installing a new top end....

[livetoride249]

Just got my top end in the mail. pulled the old piston, and it looked almost new, I just wanted to make sure since I bought it used. Decided i was going to do a top end at that point cause i wasn't as careful as i should've been pulling the circlips. I just bought all the honing equipment for my cylinder. I just wanted to make sure my procedure was correct since this is only the 2nd top end i've done on a two stroke. (only done 1 on a four stroke). I'm only 16 and want to make sure i'm doing everything exactly right. I found out my motor was from an ATC, motor mounts were different, and my cylinder was punched out, to 249cc, I ran the numbers from the old piston on Wiseco's website and it measure to be 66.25mm so I ordered my entire new top end kit from them with those same measurements of course and also it's forged not cast. I also measured the cylinder with a micrometer to be positive everything would fit properly. I checked my crank as well and it is still within spec. So anyways, I have my motor pulled, cylinder and head off, and I want to do the top end tonight. First I have to hone my cylinder, then I clean my new piston, cylinder, head, and rings with warm water and dawn soap, with latex gloves on for the rest of the procedure. Then after everything is dry I apply some premix to the piston, rings, and install them. Then i put on the gasket, put on my cylinder, then put on the other gasket and head, I know I use the star pattern with these bolts. (I do not know the correct torque specs for the cylinder and head bolts though) Once I have everything all together, all the gaskets in place and the motor reassembled and back into my frame etc. I'm ready to run it. I usually use the NGK br9es plugs, do you have any other recommendations? Also Should i mix it much more fatter? I usually mix 32:1 with 93 octane gas. I use amsoil dominator premix. I read the break in procedure sticky and I'm curious to know that since it is a forged set up do I still have to break it in? When I did the top end in the four stroke crf250r I rebuilt with a Forged JE top end kit the people on thumpertalk said it wasn't necessary to break in, and I've put 45 hours on that top end with no problems. Also I'm in Maine, it's about 25-40 degrees Fahrenheit from day to day, it's been a warmer winter for sure. My jettings a little on the fat side. Not positive what main i'm running I just know it's running rich. I'm just looking for input on the plugs, torque specs, and break in procedure and to make sure I'm doing everything right with the honing, and installation etc. I will post pictures of the entire build once it's complete!

[deathman53]

a few things, Atc motors don't have different mounts, cases are the same as quad cases. base stud torque is 35 ft/lb and head is 20-25 ft/lb. I would get copper washers and put them under the nuts in the head, they shouldn't be hard to find. 32:1 is a good ratio, you will get people to tell you 20:1 to 100:1. Some years ago, there was a dyno comparing oil to fuel ratio's(each was re-jetted when changed). 16:1 made the most power, but fouled plugs alot, 20:1 was somewhat less plug issues, 32:1 seamed to make less power, but didn't foul plugs and lubricated just right. When it got around 40:1-50:1, cylinder wear increased and so did crank life decrease, but less fouling and it burned much cleaner, 100:1 burned the cleanest, but LEAST power and shortest cylinder/crank life.

Pick your evil, to me......not so clean burning, but longest life, least plug issues and reasonable power. I use 32:1, leaded race gas(on the 250r's) and klotz tcw-3 snowmobile 2 stroke oil. the ktm 2 stroke dirtbikes uses 93 octane, same oil and ratio. The reasoning behind the oil-power as explained in the dyno thread was the more oil, the more compression and better ring sealing and cylinder/crank lubing decreases wear on it.

[livetoride249]

Thanks for the input, I'm going to mix it at 20:1 for the break in procedure. I've heard so many mixed things about forged vs. cast i'm not sure what to do, so i believe i'm going to just do the break in cycles that would normally be done to be on the safe side.

[fearlessfred]

lots of good info deathman 53. keep in mind that when you go to 20 to 1 for the break in , that you will be leaning out the motor in all circuts to a small degree