Piston replacement.

[Blastersa]

I am currently busy replacing a friends blaster piston. Was called in after the usual it used to run and now it doesn't. Got to his house thinking it might be the tors but with the first kick I knew something is terribly wrong. Told them it has basically no compression but they told me it still feels the same...
After checking all the usual things (tors, spark fueling etc) I decided to follow my gut. Surely enough the piston was badly scored. A part of it actually is still stuck to the barrel/cylinder. I'm taking the lot to work tomorrow to get it micced, but I just want to find out what is the run out limit of a standard piston? I have a few pics aswell but I'm posting from my phone, so I'm not sure how to upload them.
That was all yesterday, told the guy I'll fix it up paying for all the parts and work that I can't do by myself, but I want his 2004 kx85 (also broken) as payment. He agreed, but wants the blaster back before December. Hoping someone can assist me.

 

[Blaaster]

 

[speedyslyder]

sounds like you need a bore and top end rebuilt
there is info on posting from phones.
http://www.blasterforum.com/threads/posting-pics-from-phones.58877/

 

[Blastersa]

Thanks alot. So I got it micced. Sleeve is at 66.35mm and the piston at 66.05mm... Taking it to the machine shop today to confirm. I'm thinking of a second oversize bore and piston which will be at 66.50mm?

 

[Blastersa]

Test

 

[tbrooks]

Now that is a melted piston! As long as the cylinder cleans up good than that should be fine. The shop should match the bore to the piston for a perfect fit. Looks like there could be some debris from that carnage, in which case the cases should be split, cleaned and new bearings and seals installed

 

[Blastersa]

Update. I'm glad to report back that the blasty is running good. Starts first kick, now I just need to get the jetting good. The sleeve cleaned out real good. It's now at 67mm. Yesterday I was riding it and noticed some oil which looks like 4stroke engine oil on the bike, checked the entire bike and didn't find any leaks, drained the gearbox oil and it was not of the same consistency or smell. And by the look and smell it seems like they put 2stroke oil in there xD. Trying to educate the dude on proper mixing and where which oil needs to go, but if he does break it atleast I'll have some income by fixing it hehe.

 

[Blaaster]

Was a leak test performed before starting the engine, if not do one now!

 

[mastro490]

Was a leak test performed before starting the engine, if not do one now!

Hey man o have a few question.

View attachment 12649

I just bought a blaster and it has a yz 490 in it. The piston was bad so i put new piston and rings in it and had it hooned. Now it issuper hard to kick ofer and when it starts it runs. For a shorttime then it stalls. The time it is running it back fires a little. Is that ok or not.

 

[jus_me]

Hey man o have a few question.


I just bought a blaster and it has a yz 490 in it. The piston was bad so i put new piston and rings in it and had it hooned. Now it issuper hard to kick ofer and when it starts it runs. For a shorttime then it stalls. The time it is running it back fires a little. Is that ok or not.

^^ You should start a new thread. You will get more responses that way..