piston ring gap orientation

At the suggestion of an A&P, I removed the #2 cyl of my 0-320E2a used engine to inspect camshaft for corrosion, etc.

Camshaft looks great. Piston top has lead fouling but everything looks good.

Now my question for you engine gurus:

How should the compression ring gaps be oriented? In car engines I've built it was always 180 degrees.

When I looked at my lyc piston, it looks like they were lined up. Can this be right?

Now I just need a ring compressor for that big piston. none of my car tools will work.

Dave

Typically ring gaps are set offset 120-180 degrees. The ring gaps do rotate around and occasionally end up in alignment. This is why when you find low compression on a cylinder, the first recommendation is to run the engine for a while and recheck.
If the gaps didn't rotate, you would end up with a "notch" worn into the top of the cylinder.

ring gaps

thanks Mel!

I didn't realize the rings rotate.

I'll install with gaps at 180 deg.

what would we all do without this forum.........

Dave

Its 120 for each ring on a Lyc, since there are three rings.

I have a nice ring compressor I made by cutting off the bottom of a cylinder barrel, and cleaned it up on a lathe. I also turned a taper inside it for the ring to compress, and milled a slot to clear the rod to remove the ring.

The lycoming overhaul manual specifies that the ring gaps be oriented 120 degrees apart, although if you oriented 180 degrees I wouldn't think there would be a problem. You just don't want the gaps aligned.

I attended the Lycoming Assembly forum at Osh and the Lycoming folks said to face the oil ring down, the next compression ring to the left, and the last compression to the right 180*. He also said that the do move around but "thats just the way we do it".

ring gaps

Thanks to all for the quick responses.

I have a nice ring compressor I made by cutting off the bottom of a cylinder barrel, and cleaned it up on a lathe. I also turned a taper inside it for the ring to compress, and milled a slot to clear the rod to remove the ring

Click to expand...

I wish I had a spare cyl to fab one of these. I have the lathe & mill.

Dave

Ring compressor

A ring compressor for the 5.25" pistons can be had for about $19 all over the internet. These are the sheet metal types that tighten with an allen- style wrench. Works fine for low volume.

I agree with the gap staggering statements, for installation of the piston into the cyl, what I have done is to load the piston and rings into the cylinder on the bench, I use my fingernails to compress the ring and work the piston into the cylinder.

After the piston is in far enough to capture the rings, take it to the engine short block, put it into place (on the studs if they are long enough) and slide it toward the crankcase to mate up with the rod. Insert the wrist pin, and keeper, and then seat the cyl on the crankcase.

This will not work for pistons that have the oil ring so low as to cover the pin hole, or pistons with two oil rings, one below the pin.

Having just said all that, I have never been inside a Lyc, but the above works well with Franklin aircraft engines, and air cooled VWs.

Good luck.

Daver said:

Thanks to all for the quick responses.




I wish I had a spare cyl to fab one of these. I have the lathe & mill.

Dave

Click to expand...

Just ask around, someone around you has junk cylinders.

Also, if you cut the cylinder flange off, it makes for a nice tool for use instead of washers to torque case halves together before you bolt the jugs on.

If you have the automotive type with the removable bands, just make a 'lycoming' band from a strip of aluminum with right angle lips to catch the plier type squeezer.



I have even seen one made from a strip of aluminum and a hose clamp.

Its one of those tools the average person doesn't use daily.

Daver said:

...I wish I had a spare cyl to fab one of these. I have the lathe & mill.

Dave

Click to expand...

Some scrap aluminum, thick safety wire, and safety wire pliers will do the trick.

(Not my idea, learned from an old IA friend.)

rocketbob said:

Just ask around, someone around you has junk cylinders.

Also, if you cut the cylinder flange off, it makes for a nice tool for use instead of washers to torque case halves together before you bolt the jugs on.

Click to expand...

The guys from Lycoming at the reassembly forum were very adamant about NOT using washers for torqueing the case together. Use torque plates instead. You can make some out of old cylinders or steel (as I did), but do not use washers. I used washers when I reassembled my IO-540 right before attending Oshkosh. I also coated the bearings all over with oil before installing them, along with coating the mating surfaces on the inside of the case, which I found out is a no-no. Upon returning home, I disassembled and reassembled per Lycoming proceedures not in my overhaul manual. Glad I attended that forum!

Is it a good idea to remove the piston completely from the cylinder and re-install the same rings? If it is ok, why do some use the rope trick remove and relap a valve? Maybe a re-hone and new rings should be installed. I have wondered about this for a long time.

TO ALL THE EXPERTS

FIRST GET LYCOMING MANUAL , READ IT, IT TELLS YOU TO SET THE RING GAPS WITHIN SO MANY DEGREES OF RIST PIN, RINGS DON'T ROTATE ALL THE WAY AROUND THE CLY, THEY WILL FOLLOW THE HONE PATTERN. IF YOU PUT RING GAP 180 FROM RIST PIN IT WILL BE AT THE TOP OR BOTTOM OF THE PISTON, AS PISTON GOES UP AND DOWN IT TRIES TO **** , THE RING'S TRY TO HOLD IT STRIGHT, SOME ENGINES HAVE A PISTON RING AT BOTTOM OF PISTON TO HELP PREVENT THIS,
A GOOD RING COMPRESS CAN BE HAD AT A LOCAL AUTO PARTS STORE, NAPA, ECT.
PUT RINGS ON PISTON, COMPRESS, INSTALL INTO CLY. REMOVE RING COMPRESSOR, LEAVE RIST PIN HOLE OUT OF PISTON, INSTALL RIST PIN, PUSH CYL. ON TO ENGINE CASE, INSTALL NUTS, DON'T FORGET O RING ON BOTTOM OF CLY, RUN ENGINE IN ON MINERAL OIL , AT LEAST 25 HRS, CHANGE OIL AND FILTER, YOU WILL FIND THIS INFO IN LYC. CONT, AND SEVERAL OTHER MANUALS, I WAS A MECH IN AIRFORCE AND WORKED FOR AIRLINES FOR 40 YRS, [edit]