what tends to break on the HT engine?

Yep, the King (not powerking) engine was by far the most powerful and most reliable HT engine I ever owned. I used one with a 44 tooth sprocket to climb mountains that a 65cc HT can't conquer with a 50 toot sprocket.

well more what my question was aimed at was when souping them up what tends to break
Ive found that the lower rod end will stretch when you spinn them fast so no more then mid range power should be expected from them
Ive also had main bearing failure too but I think that was just a bad bearing

the other thing I had happen was one of the dowels that locate the piston rings came out & wrecked an upper end
this is on the engine that when I tore down had the stretched journal & the bad main bearing which by the way wrecked the left side case
take care
JAK

First of all the lower end on all of the dissasembled chinese HT engines have not been Bushing even if the top end is they are HA HA UNCAGED NEEDLE Bearing sets that appear to be a bearing short and are not stainless. For one if you want this machine to be buildable this rapture of vibration causing slap is going to need to be tightened up by replacing the needles with the correct sizes(of course) stainless needle bearings, maybe they are case hardened and actually that sound more right than stainless on needles SOrry. But the lengths are different sizes on the same lower end. This alone causes abnormal twisting of the rod at 1000 miles if a text book break in was'nt done. I do agree that they are a 10k engine but don't expect it inspect it if you care! Any of the name branders out there you can expect a good 4500-10k with top end rings and ristpin and bushing replacements at 3000 miles.

I have 5k on mine. So I put new rings in it and it runs awesome. had a little blowby but it wasnt audible. Inspected the upper and lower connecting rod bsh and bearing looked good normal wear. probably another Id say 2500 then Ill put some new rings in it. I could get 8500+ plus out of this Engine.

Oh as far as the lower end it is pretty dependable. Roller bearings shouldnt be lubed by 2 stroke oil so that'ed b eyour time limiting on these as for the 30 mile rule. so the double side sealed roller 6200?? Or 6400?? maybe just might be what your looking for for your mains.

Oh as for porting Id be widening your transition ports and as for the port timing Id lift up the exhaust also widening, The intake volume not to exceed the area block taken out of youaverage exhaust to transition port on the intake and due to our manifold (unless you switch to a honda xr75 carb) in dia. the volume will be duration instead of sample @ rate Thus lowering your intake port 3/16" on mine any way. Then not starving it of burnable gases Id go with a tuned pipe and bore your jet to 70-74 # and run the needle as high as you can yet slightly rich say 28 is what ive ran for 4800 miles. Oh the time you can run them is also limited without the expansion chamber another reason for the volume sizes and timing they use to keep the engine predictably reliable.