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JohnF2015
JohnF2015, Small Engine Technician
Category: Small Engine
Satisfied Customers: 1082
Experience:  Owner/Service Technician at S & J Small Engines
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I have a Kohler KT17s,with 1200 hours, blowing a lot of oil out of front seal. A weird sou

Customer Question

I have a Kohler KT17s,with 1200 hours, blowing a lot of oil out of front seal. A weird sound is, I think, coming out of the air intake of the air cleaner and most noticeable at idle. When putting my hand over the air intake on the air cleaner, the weird noise disappears and engine keeps on running, albeit, a little slower. Compression is 80 and 85. I see that the engine should have crankcase vacuum, but if I take out the dipstick, oil comes spraying out. What say you?
Submitted: 1 year ago.
Category: Small Engine
Expert:  JohnF2015 replied 1 year ago.
It sounds like you have an extremely worn out engine. The compression is low, you should have 110-115. The engine is blowing oil out of it at front seal and if you take the dipstick out it blows oil out of the dipstick tube.The first thing that you can do is to do a vacuum check on the engine. This engine is designed to run under vacuum if it is not then it will blow oil out of it or burn oil.You would need a vacuum gauge or water manometer to check vacuum, you should be pulling around 13-14 inches of vacuum.You could also do a cylinder leak down test to help identify where your problem is but I am thinking that you have excessive ring wear, possible ring broken, or extreme cylinder wear.
Customer: replied 1 year ago.
Actually, the problem turned out to be a blown breather valve under the access cover for the valve springs. This caused the front seal to blow out and that was where the noise came from. The manual calls for 90 psi compression, so I am a little low at 80. Crankcase vacuum is not supposed to be 13; maybe .5 or 1, which is has now. Works fine now and uses no oil. Bob
Expert:  JohnF2015 replied 1 year ago.
That would cause the crankcase to run under pressure instead of vacuum. Vacuum on the engine should be higher than 1, that is not enough. Compression is a bit low which would cause vacuum to be low, too much blow by in the cylinder. As long as the engine doesn't seem to be using oil then you will be okay for a while.Thanks for the update on what you found.Please take a moment to rate your experience.
Expert:  JohnF2015 replied 1 year ago.
That would cause the crankcase to run under pressure instead of vacuum. Vacuum on the engine should be higher than 1, that is not enough. Compression is a bit low which would cause vacuum to be low, too much blow by in the cylinder. As long as the engine doesn't seem to be using oil then you will be okay for a while.Thanks for the update on what you found.Please take a moment to rate your experience.
Customer: replied 1 year ago.
I am talking about crankcase vacuum here, not manifold vacuum. That little valve on the breather is a one way check valve that lets crankcase vapors out but no air back in. Parts guy told me they sell lots of them and the updated part that I put in is now actually a metal reed valve. This is an unusual setup here, I think, because both pistons go up and down at the same time with, with, what would have to be, a considerable rise in crankcase pressure on the downstroke. All I know is that it runs great now and burns no oil. The engine has about 1600 hours and a valve job would probably raise the compression which is a little low. Bob
Expert:  JohnF2015 replied 1 year ago.
Not unusual, most all of our small engines regardless of brand use the same or similar setup with a crankcase breather system and reed plate. It has been this way for 40+ years. Yes it does affect crankcase vacuum and/or pressure. If it is bad or broken it will cause and internal pressure in the crankcase and you will blow oil out through the breather and it gets circulated back through the carburetor and burnt as long as everything is hooked up properly. I have been in the lawn equipment and small engine repair industry for 30 years I do know what you are referring to. I do also know that the engine manufacture recommends a engine vacuum of 13 - 14 inches of vacuum on the crankcase of the engine. You may be okay with what you have currently but it is low for what I would be looking for if I were doing a vacuum check on the engine. As long as your engine is running okay and not using/burning oil at this time then I wouldn't be too concerned but the vacuum is low based on what I would be looking for and what the engine manufacture states that it should be.