Piston free play?

[Ieat4strokes]

I know some of you been following my thread on the 4mill knocking sounds etc, well i took off head this morning, no marks on pistons or domes everything seemed fine until i rotated crank to push piston out of cylinder top, remember its a 4 mill, I grabbed the little 2mm of the piston and it moves in the cylinder a pretty good bit, more than my other cylinders on a fresh bore, I mic'd everything and got 64.96-64.98mm on both cylinders and 64.36-64.39mm on my pistons, is that to much free play? Pistons are 65.00mm per the stamp on top...... The sound I hear when I jiggle them is about the same noise i hear when its running.....Even though my 4th is ruined I hope this is all thats wrong....What you guys think? The side where I think the rattle is coming from has the most play 64.36 piston and 64.98 cylinder.

 

Thanks,

Brad

[sleeper06]

Its really hard to say with just a mic,your micing the skirt not the top rite,if you take a ring off the piston whats the ring gap?Do you have a bore guage?With a bore guage you can check if the cylinders bore is true the whole way down.I had some noise in a motor and it turned out to be an untrue bore.The other thing is,if your detonating you could have collapsed the skirt of the piston,causing some noise

[Ieat4strokes]

Its really hard to say with just a mic,your micing the skirt not the top rite,if you take a ring off the piston whats the ring gap?Do you have a bore guage?With a bore guage you can check if the cylinders bore is true the whole way down.I had some noise in a motor and it turned out to be an untrue bore.The other thing is,if your detonating you could have collapsed the skirt of the piston,causing some noise

 

yea jeff just msgd me and told me to mic the skirt hahaha, doing that I got 64.92 piston and 64.98-99 on cylinders, ring gap is 4.35mm or.171in from tip to tip of ring, from recessed area on ring its 5.46mm or .215, I dont have a bore guage but Jeff listned to video and doesnt think its piston slap ....

 

i mean what could i have screwed up just by pulling old crank and dropping in new one, aint like there was alot involved....is there c-clips on both sides of crank? i only had one on output side?

[Rodneya]

Your ring end gap seems huge. I thought the minimum should be 0.004" for every inch diameter of the piston.

Stock bore = 0.010"

[gregrob]

You need to measure your piston-to-bore clearance with the piston in the cylinder. The spec is .003, however that is the spec perfectly centered in the bore.

 

Use a feeler gauge and stick it beside the piston at a few different places. You would use a .006 feeler gauge and go up from there. The .006 gauge on one side = .003 all the way around

 

 

 

 

[Martinm210]

Ring gap should be .010" minimum, but it should be a whole bunch more or it's probably a good indication the bore is worn a bit too much..

 

FWIW, on my last rebuild I had something like .040" it ran OK until my lack of squish killed both pistons, but the compression was pretty low. Since then I had the cylinders bored and matched, ring gap is now .012".

 

I would do the .006" feeler guage test on one side...that seems like a better means to check.

 

On my bore job, I thought I would be going from 64.75mm to 65.00mm, but I think my bore was soo wore out, the shop had to go clear up to 65.50 to clean it up.