What causes this?

[KB171]

Not sure what you mean by " relieving the bridge"

Dunno if this will help.

[evo550]

Perfect, I will get a straight edge onto it tomorrow and see if there's any daylight there.

[OverTheHill]

Talking Wiseco verse original, sometimes manufacturers change the bore & stroke from one model to the next for various reasons & [not sure with yours] you might find one model is ummm 68x70 bore & stroke where next model change the think 70x64 is better & pistons might be identical but a couple of mill bigger. Worth researching maybe.

[KB171]

This's the other half, Fortunatly a mate gave me this to refer to, so i could check my freshly rebored CR250 motor ,done by a so called expert down here,  when i first got into VMX, The bridge wasnt relieved and no holes were drilled in the piston  , along with a host of other examples of shitfull workmanship , I done it myself.
Cheers.KB

[Stewart Allen]

Rule of thumb, Ring end gap should be 0.003"-0.004" for every inch of bore.

[lc4]

Rule of thumb, Ring end gap should be 0.003"-0.004" for every inch of bore.

What he said, as per Wiseco instructions supplied with new piston.

I recently fitted a Wiseco piston and one ring gap was spot on out of the box and the other needed filing as there was no gap.

[holeshot buddy]

piston to bore clearance too tight

[evo550]

The only instillation detail that came in the box was position and size of the holes to drill, nothing like KB posted, I'm now wondering if it is a wiseco or a wossner piston  
Is a nicosil lining an option for repair of something like this ?

[Lozza]

Does the ring end gap run on the bridge between transfer and boost ports? If it does ring end gap is much more critical than running through the middle of the boost port.

[Davey Crocket]

Wossner have a grey coating on the sides of the piston, but looking at your pickie, you got a seizeco.

[JohnnyO]

It's obviously getting too hot, if the jetting is standard are you running more compression(has the head or cylinder been machined) or is the ignition timing advanced? There's nothing wrong with wiseco pistons but you may need to relieve the exhaust bridge as stated if not already done...

[evo550]

Does the ring end gap run on the bridge between transfer and boost ports? If it does ring end gap is much more critical than running through the middle of the boost port.

The ring end gap is behind the inlet port..If the arrow on the top of the piston is 12 o'clock, the top ring gap is at about 20min past and the bottom ring is about 20 min to the hour.

It's obviously getting too hot, if the jetting is standard are you running more compression(has the head or cylinder been machined) or is the ignition timing advanced? There's nothing wrong with wiseco pistons but you may need to relieve the exhaust bridge as stated if not already done...

As far as I know everything is standard, I think your on the money with it getting hot, especially looking at the photo to the valve on the left, starting on the outside it looks nice and tan, but it changes colour the closer you get to the exhaust bridge, with the tip looking like it's got white hot.
Why is it getting so hot though?
My question is, Could the powervalve thats not operating and remains closed cause heat build up at higher revs through resticting gas flow?

[tmman]

pv clearance? by the photo looks like it might have even scuffed the piston on the left.... not enough clearance n not opening...

[Lozza]

Does the ring end gap run on the bridge between transfer and boost ports? If it does ring end gap is much more critical than running through the middle of the boost port.

The ring end gap is behind the inlet port..If the arrow on the top of the piston is 12 o'clock, the top ring gap is at about 20min past and the bottom ring is about 20 min to the hour.
As far as I know everything is standard, I think your on the money with it getting hot, especially looking at the photo to the valve on the left, starting on the outside it looks nice and tan, but it changes colour the closer you get to the exhaust bridge, with the tip looking like it's got white hot.
Why is it getting so hot though?
My question is, Could the powervalve thats not operating and remains closed cause heat build up at higher revs through resticting gas flow?

The end gaps run on the bridges between ports. There is to much black soot carbon in there for any jetting ignition issues, head gasket would fail if there was water problems.
You would know if the PV was not opening they just struggle to rev and generaly very flat. The exhaust bridge has aluminium smeared all over it.
There's my $0.02 not enough end gap/to little clearnce/no relief is rubbing on the bridge and bulging  and heating the piston. Is the ring stuck in the groove at the front of the piston.

[Nathan S]

Wiseco pistons are forged, which require more clearance than cast (due to expanding more with heat). Their older pistons were made of a material that had a lot of expansion, even for a forged piston.
Lots of engine shops would hone for a cast piston which was too tight for a Wiseco, causing them to seize.

This is where the Seizco name came from.

I'd be amazed if Serco made this mistake, especially with the newer Wisecos that are much more stable (and by newer, I'm talking "made in the last twenty years"...).

The brand of piston is not the cause of your problem.