Anal Retentive's Guide to File-to-Fit Piston Rings

Part of the build-up for my new engine necessitates filing the Total Seal TS1 Rings to fit the cylinder bores properly.  It occurred to me that some folks may not have ever done this, and that it might be a good idea to put together a "How-To" guide on ring filing.   Now, as anyone who knows me will tell you, I am somewhat particular about how I do certain things.... well everything actually.  So, this article illustrates the method "I" used to fit my piston rings.

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Here are the basic tools and materials I used:  manual crank ring filer clamped to table with a 12' clamp, 320 grit wet-dry paper on a sanding block, flat diamond file, feeler gauge set, ring squaring tool, and of course the Total Seal documentation for the TS1 Gapless Second Ring set.

I bought both the ring filer and the squaring tool from a Total Seal dealer here locally.  If you don't have these tools, get them.  They are not optional.  You can't do a proper file-to-fit job without them.

Next thing I do is to install the raw ring in the bore to get a quick pre-measurement to see where I am at.  You should install the ring oriented to the cylinder just how it will be installed on the piston.  In this case, the ring is 180 degrees reversed from where it should be,  but I'm just getting a quick reference for starting purposes.

Note: it should go without saying, but you MUST install the ring in the cylinder bore into which you will install the ring during final installation.  The way I do it is to take all the rings out of the box and make up individual cylinder "ring sets".  Then I place each ring set in its own Ziplock bag, and label it with the corresponding cylinder number.  AND I NEVER have more than ONE bag open at a time.

A couple of revolutions on the ring filer confirms that the faces are NOT true.  Note in the image the shiny portion of the gap face.

You should file BOTH faces just until the face is flat (equally shiny across the entire face).  Don't get carried away and file too much.  You don't want to open the gap too wide.

Now, keeping the ring against the posts, rotate it until the gap face contacts the abrasive wheel.  Hold the ring down tightly with your finger et al. device.  Then begin filing by turning the handle/wheel AWAY from you.  This is so the filing motion is toward the INSIDE of the ring.  This is very important.  The abrasive wheel will leave a sharp bur on the exit side.  If this bur is on the bore face, it may scratch the bore, and it will at minimum hold the ring away from the cylinder wall.

File a little bit off the gap face...

Insert the ring into the bore with the squaring tool as described above.  use the feeler gauge to determine the "good" starting gap measurement.

The standard I use for what is a "GO" and "NO GO" on the feeler gauge is:

A "GO" is when the feeler gauge will drop vertically through the gap under its own weight.

A "NO GO" is of course when it will NOT slip down under its own weight.

Here we have a "GO" measurement, as the feeler gauge dropped into the gap under its own weight and is resting on the block deck.

Also note that the blade is flush against the cylinder wall.

Here is the starting measurement for this ring on this cylinder.  I do this so I will know approximately how much material needs to be removed.

Now, remove the ring CAREFULLY from the bore, and begin filing it a little at a time. Reinsert into the bore, square it up and re-measure.

Repeat this procedure until you achieve the required ring gap for that specific ring for your application.  As you do it more, you'll get a "feel" for how much material to take off.  But it's better to file material off VERY gradually to make sure you don't overshoot the required gap.

You can ALWAYS take more material off, but it's impossible to put it back!

Lather, Rinse, Repeat...

For this ring and my application, the gap is 0.022".

Total Seal includes a table/formula in its documentation to assist you in determining an APPROXIMATE ring gap.  However, certain factors in your application may/will require you to increase or decrease the gap size.  in my case, I have widened the suggested gap by a few thousandths of an inch due to it being a turbocharged engine AND because the block is filled.

Just so you can see an example, here is a picture of the feeler gauge set at 0.023" on the ring above.  Note that although the feeler gauge went into the gap fairly easily, it would NOT drop through the gap under its own weight.

Also, note that I have the ring gap oriented as it will be installed.

Here is the machined gapless second compression ring just after I have done the initial facing procedure.  Note the bevel on the inside face, and the step machined into the outside face to accept the rail.  This ring is currently UPSIDE DOWN.  It installs into the bore with the bevel and step facing down.

The filing procedure for the gapless second ring is essentially the same as the top compression ring except that you have to file the rail too.

I file them separately since the rail tends to slide back into the groove when done at the same time.

Note: the rail when installed on the machined ring is slightly undersized in diameter.  This is normal.  It expands when in use to seal against the cylinder bore. Thus it is not necessary to cut the gap in the rail quite as large as the one used on the machined ring.

The oil ring rails are done the same exact way as the top ring, though mine were above the minimum required out of the box.

Have fun, and be safe!
Clay