Bad piston ring?

[optmaxx]

I've been having blow by from my crankcase and rough idle, things that I didn't have before but probably slowly developed. I did a compression test while the engine was warm and here's what I got:

1: 180

2: 180

3: 190 or 185, I was trying to figure out how to read my gauge, but it's most likely 190

4: 190 or 185

5: 180

6: 50, wet 60

I cranked it for 8 sec for each cylinder, and for the wet test I squirted two big squirts from my oil can so that it can reach the edges better. If it's the #6 piston ring, I'm pretty confident that I can do it without removing my engine, and of course I'll have to remove the head. Should I re hone the cylinder wall when doing this? I know that I still have extra new rings around, and should I change the bearing for that piston too? I have extra bearings too.

[optmaxx]

I'm thinking of getting a leak down test because I'm not sure if 10 psi is a big enough difference for it to mean bad piston rings. At the same time, I don't know what else could cause my blow by? It smoke from my crankcase, and I can feel puffs but it doesn't smoke from my tail pipe, my plugs are dry, but they are changing color from the blow by circulating back into the intake I suppose.

When I tested the cylinder with the lowest compression, my engine cranked slower and I had all of the plugs off. I thought that my battery was going low, so I checked another cylinder that had good compression and my engine cranked normal.

[Cheromaniac]

I'm thinking of getting a leak down test because I'm not sure if 10 psi is a big enough difference for it to mean bad piston rings. At the same time, I don't know what else could cause my blow by? It smoke from my crankcase, and I can feel puffs but it doesn't smoke from my tail pipe, my plugs are dry, but they are changing color from the blow by circulating back into the intake I suppose.

I'm willing to bet that the rings are intact and you have a cracked piston. The no.6 cylinder, being furthest away from the water pump, tends to run hottest and the piston may have been damaged by detonation.
One thing I can guarantee is that you're gonna have to pull the head off to find out. There's a fair chance that the only thing you'll need to do is replace the piston/rings but you won't know until you check the cylinder wall. You'll also need to look for the underlying cause of the problem and fix it so it doesn't happen again.

[optmaxx]

I'm actually kind of looking forward to this. My power has been ok, but after finding out that it could be better has me wanting to tear into it as soon as possible.

When I look for the crack, will I only be looking for it on the top of the piston? I've actually recently last week removed the head to replace the lifters because they stayed noisy, so this will be the second time removing the head bolts, they probably are no good to use again huh. Also, a bad head gasket wouldn't cause blow by in the crankcase will it? I started to get the blow by after replacing the lifters, and I've been trying to figure out where I went wrong. The new lifters did improve my valve train noise a lot.

[SilverXJ]

What were the old lifters? What were the new lifters?

Yes, a damaged head gasket could cause blowby into the crank case.

[optmaxx]

Old lifters were Millings and the new ones are Sealed Power. I remembered having to push in the Millings lifters with my thumb, and after finding out that lifters are supposed to slide in with almost no effort is when I decided to change them. The Sealed Power lifters went in like butter, but I did carefully clean the lifter bores a little with a pipe brush. I also didn't bleed the Milling lifters because I didn't think it was necessary, but a mechanic friend recommended to do it, so I did. I could of had bad set of Milling lifters to begin with.

[Cheromaniac]

Also, a bad head gasket wouldn't cause blow by in the crankcase will it?

It's a long shot 'cause the oil galleries are far away from the combustion chambers. However if the head wasn't torqued down properly that would make it more likely.

[optmaxx]

I got the head off and I didn't notice any cracks on the piston, or anything weird with the gasket; I'll pull out the piston next. I did notice some vertical marks, but the other cylinders with the higher compression had them too and the wall still have cross hatches, so I don't know what to make of the vertical marks. They look like they're from the piston skirt and are all pretty similar from cylinder to cylinder. If I need to hone, is there a certain hone I should use? I know that the ball b\hone is recommended, but are there different types?

[Cheromaniac]

There doesn't seem to be a smoking gun but you might need to pull the no.6 piston out of the bore and inspect the rings.

[Russ Pottenger]

When installing new rings make sure you take the Plumas stone or jewelers file to smooth out the sharp edges
of the ring end gaps. That's the source of a lot of vertical scratches

[optmaxx]

Took out the piston, both compression rings were toast, the walls look ok. I'm not going to worry about the scuff marks, I'm sure all of my pistons have them. I probably should give the rings a bit more gap? I had them at .018 to .020, the top one i would put at .020.

[jasonb]

What kind of rings were they?

[jasonb]

Also, why the full dish pistons? were you running some kind of boost?

[optmaxx]

Hastings cast rings. I'm not running any boost, when I ordered my pistons and asked for -26 cc, that's what I got. I guess at the time that's how they dished their pistons.

[IH 392]

General rule of thumb on piston ring gap is .004" per inch of cylinder bore, the spec you stated should have been fine?
MANY! times I've measured the end gaps they are to wide! right out of the box.

The scoring may be from the piston skirts by the wrist pins?, it's obvious the piston has scuffed there.