2 Strokes Down Under

That tang is designed to run on the bridge of the RZ intake port.
The earlier engines (LC or AC) do not have this bridge. It's one big port.

That tang can get caught in the port, and there is clear evidence of that happening and causing the crack in his piston.

This problem will also be exacerbated when there is more clearance in the bore to allow the piston to rock more.

None of the older pistons are designed that way. They all have a flat base.

I'm no expert and I'm sure all your points are correct, to reply to the little tab point though, its there in a YPVS motor to slide along the bridge in the inlet port, the YPVS port being a squarish port divided by a bridge of cylinder down the middle. The LC has what looks like a peculiar keyhole shaped port with no bridge, and the tab at the bottom of a YPVS piston is a similar width to the slot shaped bottom bit of the port, leading to a bit of conflict. Taking the tab off removes a bit of interference at the edges presumably.

I'm interested in the best methods of getting that tab off without distorting the piston skirt, a hand file OK? A Dremmel better?

I used a hand file on mine. Run it along the skirt, not across it and it should put very little load on the piston.

well I can appreciate that point of view, but piston tabs don’t stick out any further than the actual base of a piston, so if in fact that theory is plausible the skirt of any piston would clip the base of the intake port????
One major point here is the thrust side of the piston is the exhaust side, so after the firing and on the downward stroke, would in fact force the intake side of the skirt away from the base of the intake port. I think that crack is from the matter that has lodged between the piston and bore.

It's a well known mod in the UK, has been done for years because of this interference. The LC I bought over there many moons ago needed it done, as it had been bodged back together for a quick sale, complete with cheap gaskets and unmodified YPVS type pistons. Broad consensus from those re-doing the engine and others was that this mod is necessary as a matter of course.
Given the clearances involved, the mention of piston rock etc I'd be inclined to think this is one of those details, like easing the edge of a port, or keeping piston/bore clearance within a certain range.
I have little doubt from what I've heard and seen in the past that leaving the tab on will f$$$ up the piston in short order in most cases, but I'm no expert.

Anyway, very nice looking bike and eminently fixable, looking forward to the images of its journey and it being back up and running again.

How's your new rd coming along Stankflapper? Must be close..

Thanks everyone.

Really worried about said "chip of aluminium".

Where could it be and what's it likely to do to my engine if I can't find it?

What about pistons such as TKJR, Vertex and Pro-X? Is one 'better' than another? Couldn't find much doing a search.

Blue

How come you can't get OEM spec pistons from someone like Wiseco

Just read Classic Mechanics article by Saint Stan of Stephens, repairing a TZR250 race motor with a holed piston as an example. He reckons to always strip a motor to find and clean out all fragments thoroughly. Photo of a big end bearing with an alloy chip nestled in the rollers put the message across pretty clearly that you just can't tell if the debris is hiding without opening the cases.
On the other hand the motor he was working on was a mess of tiny shrapnel, your chip might have blown right out the exhaust pipe or it might be still in there somewhere.

Blue wrote:Thanks everyone.

Really worried about said "chip of aluminium".

Where could it be and what's it likely to do to my engine if I can't find it?

What about pistons such as TKJR, Vertex and Pro-X? Is one 'better' than another? Couldn't find much doing a search.

Blue

It would have blown out the exhaust many revolutions ago mate.

Simple physics says that when the piston is tilted, the longest part will protrude the furthest.

Endless debate will ensue on most forums about piston makers, add Wossner and WiseCo to the list. I'm donning my tin helmet and warming up some popcorn....

Greasemeup wrote:How's your new rd coming along Stankflapper? Must be close..

Got 3 on the go at the moment mate. Will post up some pics soon.

hybrid wrote:Simple physics says that when the piston is tilted, the longest part will protrude the furthest.

in the event of too much clearance you do get a lot of piston rock causing the slapping sound while running, however in my opinion on the power stroke the thrust side of the bore is the exhaust side, which pushes that exhaust side of the skirt onto the bore face.