To Hone or not to Hone

Ronald Technical Support Specialist Trail, British Columbia Posted   Latest  
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Drivetrain
2012 Audi A4 Quattro 2.0L (CAEB) 6-spd (0B2)
Failed Piston From Lspi?

The ring lands broke off one piston in this vehicle. The consensus from my previous post was the failure was the result of LSPI (low speed pre ignition). There is just the lightest of scratches in the bore of the broken piston while the rest of the bores look perfect. We are going to replace the pistons, rings, and rod bearings in this motor. My question is whether to hone the cylinders. The dealers replace rings and pistons in these vehicles all the time for oil burning. They do not hone the cylinders as far as I can tell. Does it make sense to put new rings and pistons without brush honing the cylinders? The engine has only 45 000 miles.

Thanks for your insight.

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Eric Mechanic
Chapel Hill, North Carolina
Eric Default
 

I would hone the cylinders. Too hard to go back and do it later.

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Jon Owner/Technician
Trussville, Alabama
Jon Default
 

On any engine I repair, if the pistons are replaced everything is measured (cylinder taper, out of round, piston diameter, ring gap, etc.) Any deviation from specs gets a second opinion from my machinist. I have seen folks get away with re-ringing pistons and not checking cylinders and I can understand that the law of averages is on their side as the pistons have already broken in with the…

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Ronald Technical Support Specialist
Trail, British Columbia
Ronald Default
 

We are definitely not going to skip the measurements. The scratches are not detectable with a finger nail. From what I know many of these engines were reringed and had updated pistons installed under warranty for oil usage problems.

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Brad Diagnostician
Pullman, Washington
Brad Default
 

I can't vouch for Audi but GM says if the scratch can't be felt with a finger nail and the cross hatch looks good roll pistons in it. If the cylinder is scorn or the scratch is deep put a engine in it.

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Alan Mechanic
Raleigh, North Carolina
Alan Default
 

I bought a 2011 q5 2.0t that suffered timing chain tensioner failure along with piston and cylinder wall damage due to valve interference. This engine had updated pistons installed for oil consumption at the dealer. As best I can tell, whoever did the work decided to hone the cylinders, because I refuse to believe the factory left such a poor looking hone on a block. The pistons I ordered were…

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Ronald Technical Support Specialist
Trail, British Columbia
Ronald Default
 

The hone in this block has a very high angle (the lines are way closer to straight up and down than you would expect). Is that what you found? Maybe that is the factory hone.

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Alan Mechanic
Raleigh, North Carolina
Alan Default
 

Yes, I looked back and don't have any pictures, but I'd guess it was 60 degrees on the vertical and 120 degrees from the side. Much steeper than you would expect. What led me to believe it was done by hand, were the arcs joining the tops of the crosshatches. I know on a flex hone some balls have to change direction in the bore, causing the arc, but I've never seen this before on any engine I had…

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

HI Ron. My information about whether to hone or not is related to GM, so whether it is applicable to Audi products I do not know. When cylinder blocks are finished during engine manufacture, the precise cylinder size is verified with an air gauge. The micron depth of the honed finish is also very precise and is used to visually gauge whether the cylinder is worn or not. The depth of the…

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

Ron, just to add another comment. The moment a tech hand finishes the bores with a flex hone, all bets are off on the condition of the cylinder. As always, physical measurement of the cylinders and pistons will determine what the next step is, whether a cylinder can be re-bored. In the original Ecotec 2.0L, 2.2L and 2.4L engines, we replaced sleeves. The current 2.0 and 2.5L engines can be…

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Jason Owner/Technician
Taren Point, Australia
Jason Default
 

If the bores are good give it a light hone, flex hone would be best, be sure to thoroughly clean it before reasembly

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Ronald Technical Support Specialist
Trail, British Columbia
Ronald Update
   

I did find the procedure in Audi service information for "Pistons and Cylinder Bore Checking". All the procedures seemed similar to what I remembered for general engine rebuilding but I did see this highlighted information I quote; "Do not bore, hone, grind or rework the cylinder bores with shop tools. Reworking damages the surface of the cylinder bore" It seems as if messing with the surface…

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Martin Instructor
Burnaby, British Columbia
Martin Default
   

Hi Ron. I agree with the fact that re-working cylinder surfaces at the bench level is not going to replicate the quality of surface finish that was originally achieved during manufacture. Also, cylinder bores are created and finished hone with the block supported in a specific manner and until the structural assembly is bolted together, the measurements might not be accurate. Blocks were…

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Andrew Technician
Norwood, Minnesota
Andrew Default
 

I have had this discussion with my machinist, and his position is that honing a cylinder on a modern engine will do more damage than good. This is based on information he has gotten from others, as well as personal experience.

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