds up on valves, guides and in the combustion chamber.  If a chunk of carbon gets between the valve and its seat, then compression is lost.  There are three things a gasoline engine must have to run; they are fuel, compression and spark.  If you lose compression, then the engine will not run.  If carbon builds up on the valve stem and in the valve guide, the valve can stick when the engine cools down.  That holds the valve open and there is no compression.  If enough carbon builds up in the combustion chamber above a valve, then the valve can hit it repeatedly when the engine is running and stress the camshaft and camshaft drive-gears.  Enough stress and the camshaft can break or strip the drive-gear teeth.

A broken valve-spring is usually a different problem.  A log splitter tends to sit unused during the summer because it is too hot to split wood, so condensation can occur in the engine.  The spring steel in the valve springs can get weak and break if some of the condensed moisture causes a rust spot anywhere on the spring.

So what happened?  Until the mechanic has time to pull the head and do a little diagnosis, we really won't know.  If it is just carbon buildup that is causing the problem, have it cleaned out and you may get a few more years out of the old Briggs & Stratton.  Anything much more than that and I would suggest that you scrap the engine and get a new one, but only if the hydraulics are still OK.  Of course, there is always the old maul or the wedge-and-sledge-hammer over in the corner collecting dust. 

Happy Splitting.

Herr Professor Nuzanbolts