My First Top End Rebuild - A Few Questions

[sneaky98gt]

Hello all.

First off, I apologize for yet another "what do you think of my piston / cylinder situation". I know there's hundreds of those threads out there, and I've read all of them, but it still feels prudent to make my own, just because it's mine.

Also, I'm a little long-winded; I apologize. I'll summarize my questions in bold at the bottom of the post, if you want to skip to there.

Anyways, as mentioned, this is my first 2-stroke top end...ever. I've rebuilt multiple car engines, but never had a 2-stroke apart before. So forgive my noob-ness.

Bike is a 2011 EC250. The bike ran fantastic before tear down. I've never ridden a 250 with as much grunt as this one has, and haven't yet ridden a 300 that seems to be any better. It really did run well. I run 50:1 Amsoil Interceptor. Jetting is 178 main, 40 pilot, CEK needle on 5th clip. The previous owner had the RB carb mod done, and supposedly the RB head mod; I believe it, as I measured the squish at around 0.8mm before final disassembly.

I've put somewhere around 80-100 hours on it since I bought it; previous owner supposedly put a new piston in and only rode a few hours (< 10) before selling it to me. Not knowing how true that was, I figured it was time to freshen it up and create a known T-0. Foolishly, I did not measure the ring gap, or the compression, before disassembly. Oh well.

Here are some pictures of the piston and cylinder. At the time of pictures, all that had been done is just wiping everything down.















Honestly, it doesn't look quite as good as I was hoping. There's a bit more carbon on the top of the piston than I was expecting. Also seems there's a good bit of scuffing on both the piston and cylinder, definitely more than I was expecting. That said, I may have had unrealistic expectations based on tearing down car engines.

Good news is that nothing can be felt with a fingernail. Also, at least some of the crosshatching can be seen in most places. And I was surprised that there was virtually no blow-by past the rings.

The other good news is that after doing some research on what these things might should look like, it doesn't seem that anything looks too out of bounds. Thoughts?

I measured everything, which gave mostly good results (I think). The piston measured 66.30mm, compared to the 66.33mm nominal that's stamped on it. So it's worn a decent bit, but I'm replacing it anyway, so not worried. The cylinder measured 66.382mm just above the rings at TDC. It measured 66.385 just below the rings at TDC, and the same just above the ports. Just below the ports measured 66.395. See pictures:







I take all of this to be good news. It certainly seems everything is still well within spec, and there's barely any taper in the cylinder or "lip" above the rings. These measurements also repeated very well around the cylinder, so it doesn't seem egg-shaped at all.

My plan is to clean up the cylinder with some WD-40 and scotch-brite, grab a gasket kit from North Tahoe Motorsports, and to slap a Wossner "A"-piston in it, and let it fly.

Piston: https://wossnerpistons.com/products/8052
Gasket kit: https://www.ebay.com/itm/TOP-END-GAS...4AAOSw6qpa7MXa

Alright, summary of questions:

1. How's the piston and cylinder look? Anything to be concerned about? Just scotch-brite-ing and cleaning the cylinder good enough?

2. The cylinder measures ~66.39 on average; the A-size Wossner posted above (66.33mm) calls for 0.07mm PTW clearance. Is the fact that I'm only at about 0.06mm cause for any concern? I wouldn't guess so.

3. The base gasket is green in color (which usually means 0.30mm thickness), but it's definitely about 0.45mm thick. The N.Tahoe kit looks to have 3 gaskets supplied. Are any of them 0.45mm thick? Or a combination that equals that?

4. Related to #3, but if I have to compromise on gasket thickness, would it be better to increase or decrease the squish? I.e., since I have 0.8mm squish right now, would you go with 0.7mm or 0.9mm if I have to chose via the gasket thickness?

Thanks in advance for the help! This forum rocks!