Vibration before piston skirt broke

[chuck_neste]

Hello All,

I had a good running blaster until I noticed some vibration over the last few rides. When reving the engine, the bike seized . Once I remove the jug, The piston skirt was broken (1 side) but the cylinder walls looked very clean after a quick ball hone. I still need to tear down the bottom half to clean / inspect. I had 120 psi last week and the plug looked great. Why do these things blow up when they run half decent. I have been mixing yamalube 40:1 over the last 2 years and there is no unusual marks or discoloring on the rings and piston. Is this just a typical piston to cylinder clearnace slap that caused this? I guess I will need to send this out and have it bored over and will get actual numbers before they do this. Any input would be great


Chuck

 

[99LRDblaster]

Hello All,

I had a good running blaster until I noticed some vibration over the last few rides. When reving the engine, the bike seized . Once I remove the jug, The piston skirt was broken (1 side) but the cylinder walls looked very clean after a quick ball hone. I still need to tear down the bottom half to clean / inspect. I had 120 psi last week and the plug looked great. Why do these things blow up when they run half decent. I have been mixing yamalube 40:1 over the last 2 years and there is no unusual marks or discoloring on the rings and piston. Is this just a typical piston to cylinder clearnace slap that caused this? I guess I will need to send this out and have it bored over and will get actual numbers before they do this. Any input would be great


Chuck

Piston to cylinder wall clearance when too large creates piston slap that you can hear and will cause the skirt to break when it slaps the cylinder wall. Measure it, but you will most likely need to have it bored 0.010 to 0.020 larger than your current bore and buy an oversized piston for that bore size.

 

[royalt67]

Yep, over time you are gonna wear out a cylinder/piston causing excessive clearance and eventually piston slap. Slap=broken skirt in time. Normal wear for a 2-stroke, but topend jobs are a lot cheaper than on 4-strokes.

 

[99LRDblaster]

Yep, over time you are gonna wear out a cylinder/piston causing excessive clearance and eventually piston slap. Slap=broken skirt in time. Normal wear for a 2-stroke, but topend jobs are a lot cheaper than on 4-strokes.

I don't find the price between 2 stroke and 4 strokes all that different as long as you do it yourself. It's a new piston and a borejob in both cases. Now if it's somebody that is a dumbass and grenades the engine, then yea, you have to clean up the head, possibly replace valves, etc. etc., but even a 2 stroke head needs work done if it's pitted all the hell and and has shards of metal belted into it.

 

[chuck_neste]

Thanks for the replies, I had the bottom end torn apart a few years ago and will dismantle to clean it correctly. I will send the cylinde rout for repair

Chuck