Export thread

I have a jd 14sb I moth balled for ten years. I got it running after fiddling with carb. The reason I put it away is it burned oil only after two years of use. I figured the rings were bad or the cylinder scored I pulled the head last week to find the cylinder in beautiful shape with crosshatching still evident and everything smooth and in perfect looking condition except for the evidence of burnt oil with carbon buildup Has anyone ever seen the crankcase vent cause an engine to burn oil? This is the silver john Deere mower with the Kawasaki 150v engine

Visible cross hatch says the bore is not run in. Oil burning...as discussed a while back bore-piston clearance is unforgiving . Newly machined or new engines should not smoke on start up. Is the engine a rebuild? If you do not have the tools to remeasure a disassembled engine , see if you can wiggle the piston by hand in the bore (a no-no IMO), and, and then try to fit a .001-002" feeler gauge or shim strip between the piston and bore and pull. Should be tight (yes totally unscientific). If loose keep putting thicker strips in till you sense resistance. This was formerely an accepted check on bore clearance, but alway very precise by the mfgr as to strip thickness and resistance pull in inch pounds. Hey, only an idea and I hope your engine just needs run-in.

Is there any oil in the air filter, or just below the air filter where it connects to the carb. Worn rings, or damaged breather will blow oil into where ever the vent line connects. absent oil there, most likely other causes of oil consumption are blown head gasket, leaking valves, or loss of crankcase vacuum.

This may be a good case for a cylinder leakdown test. If you have a compression gauge you can remove the valve out of the hose, and then connect the other end to your air compressor hose, to find out where the air is coming out. Must be performed on TDC compression stroke. A degree or two off will cause the piston be forced down.

Visible crosshatching means there is less than .002 wear on the cylinder walls.

Thanks to both of you guys for responding. I hoped to see blow by but there was none evident. The head gasket was in perfect condition. I bought this mower in 1992 new and ran it for two years on 20 k sq ft lawn before it started to smoke. There is no oil anywhere in the intake /carb area. Filter and all areas show no signs of oil. I received a new mower from a friend who retired and I put this mower away for the years I mentioned. I am meticulous about changing oil/ maintenance etc. so when I pulled the head I expected to see blowby or some freak cylinder damage. I was trying to find another reason that this mower would burn oil. It will smoke for ten minutes and stop for a short while before smoking again. It's a mystery. I thought the engine was ruined but was so surprised at the condition of the cylinder walls. I've yet to try to slide a feeler guage between the piston and cylinder. I see the crank case venting. It is two metal flaps. One spring steel the other a stop above it I have some video of the cylinder if that might help

Ten minutes, then stop for a while and smoke again.
Two things come to mind.
Obstruction causing oil to pool up around exhaust valve and leak down the guide & into the exhaust pipe.
Crack in the cylinder head.

Without checking your specific engine, it is common to run only 1 valve stem oil seal on the inlet to prevent oil getting sucked inot combustion chamber and nothing on the exhaust as worse case it will leak into muffler.
Oil leaking down valve stem will show up as thick burned on oil deposits on the back of the exhaust valve, particularly around the upset from the stem to the head.

Sounds like an oil pooling problem like Bert mentioned. Oil drain back hole in head clogged would be my first guess, but could also be a hairline crack in the head.

On a Briggs I do know from experience correct crankcase pressure is important. I once failed to tighten the dip stick back correctly and that thing smoked like a steam freight train.

I've found the crankcase vent system a difficult subject to locate information on. Hope you have better luck. If we knew what the crankcase pressure should be we could rig a water manometer to check it.

I recently surfed "crankcase pressure gauge," hoping to find a reasonably price unit to use along with a compression gauge-in my dreams.... Race shops monitor crankcase pressure carefully and there are some formulas online to calculate expected crankcase pressure based upon engine size , rpm etc. Most unit are expensive ($1500) and hook to a pc for "data logging."
A theme seen repeatedly was that ring/sealing is better at "higher" rpm which probably does not apply to the 3000 rpm ac tractor units (edit). So I imagine staying satisfied with a comp gauge makes more sense. I can only state that my Intek will splatter me with oil droplets if I remove the oil dipstick during hot idle - pretty strong blowby for the engine which seems to run properly. Maybe this strong blowby is relied upon to direct oil mist down the pushrod tunnels to lube and "cool" the valve stems .

TRIVIUM" GP race bikes have vacuum pumps to pull out crankcase pressure good for up to 5 HP in a 200 HP bike engine.

motoman said:

I recently surfed "crankcase pressure gauge," hoping to find a reasonably price unit to use along with a compression gauge-in my dreams.... Race shops monitor crankcase pressure carefully and there are some formulas online to calculate expected crankcase pressure based upon engine size , rpm etc. Most unit are expensive ($1500) and hook to a pc for "data logging."
A theme seen repeatedly was that ring/sealing is better at "higher" rpm which probably does not apply to the 3000 rpm ac tractor units (edit). So I imagine staying satisfied with a comp gauge makes more sense. I can only state that my Intek will splatter me with oil droplets if I remove the oil dipstick during hot idle - pretty strong blowby for the engine which seems to run properly. Maybe this strong blowby is relied upon to direct oil mist down the pushrod tunnels to lube and "cool" the valve stems .

TRIVIUM" GP race bikes have vacuum pumps to pull out crankcase pressure good for up to 5 HP in a 200 HP bike engine.

Click to expand...

Rex Bunn was for a short time the world expert on crankcase venting, it is almost as back a science as exhaust systems.
Most practices go back to the days of oil slingers & no seals and have never really been changed or thought about.

Don't mix up blow by with crank pressurisation ,
Blow by is gasses that bypass the rings
Pressurization is the pumping effect from the underside of the piston which is why you get covered with oil when you take out the dip stick

FWIW through venting with check valves at both inlet & outlet was found to be the most efective and his system is now fitted as std to a lot of moern motorcycles ( not race bikes ) and a lot of Historic racers when they canget up to 1 Hp on a 60 to 90 Hp engine. Pulling against a vacuum gobbles up almost as much energy as pumping up pressure

Good point on the pumping.