Do port edges really catch rings?

[rothfm]

Heres why I ask....rebuilt motor last year, myself (not my first). Came out great. Ran it all season. I also decarb and do carb kits and soaks annually on my motors.

Was gonna sell this motor (1984 115), and was doing a freshen-up on it first. Low and behold found a small missing piece of ring, even though it has 118psi

Holes, pistons, everything clean as a wistle still. I have had no heat issues and really maintained this motor (again 1 yr since rebuilt)

HOWEVER, I did NOT bevel the port edges. After taking it apart, they are indeed razor sharp

So I just measured, honed and champhered(sp?) all port edges on this hole only.

Did these sharp edges really catch and break a piece of ring? I was dis-believing the need when rebuilding......but now 2nd guessing.

 

[racerone]

What NEW parts did you install in your " rebuild " last year ?

 

[fhhuber]

They can... if not machined quite right or the ring is too tight in the cylinder.

Or if the ring end lines up inside the port, that is asking for the ring end to get caught. (one reason there's a pin to prevent the ring from spinning around the piston)

Generally the champher of just hitting the port edge with 600 grit emery paper one quick swipe from in cylinder going into the port is plenty to take off any potential machining lip. Like hitting a knife blade to dull the edge. This much is being paranoid if you didn't have the ports opened after the cylinder was honed.

 

[Faztbullet]

This usually is done if rings installed with screwdriver instead of ring compressor

 

[rothfm]

Rebuild: all new WSM pistons and rings, all rod and wrist-pin bearings(BRP).

I Always use a ring compressor.

Locating pin still present.

I have another theory. At time of rebuild a year ago, one ring of the new ring-sets arrived damaged out of box, it was replaced with same. Maybe another was weak/cracked...dont know.

I hit the edges with a small dremel stone now anyway.

 

[Bosunsmate]

I always give mine a smooth down with sandpaper as i figure its a risk that i dont want to have to go through what you have had too.
Interested to know what oil mix ratio you are running her on?

 

[flyingscott]

Was it bored or honed at the time of the rebuild.

 

[racerone]

OMC factory type ring compressor or typical 4 stroke engine ring compressor ?

 

[boobie]

If I had a block bored I'd run a ball hone in the cylinders to round off the port edges. This was also recommended in the OMC Service Schools.

 

[rothfm]

Honed originally by me. I left the edges. A year later they are very sharp. I just touched them yesterday with a small dremel, and a quick light hone(Flex-Hone)

I can actually seat and install these rings by hand without a tool. But I do have a normal engine type vs the OMC tool.

I mix 50:1, do Engine Tune decarbs, seafoam in tank, and yearly carb kits.

Thus far I dont have an explanation for this breakage. But like I said earlier, last year during the rework, a ring arrived in mail broken in the box....wondering if another was affected and I didnt notice it at the time.

Im removing the other 3 to go over them checking. If they look good and measure as they did, I will be putting it back together.

I ran this motor all over, offshore and propably places I had not right to be! Never a hiccup. Happened to notice when I was freshening it up for possibly selling.

 

[racerone]

Where was the ring broken ?--------Pictures ?

 

[HighTrim]

Yeah I'm curious too, where did you find the piece of ring?

If you used a ball hone the first time, that should not have left a sharp edge on the ports. I've seen that more when boring oversize and not taking the edge off, or as stated if the pin comes out and the ring rotates in its land.

 

[rothfm]

Pics:


Shot of the "ding" first noticed when doing head gaskets..Prompted me to take it apart.


Shot showing the portion missing







Again, Motor was put together my me 1yr year ago with new rings, pistons and bearings. Still very clean. No carbon at all.

Below are a few pics of the Cylinder after clean up and touching the port Edges to "unsharpen" them, the couple lines
visible are Color only, and have no depth at all. Cyl was not damaged, or scuffed. both Ring locating pins were still present.
I have measurements in my shop, but were ok, on the outter limits, but in spec per OEM manual.

The Ring piece was crushed and blown out..It did make a ding on the head and piston dome but that was surprisingly it..I have another head.








New Rings and Piston is now in place, End gap good, side clearance good per OEM Manual.

This was not a breakdown situation. I had no idea until "refreshing" head gaskets for possibly selling. Still had 118psi. I used this motor alot and didnt notice any heat issues. Was surprised to find this.

P-head is back together and this hole tests at 120psi cold on bench.

 

[racerone]

What is the bore diameter now ??-----So you put new pistons in a bore that looks good but might be worn out of specification ?

 

[shaw520]

You should have seen a point of impact on the port edge as well.

 

[rothfm]

Racer......Negative. I dont go by Looks... measured multiple times pre original-rebuild last year, and again after this ring failure...IN SPEC, According to all methods, locations and dimensions listed in the OEM manuals. Even had a neighbor who builds auto race engines double-check the numbers. Still remains a Std bore block.

There is one exhaust port that has the typical U-shape ding-very slight, that flattened out nicely after using the Flex-Hone (globule ball hone).

 

[racerone]

What is the bore diameter now ?-------3.502 "--------3.503 "------Any taper ?-----Any out of round ?

 

[flyingscott]

How sure are you something did not go through the motor?

 

[Faztbullet]

Got pics of other pistons as that one looks way rich....been lugging engine?

 

[rothfm]

Im away from my shop this week. Spec numbers are there, I cant remember off top of head, but were ok, taper numbers good. Roundness numbers good

As far as going thru motor, how can I tell? It was apart. Those ring pieces usually go thru ok. I checked exhaust area and housing with flex camera. These parts are 1yr old now, still looked new.

Lugging....might be something there. Dont have pics of other 3. I did have them out to measure (good) and they looked very clean no carbon at all, bearing look unheated and fine

Last couple trips out I did notice I had dropped some rpm at WOT. Usually ran 53-5400. I was seeing about 5k. Lugging or post-ring break? Dont know