In This Article:
The old piston rings are removed. The ring grooves are scraped clean, and the pistons are cleaned in solvent. New rings are installed and the wrist pins are oiled.
4 - 6 Hours
Bruce W. Maki, Editor
Before replacing the piston rings, I took the entire set of pistons to a local automotive machine shop so the connecting rod bores could be checked and machined if necessary.
The machine shop tightens all the rod nuts to the required torque and measures the diameter of the rod bores with a precision micrometer. All of the rod bores were okay, except for number 6, which had stretched by at least .002". The machine shop then removed the rod cap and machined a couple of thousandths of an inch of metal from the mating surfaces. Then they replaced the cap and re-bored the connecting rod hole to the proper diameter. This is standard procedure for any engine that has experienced a rod knock.
Checking all six connecting rods and machining one rod cost me about $65.
Note that before I removed the pistons, I used a set of number punches to stamp the cylinder number on each rod cap, just to ensure I would have no problem keeping track of which piston belonged in which cylinder.
When I got the pistons back from the machine shop, the connecting rod nuts where tightened to the proper torque.
But there was no way I could remove those nuts without some type of fixture to hold the rods. So I simply placed the end of the connecting rod on a clean 2x4 block of wood on a workbench, covered the rod with another block of 2x4, and clamped everything to the bench with two 12-inch bar clamps. Then I was able to remove the rod nuts easily.
Notice how dirty the pistons were after 163,000 miles.
The brownish-black stuff is oil residue that has become baked on. Behind the piston rings there is even more residue, and it doesn't come off easily.
This is a piston ring installer tool, which is also used to remove piston rings. This cost $8 at my local auto parts store.
The top two rings are called compression rings. These create a tight seal between the piston and the cylinder wall.
I pushed the piston ring so the ends were sticking out, then I placed the tips of the piston ring pliers over the ends of the ring, and spread the ring apart so it would slip over the piston.
WARNING: It's tempting to "spiral" the piston rings into the grooves, but that can bend the rings and make them bind, causing serious wear. It's certainly okay to remove the old rings without this special tool, but the tool MUST be used to install new rings.
Note the dot near the end of the piston ring. This dot (or any type of marking) indicates the top of the ring.
This is important when installing new rings, the rings are NOT reversible.
The oil control rings consist of two thin rings separated by a waffle-shaped spacer.
The ends of the rings are not supposed to be adjacent to each other. It can be difficult to find the ends of these rings (red arrows).
I used a curved hook tool to pry out the end of the oil control ring, and I removed the ring by "spiralling" it off.
This is acceptable for oil control rings. The piston ring pliers don't work on oil control rings.
Then I removed the oil control ring spacer.
After trying various methods of cleaning the baked-on oil from the back of the ring grooves, I decided to cut an old ring in half and use the factory-cut end as a scraper.
I DIDN'T LIKE USING THIS TECHNIQUE, because it scratched the back of the ring groove, but nothing else seemed to work, and my local parts store didn't have a ring cleaning tool.
When scraping the back of the ring grooves I was very careful to keep the scratching to a minimum. The scraping did create some small flakes of metal, which I blew out with compressed air.
If I was rebuilding a more valuable engine (for a more valuable car), I would seriously consider investing $20 to $30 in a piston ring groove cleaner tool.
Once the ring grooves were clean, I dipped the end of the piston in Xylene and used a brass brush to clean the oil residue from the aluminum piston. This involved A LOT of scrubbing.
Note that carburator cleaner is often made from xylene, with other solvents added sometimes. Brake parts cleaner would also work, but a quart can of xylene is cheaper and leaves no residue (that I know of).
After cleaning, I dipped the piston in xylene again and blew it dry with compressed air.
Since cleaning in xylene also removed the oil between the wrist pin and the piston, I applied some regular motor oil to the small notches on the outside of the piston.
I presume these notches catch oil scraped off the cylinder wall by the oil control rings, and direct the oil towards the wrist pins.
I also applied a few drops of motor oil to the wrist pin from the underside.
Then I swivelled the piston back-and-forth to spead the oil around.
Note that the wrist pin is pressed into the connecting rod, so the swiveling occurs between the piston and the wrist pin.
At first I tried assembly lube, and the thick gooey liquid didn't seem to spread very well. I could still hear a slight squeak when I rocked the piston back and forth. So I applied some regular motor oil to the same points, which seemed to help. I guess assembly lube doesn't flow very well INTO small spaces, and should mostly be used on journal bearings where the lube won't flow OUT of the small gap between bearing and journal.
When I removed piston number 6 from the engine, the top ring (upper arrow) was stuck. Note how small the gap is between the ends of the ring. This is typical of the end gap when the pistons are inside the cylinders.
The lower piston ring (which runs across the middle of the pcture), was not stuck and expanded properly when the piston was removed.
The arrow near the bottom points to the gap in one of the oil control rings
It turned out that this stuck ring was rusted on top, probably because some water got into the engine while it was sitting in my garage for a year and a half. I think water would sometimes drip from the gaps between the panels of the overhead door, and those drops landed in the intake manifold that leads to cylinder 6. I'm guessing that this minor issue is completely separate from the rod knock on number 6.
If you attempt to rebuild an engine that you acquire from somebody else, it's important to know where it has been. An engine that has run recently is much less likely to have this sort of problem than an engine that has been laying on the ground in an old barn, or outdoors behind some guy's garage. This stuck piston ring, and the small patch of rust on the wall of cylinder number 6 were minor problems. I'm sure there are a lot of other problems you could find inside an engine that received more exposure to the elements.
Note the notch molded into the top of the piston (red arrow). When the piston is installed, this notch points towards the front of the engine.
Some automakers mold an arrow into the piston, which points to the front of the engine.
I spread the oil control spacer apart and slipped it over the piston and inserted it into the lowest groove.
The arrows point to the ends of the waffle material, but there is a curved wire threaded through the ends, which holds the ends of the spacer in the proper shape.
Then I inserted the lower oil control ring at the bottom of the spacer.
Oil control rings are flexible and you can "wind" them or "spiral" them into place. I made sure the end gap was about 45 degrees away from the wrist pin.
I installed the upper oil control ring.
The gap was 180 degrees from the lower oil control ring.
Note the letter "N" near the end of the compression rings.
Any mark near the end of a compression ring is supposed to indicate that side goes towards the top of the piston.
I used the piston ring pliers to install the second (lower) compression ring.
Then I installed the upper ring, which is narrower.
Each of these pistons has 5 rings, and the end gaps need to be staggered to minimize the amount of combustion chamber gases that escape.
This picture shows how I placed the ends of the piston rings:
1. Oil Control Spacer
2. Lower Oil Control Ring
3. Upper Oil Control Ring
4. Lower Compression Ring
5. Upper Compression Ring
It's fairly easy to rotate the rings a bit after they have been installed.
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I removed the cap from the piston and pressed a bearing shell into place, making sure to align the tab on the bearing with the notch in the connecting rod. I also installed a bearing shell in the rod cap. Before installing these bearings, I cleaned everything with brake parts cleaner to remove as much oil as possible.
The bearings need to be clean when the piston is installed so I can use Plastigage between the bearing and rod journal to measure the clearance.
I placed these plastic boots over the connecting rod studs to protect the cylinder wall and crankshaft journals during assembly. Even a small nick in those surfaces can cause early engine failure.
When I removed the pistons, I used a short piece of fuel hose to cover the rod studs, but these nifty little plastic boots are much easier to use. They cost a dollar a pair at the automotive machine shop where I had the connecting rods checked and machined.