DrX

iTrader: (6)

What's the cause fix for this? All 8 pistons/cylinders on both top and bottom sides. LSX block.

LLLosingit

iTrader: (4)

How many miles on it before tear down? What is the bore/stroke?
There could be a few things that cause this but it's not uncommon on a stroker engine.

LLLosingit

iTrader: (4)

I guess I could try to give you more answers. Many stroke/bore combinations actually pull the piston slightly out of the bore add that to the fact that pistons are clearanced for the crankshaft and or short skirt can leave a lot to be desired when in comes to keeping the piston from rocking in the bore= causing accelerated piston skirt/bore wear. Pistons to wall clearance can also cause this but due to thermal expansion of the piston there is only so much you can do.

DrX

iTrader: (6)

Thanks. 2000 miles. LSX block. 4.0 stroke, 4.125 bore IIRC. PB clearance .005" PD blowers 20 PSI. Shift 6500-7000. See teardown thread below.

DrX

iTrader: (6)

After cleaning up a few piston tops, it looks like detonation has been occurring. Is this the typical skirt pattern seen from detonation? Possible lubrication or clearance issue? Cooling issue?

KCS

iTrader: (20)

Rub your finger along the bottom of the cylinders. Does it feel sharp or like it was deburred?

DrX

iTrader: (6)

This how it is finished:

DrX

iTrader: (6)

Cylinders measure pretty round and straight at 4.1275 +/- .0005 with the +/- being at the bottoms. Measured in 4 directions at 3 depths.

Piston skirts all measure 4.125 at widest dimensions. Land diameter is 4.084.

So I get .00125 for PB clearance?? (4.1275 - 4.125) / 2
Or is it just calculated as bore diameter - piston diameter? In that case it would be .0025

KCS

iTrader: (20)

The piston-wall clearance is just like bearing clearance; ID minus OD.

With a torque plate bolted on, the taper in the cylinders might go away.

KCS

iTrader: (20)

That looks sharp. It's probably where you're getting your skirt wear from. I deburr the bottom of the cylinders with a sandpaper cartridge roll and it ends up nice and smooth.

DrX

iTrader: (6)

Still tight at .0025" ?


On both the bore and counterbore edges?

helicoil

iTrader: (104)

Ideally, all the way around the bottom of the bore. It is most critical on the thrust side. This is often neglected, very critical step, especially on strokers.

helicoil

iTrader: (104)

Just break the corner with the cartridge roll, it is hard to do it too much

KCS

iTrader: (20)

Depends. For a 4032 alloy, it's probably just right but since it's a power adder I'd assume it's 2618, which would be tight. I'm also assuming you're properly using a dial bore gauge and micrometer accurate to .0001" as well.

DrX

iTrader: (6)

I think it is probably correct at .005 PB, but I was reading the bore gauge(.0005) wrong. What threw me off was I used a dial caliper at the top of the bore as a sanity check and it was telling me it was under 4.130. Now it looks like that caliper reads around .002 under actual.