Help 07 YFZ 450 Just Shuts down like piston siezes

[agiler]

I have a 07 YFZ450 after it warms up it just shuts off abruptly like you turn the key off,
All electrical checks out, I tore it down to find a piston looked bad scared on the piston skirts like it was trying to seize I honed the cylinder and put a fresh piston and rings in her,
Got it back together and now it is doing the same thing starts runs fine and then after it gets up to about 185 degrees it shuts off and when you try to restart its like a very week battery or a bad starter.
Starter and battery both check out great.

After it cools it fires right up perfectly until it warms up and it shuts down even when you have it around 2000 rpm it will just abruptly shut down.

When engine was apart the crank looked fine and spun free no up and down play at all.
Any ideas?

[Terse]

Lower rod bearing.

Maybe crank bearings.

Side note.... how did you "hone" the cylinder? Not that I think that has anything to do with your problem, but I think the jug could be junk now.

[agiler]

Lower end seems good on it not sloppy at all
Light hone from shop

Originally Posted by Terse

Lower rod bearing.

Maybe crank bearings.

Side note.... how did you "hone" the cylinder? Not that I think that has anything to do with your problem, but I think the jug could be junk now.

[Terse]

Well seems good and being good are two different things.

Scored piston skirts and cylinder walls and it shutting off the way you describe sounds exactly like a bad lower rod bearing, or crank bearings.

[agiler]

Ok here is what I tried just now
Oil is getting to top end as I pulled the plug out of the head and it spood oil out soil oil pressure should be adiquit.
I started it ran till it shut down and went to retart it it just clicked like it was locked up.
I quickly puled the side plug and put socket on the crank and it spun it clock wise with little resistance until got to compression then of course there was resistance.
I also noticed the starter was making noise as I turned the engine in the clockwise direction then turned it counter clock wise it did not make the noise and also spun freely.
Just adding to thisw post maybe this may help

Originally Posted by agiler

I have a 07 YFZ450 after it warms up it just shuts off abruptly like you turn the key off,
All electrical checks out, I tore it down to find a piston looked bad scared on the piston skirts like it was trying to seize I honed the cylinder and put a fresh piston and rings in her,
Got it back together and now it is doing the same thing starts runs fine and then after it gets up to about 185 degrees it shuts off and when you try to restart its like a very week battery or a bad starter.
Starter and battery both check out great.

After it cools it fires right up perfectly until it warms up and it shuts down even when you have it around 2000 rpm it will just abruptly shut down.

When engine was apart the crank looked fine and spun free no up and down play at all.
Any ideas?

[Terse]

Turning it one way the starter is engaged, turning it the other way the starter is disengaged, so that makes sense why you heard it one way and not the other.

A lower rod bearing going out will be scored in one spot and will turn over fine when cold, but once it warms up the clearances tighten and the piston seizes, when it's locked up the battery works so hard to turn it over that the battery will actually go bad.

[SuperCrew]

Originally Posted by Terse

Turning it one way the starter is engaged, turning it the other way the starter is disengaged, so that makes sense why you heard it one way and not the other.

A lower rod bearing going out will be scored in one spot and will turn over fine when cold, but once it warms up the clearances tighten and the piston seizes, when it's locked up the battery works so hard to turn it over that the battery will actually go bad.

Agree completely with Terse your best bet would stop guessing at it an tear it down replace the crank bearings, and the lower rod bearings along with anything else you noticed is worn while your in there. No poinr in keep messing up new pistons, and cylinders.

[agiler]

Well looks like I am gonna start tearing it completly down
I will post my findings when I find something

I am a two stroke fan that is starting to get into 4 strokes
Thank you very much for all the help

Originally Posted by Terse

Turning it one way the starter is engaged, turning it the other way the starter is disengaged, so that makes sense why you heard it one way and not the other.

A lower rod bearing going out will be scored in one spot and will turn over fine when cold, but once it warms up the clearances tighten and the piston seizes, when it's locked up the battery works so hard to turn it over that the battery will actually go bad.

[agiler]

Terse,
You were right !
After Splitting the cases I found multipal things
The lower rod bearing was not good, it felt good in the case when I could only move a little bit
Once I got the crank out diffrent story lower rod bearing is toast

Also the crank bearings were also starting to go
Big bore kit with a hotrod crank bearings the hole nine yards is bought paid for and on the way

Thank you everyone

Agiler

Originally Posted by Terse

Well seems good and being good are two different things.

Scored piston skirts and cylinder walls and it shutting off the way you describe sounds exactly like a bad lower rod bearing, or crank bearings.

[Terse]

I know it wasn't what you wanted to hear, or have to tear it down that far, but I am glad you did and found out what was causing the problems.