new engine seized, what went wrong (pics included)

[sbjones73]

thanks for all of you comments and opinions here, i think i may have it solved. i took my piston and everything to a couple of long lost friends of mine that have in the past raced snowmobiles and go carts (all 2 strokes) the figured that it was a clearance problem. one of them took out some tools and checked it for me. it is about 3/4 what it should be. also, they looked at the plug. all of them said that it was slightly lean, but not enough to do this type of damage. wait there is more!!

i took it to a machine shop (not the one that did the boring) and they confirmed the clearance issue, but they mentioned that i should have seen this prior to this. i asked them if they do small engines like m ine and they don't. they are mostly big engines like detroits and cummins semi engines.

so tomorrow i will take it back to the machine shop that performed the boring for me and see what happens. i will keep you guys informed.

but now i have a question for dadio, what do you mean beveling on the ports. the only port that is beveled in any way is the exhaust. do i need more work to be done? any one with pictures that would be great.

i found a site that has good pictures of 2 stroke piston problems. let me find it again and i will put it up here. one of my snowmobile buddies told me abou it.

[sbjones73]

ok the web site that i found for piston diag is this....lloydy.org. then go to diagnosis and click on 2 stroke pistons diagnosis. they have some good pics of damaged pistons like mine.

[tecat-z]

It's referred to as champher. It's done at time of bore/hone. It would be clearly evident if you snagged a ring. Ring snaging is not siesure, and often times catastrofic for the cylinder and rod.

[3Razors]

Sbjones you friends cannot acurately diagnose that plug because the plug isn't even the correct length to sit in the dome. A plug that is short like that and probably the wrong heat range will give a false reading so whatever color it is makes no difference because it is viod.

[leokendall]

had a lil incident like that before, only it was a rv125 dirtbike. i was drivin along and next thing was the trottle stuck wot and i jumped off, the bike went towards some trees snapped the chain and reved high for 5 or 10 min, then stoped. tryed to crank her over no go. i guess since the bike was high riving for a period of time and the bike was in one spot air really wasn't cooling it down because it wasn't blowing through the air fins on the head and she over heated. pulled the top end of and everything was melted, and a cracked piston skirt.

[sbjones73]

3 razors, yea they said that also. i do realize that it is the wrong plug. should i have used it? no. i do know that. and i am sure that it didn't help the situation. will i do that again? HECK NO!!!!!!! i guess it was just me being impatient like i can get some times.

can anyone show me a good plug as far as coloring? i would like to see what i should have when i get this thing redone.

thanks for all your guys help!!!!!

[88 Turbo Coupe]

too lean. a cold seizure happens if you run outside, start the machine and immediately take off flying down the road. it will seize in that case.

I would let it have lots of fuel (big main jet) next time and try to tune the blubbering/fouling out with the air screw

I gotta laugh. You don't know how many times I've seen riders at the track start their quads and rev the shirt out of them when there stone cold and then take off on them. I just shake my head.

[atc500x]

I had the same problem with my 87 cr500,exactly the same problem....I had a wiseco .80mm...plug was brown/gray.... I change the cylinder and put a HONDA piston in it without changing the jet ,problem solved.Wiseco expend more than honda

[ThinktwiceZ71]

how did you ever make out on this ? did yuo get it up and running again ?

[Tech23]

I may be jumping in too late here, but make sure the cylinder head studs are not pulling out of the cylinder. I had to heli coil the studs on my "83". It was running fine...and over a small jump the engine seized. It restarted after it cooled. The studs where pulling the aluminum threads right out of the cylinder. The nuts took proper torque on assembly too. When I took it apart I was also at at loss, so I tried to remove the studs and the threads came out with the studs on many of them. Still had compression but enough to cause a vacuum leak. May want to check the cylinder base studs too. Also I am not sure you have the correct spark plug, the plug gasket is missing too.

Tech23.

[sbjones73]

ok guys. i know that this is an old post, but i do have a new piston to install.

now i am getting to the jug boring. my box says .020 clearnace. i called wiseco and they said that it needs to be .030? so what is the right number.

remember this is on a 84 250r air cooled trike. let me know please asap. jug is at machine shop right now waiting for me to call back.

thanks

[Daddio]

Is the piston cast or forged? That makes a difference.

[2quicktecate]

i think wiseco's are all forged so go with the .030" my wiseco is pretty loose in my tecate but it runs really strong. you can hear it slap at low r's

[sbjones73]

they are forged pistons.

[Tri-Z Pilot]

had a lil incident like that before, only it was a rv125 dirtbike. i was drivin along and next thing was the trottle stuck wot and i jumped off, the bike went towards some trees snapped the chain and reved high for 5 or 10 min, then stoped. tryed to crank her over no go. i guess since the bike was high riving for a period of time and the bike was in one spot air really wasn't cooling it down because it wasn't blowing through the air fins on the head and she over heated. pulled the top end of and everything was melted, and a cracked piston skirt.

Why in the world would you let it just sit there waiting to melt itself down? I mean I'm sure the killswitch wouldnt work, (or pullin the plug cap for that matter), but you could have shut the fuel off, and put your hands over the airfilter to choke it out.

SB, a word of advice for you. Nothing but NGK, ever!