"Honing rings"

[tarcigam]

Just want to share something I did twenty years ago. I picked up a Merc MK 30. Decent motor but kinda low compression on all cylinders. upon tear down I found no real damage. The cylinders and rings were glass smooth. Being low on funds at the time I tried out a theory I had. I honed the cylinders. But I also "honed" the rings. I took all the rings stacked them up into a cylinder. I roughed up the outside of the rings with some 100 grit sand paper. If the cylinder needs honing, the rings should need the same. This has turned out to be one of the best motors I have ever built. I have built many. Just a thought if you cant find rings for your motor.

[adam1961]

I have often wondered about the surface finish on rings. The OMC rings through all of the classic era motors came with a surface that was ribbed parallel to the diameter of the ring. I can usually get an indication of the use the engine has seen by how much of the ridges are left, if any. I have never done it, but often wondered if scuffing the rings would be worthwhile.

[pm-t2]

Must admit that I’ve never heard of nor thought about sanding the outside diameter of piston rings. I have lapped the flat surfaces of old rings that I was going to use again, but don’t make it a habit to go after the OD. Can’t imagine that sanding the rings helped as much as you think.

One of the reasons rings start to leak compression is they wear and have thinner cross-sections in critical area, and sanding them is only going to remove more metal. That’s just one reason for lower compression, of course there are many others.

Deglazing the cylinder walls probably helped more than you give it credit for. Removing carbon buildup on the ID of the rings (and grooves) and making sure they move freely in the grooves would be more important (in my tiny little mind at least) than scuffing the OD.

Jay Walls has learned a lot about piston rings and getting them to seat better after honing the cylinder(s), so he’d probably be a better guy to discuss it than I.

FWIW the "ribs" on the OD of the rings are machining marks from being turned in a lathe, which is how most piston rings are made.

and in another "FWIW" Harry Brinkman used to always recommend replacing only the top ring on a piston, he just thought that it didn’t make much sense to replace all of them when the top ring does most of the compression work anyway. Plus, with some of our old motors, ring supplies are getting smaller in certain sizes, so it helps stretch out the supply, and saves a person a few dollars as well. Just a thought.

Hope it helps.

Best,
PM T2

[frankr]

Honing the cylinders leaves a bajillion little sharp edges that the rings slide against. That action probably revived the rings’ surfaces as much or more than your sanding effort. JMHO.

[fleetwin]

Well, your theory makes some sense. Honing the cylinders rough up the surfaces a bit, creating valleys for oil to hide which helps seal the rings to the cylinders. So, honing the rings would seem to enhance the sealing a bit also for the same reasons. Who knows, it was worth a try and seems to have helped, which is all that matters.
Honing cylinders is a science in its own right, there is so much to know, much more than I have the education to understand, but very interesting indeed…

[squierka39]

When you can’t get new rings, or are just to cheap, what do you think of swapping the bottom ring and the top ring, sort of fits with Harry Brinkmans suggestion about the top ring being the worn ring.

and in another "FWIW" Harry Brinkman used to always recommend replacing only the top ring on a piston, he just thought that it didn’t make much sense to replace all of them when the top ring does most of the compression work anyway. Plus, with some of our old motors, ring supplies are getting smaller in certain sizes, so it helps stretch out the supply, and saves a person a few dollars as well. Just a thought.

Hope it helps.

Best,
PM T2[/quote]

[jeff-register]

Question,
Honed with what…micrometer & end gap??? land clearances 😉

[need2fish]

Perhaps someone out there with extra time on their hands (!) could do an empirical test:

1) Teardown/cylinder hone/reassemble/wet compression test, then repeat after scuffing the rings.
or 2) Teardown/cylinder hone/scuff rings on one cylinder/reassemble/wet compression test.

This is not a definitive test as it pre-ring seating, but will define if the start point of scuffing the rings results in higher compression.

After the rings have seated, who knows.

K

P.S. if done on a 4-cyl, the test could include swapping out the top ring.

[The Boat House]

This is the process as best as I can understand it
and is not meant to agree or disagree with any
comments that have been posted.
Keeping it as simple as possible honing creates
a surface that allows the ring to only come in
contact with a small percentage of the cylinder. As the
motor runs the highest part of the cylinder material
is worn away achieving more and more contact until
100 % contact is achieved. At this point the ring has
become seated. If a ring is moved from its seated
position it is no longer seated. The result this will
have will vary as to how it will effect compression
from one motor to another but a ring won’t seal as well
as it did in its seated position. Reusing a ring that can’t
be returned to its seated position requires the surface
of the cylinder to again be put in a textured state so this
process can re-occur to achieve the best possible ring
seal. That will occur when the cylinder is completely
smooth again but you have only added years of wear
just to get back to where you started. Taking an old
ring that is probably out of round to some degree
and is worn down (check the end gap) so it no longer
has the tension against the cylinder wall to ware it
smooth again is asking a lot in my opinion. Its best
not to disturb the rings unless you have the parts to
rebuild the cylinder properly because your likely to end
up with less compression than when you started. If the
the rings are stuck so bad you cant get the motor started
or the compression is so low it won’t run properly, and
all that is available is used parts – you got to do what
you got to do. If you mike a worn ring you will see they
don’t ware evenly. The thickness at the end gap will be
the thinnest. If you find the ring measures evenly all the
way around you never should have taken the motor apart.
Honing the cylinder and putting the used parts back in
only adds years of ware. If both the cyl. and the rings
are out of round enough there may be places around a
ring that it will never completely seal.
I always get a pre WWII motor running first and give it
a chance for the rings to free up. Today’s oil will clean
out the old carbon and varnish. If the rings are stuck in
places you will notice improvement in how a motor runs
over time as the rings free up. The smaller the motor the
more noticeable this is. If I get to the point where I believe
the rings should be free but don’t feel a motor is running
as well as it could then I will check the compression to see
if that is in fact the issue.
I couldn’t get this motor to run so I had to hone the
cylinders and replace the rings. It runs fine but have you
ever raced anyone with the same motor as you and they can
just creep away from you? I’m guessing I lost a mph. or 2.
https://www.youtube.com/watch?v=KjSPM6mp4eY&t=38s

[need2fish]

Nicely put. I’m going to add this to my personal "mechanics bible".

[Author]

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