6.5 HP Craftsman mower leaking oil

Old 05-09-04, 01:18 PM
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Unhappy 6.5 HP Craftsman mower leaking oil

My son-in-law has a 5 year old 6.5 HP Craftsman 22" self-propelled mower with an Eager-1 (Sears part #143.996510) engine. The mower "shakes" (vibrates) while running and blows oil out through the engine breather (on top of the engine under the flywheel). At first I thought it was an out-of-balance blade (it wasn't) or worse, a bent crank and the upper seal had been wallowed out but after removing the flywheel I could see the oil was concentrated around the crankcase breather and the upper seal had only a normal amount of accumulated oil and dirt. Now I suspect the mower may have been run with the oil low and the rings are shot causing blowby and abnormal crankcase pressures, but I pulled the head and there are no signs of cylinder scoring. Maybe a broken piston oil ring (?) or would a worn out valve shaft seal cause this ? And why the vibration ?

In any case, before I pull this thing completely apart, does anyone have any suggests as to what to look for or what might be causing the symptoms (vibration and oil blowing out the breather) ?
Old 05-09-04, 01:30 PM
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You have covered many possibilities. Before you take the whole engine apart. Check your blades to make sure they are not hitting the deck, and also check the blades to see if they are bent or unbalenced. It very well could be that is the cause of that. Now as far as the oil is concerned, it could also easily be that the carberator needle valve and or float are not working properly. Cause would bet that the needle is not seating proplery due to wear or trash in the carb. Your inlet could be another culprit. Clean your carb very well with automotive Gumout spray. Or if you want to take the carb off of the engine, then you can dip the carb in Nappa #6401 Carb Cleaner. This stuff is much stronger than Goumout, because it can eat away at plastic and rubber parts. Make sure that you remove any plastic or rubber parts in the carb before using Nappa #6401.

Aftor you do all that and you found that was not the problem that what you said in your post mabie dead on. Check that flywheel key to see if it is parshaly sheard. You will most likely have to drain all the oil out of the engine aftor you clean everything and reinstall with new oil. Use SAE30 weight engine oil. Others will give you advice too. Let us know how it goes.
Old 05-09-04, 03:42 PM
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It sounds to me that you might have two,unrealed problems???????

If your mower is verbating I can just assume that the blade hit something while mowering (like a stump,brick or pipe).Check the blade. See if it's bent.And while you've got the flywheel off,replace the flywheel key too.While your doing this IF THE OIL ISN'T OVER FULL,REPLACE THE BREATHER.

It's the breathers job to maintain a vaccum in the crankcase,it has a one-way reed valve in it,if that is "spung" oil will be pulled out of crankcase with any air.And since the tube that runs from the breather goes to the carb.you will have to clean the carb.And prob.replace the air filter too.

If you still have problems,post again and someone will help you somemore.
Old 05-09-04, 04:47 PM
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Hello: rszanti. Welcome to the Do-It-Yourself Web Site and our Small Engine forum.

Your quote:
"Now I suspect the mower may have been run with the oil low and the rings are shot causing blowby and abnormal crankcase pressures,"

You could very well be correct. Compression is getting passed the worn rings and entering into the crankcase. The breather is than exhausting the pressure out. And with it some oil vapors or liquid oil.

Providing the oil level is currently correct. Not overfilled. All of which can cause vibrations. As well as the possible conditions already mentioned by the other members.

Pulling the head will not reveal worn rings. Score marks may be present and visable. A lack of oil will cause excessively quick ring wear. As well as excessive heat prior to the developement of the original condition, when the engine was running well.

Not likely a broken ring. But still possible. A close inspection down the bore with a high beem light will reveal a top broken ring but not a lower oil ring.

Small engine repair parts, generic repair manuals and additional help are all available at all local small engine repair shops and or lawn mower repair shops in your area. Shops and dealers are listed in the phone book directory.

Some Links To Help Provided Here:
Sears Site Included, as well as engine Manufacturers Site:
Engine Codes: ...(Engine Manufacturer Web Sites Included)

Tecumseh Home Page Site:


Regards & Good Luck. Sharp Advice.
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Old 05-09-04, 10:55 PM
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Hello rszanti!

Before spending too much time and money on this thing, check the crankshaft first. It may be bent, and that combined with the other problems would probably make the unit un-economical to repair. A bent crank is common. Happens when an object is hit with the blade. A bent/broken blade can also cause this. The carb shouldn't cause the oil leak.
Old 05-12-04, 08:21 PM
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The blade balances fine and when rotated, each end measures the same distance from the deck at the same spot so I doubt it's bent (the blade nut was tight).

The oil level was correct when I checked it before even starting the mower.

The flywheel key was good.

I checked the crank with a dial indicator - runout was less than +/- .0015" at both ends. I went ahead and pulled the case apart - the rings were good, nothing broken and no noticable wear. And the cylinder wall had no signs of scoring. There were no signs of discoloration due to overheating so the oil level was probably never low.

The breather valve seems to be functioning, you can easily blow through it in the exhaust direction and it closes tightly in the other. Actually the oil I saw had to have leaked out around the breather valve assembly - this valve is in a large rubber plug that is pressed into about a 1" diameter hole in the top of the crankcase. The oil leak must have been around the edges of this plug.

I've put the piston back in, I have a new head gasket on order (I torn it when I removed the head and Sears didn't stock one) and I bought a new breather valve to replace the original (just in case). I also ordered an engine manual (another item not in stock )

Since up to now I haven't found a thing that might be causing the problem(s), I plan on putting it back together and see what happens when I run it again. With everything cleaned up, fresh oil and a bit of luck ... ?
Old 05-12-04, 09:14 PM
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Thanks for giving us the update. Your covering all the bases. We will just have to see what happens next. Let us know how it goes.

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