Why did my top end go?

[Upbasher]

Okay so I just recently rebuilt my blaster. I put all new bearings and did a full top/ bottom rebuild. A few days ago was riding 6th gear at about half throttle and it decided to start seizing up on me. It would run fine for a mile or two if you let it cool but as soon as it got hot it would seize up. Prior to this I noticed it was getting pretty hot, which is weird because I checked thoroughly for air leaks and there were none, so I didnt think much of it. It had also been making weird noise ever since I rebuilt it that I could not pinpoint. Kind of like a rattling noise coming from the engine at about 1/4 to 1/2 throttle. It would not make the noise if you revved it in neautral. I checked for any slop in the crank and connecting rod and there was none so I didnt think too much of that either. So any way heres pics of the piston exactly how it looked when I removed the cylinder minus the parts on top where I smudged the carbon with my finger. My question is what caused this amd the overheating/noise so I wont make this mistake again?

 

[speedyslyder]

what does the cylinder look like on that part
where piston i scraped?

 

[Awk08]

could be many reasons .........

was it bored/honed for the new piston ?... to the proper specs for that exact piston ?........
ports chamfered after bore/hone ?
was it leakdown tested ? how long did it hold how much psi ?
properly heat cycled, head/base nuts retorqued, and break in procedure before ripping on it ?
was it properly jetted for the mods you have and confirmed with plug chops ?
genuine mikuni jets and stock needle ? float height correct ?
airbox/filter setup ?
what oil and ratio are you running if the injection has been deleted ?.........
injection nipple blocked off on the carb ?
properly warmed up completely before each ride ?

 

[jbuckster07]

Awk, that should be a sticky as to the start of a "why did my motor blow" thread or something lol. Answer all of the above questions honestly, if you have found somehting you didnt do we can go from there.

 

[Bluesman]

And after it blew, did it pass leakdown test before you pulled the cylinder off?

 

[Larry's Shee]

And after it blew, did it pass leakdown test before you pulled the cylinder off?

This ^^^
Especially if not re-torqued.
Did you use new crank seals?

 

[jus_me]

Inproper warm up 4 corner seizure. Or multi point seizure from cylinder being bored to tight to the piston. Was piston sent with the cyl to be bored ? Is this a trust worthy shop you sent it to, to know to have piston in hand for this exact reason? Any way on measuring both for us?
Now that i look closer it certainly looks like a multi point seizure due to cylinder bore being to tight a tolerance to the piston.

 

[Upbasher]

1. Cylinder looks the same as the piston in that spot
2. Cylinder was completely stock in what appeared to be great shape with no scratches at all. I never honed or bored it over ever. Stock size 66mm wiseco piston is what I put in.
3. Don't know what a leakdown test is or how to do it
4. Yes, properly heat cycled and broken in
5. Stock jetting with fmf pipe and vforce reeds. Don't know what a "plug chop" is
6. Carb completely stock with mikuni jets.
7. Completely stock airbox/filter set up
8. 32:1 Amsoil interceptor full synthetic. Oil pump deleted, nipple is sealed completely with a cap.
9. Yes warmed up before every ride.
10. Everything (including crank seals) was all brand new when I put it in.
11. Hope this info helps. Thanks for the replies guys! I don't wanna rebuild it again and make the same mistake. And I am very sure there were no air leaks. Its easy to tell if you have one when riding it, no?

 

[jus_me]

The list of mods and what you have done help us but the most important thing to do is the one thing you didn't, a leak test. Specifically after a rebuild. There is no way of knowing if you have a leak other than performing a proper leakdown test. You need to build or buy a leakdown tester. An air leak can seize an engine quick. An air leak makes the motor lean which in affect makes it run hotter. You should also check the cylinder for out of round and taper. The right thing to do would be to re bore and a new piston but there is a slim chance it could hone out. No way of knowing until it is measured properly.

 

[MURPH]

that piston most likely seized up because it is a forged piston and the original cylinder specs are for the oem cast piston. you should always have your cylinder bored for a new piston and the guy doing the boring should have that particular piston in his hands so he can set the tolerances

how to leak test http://www.google.com/url?sa=t&rct=...HYE7JzH4amPAsgNlTEgurgA&bvm=bv.92765956,d.cWc

did you re torque the nuts after the heat cycles as asked before?

 

[jbuckster07]

1. Cylinder looks the same as the piston in that spot
2. Cylinder was completely stock in what appeared to be great shape with no scratches at all. I never honed or bored it over ever. Stock size 66mm wiseco piston is what I put in.
3. Don't know what a leakdown test is or how to do it
4. Yes, properly heat cycled and broken in
5. Stock jetting with fmf pipe and vforce reeds. Don't know what a "plug chop" is
6. Carb completely stock with mikuni jets.
7. Completely stock airbox/filter set up
8. 32:1 Amsoil interceptor full synthetic. Oil pump deleted, nipple is sealed completely with a cap.
9. Yes warmed up before every ride.
10. Everything (including crank seals) was all brand new when I put it in.
11. Hope this info helps. Thanks for the replies guys! I don't wanna rebuild it again and make the same mistake. And I am very sure there were no air leaks. Its easy to tell if you have one when riding it, no?

#2 - When doing a fresh top end it is highly suggested that you bore/hone it up to the next piston size. With these motors you can get many many bores out of the stock sleeve. Just replacing a work out piston with a new one will most likely end up with this exact result.
#3 - Awk08 sells leak testers. BUY ONE. It is one of the most important tools to have in your toolbox for this 4 wheeler.

You will most likely have to buy another piston and get it bored out by a REPUTABLE engine/machine shop.

 

[Upbasher]

I did not re torque the nuts but they didn't need it. They were all tight when I took it apart. Thanks all for opinions, I appreciate it, Will check out the leak test video.
Also another question...Im sure you all have seen those $100 cylinder/piston kits on ebay? Are those any good?

 

[MURPH]

i would stay away from them unless your cylinder is on its last bore. they do not champher the ports on those cylinder kits so you can snag a ring and buy another one

 

[Upbasher]

Thanks for posting the leak test video that helped. That's simple to do I could probably build one myself lol

 

[MURPH]

ya a lot of people build there own or you can message a member on here named awk. he builds them and sells them cheaper then you can build one yourself

Thanks for posting the leak test video that helped. That's simple to do I could probably build one myself lol

 

[Upbasher]

So how hard is it to chamfer the ports on one of those 100 dollar cylinders? Because theres no one around here that can bore cylinders?

 

[Bluesman]

Ship your cylinder to a reputable builder and tell them to fix it. Buy all your engine parts from them at the same time. If you have money left over, tell them to port the cylinder and rechamber the head.

 

[rich1]

I say the piston to cylinder wall clearance was improper too.
Yamaha and Motion Pro are CAST pistons and set @.002-.003.
Wiseco pistons are FORGED and set up @ .003 -.005.

 

[jus_me]

You will be better off just boring your cylinder that you have already. Then get a new piston and be done. Most shops ,,,,, well any good one will chamfer the ports after a bore/hone. Its not hard to chamfer the ports but you need the right tools.

Also did you torque the head and cylinder base studs down with a torque wrench or just any ole wrench/socket and crank it ? Im not trying to be a #!$% or nothing but you cant just say it was tight it's leak free. There are torque specs for reasons.

 

[Awk08]

Stock size 66mm wiseco piston is what I put in.

my thoughts exactly \/

I say the piston to cylinder wall clearance was improper too.
Yamaha and Motion Pro are CAST pistons and set @.002-.003.
Wiseco pistons are FORGED and set up @ .003 -.005.