Rebuild failure

[Capz85]

Ok so.... I've had my 2011 ec300 supermoto apart for a top end freshen up over the winter, it's had the cylinder honed and I also had the head cut down and now have a 1.3mm squish. All was looking good, ran the bike for around 2 hours in total did notice a slight noise when opening the powervalve but I thought it maybe be the on arm as it was touching the casing, so I adjusted that and still the same, then when I went to test after that I had a problem that tuned out to be the tip of the spark plug had snapped off so I checked the cylinder for damage and it all looked good so I replaced the plug and took it out today for an hour or so and it was running well but something wasn't feeling right after half throttle, so I came home and stripped it to find that a lot of the nickel plating has come away and the piston is screwed.

To me it looks like it's been running hot, and I'm assuming this is down to having the head machined down.

So I'm thinking now just replace the piston and get the cylinder re plated and use an s3 head.

[shang]

How was the cylinder honed? It shouldn't need much more than a quick clean up. Maybe a quick run of a diamond bottle brush to get the cross hatch back. Maybe the plating was too thin?

[Zman]

It could have been a worn bore and if they used a diamond hone to straighten the bore, they could have gone too thin. I hope the bottom end is ok. I cant imagine the crank and rod bearings are very happy now.

[Capz85]

Yes I belive it was diamond honed, I'm just trying to figure out what the cause was as all that was changed was the head and a hone and piston.


And yes the bottom end in now a question as where did all the plating go and how can I check the crank without splitting,The bike was running when I got back with no sign of a problem until it got to half throttle where it felt like a pv noise

This pic was after the honing


Just need to figure out where to go from here

[Zman]

Diamond hones are awesome tools and can true up a cylinder that wore unevenly, but you need to be careful you don't take off too much material. I am not sure if that is what happened here. It almost looks like the plating flaked off so maybe the original plating did not adhere properly to the aluminum substrate.

You can pull the engine from the frame, rotate it 90 degrees (around the crankshaft) with the swing arm mounting holes up and secure it so it does not fall. Then flush out the crank case with solvent or maybe kerosene. You should be able to hear if pieces of plating are in the bearings. Good bearings will rotate quietly, smoothly and consistently.

[Capz85]

Yes that sounds like a good idea, I will pull the motor tomorrow and flush it and see if anything comes out.

All in all a disaster

[stian]

1.3 squish is on the low side. Still, it would not result in this. Even if you were running lean, it would probably hot-seize, and even if it did not hot-seize, you would have noticed it pretty fast.

I am guessing honing is the one to blame here. The nicasil isnt thick, so the layer was broken, the oil would not cool the area, and its a question of <hour it would operate.

If there is a friction in the crank bearings, new ones are required.

Good luck!

[Capz85]

I think I'm just going to use the s3 insert next time, hopefully having it re plated will solve this.

As for the crank it feels as smooth as before and I can't see any damage, so fingers crossed a good flushing will be enough, will take it to my mx shop to get a second opinion aswell

[gasgasman]

Originally Posted by shang

How was the cylinder honed? It shouldn't need much more than a quick clean up. Maybe a quick run of a diamond bottle brush to get the cross hatch back. Maybe the plating was too thin?

+1
Looking at the pic, it was honed excessively.
It should only be done to knock the glaze off.

I don't think machining the head had any effect on the plating.

[arminhammer]

It looks like someone used a ball hone. Don't hone plated 2 stroke barrels with a ball hone it chips the plating at the ports and will cause the plating to peel like old paint. Guys just take a green Scotch Brite pad and some soap and water to clean up those barrels, no real need to hone a plated cylinder.