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Discussion Starter #1 (Edited)
I am rebuilding my corolla 1ZZFE engine because it was burning oil. Got my new pistons yesterday and wanted to compare them with the old ones to see if there really was a difference between the two .

Three of the old pistons had stuck oil control rings. They had carbon between the two oil control rings and a build up of carbon behind the rings of almost 1/16 of an inch. Also all four of the oil drillings that go from behind the oil control rings to the under side of the piston crown were totally blocked. The carbon went completley around the piston oil grove but was a quite a bit thinner over the blocked holes. The forth piston did not have stuck oil rings and even though it had quite a bit of carbon beneath the rings, the oil drillings were open ( There was no carbon within an inch of the holes) .

I cleaned up one old piston and compared it with the new one from Toyota.
At first glance they looked exactly the same, but I could see differences in the casting marks and numbers, same overall design though. Same weight( a couple of grams lighter), same diameter. There is a small difference in the cutouts for the valves though. The biggest difference is the oil drillings / holes behind the oil control rings. Instead of two small holes on each side over the skirt ( about 1/16 of an inch dia.) now there are four holes on each side almost double in size ( about an 1/8 of an inch dia. ). The holes are also drilled lower in the ring grove( actually about half of the hole is in the grove, and about half is below the grove in the piston body). You can see the bottom half of the holes even when the oil rings are in place.

The old oil control rings had very little wear compared to the new rings, again same overall design also.

Apparently when the oil holes become blocked , oil is no longer directed from between the rings to the underside of the piston and then to the crankcase, but is instead burned/carbonized onto the piston causing the carbon build up ,stuck rings and burning oil.

This is what Toyota says is the fix to the oil burning problem.

Look here to see a Toyota tech document, scroll down to attachment : http://www.toyotaownersclub.com/forums/index.php?showtopic=75536

You will have to register to read the attachment, but it is worth it.
 

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Discussion Starter #3 (Edited)
No problem

Toyota part # 13101-22142

My part # does not show up on the toyota document and even though my new pistons have the 8 large holes( my old ones had 4 small) they dont have the slit in the oil ring grove that is in the picture/ description. My rings dont match any of the part numbers in the document either.

On that same thread there is a picture of two pistons side by side, describing one as an old1ZZ piston and one as a new 1ZZ piston. The new piston is larger, thicker top and longer skirt and what looks like 7( 14 total) larger holes on one side. I dont know the origin of the picture and how accurate the information is.The larger piston looks nothing like what is shown in the Toyota document though.

I just called the Toyota parts dealer where I ordered my parts.They checked and told me that there have been three changes to the pistons ( new part #'s) since 2000 and that I have the latest piston for the corolla.

The Toyota document says : "The lower part of the piston( especially around the oil control ring) runs hotter( 160C) than the target (120C)." Maybe those larger pistons are to dissapate the heat beter?

Can anyone shed some more light on the subject?
 

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sam333 - great post !! had exactly the same porblem (only I had spun bearing stoo! - my fault for not fixing it sooner and not being able to keep up with oil burn) I am looking at 2005 motor to replace it - did your guy happen to say when Toyota recognized the problem and started making corrections? I am wondering if I shouldn't be proactive with this new engine and just replace everyhting now, or if they made some mods befreo 2005, just stick the motor in and see if the problem recurrs. I drive over 2500 miles a month so reliability is an issue.

Thanks again for the great info!!
 

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Discussion Starter #5
Pete , I beleive the problem had been fixed by 2005( or at least improved with the new pistons). I think the oil burning was mostly in the 8th gen toyotas 98-2002.
 

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Thanks Sam for the post on oil consumption. Read lately that the problem is solved by using a new measure dipstick. Does it help.

Thanks and best
 
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