I was always taught that when you tear down an engine with any time on it at all you need to replace the piston ring's(auto/truck)
IF you remove the piston from the cylinder as there is no way to get the ring back in the exact same spot. When a ring is seated it has worn into the little hill's/ valley's(small un seen scratches) of the cylinder/ring. If the ring is reused it will seat on the hills but that leaves low spots on the ring that will never seat and on the cylinder also if the ring/cylinder low spot's lined up.
So i have a few times tried to reuse a ring in our small engines and never had satisfactory compression return with out putting in a new ring
I have also read where people reuse the old ring and say it works fine. If this is true how are they doing it?
pat

In car engines and model 4-stroke engines the ring is free to turn, and in fact it will, so wear is even all around the bore. In two strokes, the ring is pinned, and it will move to and fro just a little. It does move though, the more so if the ring wears down.
Removing a ring without distorting it takes a bit of practice, and above all, a piston that is located and fixed well. To that end I use a piece of plywood in my vice to grip the connecting rod and push the piston down until it seats against the wood. I then pull the ring slot outward with my thumbnails, and push the ring inward with my index fingers until it JUST slips over the piston. No more!
The torque generated by the index finger pushing action keeps the ring round when the slot is pulled open, and the outward bending is distributed over the whole ring circumference.

Some two strokes are pinned; but some, K&B 4011, for example, are not.

Ok upon further reading it is true. Rings do rotate. I thought they do not. So that leads me to this question. Sense the rings are rotating what exactly is going on with the ring/cylinder that makes them seat in and have more compression after an hour run time opposed to a new none run engine. I had always wrongly assumed that the ring's kinda key into the micro scratches and wore into the small voids increasing compression/locking the ring in place,,But that ain't what's happening
Pat

Rings do not only have to seat against the cylinder wall, they also have to seat into the ring groove of the piston. Sometimes this is where the most loss in compression is seen. This is where a new piston is required where the ring groove in the piston is past it's service life. It will show up as broken or cracked rings after a new replacement of the ring.

The pin are necessary if the ports in sleeve are large to prevent the end of ring are coming out of port and jamming the piston. The sleeve with many small ports are pinned ring uneccesary.

See my homemade piston with ring and sleeve in the OS 61 engine in these photo.

Jens Eirik

Jens,
How does the ring stand up to the high combustion pressures in the diesel? did you make it of meehanite or other iron?

Pe reivers

No problem with the high pressure against piston ring. I calculated the size of piston ring adapted for cylinder bore after Prof. Chaddocks methods how to produce own piston ring. The material in ring are made of camshaft from Peugeot engine, the camshaft are made of cast iron with hardened camlope, camlope are impossible to machine with tool. Between camlope are soft and are used to make piston or piston ring to model engines. I has used brake disc to produce small piston to my 0.5 cc diesel engine and piston ring to some of my model engines. Brake disc are made of cast iron.

Jens Eirik

hmm...
the problem always is getting materials that can be machined. I once used a car rear axle to make (hand file job) a new side valve engine camshaft with special timing, and I NiCoTrated the soft Veco .19 cylinders to make them glass hard. That made the engine as durable as the best Webra of that time.
I like your idea of using camshafts for piston rings It is a very fine grained material with a lot of shock resistance and excellent wear properties. Car engine materials are the best one can get at scrap prices!
Dykes rings I made out of scrap cast mold meehanite for a ST.25 lasted well in CL, but not very long in prolonged full bore RC operation.
BTW, That ring experience was the reason I asked.

There's an article on making piston rings at http://www.supercoolprops.com/articl...iston_ring.php where the grade of meehanite is suggested plus the heat treatment to set the ring gap and so on. If you go back to http://www.supercoolprops.com/articles.php you'll find many more articles on a great variety of subjects.