What is this piston telling you?

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12/30/2017 3:36 AM

It's out of a CR500, 168 main, 55 pilot & the clip is on the fourth clip down. Normally run at 40:1 but did run it on 32:1. What does the carbon build up mean?

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12/30/2017 3:42 AM

"Hi. I'm a piston."

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12/30/2017 4:00 AM

I am no expert but looks like poor quality fuel. Maybe also rich.

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12/30/2017 4:16 AM

I’m no expert here, but even burn pattern and rich jetting.

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12/30/2017 4:25 AM

Nota antes expert. post picture of the Sideshow and underside

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12/30/2017 4:39 AM

It means you need to need to run that beast WFO more often to burn more of the fuel/oil mix in the combustion chamber.

If you're a normal human being running a 500 WFO probably ain't gonna happen.

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12/30/2017 4:43 AM

ratonmacias wrote:

Nota antes expert. post picture of the Sideshow and underside

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12/30/2017 4:43 AM
Edited Date/Time: 12/30/2017 4:48 AM

Synthetic or Dino premix? A bit rich but ok for a 500 with all the low rpm lugging around. Run a good synthetic oil at the recommended ratio. You could mess with the jetting and clean up the bottom end but if it's not spooging the exhaust or sluggish I would let it rip, better a bit rich on the bottom than lean on top and end up possibly locking her up on a WFO situation. How many hrs on that piston, looks a bit overdue.

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12/30/2017 4:53 AM

markit wrote:

Synthetic or Dino premix? A bit rich but ok for a 500 with all the low rpm lugging around. Run a good synthetic oil at the recommended ratio. You could mess with the jetting and clean up the bottom end but if it's not spooging the exhaust or sluggish I would let it rip, better a bit rich on the bottom than lean on top and end up possibly locking her up on a WFO situation. How many hrs on that piston, looks a bit overdue.

Running Rock Oil Synthesis 2. Probably a good 75 hrs.

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12/30/2017 5:08 AM

Looks like some dirt/sand got by your filter at some point or you're not getting a good seal, are you greasing the base? Make sure to replace the wrist pin bearing there is visible wear there too. 75 hrs on a 500 isn't a crazy amount of hrs so I think the d/s was the main issue and that could have been anything like a creek crossing where you got the filter wet.
Do a fresh top end and you should be good to go. MX or woods ridin/racing?

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12/30/2017 5:11 AM
Edited Date/Time: 12/30/2017 5:18 AM

markit wrote:

Looks like some dirt/sand got by your filter at some point or you're not getting a good seal, are you greasing the base? Make sure to replace the wrist pin bearing there is visible wear there too. 75 hrs on a 500 isn't a crazy amount of hrs so I think the d/s was the main issue and that could have been anything like a creek crossing where you got the filter wet.
Do a fresh top end and you should be good to go. MX or woods ridin/racing?

Not greasing the filter seal & a fresh piston has been put in. Not my bike but my brothers so I'll pass the information on.

MX mainly and a couple of hare & hounds but definitely no river crossings.

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12/30/2017 6:19 AM


That bike is running rich.
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12/30/2017 6:21 AM

Its telling me your slow

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12/30/2017 6:31 AM
Edited Date/Time: 12/30/2017 6:32 AM

What did the plug look like as well?
I was obsessed with jetting on my 2 strokes.
Probably too obsessed blush sad

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12/30/2017 6:58 AM

Looks, fine to me. Like a few others have said, a shade rich. Tell him to drop the needle a clip, or even drop the main down one, depending on where is feels fat or blubbery. If he does not feel like playing with the jetting, the engine will certainly survive for a long long time with that set up. Make sure he warms the bike up well with Wiseco’s. Only piston I will run in my two strokes, but they are rattly until the engine is at operating temperature.

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Tomac and/or Anderson for 2020.....

12/30/2017 7:12 AM

BobPA wrote:

Looks, fine to me. Like a few others have said, a shade rich. Tell him to drop the needle a clip, or even drop the main down one, depending on where is feels fat or blubbery. If he does not feel like playing with the jetting, the engine will certainly survive for a long long time with that set up. Make sure he warms the bike up well with Wiseco’s. Only piston I will run in my two strokes, but they are rattly until the engine is at operating temperature.

Why does Wiseco tell you to drill holes for the exhaust bridge? They tell you to do it but they don't do it from manufactur. A Wiseco piston for my YZ125 has them drilled straight out the box. Why doesn't Honda feel the need to do it then?

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12/30/2017 7:13 AM

KMC440 wrote:

What did the plug look like as well?
I was obsessed with jetting on my 2 strokes.
Probably too obsessed blush sad

On the rich side.

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12/30/2017 7:22 AM

You running Yamalube?

Switch to Golden Spectro @ 50:1 and there will be no carbon but a good oil coating instead.

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12/30/2017 7:24 AM

lumpy790 wrote:

You running Yamalube?

Switch to Golden Spectro @ 50:1 and there will be no carbon but a good oil coating instead.

Rock Oil at 40:1

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12/30/2017 7:27 AM

Holes are to allow more oil to that area as that spot is prone to lack of lubrication related failures. Two stroke fans talk crap about 4 strokes but a 2 stroke engine can be equally temperamental.

