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Decarbon piston & head cause higher oil consumption?

23 posts in this topic

ID: 1   Posted

I have heard of this before.  But heard it again at the local garden center when I was pricing a headgasket for my M12.  It has 525 hrs now and should be decorboned per the manual.  So is this a wifes tale?

 

I can;t see how this would cuase oil burnining unless you scratch the cylinder. 

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ID: 2   Posted

No it should not have any effect on oil burning . You would have to

do more than a lite scratch on the cylinder wall to have any effect.

And it would have to be far enough down the cylinder that the oil rings would see it

Which would be 12 inch or so. If your concerned just keep the piston at the top .  :tools-wrench: :tools-wrench:

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ID: 3   Posted

There is still a lot of urban folklore about the "carbon seal," being broken and causing more oil useage, which IMHO is crap-ola.  Excessive oil in the chamber comes from the wide end gaps in worn rings, glazed or scored cylinder walls, and/or from worn valve guides.  I'm not sure where these people think any sealing from carbon helps to lessen any of that, and in fact excess carbon constantly breaking away in the chamber is likely causing a lot of that wear. 

 

-Mark-

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ID: 4   Posted

So to clean more safely, would it be better to pour seafoam into the piston so it disolves overnite before it is scraped?  Or doesn't it matter?  The carbon I just cleaned off my 18HP twin was rock hard and took wire brushes, carb cleaner, and scraping.  I hope this M12 is not that bad.

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ID: 5   Posted

Since you have the piston out of the engine, soaking it in Seafoam or virtually any solvent will help loosen the carbon before removal.  I use a baking soda blaster to clean loose engine parts, but any method of carbon/gunk removal that doesn't scratch or pit the aluminum is fine.  Sometimes the carbon in the ring landings, the most important place to get it out of, can be time consuming depending on how bad it is no matter what method you use. 

 

-Mark-

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ID: 6   Posted

This can cause oil burning if...when spaying/cleaning the carbon off the piston it runs down and gets in the rings. This may cause the rings to stick in the piston and not float against the cylinder wall like they are designed to do and then it will burn excessive oil.

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ID: 7   Posted

So do the cleaning, then vacuum instead of blowing with compressed air to prevent the carbon from working into the rings.

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ID: 8   Posted

Work a piece of string/cord into the gap between the piston and the wall. Go twice around.  Leave the end hanging out.  When done cleaning, grab end of string and pull out along with any carbon crud on top of string.  Then vacuum.

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ID: 9   Posted

Another trick I have seen when de-carbonizing with piston installed is to put a layer of grease around the top edge of the cylinder with piston down, then move piston to the top and clean.  Grease catches the carbon, then clean away the grease and carbon.   

 

-Mark-

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ID: 10   Posted

Yes removing the head bolts and then installing them again even to the same specs will change the shape of the cylinder just enough that the

 

 

 

 

 rings will need to reseat. If ring tension is to weak it will cause the engine to use oil

Keith 44 years auto mech 

 

6 horses in my herd

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ID: 11   Posted

Yes removing the head bolts and then installing them again even to the same specs will change the shape of the cylinder just enough that the

 

 

 

 

 rings will need to reseat. If ring tension is to weak it will cause the engine to use oil

Keith 44 years auto mech 

 

6 horses in my herd

 

This might hold true for automotive engines, and I can see the logic with an all aluminum small engine.  Yet on a cast iron Kohler engine where you are only using 20-25 ft/lbs of bolt torque to hold an aluminum head down to an iron block with a composite gasket sandwiched in between, the cylinder doesn't likely distort enough to be of any factor with ring seating or oil consumption.  De-carbonizing the piston and chamber on an L head engine every 500 hours or so will do more to prevent oil consumption from contamination wear than it should to cause it.   With modern OHV mower engines, de-carbonizing is not necessary and most don't recommend doing it. 

 

-Mark-

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ID: 12   Posted

I can't see it holding true for automotive engines either...  I've probably done several dozen 'valve jobs' on automotive engines which obviously would include 'de-carbonizing' as part of the process.  I think it's a big enough statistical sample to be valid data.  None of them ever used more oil afterward.

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ID: 13   Posted

Bit late to this thread, but I also agree that De-carbon and Oil Consumption increase is a Myth. Carbon is a danger to your engine in several ways.

Here is an example on the Engine I purchased as a replacement and found this....All caused by Carbon breaking off around the exhaust valve and it stalled the piston on the upstroke damaging the top edge-

 

DSC00599.jpg

 

Needless to say I had to fully re-bore and rebuild this one, but the Carbon was mountainous around the Exhaust Valve and must have been glowing when the engine was running.

 

I always find pre-soaking the carbon deposits to loosen then off works well and only needs a piece of blade shaped wood to clean it all off.

If you can get it like this, it's well worth doing and will run nice afterwards-

 

post-3520-0-30997500-1371828118.jpg

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ID: 14   Posted

That picture is exactly what I don't want to have happen.  Once this gouges out, the top ring will just burn up.

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ID: 15   Posted

Excessive carbon build up on the head and top of the piston, can cause

the rod to break when the two collide, as per the Kohler class I went through

back in 1985.

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ID: 16   Posted

Will adding seafoam to fuel help decarbon piston, head over time?

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ID: 17   Posted

I am wondering that as well.  Such as maybe even a piston soak overnight without taking the head off.

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ID: 18   Posted

Has anyone ever tried taking the spark plugs out and spraying seafoam or something else. With some success.

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ID: 19   Posted

A lot of what people call carbon is actually burnt oil build up, so yes it will use a little more oil when clean due to the fact you have broken the seal the oil build up sealed.

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ID: 20   Posted

I also read something very interesting about carbon patterns on the top of the piston.  A bad throttle shaft bushing can cause the engine to use oil, and a wet oily combustion chamber can really carbon the ring packs.  This over time will create a polished bore and increase ring wear.

 

Low and behold, I found that all my kohlers with tight throttle shafts have a dry sooted piston top, any of them with a loose one, had an oily greasy piston top.  I found this to be quite interesting.

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ID: 21   Posted

  Let me take a stab. I dont think the throttle shaft being loose is a cause, but more of an effect of improper maintenance which caused these problems. Poor husbandry of changing the clogged up air filters in a timely manor and keeping that are clean causes dirt build up in the carb and forces the carb to pull unfiltered air from places it would not normally do. Like the throttle shaft, choke shaft and so on. That unfiltered air wears down the bearing surfaces of the shafts, valve guides and does serious damage to the bore over time.

 

  So finding a motor with worn out throttle shafts/bushings either means improper care and maintenance. You can bet it has some internal wear also. Or its just plain ole worn out and tired from many hours of use.

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ID: 22   Posted

To some degree you are correct, however even perfect maintained engines can get loose throttle shafts. 

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ID: 23   Posted

Last part of my post states. Sometimes they are just plain worn out. They will not last forever. Generally pointing to high hours or abuse.

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