It is normal for pistons to do this?

[dhen]

I decided to start a different thread because I found something strange when I pulled my cylinder head off. My pistons wiggle around inside the cylinders. They only do it if I move them parallel to the crank - not side to side. Also, I don't seem to be able to get them to move at all unless the piston is at the top of the cylinder.

I took a picture and a video.

[youtube]http://www.youtube.com/watch?v=WUGGN1SO ... e=youtu.be[/youtube]

This doesn't look right to me. All of the pistons do the same thing, but the #1 piston seems to do it a little more. Is this the source of my knock?



I'm not sure what the little lines on the top of the cylinder are, but I can't feel them with my finger.

post6209759.html#p6209759

The engine only has maybe 400 miles on it. It overheated once. I took it to the machine shop after that and they they honed it, checked it out, and said the bearings were OK. I put the cylinder head on myself and that's when the knock started.

Any ideas are welcome.

[float_6969]

My pistons do something similar, but they're CP pistons and slap around and make a lot of noise when they're cold as well. The CP's do it because of the aluminum that is used. It's very resistant to detonation, but has a high rate of expansion.

If those are stock pistons, you might look in the FSM and see what the acceptable clearance is. If it's out of spec, that could be the noise.

[dhen]

My pistons do something similar, but they're CP pistons and slap around and make a lot of noise when they're cold as well. The CP's do it because of the aluminum that is used. It's very resistant to detonation, but has a high rate of expansion.

If those are stock pistons, you might look in the FSM and see what the acceptable clearance is. If it's out of spec, that could be the noise.

Thanks. I forgot to mention that mine are forged Wiseco pistons. Any idea if they're supposed to do the same? Since they're not stock, how do I find out if they're in spec? Sorry if that's a stupid question.

[blownhemi]

My pistons do something similar, but they're CP pistons and slap around and make a lot of noise when they're cold as well. The CP's do it because of the aluminum that is used. It's very resistant to detonation, but has a high rate of expansion.

If those are stock pistons, you might look in the FSM and see what the acceptable clearance is. If it's out of spec, that could be the noise.

Thanks. I forgot to mention that mine are forged Wiseco pistons. Any idea if they're supposed to do the same? Since they're not stock, how do I find out if they're in spec? Sorry if that's a stupid question.

You should have received a sheet with your forged aftermarket pistons stating the required clearance. My forged CP's are also frigtheningly loose in the bore when cold. They are +0.5mm oversize, but the cylinder bore needed to be ~83.42mm for the correct clearance, instead of 83.50mm, like common sense would have you believe. Good thing I didn't send the block to the machine shop before I got the pistons.

If you have forged pistons, don't go by the FSM, always go by the sheet you got. If you don't have the sheet, get ahold of it first. (This might come late though, now that your engine is already put together, machine work done... )

Did you assemble your engine yourself? Were your pistons this loose at assembly time? Do you know what clearance they were assembled with? Do you have the Wiseco's data/installation sheet?

[dhen]

Thanks. I'm going to call Wiseco tomorrow and get the specs.

I showed the video to the machinist and he was concerned about the sound. I'm going to pull the engine and take it by.

I'll update when I know more.

[float_6969]

blownhemi is dead on. The piston-bore clearance is dictated entirely by what the piston manufacturer states it should be. The first time I built my motor I was floored at the amount of cold clearance it called for, but the machine shop was very familiar with race pistons and told me it was very normal. It needs checked out, but it's probably normal.

[bentvalves]

do they all move that freely? the noise is whats strange, and not how much the piston is able to move, but how easily (collapsed or stuck ring maybe?)

[bimeur]

the clearance for Wiseco pistons, for street use, is 0.1mm if I remember well, that's what my machine shop recommended to me.

as hard you're gonna use the engine, as higher the clearance is (drag use should be aprro. 0.20mm of clearance)

[dhen]

I took it by the machinist yesterday. The cylinders are in spec by the specs Wiseco emailed me. But it turns out that the gear on the end crank is very loose - the key doesn't keep the gear tight. He wasn't sure, but he thought this was the source of the knock. It does sound like it.

I was thinking about shoving some shim-stock into the gap to tighten it up but I was wondering if solder would work. That's much easier and I don't think the balancer gets hot enough to melt it. If anyone knows please say something. I googled the melting temp of solder and the lowest one was 250 Fahrenheit.

I don't know if the loose crankshaft gear is the knock, but the machinist said that if it were the rings, the walls would be f*** up and they look great, and as I said before, the clearances on the cylinders are very good. In addition, I'm running 14.5:1 air:fuel when I'm not boosting, so the knock sensor isn't detecting anything.

I'll post a video once I get it back in the car and running - I'll be a few weeks since, like all of us, I have family and work commitments.

All the same, any comments are welcome.

Thanks,

Darian

[blownhemi]

If the problem is not the with the crank keyway being worn out:
- woodruff key bent? -> ebay has them OEM new $5 a piece
- timing gear slot worn out? -? ebay has them OEM new $40 a piece

[float_6969]

yea, I'd just replace the sproket and key and be done with it. The problem with soldier wouldn't be the melting point, but compressive strength. I'd be worried about it compressing and squishing out over time.

[dhen]

I took an old shim and jammed it into the slot on the crank to tighten the key up yesterday. I trimmed the top of the shim on top with a dremmel. The sprocket's tight now - I'll let you know how it holds up. I could tack weld it, but that's kind of the nuclear option.

[TheMAN]

I'd still replace the parts with new if I were you.... just mcguyvering it sounds like asking for trouble... these engines are getting harder to find and if it breaks, it'll be an expensive fix!

but if it's just a test to see if it's still making that noise, then go for it!