piston seized after doing top-end.........

Joined
Jul 5, 2001
Messages
120
Likes
0
#1
Recently, I did the top-end in my 99 CR125 w/wiseco pistons. I took my bike to the dealer afterwards and they jetted it perfectly to what FMF suggested. I have a FMF Fatty with a PowerCore II Shorty Silencer, and Boyesen CarbonFiber Reeds. I also used a BR8ES spark plug at the time. Once I got my bike back, I putted around my lawn for about an hour, taking my time to break it in. After that, I went inside for about a few hours and came back out to have some fun ;) So I took my bike up the road and revved the hell out of it. I was in 4th gear and all of a sudden i lost the power...nothing. When I got home, i tried kickstarting it and it was stuck. So i took apart the top end and noticed that the piston had scuff marks on all four sides. Did I forget to put more pre-mix oil in the lubricate the piston? Or was it cause I used a hotter spark plug? Any suggestions? Thank You!
 
Joined
May 4, 2001
Messages
192
Likes
0
#2
First of all...

First of all, you didn't break that engine in. 1 hour isnt nearly enough to break in a new piston and bore.

Did you do the ring gaps correctly? If you didnt, they will expand and destroy the top end about as quick as you said yours went out.

Let us know...
 
Joined
Jul 5, 2001
Messages
120
Likes
0
#3
I checked the ring gap and it was all good. I must've not broken them in long enough. I must've been going 35 when it seized (good thing i didnt flip it!!). Could the plug have been the problem? When i took it out, it was almost melted just about? Next time im gonna run 9's. Thanks for your post.

Ryan
 
Joined
May 4, 2001
Messages
192
Likes
0
#4
Melted...

If it was melted, that could mean an extreme heat problem...

Check your jetting! Check your jetting! Check your jetting!

There is a possibility that the dealer didnt do it right. You also need to break the engine in better next time...
 
Joined
Jul 5, 2001
Messages
120
Likes
0
#5
Thanks! I will give my dealer a call in the afternoon and tell them what's up? Geez, after I just spent $300 for them to fix it look what I get! Thanks bud!
 

EricGorr

Super Power AssClown
Joined
Aug 24, 2000
Messages
708
Likes
1
#7
Although FMF makes a valiant effort to post baseline jetting specs on their web site, they don't post other important data like;
1) Fuel brand and specific gravity
2) Oil brand and pre-mix ratio
3) Air temperature or density altitude
4) Spark plug heat range
They also don't have any disclaimers like your riding ability, terrain where you ride, and bike condition have a bit more to do with jetting than your choice of exhaust system. Boyesen does the same thing, instructing people to drop their jets by 3-4 sizes. I can't tell you how many people seize their bikes from well meaning instructions then call me up asking what went wrong.

Don't blame your dealer for your bike seizure, most mechanics try their best and assume that if a big company makes a particular suggestion that its good as gold. Your bike seized because the piston expanded at a faster rate than the cylinder. So it either has too lean of a main jet, you loaded too hard just after start-up before the coolant temperature stabilized, or perhaps the left crank seal is leaking (very common problem on CR125s) and the extra air seeping by the seal leaned the mixture like too small of a main jet and caused the seizure.

Good luck, Eric
 
Joined
Mar 29, 2000
Messages
30
Likes
0
#8
Since you seemed to seize all the way around the piston, it sounds like it got way too hot. Being lean I would think would have seized it up on the exhaust side. Perhaps the coolant level was not adequate. Sometimes there are air pockets that do not get purged and those areas steam and obstruct water flow.
 
Joined
May 30, 2001
Messages
25
Likes
0
#9
sneezed

If you would check eric gorr web site, it has a piston diagnostic area that shows the different types of seizures and the common causes. A four corner seizure like you discribed is usually cause by either a cold seizure or to small of main jet. FYi:(
 
Joined
Apr 3, 2001
Messages
349
Likes
0
#10
OEM Rules!

I hate forged pistons.

So i took apart the top end and noticed that the piston had scuff marks on all four sides......This is 4 Point seizure ...caused by Inproper warm up or too much heat.....could also be an air leak.

My experience with Weisco is that you need to really let it warm up even after your have warmed it up early on.

example take aluminum foil and heat it up ...in seconds its ambient again.

The piston expands at a much faster rate then your Cylinder and if its not fully wamed up you will seize yor piston.


Did I forget to put more pre-mix oil in the lubricate the piston? If you forgot to Premix your gas then thats your problem.

You did refill the radiators? RIGHT?


I think you have an air leak or you were way to lean....did you hear a shearing noise when you got on the bubble.

Melted spark plug ......another lean symptom
 
Joined
Dec 3, 1999
Messages
95
Likes
0
#11
As for those saying "an hour isn't enough of a break in" that just isn't true on a 125 two stroke. I put a new top end in my 250, warmed it up for five minutes, then revved the crap out of it riding sand dunes. If you've installed everything right and jetted it right, there really is nothing more than a little warm up required before you twist away!
 
Joined
Apr 3, 2001
Messages
349
Likes
0
#12
Originally posted by Mudboy
As for those saying "an hour isn't enough of a break in" that just isn't true on a 125 two stroke. I put a new top end in my 250, warmed it up for five minutes, then revved the crap out of it riding sand dunes. If you've installed everything right and jetted it right, there really is nothing more than a little warm up required before you twist away!
Thats the way i do Mine ....let it warm once shut it down...start and let warm .....then beat the Bajesus out of it.OEM

Weisco takes longer to warm up and brake in because its Forged not cast.

I still think he has an air leak....boot to the carb,seal,lose spark plug ...SOMETHING

that or just jetted WAY to lean.

Maybe we will see.
 
Joined
May 20, 2001
Messages
870
Likes
0
#13
Even the jap manuals don't tell you to break in after a top end for more than an hour (although the tell you to only heat-cycle the engine for a few times (warm up and then let it cool down)). And these guys tell you to change your piston after 5 races on a 250, so they are a bit on the safe side.

My guess is on imsufficient warm-up after you took your little break.
 
Joined
Oct 3, 1999
Messages
2,247
Likes
2
#15
Mudboy, what piston did you use?
Did you look in the motor after break-in?

You're lucky you didn't seize the engine.. I bet it's going to look pretty rough inside when you pull the cylinder.