A bit of back and forth piston play?

[89hatchman]

If I set piston 2 and 4 to TDC (not at the same time, thats impossible) and wiggle it it has more play than pistons 1 and 3.

Not a whole ton of play but a noticeable amount. Could this be from worn rings? I was getting some blow by that forced oil out of the crank pulley seal.

If I replace the rings will I be good to go? Does replacing the rings tighten up a piston in the cylinder a bit?

[EDacIouSX]

i'm guessing you mean side to side play and not up and down play? I dont' know much about these things but I think that might be important.

[codyace]

I'd measure the bore first to make sure it's not out of spec. Wore rings can make a piston feel loose in there, but it's marginal feeling to say the least. Could be play in the wrist pins too.

[OrangeVirus1]

that is kinda normal in a older engine. When pistons are at TDC they can rock back and forth a little bit. not really gonna hurt anything ( unless you could get the piston totally sideways lol!)

[89hatchman]

I'd measure the bore first to make sure it's not out of spec. Wore rings can make a piston feel loose in there, but it's marginal feeling to say the least. Could be play in the wrist pins too.

Is there a way to measure the bore without using a micrometer? I don't have one.

that is kinda normal in a older engine. When pistons are at TDC they can rock back and forth a little bit. not really gonna hurt anything ( unless you could get the piston totally sideways lol!)

Ya, I suppose thinking back on it now, that it isn't too bad. Just a little more than the other 2 pistons. I'm going to throw new rings on it, hopefully that'll help tighten it up.

[OrangeVirus1]

it probably won't tighten it up man, it is because over time the bores go out of round. you can't see it with the naked eye but they actually oval-ize themselves

[dawagarage]

it could be play at the pins/rods, that the bore is out of round, or from the rings. i'd said cheapest fix and most likely is the rings are loose.
bores being out of round would be the biggest bitch, requiring them to be bored over, then youd need bigger pistons with matching rings.

[Croustibat]

If it has been rebuilt, it could also be the machinist did a poor job and did not center its tool on the bore. It happened to a friend, its engine ended up making noise like worn hydraulic lifters, so he went mechanic lifters ... but the noise was still there. After the engine died, we discovered that it had been poorly machined.
The slap was so hard it cracked a bore on the 3rd cylinder, where coolant goes. It happened at the end of a drag run, after many of them though. We were impressed at how a 1.8L engine would still produce north of 500HP with that kind of piston slap :D

[ShakotanGazelle]

Would this cause sort of a knocking sound on cold startups? My S12 sounds like it's knocking for like 2 seconds on some cold starts.

[dawagarage]

^loose rings can create a sound similar to knocking, which goes away after the engine warms up (metal/rings expand.)

the guy i bought my motor (datsun L20b) though he had a spun bearing but once the machinist disassemble and mic'd it, he said the bearings are fine but the bores were too large for the pistons/rings.

[Croustibat]

Would this cause sort of a knocking sound on cold startups? My S12 sounds like it's knocking for like 2 seconds on some cold starts.

If it is only for 2 seconds i'd rather say dead hydraulic lifters, or worn oil pump. It is hard to talk about noises on a forum though...