Can you translate for this piston?

[mtnmanseth]

Mission: Install my first/bike's first (?) top end in a 2005 EC300

New parts purchased: Vertex "A" piston kit, wrist bearing, gaskets

Current carb setup: JD jet kit installed, blue needle 3rd clip, 178 main, 40 pilot, air screw ~3/4 turn out, Motul 710 @ 40:1 with premium pump gas

Riding conditions: Between sea level and 3,000 feet, 65-85 degrees F, mostly technical singletrack trail riding but occasional high speed blasts through desert dunes and sand washes

Result: My jaw dropped to the floor when I pulled the jug off my bike for the first time. I'm the 3rd owner, but the former owners barely rode the bike, so I ESTIMATE the bike/top end has 120-150 hours on it. What I found was a badly warped piston with a chunk of the sidewall missing between the rings. Fortunately, the chunk was missing on the exhaust side, and due to complete lack of dents/scratches in piston surface or cylinder walls, can only assume the chunk of metal was perfectly spat out the exhaust hole. Right? Before you guys scold me about how I went WAAAAY too long before refreshing the top end... trust me, I know! This is my first dirt bike, first 2T at all, so I'm learning here. And, really, I have no idea whether this damage was done by a previous owner (with stock jetting) and I've been riding it with this damage. Regardless, I will be checking piston condition from now on and plan to replace again at ~70 hours, now that I have an hour meter installed on the bike. It would be great if you guys will help me learn from the experience. Was the damage to this piston likely done during WOT events i.e. too small main jet? Or could it be a needle issue? As written above, I rarely am at WOT but have brought the bike to the desert a few times (at sea level) and have had her wide open through sand washes and up and over sand dunes. I do recall that the idle tended to hover high and undulate high/low/high/low for several seconds after some time at WOT in the sand. Again, being new to jetting/bike setup maybe this was a major sign I was doing damage and didn't know it. Again, pure sand and WOT riding was definitely rare as I prefer to tackle steep technical singletrack climbs and riding areas.

Anyhow, here are pictures of what I pulled out of the bike:

Photo showing warped/divotted top and "chunk" missing from between rings

Placed main jet in depression to show scale

Obvious blow by

Jug looks good

New piston ready to go

My head is being modded by RB as I type this, hope to have it back by this weekend. In anticipation of the these major upgrades, I want to make sure I don't melt another piston. Please review the jetting setup provided above and let me know if this is a good start. I have done a lot of homework here and see that most guys find that they need to lean their jetting after getting their head mods/reduce squish/increase compression... so maybe my current setup is actually perfect? Any advice would be much appreciated. Sending a virtual cold beer to you all...

 

[hamilton]

You been using the correct heat range spark plug?

 

[mtnmanseth]

You been using the correct heat range spark plug?

Good question. I have had an NGK BR8EIX (Iridium) in it for 8+ months. I know this is the correct heat range, but would the Iridium option cause this much more heat? I've definitely done some plug checks over the last year since I've owned it, and they were always black and wet looking... sign of rich condition. However, the Iridium plug when I pulled it on Saturday was a nice dry chocolate brown color - I was happy with it. Plug has never been white or ashy to indicate super lean condition. Weird.

 

[Jakobi]

Jetting specs look ok. The psiton wash is interesting. A hot piston should be hard coated in carbon both on top and the bottom sides of the dome. Really hot will melt a hole right through.

Front skirt of the piston is quite polished, which indicates its been rocking in the bore a bit.

Did you measure the ring end gap? MY guess would be that the rings have been floating and fluttering for some time.

 

[memphis2857]

Looks to me like it has been in this condition for a while. Looks like it got REALLY hot a long time ago. 2 strokes are pretty forgiving and will run long after they should have quit. With that new piston you are gonna have a whole new bike!


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[Rick]

The underside of the piston would also tell a story if it was lean and got hot at one time. Based upon the jetting specifications that would be close.

