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🗜️ How to File Piston Ring Gaps [FREE LESSON]

October 12, 2019

– Here’s just one of the specialist tools you’ll learn about in the engine building fundamentals course. In this module, we’re
going to take a look at how to use a ring
file to correctly file our piston ring end gaps. Now in front of me here I’ve
got two different ring files, we’ve got our cheap, manual ring file, which is going to be ideal if you don’t want to spend a lot of money, and perhaps you’re only
going to be building one or two engines, and we’ve also got an electric ring file, which is also fitted
with a dial indicator. Now the dial gauge on
the electric ring file makes it very easy for us
to make very precise changes to our piston ring end gaps, and this allows us to get very repeatable and precise end gaps
across the entire ring set. The manual ring file is
a little bit more fiddly and a little bit more tricky to use, it also tends to take a little bit longer to get the right result, because we’re forced to use
the trial and error method, where we will fit the ring into the block, measure the end gap, file it slightly, and then take it back out of
the file and check it again, so this is a process that we’re
going to iteratively repeat until we get our end
gaps where we want them. Now before we actually look
at using the ring files, we’re going to check out how to go about measuring our ring end gap, and we’re going to do that
by taking our ring here, and we’re going to fit it into the Toyota 2JZ cylinder block behind me, so let’s start by doing that now. So we’re going to begin
by placing the ring into the top of the bore, and here I’m just looking
at number one cylinder. So I’ve just done this by compressing the ring slightly by hand. I’ll also point out
here that it’s important when we’re going to be filing our rings to make sure we assign our
rings to a particular cylinder. There’s quite often going
to be very minor differences in our bore diameters, and this can ultimately
affect our ring end gaps, so we’re going to file our ring set to suit a particular
cylinder, once that’s done, those rings are going to stay
with that particular cylinder. Now we’ve got our ring located
in the top of the bore, but this isn’t where we want to actually make our measurement, what we want to do is move the
ring slightly down the bore before we take our measurement, and we also want to ensure
that the piston ring is square in the bore before we
take our measurement. If we’ve got the piston ring
slightly offset in the bore, this will make a big
difference to the ring end gap. Now there’s a couple of
ways we can achieve this. I’ve got here a relatively cheap tool that can be used for squaring
the piston ring in the bore. This will suit a variety of
different bore diameters, and all we need to do is
rotate it and lock it down so it fits inside our
specific bore diameter. Once we’ve done that, we can just push down on
top of the piston ring, and there’s little sleeves here
that stick out and protrude, and these will locate on the
deck surface of the block, ensuring that the piston ring is located the correct distance down
from the deck surface. Once we’ve done this, we
can use our feeler blades to check the ring end gap. Now, if you don’t have one of these tools, another really common way of
achieving the same result, we’ll just take our ring back out and locate it at the
top of the bore again. Another really common
way of achieving this is to use a spare piston
or a secondhand piston, and what we want to do is
install one ring on the piston, and then we can install the piston into the bore upside down, and this is just going
to move the ring down and we’re going to move
down until the ring installled on the piston hits
the deck surface of the block. This is going to achieve the same aim, we’re just simply making
sure that the ring is square in the bore and it’s down
slightly from the top of the bore. Now, when we’re measuring
the piston ring end gap we’re obviously interested in
the width of the ring end gap, but another aspect that’s
really important to take note of is whether the ring end gap is square, we really want a parallel ring end gap. If there is a taper and
the ring end gap is offset, we’re going to need to correct this when we’re filing the ring end gap. OK, so we’ve taken our measurements, now we know what clearances we need, or what additional filing
we’re going to be doing to achieve our target end gap, let’s now look at how we can use the ring files to achieve this. While the manual ring file
is a relatively simple piece of equipment,
there are also some traps and it’s important to
understand how to use it to get the best results. One of the key points we need to remember is any time we’re filing the ring, we always want to watch the
rotation of the grinding wheel. What we want to do is grind from the outside of the ring inwards. Now what this is going to do
is prevent any of the inlay being pulled out of the
ring by the grinding wheel, and this is particularly important if you’re using a ring
that has a moly facing, so we always want to be grinding from the outside of the ring
towards the inside. Now typically, when you’re
using one of these ring files it will be located in a vice or bolted to a workbench so it can’t move, for our demonstration though, we’ve just got it sitting
here on the workbench. Now, a lot of people when
they use these ring files, they will locate the ring on the side of the positive stops or dowels, and then they’ll squeeze
the ring together so that both sides of the ring are
being filed simultaneously. Now, while that might
sound like a sensible way of approaching grinding the rings, what that’s actually going to do is ensure that your ring end gaps don’t
remain square or parallel, once the ring is installled in the bore. And in fact, the only way you’ll end up with parallel end gaps,
