Seized!!!!

[SSpeeDEMONSS]

yup, just as the title says. i seized my bike this weekend. '00 426. im not sure what i could be. lemme start at the beginning and see if someone can help me out on this one. the oil and filter had been changed 1 ride before. not internal engine mods. BK carb mod. stock header wrapped with exhaust wrap. cut stock silencer with PMB end cap. 170 main jet up from 162 stock. engine ice. motul 3000 SAE 10W-40. nothing but 91 octane. CR8E plug. when it seized i was riding out in glamis. i had only been riding about 10mins. nothing really hard. cruising. was in 3rd about half throttle through some whoops when i let off and it died. so i pulled in the clutch to roll start it and it just stayed locked up. so i stop. pull in the clutch and decomp and go to start it and the kick starter wouldnt budge. so i put it in neutral and nothing. as i sat and waited for my buddy to come back with his truck i noticed there was a leak between the carb and the airbox. the plastic part the is bolted to the carb that is between the airbox and carb had been pulled away from the carb. the screw wasnt loose though. the metal sleeve inside the plastic part had pulled away from it. i didnt notice the bike running lean or it overheating at all before this happened. as soon as i was able to i pulled the carb and check for any excessive amount of sand in there. none. nor was there any in the intake track on the cylinder head. i then pulled the plug and it didnt show any signs of being too lean. i am stumped. it is full of oil and coolant, i checked before i went on the ride. transmission still shifts and the clutch isnt stuck. i am hoping it is just a ring maybe? top end only? i dont want to have to pull it apart for the bottom end. what do you guys think it could be? ? sorry for such a long post.

[grayracer513]

Start tearing it down from the top down, but it sounds to me like you lost the big end of the rod. Piston siezures in a four stroke don't normally happen as with smokers. If you break a ring, it is sometimes possible for the piston to tilt forward or backward in the bore and get jammed. Sounds messy, but you might not be too badly off.

Good Luck! :crossed fingers:

[SSpeeDEMONSS]

thanks, ive never tore into my engine before so im a little scared. i know i can do it but there is a lot involved(like you dont already know that). how much do you think it would cost to have a shop rebuild it? and does anyone know of a good shop in southern california that does this type of work. thanks again guys.

[harider19]

It's real spendy to get a shop to rebuild. My friend seized his 250f and i think it cost $1100 if i remember right ? His was alot worse than yours sounds so it might not be that big of a bill.

[MX2Havasu]

My 01' had the same "seized" characteristics as yours. My ended up being two dropped intake valves and one bent exhaust. So far around $600 in damage. (was able to re-salvage head and cylinder)

[bushy]

When was the last time you replaced your cam chain.

[Scooter426]

my 2000 yz426 just seized and it was the big end rod bearing. The cage failed and this casued the crank pin and the rod to be galled. The motor had no other signs of problems. Check your oil filter and see if there are any silvery shavings. Also, drain your oil. Do not run the motor after it seizes. It must be torn down and inspected at the very least. I replaced the piston ring, rod, crank pin, bearings, gaskets and it runs like a raped ape again.

[SSpeeDEMONSS]

When was the last time you replaced your cam chain.

i've never replaced it. ive only owned this bike for 5 months and before me and older guy owned it and sold it because it was too powerful for him. im going to start to pull it apart today. maybe this is just a sign that i need to do the stage four big bore. Head porting with Xtreme Piston and gasket kit, new valve seals, springs, and intake and exhaust Hot Cams.

[yz426onNOS]

You never have to replace the cam chain. I don't know of a singal person that has, nor has my dealer.

[FFRacing79]

You never have to replace the cam chain. I don't know of a singal person that has, nor has my dealer.

Hmmm...a part that never wears out...hmmm ?

[machoman_#618]

rotfgtyf @ FF

[yz426onNOS]

Hmmm...a part that never wears out...hmmm ?

It wears out, but you will never wear it out in your lifetime. Maybe if you put 10,000's of miles on it.

[SSpeeDEMONSS]

well, i just got back from my buddies house. it was the bearing on the big end of the rod. the case has already been cracked and it's going to be taken in tomorrow. also, while it's apart i figure i might as well make some changes. like my buddy said, "now that you tore it apart, you know what you have to do? make it faster." im thinkin hot cams intake and auto decomp exhaust cams, '01 clutch mod, and MAYBE 13.5:1 hi-comp piston. what do you all think?

[gcally]

well, i just got back from my buddies house. it was the bearing on the big end of the rod. the case has already been cracked and it's going to be taken in tomorrow. also, while it's apart i figure i might as well make some changes. like my buddy said, "now that you tore it apart, you know what you have to do? make it faster." im thinkin hot cams intake and auto decomp exhaust cams, '01 clutch mod, and MAYBE 13.5:1 hi-comp piston. what do you all think?

If you are interested I am parting out a entire 01 426. I can sell you the motor for $1000.

Thanks Greg Callahan

[sirthumpalot]

When you take it apart, check everything as you disassemble. For example check the cam timing before you remove the cam chain, etc.. That will help you determine what happened. On 4-strokes the drive cam sprocket is often the first to go, especially if it has lots of hours or did not have short enough oil change intervals. Hope this helps, let us know what you find!

[Birdie426]

i noticed there was a leak between the carb and the airbox. the plastic part the is bolted to the carb that is between the airbox and carb had been pulled away from the carb.

Hit the nail on the head right there! When you pull it apart, your gonna find sand in the cylinder...enough to score it and cause the piston to stick. There is so much air velocity (especially at part throttle) that the fine sand at Glammis would be sucked right on into the intake, and woldn't stick int he port or carb.

[sirthumpalot]

This new layout is really screwing me up. I keep posting to threads that are already finished. ?

[SSpeeDEMONSS]

there was actually no sand in the cylinder at all. i was very surprised. i took the motor down to the guy that is going to do the work. after inspecting everything, i determined i need the rod kit, crank bearings, one of the transmission bearings, complete gasket set, front sprocket, drive chain, and to have the crank pressed apart, trued, and pressed back together. this plus a few oil filters is going to be 500-550. so its not too bad. i also figured, after talking to my buddy, that i shouldnt do any performance mods(not for now at least) and instead do a few things to suspension and whatnot to make it handle better. oh, and does anyone have any tips for me for when i go and put it back together? thanks again everyone for all your help.

[Stookes24]

if it has been run hard at all it will be the rod bearing! 426 throw them like crazy!

[tool]

Hmmm...a part that never wears out...hmmm ?

ive replaced mine, and the new chain was alot tighter on the cams than the old one. its like the piston, you can go forever on the stock one, but it may break and trash some stuff.

pay now or later.