KX85 piston comparison

[LittleJohn]

Right, twenty eight bucks, same day service, bore all nice and honed. Thanks spectrum and engine specs!
And of course thanks everyone on here for all your info and suggestions, it's been much helpful, don't know where I'd be without KB !

Good team of tradespeople you used. Bet you feel a lot better now. So have you rebuilt it yet???

[camchain]

Spectrum said that it looked like this piston has been too hot which caused it to nip up. Basically said it was running lean. So time to put the needle back up to the factory position.

An alternative explanation is that it 'cold seized'. Ie: Bike was revved aggressively from cold. The piston heats up faster than the barrel. This causes the piston to start nipping up. Punch did have a tendency to give it death on starting, partly because it was difficult to start when cold. This of course was due to the low compression caused by poor ring seal etc. I like this explanation myself.

The 'cold seizure' is what a mechanic once used to explain what happened to one of the guys son's on his cr80. He seized his bike by giving it death from cold. Some time later with the engine all sorted and nothing else modified the bike is still going strong. His son now lets the bike warm up a bit before giving it full noise.

Apparently the pattern of the scrapes on the barrel can be used to help identify if it 'cold seized'. Take from this what you will, I like the theory.

Cold seize seems very possible cause alright krad. Excellent to read these threads and see what others are experiencing.

I put my cylinder and piston in the oven for a rough idea of what was happening as things heat up. Piston skirt exanded very quickly, much quicker than everything else (At one point piston wouldn't even slide into bore).

I'm even more careful to warm up bike fully before riding it hard now. Likely even more important with long piston skirts on 2 tangers. My guess is modern water-cooled engines slower to warm than old air-cooled as well. I check progress with hand on radiator. When thermostat pops open (at 55 deg) and lets hot water flow into rads I feel OK to start riding but still taking it fairly easy at first.

[cheese]

I've always heated my bike up till I can feel it in the radiator through my gloves. Also my bike will just not run right until its warm.

[SpikedPunch]

Piston is in!!! Go team!
We got it going out on the back deck about 9:00 this evening (was busy during the day) sounded really good. Dad even came out to watch, seemed pretty proud haha.
So the real test will be taking her for a ride tomorrow. Yuss, been suffering withdrawals after a whole week off the bike

[barty5]

Piston is in!!! Go team!
We got it going out on the back deck about 9:00 this evening (was busy during the day) sounded really good. Dad even came out to watch, seemed pretty proud haha.
So the real test will be taking her for a ride tomorrow. Yuss, been suffering withdrawals after a whole week off the bike

good to hear im itching to get out next weekend berm buster yeha

[L Rider]

Piston is in!!! Go team!
We got it going out on the back deck about 9:00 this evening (was busy during the day) sounded really good. Dad even came out to watch, seemed pretty proud haha.
So the real test will be taking her for a ride tomorrow. Yuss, been suffering withdrawals after a whole week off the bike

Good stuff

[clmintie]

Piston is in!!! Go team!
We got it going out on the back deck about 9:00 this evening (was busy during the day) sounded really good. Dad even came out to watch, seemed pretty proud haha.
So the real test will be taking her for a ride tomorrow. Yuss, been suffering withdrawals after a whole week off the bike

So how was today at the sandpit? Bike behave itself?

Must have been chilly..................

[krad_nz]

Was mint at the sand pit today. Surprisingly it didn't rain. Excellent conditions. Bike behaved itself and survived the day. Was easier to start, had more bottom and mid range according to SpikedPunch. It sounded nice and crisp too. Also with the needle raised up to stock I was expecting it to splooge again, but it didn't. She must be riding harder, or its something to do with poor compression.

Motocross track has been reversed so watch out. Especially if you exit the farm loop. Sure the arrows point the other way but I figured someone was taking the piss. Should have a sign saying its been reversed. Was 'exciting' having two motocross bikes coming at you full noise.

[clmintie]

That sounds like good news.... well done the pair of you..

[LittleJohn]

Was mint at the sand pit today. Surprisingly it didn't rain. Excellent conditions. Bike behaved itself and survived the day. Was easier to start, had more bottom and mid range according to SpikedPunch. It sounded nice and crisp too. Also with the needle raised up to stock I was expecting it to splooge again, but it didn't. She must be riding harder, or its something to do with poor compression.

Motocross track has been reversed so watch out. Especially if you exit the farm loop. Sure the arrows point the other way but I figured someone was taking the piss. Should have a sign saying its been reversed. Was 'exciting' having two motocross bikes coming at you full noise.

I though that the motocross track was closed, until after doing the farm loop. Thats when after going the reverse way I saw the sign near the start of the track. Bummer it was the end of the day otherwise would have given it a go. Next time maybe.

Was such an awesome day out there today, great weather.

[xen]

Good to hear you guys got it sorted sweet. Some good info in this thread, thinking about doing rings or at least looking at mine now haha.

Motocross track has been reversed so watch out. Especially if you exit the farm loop. Sure the arrows point the other way but I figured someone was taking the piss. Should have a sign saying its been reversed. Was 'exciting' having two motocross bikes coming at you full noise.

Yea I'll bet !