I would clean the power valves. As for the jug I'd run a scotch bright pad and WD40 to remove and shiny spots that could be aluminum deposites.

Measure ring end gap and go from there. Makes sure your using the same base gasket thickness as before.

In your picture the ring end is not alligned with the piston ring pin....don't over look that, or there will be an issue.

You mentioned that the plug was white....lean......make sure you don't have an air leak, reed block baskets, main bearing seal (ignition side) or cracked carb boot. I'd run a BR8ES once i got it back together.

Motul 710 is a great oil, burns cleaner than the 800, however for long deep sand washes at WFO i think I'd step up to the 800 and try a 50/50 mix of race gas and 92 octane, there may have been some detenation (pinging) that went UN noticed. Those long hard runs can really heat up a motor, so a main jet increase must do the trick as well.

Food for thought.......

One other area to check, water pump impeller....make sure it's not deformed or melted. Now's the time . Do a search.....plenty of info on that subject.

 

[(F5)]

Whoa never seen a piston do that before, the warp bit. But there isn't real signs of detonation. No grey ash, no nibbling away at the centre surface or ex port edge. That's right queer, I'd almost be thinking manufacturing fault. What does the underside look like?

I can't see how it would have got hot enough to soften the piston to let it slump and not go into a self perpetuating deto meltdown. Guess it lowered the compression by itself.

 

[mtnmanseth]

Jetting specs look ok. The psiton wash is interesting. A hot piston should be hard coated in carbon both on top and the bottom sides of the dome. Really hot will melt a hole right through.

Front skirt of the piston is quite polished, which indicates its been rocking in the bore a bit.

Did you measure the ring end gap? MY guess would be that the rings have been floating and fluttering for some time.

Good catch, Jakobi. The very top of the piston is clean only because the local dealer did some scrubbing to try to expose the original piston part number. So, it was almost completely hard coated in carbon. Also, I forgot to take a photo of the underside but it too is black as can be.

Can you settle the debate once and for all and confirm that my current jetting may be spot on after the head mod/reduced squish? I've read herein that most guys can go one step leaner after the head mod. Or, should I step the jetting up just one notch (42 pilot, 180 main, one step richer on needle) to jet for my occasional trips to sea level (desert) and realize that it might just be a tad rich when riding up around 3,500 to 4,500 feet? You're the authority on jetting and any insight on the JD blue vs. red needle differences would be handy to know, too. If you prefer to send a quick summary in a PM that's fine too. Thanks in advance.

 

[mtnmanseth]

Whoa never seen a piston do that before, the warp bit. But there isn't real signs of detonation. No grey ash, no nibbling away at the centre surface or ex port edge. That's right queer, I'd almost be thinking manufacturing fault. What does the underside look like?

I can't see how it would have got hot enough to soften the piston to let it slump and not go into a self perpetuating deto meltdown. Guess it lowered the compression by itself.

I can definitely assume it was suffering from lower compression! In fact, I rode a brand new Husky 300 over the summer and it definitely boosted the front wheel easier than my bike ever has, so I'm starting to think this heat damage to the piston was done before I got the bike.

Also, as I replied to Jakobi, the underside was black as night, too. The fact that the bike ran as strong as she did after many hours with me flogging it is certainly testament to how resilient and bulletproof these GG motors are. I did, however, probably get quite lucky it didn't melt through completely, huh?

 

[Jakobi]

The jetting specs on paper look to be in the ballpark. The piston is telling you another story though. As others have suggested, I'd be looking for the cause/reason. Most likely an air leak.

 

[hamilton]

Your oil choice and mix ratio(good). Jetting is real close (works well on a 250 maybe slightly rich for 300). The only time I seen a piston crown failure like yours was a result of wrong heat range plug(ie B7ES) and mixing of two different brands of 2t oils. A lot of people think I'm fouling plugs I'll go to a hotter plug, big mistake. It might stop the plug fouling but at what cost? Your ring land failure was most likely a result from piston over heat.Your problem could of been caused long ago. Just my 2 cents.

