Piston slap?

[Xero]

My blaster was smoking quite alot of white smoke so i changed the oil seals and went out on it yesterday to test it after having problems getting the clutch back on it ran mint apart from 1. I snapped the chain But it was still smoking pretty bad white smoke but after a while when i opened the throttle right up usually in 2nd and 4th i heard a nocking noise, Never heard piston slap before but thats what i think it is, also my dad said thats what he believes it is... so with that noise and the smoke would you think if i changed the piston rings it should be all good again? providing theirs no damage to the bore or the piston?

 

[Blaaster]

The smoke could be the oil that is left in the pipe just burning off.

If you think you have piston slap, new rings will not fix the problem.

You need to remove the piston and get it and the bore measured.

 

[Awk08]

i would investigate the work you just did in the clutch area, if this noise just started after

do a compression test also
maybe someone else can confirm, but i'd think if the piston to bore clearence is bad enuf to cause piston slap, the compression should be down also

 

[Xero]

I have a feeling its the rings because when putting the top end back together they seemed to get stuck in the piston but then i got it out and seemed okay, i was going to replace them but a supposedly "more experienced" friend said they were fine, now im hearing the noise im thinking its them..

 

[Blaaster]

Could have by the stroke of imagination, when the chain broke, punchered a hole in the case causing an air leak.

To the untrained ear, detonatation can sound a little like piston slap.

 

[Xero]

No because, I heard the noise, then took the quad to my dad and was like .. huh its making a weird noise so my dad took it for a quick spin to see what i was talking about and then the chain snapped, so it started before the chain snapped..

 

[Blaaster]

Thats that one out the window.

Have you done a leak down test since you replaced the seals?

 

[Xero]

Nope, dont have one.. and i know I really should get one .. i really do believe its to do with the piston/ piston rings ..

 

[Blaaster]

You could get some idea of the condition of the piston and rings, by pulling the pipe off and looking up the exhaust port.

How long did you ride it when it white smoked before you replaced the seals.

If you rode it for a while, the piston could be damaged from running too lean, from the leaky seals.

 

[Xero]

Well, I only realised it was smoking so much when I went into the garage one morning and started it, so it could of been riden for quite a few hours the time before and i may not of noticed..

 

[Blaaster]

Well, I only realised it was smoking so much when I went into the garage one morning and started it, so it could of been riden for quite a few hours the time before and i may not of noticed..

Take the pipe off and have a look, the piston and rings could have suffered trauma.

 

[Xero]

Ill take a look later on, also would a compression test tell us anything?

 

[Blaaster]

Compression would be down if there is a ring problem.

 

[Xero]

Well last time I took a reading it was 160, should i take another now?

Just a couple of thinks to add...

Would it running out of fuel cause any damage? since it had to switch to reserve because i felt a power dip then it died, put fuel onto reserve and ran again...

It doesnt get into 5-6th gear much also since their not really anywhere big enough where I am

 

[best]

Leak down test is always a good idea on a 2 stroke.
They can leak from all sorts of places, all causing problems, and guessing won't solve them.

Piston skirts are weak on these engines and slap or over revving can break them off.
Here is a picture of a couple badly damaged Blaster pistons:

The one on the left has lost part of its skirt and the one right has cracks that did not show up in the picture. My son just snapped the exhaust side skirt off a piston (due to revs and heat) that was properly sized in the bore doing major damage to the engine. So do not keep running if you hear slap. Pull the cylinder jug (only 4 nuts) and measure the piston to cylinder clearance at the skirt with a feeler gauge or a dial indicator.

Rings will not solve piston slap, only a new piston will. It may take an oversize to get it right. Strip the cylinder and take it to a good builder to get it bored or honed oversize and fitted to the new piston. Due to the bad luck we have had with stock Yamaha pistons in this quad and my son's YZ125, I'd suggest using a forged piston.

 

[Blaaster]

Well last time I took a reading it was 160, should i take another now?

Just a couple of thinks to add...

Would it running out of fuel cause any damage? since it had to switch to reserve because i felt a power dip then it died, put fuel onto reserve and ran again...

160 compression, what fuel are you using?

Running out of fuel fo a breif period should not have caused any problems.

 

[Xero]

It was ran on usual Unleaded, (believe its 95 octane / high performance is 97?) mixed 32:1 with Castrol 2stroke , Castrol is probably the best over here..

 

[best]

It was ran on usual Unleaded, (believe its 95 octane / high performance is 97?) mixed 32:1 with Castrol 2stroke , Castrol is probably the best over here..

We only have 87-90-93 octane here in Canada, but it may be measured differently.

Standard Castrol 2 stoke oil is crap over here in Canada. They may market better types elsewhere. The only worst stuff is no-name store brands. Still, it will work at 32:1 and should not cause an engine problem but tends to carbon up the head like the one in the center picture:

The cylinder head on the right has thousands of kms on it but has run on a steady diet of Ipone and Motul synthetic premix oil at 50:1. I really like the Ipone oil. It seals the cylinder better, you can feel and measure it in the compression. There is also a noticeable power improvement using the better grades of premix oil. I am as cheap as they come, but I see the value in quality synthetic oil.

 

[Longview]

If you still have it together, run it, and place you hand on the cylinder, ( Before it gets too hot or you'll be sorry ) And see if you can feel what you hear. That's how i found out i had slap going on. And like stated before, it can damage your Skirts. And when i got my piston out, one of mine was cracked.

Better to be safe than sorry, might as well check.

Do you hear the sound at idle, or when you rev it? Because mine you couldn't hear till you gave it some gas.

 

[scotj77]

ok i breezed through this and I would think if you still have white smoke after the seals were fixed that you might be leaking between the cases into the tranny area. so it is pulling oil and air there Causing detonation. you are borderline needing race fuel already with 160psi so i would def get a leakdown tester from slick here on the forum or build one