is if your ring end gap works out to be the same
thickness as the grinding wheel, and that’d be very, very unusual. So in this case, what we’re going to do is grind one side of the ring only, and what this does require is
a little bit more attention, what we’re going to have to do is manually view the end gap of the ring, and make sure that we’re always
holding the end of the ring square against the grinding wheel. And the way we do this is we’re going to constantly make small
adjustments by grinding the ring, then take the ring off
and check it in the bore. This allows two things, first of all, we’re going to be able
to check our progress, so we’re going to make sure that we don’t end up with
an end gap that’s too wide, and it’s also going to allow us to ensure that we are still maintaining
a square ring gap. So the process is to
gently apply some pressure against the locating dowel, as well as locating the ring
against the grinding wheel, and then we’re just going to manually turn the grinding wheel until
we’ve removed some material. And it is an iterative process, we’re going to be constantly
rechecking our progress in the bore to make sure
that we creep up slowly on our end gap, without going past it. Our electric ring file
offers many advantages over our manual ring
file, not least of all is that it’s much easier
to locate the ring, to ensure that we are grinding
the ring end gap squarely, and there’s a couple of
features on the ring file that allow us to do this. First of all, we have an adjustable stop, which we can move so that we
can always locate the ring or relocate the ring on the
ring file in the same place, so we can adjust the stop, depending on the bore diameter
that we’re working with. Then we also have of
course the dial gauge, which allows us to make much
more precise adjustments to our ring end gap. So the process is to
start by taking our ring, and we’re going to locate
this in our ring file. Now I’ve already adjusted
our stop or our locator, to make sure that my ring end
gap is going to remain square, I’m going to install the ring
with the ring protruding slightly from the platform
here, or the deck, and then I’m just going
to tighten the stop down to positively retain the ring. Now what we’re going to do is
just slide the mechanism down, and I’m just going to adjust it until I’m just barely making contact
with the grinding wheel. Now at this point we
can zero our dial gauge, and this is going to
give us our zero point. What we can do now is
begin by moving the ring back down with our file now going, and we can simply turn the
knob and remove material, slowly but surely. What we want to do is remove a
very minor amount of material with each pass on the grinding wheel, somewhere in the region of
about 1/2 a thou per adjustment. And what we can do is
constantly recheck our progress using the dial gauge. Even though we have the dial gauge, I still like to stop short
of my final measurement, place the ring back in the bore, and have a final check
and see how we’re looking, compared to our target measurement, this just ensures that we don’t
overshoot our ring end gap, it’s always best to
measure twice and cut once. Once we’ve completed filing our rings we’ve got one last task to complete. The filing process is
going to leave minor burrs on the edges of the ring, where the file has been removing material, and what we need to do is
just remove those burrs, and this can be done with
a light piece of sandpaper, or a very fine needle file, and what we want to do
is just barely break the edge of the ring
and remove those burrs. We don’t really want
to remove any material and leave a chamfer as,
particularly when we’re looking at the surface that runs on the bore, this can end up actually affecting our overall ring end gaps, so we just barely want
to remove those burrs, and make sure there’s
nothing there to catch on either the bore or the
ring groove on the piston. That was just one of the modules from the engine building fundamentals course, which is the perfect starting place if you want to learn how to assemble high performance engines. This course will teach you about engine anatomy, essential machining processes, how to select and measure critical clearances in your engine, how to assemble the engine long block, and how to break in your fresh engine. For more information and to purchase the course, click the link now.


  • Reply High Performance Academy June 25, 2018 at 9:27 pm

    Sign up for the next free live lesson here –

  • Reply crunchee June 26, 2018 at 3:57 am

    That was cool and easy to follow! Thanks for this series. I think I'll have to buy in once I get myself into a big build of my own

  • Reply GordoWG1 WG1 June 27, 2018 at 2:56 am

    Mentioned this before, but if re-ringing the bore will have worn from the old rings with a bit of a taper to it, this means there could be some measurable difference between the top and bottom of the ring's travel so it may be best to check a used bore at the bottom of the bore – Remember, as little as 3 thou' wear is almost 10 thou' at the gap. Note, my personal view is that if a re-ring is required, then a re-bore is required – but sometimes budget, very low bore wear, or other concerns out weigh that.

    With some engines 'file to fit' rings may not be available and most 'jobber' or factory rings have excessive gaps for fast, safe assembly – but still need to be checked! If so, pick up a set of the next size oversize rings (supplier may allow you a discount for the unused rings) as even a 10 thou' oversize will close the gap by over 30 thou', which should be ample to work with. There will be a VERY small increase in ring pressure against the bore, but this really is in the barely measurable range and the reduced gap will be of greater benefit.

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