 

[jostby]

I'm not sure how the JD Blue needle equates to the LTR 0 needle but that's what I use in our two bikes with 48 pilot and 180 mains (in both). Seems like the older bikes liked fatter jetting but seems I've heard the 300's like to be jetted a little leaner than the 250's also. For whatever reason not many (if any) people here run as fat as the jetting I use. not sure why but it works well for us. Mind you I'm 300# out of the shower and my kid even bigger (he plays college football) so our size vs where we run with the throttle may be the reason it works for us.

That piston must have been one nano-second from vaporization, amazing picture!

 

[Moto7man]

Just an idea. Did you have someone measure your cylinder bore? You may need to go to a B or C piston to tighten things up a bit.

 

[mtnmanseth]

Case solved! I got a call from Ron at RB Designs today who said the head I sent him has already been machined... that the squish has been reduced BUT the combustion chamber and volume was NOT modified proportional to the reduced squish/increased compression! I had no idea, but a previous owner must have either done it himself or sent it away to a machinist (not RB) who did a half ass job. He said he's 99% sure that the shoddy head work is to blame for my jetting woes and deformed piston due to mismatched combustion chamber volume to VERY high compression. Additional details on the topic are above my level of knowledge so feel free to further explain things, but it's nice to know the story of the mangled 300 piston!

RB said they'll do their very best to calculate the ideal combustion chamber dimensions and complete the machining job per their successful specifications. Looking forward to reassembly and takin' er out for a rip!

Just an idea. Did you have someone measure your cylinder bore? You may need to go to a B or C piston to tighten things up a bit.

Moto7man, this is a good question. Surprisingly, I measured the bore with a friend's help and fancy bore gauge AND my local GasGas dealer matched the "A" piston to my cylinder in their shop. Both my friend and the GG dealer said that either I started with a slightly smaller cylinder and piston (both are stamped "A") or despite all the dome and skirt damage shown on the piston the cylinder has sustained a nearly immeasurable amount of wear. Odd, I know, but the GG dealer adamantly recommended installation of another "A" piston because a "B" had the potential to cold seize. So... "A" it is...

 

[Jakobi]

That'll do it.

 

[(F5)]

Yes when squish corrected compression goes to like 15:1 or more. Big cylinders must do funny things with too much comm. That said I've never seen a bike run so far over recommended level. Can't have wanted to rev.

 

[Moto7man]

Case solved! I got a call from Ron at RB Designs today who said the head I sent him has already been machined... that the squish has been reduced BUT the combustion chamber and volume was NOT modified proportional to the reduced squish/increased compression! I had no idea, but a previous owner must have either done it himself or sent it away to a machinist (not RB) who did a half ass job. He said he's 99% sure that the shoddy head work is to blame for my jetting woes and deformed piston due to mismatched combustion chamber volume to VERY high compression. Additional details on the topic are above my level of knowledge so feel free to further explain things, but it's nice to know the story of the mangled 300 piston!

RB said they'll do their very best to calculate the ideal combustion chamber dimensions and complete the machining job per their successful specifications. Looking forward to reassembly and takin' er out for a rip!



Moto7man, this is a good question. Surprisingly, I measured the bore with a friend's help and fancy bore gauge AND my local GasGas dealer matched the "A" piston to my cylinder in their shop. Both my friend and the GG dealer said that either I started with a slightly smaller cylinder and piston (both are stamped "A") or despite all the dome and skirt damage shown on the piston the cylinder has sustained a nearly immeasurable amount of wear. Odd, I know, but the GG dealer adamantly recommended installation of another "A" piston because a "B" had the potential to cold seize. So... "A" it is...

That is a litle strange, but it sounds like your head was the problem instead of excessive hours on the engine.