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12/30/2017 7:29 AM

KMC440 wrote:

Holes are to allow more oil to that area as that spot is prone to lack of lubrication related failures. Two stroke fans talk crap about 4 strokes but a 2 stroke engine can be equally temperamental.

I know why they need them, just wondering why Wiseco tell you to do it but not drill them when they make them.

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12/30/2017 7:36 AM
Edited Date/Time: 12/30/2017 7:48 AM

I’ve read a few diff piston wash articles etc. it’s a good way to help fine tune jetting for older two stroke jet skis. Based on everything I’ve read and some of my own personal experience I’m gonna go against the grain here and say that’s a tad lean. Now calm down and hear me out. Carbon buildup occurs when the temps are high enough to create the carbon. During a richer condition the temps are cooler and the carbon won’t form as much. But the wash pattern looks pretty close. So I’d say it’s dam close. It lasted 75 hrs and the wear looks good.

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2010 crf450
2002 cr125
1993 Yamaha waveblaster
1993 Kawasaki 750sx

12/30/2017 7:42 AM

KMC440 wrote:

Holes are to allow more oil to that area as that spot is prone to lack of lubrication related failures. Two stroke fans talk crap about 4 strokes but a 2 stroke engine can be equally temperamental.

Muscle-Milk-KTM wrote:

I know why they need them, just wondering why Wiseco tell you to do it but not drill them when they make them.

Stock is cast, Wiseco is forged. Doesn't help to drill them if the exhaust bridge isn't properly relieved when bored and or replated. I have always wondered how much lower end compression is lost when the holes are drilled.

And at 75 hours, how many times has that piston been pulled, cleaned and a fresh set of rings added? Betting I already know the answer...wink

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12/30/2017 7:44 AM

lumpy790 wrote:

You running Yamalube?

Switch to Golden Spectro @ 50:1 and there will be no carbon but a good oil coating instead.

Muscle-Milk-KTM wrote:

Rock Oil at 40:1

I do not know what oil brands are available in GBR but maybe Try a different brand oil? One that runs cleaner and not sooty.

Spectro is a Synthetic / Petrolium blend so you get the best of both worlds.

http://spectro-oils.com/wp-content/techsheets/GSMC.pdf

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12/30/2017 7:48 AM

KMC440 wrote:

Holes are to allow more oil to that area as that spot is prone to lack of lubrication related failures. Two stroke fans talk crap about 4 strokes but a 2 stroke engine can be equally temperamental.

Muscle-Milk-KTM wrote:

I know why they need them, just wondering why Wiseco tell you to do it but not drill them when they make them.

newmann wrote:

Stock is cast, Wiseco is forged. Doesn't help to drill them if the exhaust bridge isn't properly relieved when bored and or replated. I have always wondered how much lower end compression is lost when the holes are drilled.

And at 75 hours, how many times has that piston been pulled, cleaned and a fresh set of rings added? Betting I already know the answer...wink

The instructions tell you how to scribe the edges of the center exhaust bridge so the hole is properly centered. Maybe the center bridge can get moved one way or the other when produced?

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12/30/2017 8:04 AM

I’ve run Yamalube 2R at 40:1 in every bike I’ve owned, including all 3 of my 500’s. Put huge hours on all of them, never seen a buildup like that. Having said that, mine are used strictly for moto, and the last one saw almost exclusive sand
riding. That is to say, ridden long and hard, working all the time. All I can add to this thread.

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12/30/2017 8:23 AM

Muscle-Milk-KTM wrote:

I know why they need them, just wondering why Wiseco tell you to do it but not drill them when they make them.

I would assume they do not drill them due to variances in exhaust bridge shape and location.

I think the compression loss due to the lubrication holes would be minimal at best. Two stroke crankcase pressure is relatively low to begin with. Plus, when the piston is traveling on the down stroke, I.e. creating the most crankcase pressure...the holes are below the exhaust bridge.

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Tomac and/or Anderson for 2020.....

12/30/2017 8:24 AM

hard to tell if its lean/normal/rich without seeing the plug. But thats more carbon then I would expect to see after 75hrs on synthetic oil. but not that big of a deal. Be happy, and ride!

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2 Stroke, Drum Brakes, Finned Cylinders!!!

12/30/2017 8:37 AM

Sprocket bolts are probably loose.

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12/30/2017 9:53 AM

mx621 wrote:

I’ve read a few diff piston wash articles etc. it’s a good way to help fine tune jetting for older two stroke jet skis. Based on everything I’ve read and some of my own personal experience I’m gonna go against the grain here and say that’s a tad lean. Now calm down and hear me out. Carbon buildup occurs when the temps are high enough to create the carbon. During a richer condition the temps are cooler and the carbon won’t form as much. But the wash pattern looks pretty close. So I’d say it’s dam close. It lasted 75 hrs and the wear looks good.

Exactly. If it was rich on fuel, the piston would be washed clean.

It's either lean on fuel, or isn't ridden very hard and is just carbon buildup. Near the transfer ports there should be a bit more wash.

Big cylinders are harder to tell without knowing use habits. And/or how hard its ridden.

Being a 500, it's probably babied. I'd leave it be.

People confuse rich on oil and rich on fuel too often.

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