mtnmanseth 0 Posted December 17, 2014 Mission: Install my first/bike's first top end in a 2005 GasGas EC300New parts purchased: Vertex "A" piston kit, wrist bearing, gaskets (A piston purchased because cylinder showed little/no wear and Skeeter's - GasGas dealer - thought a "B" would potentially cold seize)Current carb setup: JD jet kit installed per instructions at 3,000' elevation: blue needle 3rd clip, 178 main, 40 pilot, air screw ~3/4 turn outRiding conditions: Between sea level and 4,000 feet, 65-85 degrees F, mostly technical singletrack trail riding but occasional high speed blasts through desert dunes and sand washesResult: 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 (no hour meter on it until recently). 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. Pure sand and WOT riding was definitely rare as I prefer to tackle steep technical singletrack climbs and riding areas. I showed all this to Skeeter's Motorsports (SoCal's only GasGas dealer) and they really didn't seem too concerned, which was suprising. They said 2 stroke motors are bulletproof, and the condition of the piston and the fact that it still ran fine is certainly proof of this. They sold me a new top end kit and gasket set, and it all went in just fine. Anyhow, here are pictures of what I pulled out of the bike: Put a main jet in the depression to show scale Close up of missing chunk on exhaust side Obvious blow by and significant skirt wear Jug still in excellent condition (WHEW!) and Skeeter's (GasGas dealer) agrees New piston ready to go For those who haven't seen the bike (the day I bought it, hardly a scratch) The head is being machined by RB Designs in Portland, OR (specialize in GasGas engine mods) as I type this to reduce squish band/increase compression, and hope to have it back by this weekend - So I have not started the bike after new top end yet. 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 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. Big THANK YOU to Spaugh for helping me to assess cylinder wear and measure the bore over the weekend... I'll get this thing running again and we'll go for a rip! Sending a virtual cold beer to you all... Share this post Link to post Share on other sites
dirt dame 559 Posted December 17, 2014 Yup, two strokes will run even when their engine bits are disinegrating. A couple of years ago, I thought my KDX200 was a little down on performance. I couldn't remember when the last time was that I changed out a top end on it, so I ordered a new piston and gasket set. The old piston was literally splitting vertically up the back. Share this post Link to post Share on other sites
PbdBlue 46 Posted December 17, 2014 Looks like it was very lean at some point. How does your plug look? Is the insulator white or a nice chocolate brown? Share this post Link to post Share on other sites
mtnmanseth 0 Posted December 17, 2014 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. My gut is that I need to up the jetting (main jet at least) for sea level/desert conditions and leave it. It might be a touch rich at 4,000 feet - and will require rejetting if ridden above that. If the pilot jet is too small, will it cause the funky idle after WOT and cause this much heat? Or is this certainly too much heat from an undersized main jet? Share this post Link to post Share on other sites
PbdBlue 46 Posted December 17, 2014 Lean pilot will give you the "hanging idle" that you are referring to. I doubt it will cause that much heat but a lean needle or main jet setting will. You may be right in that the initial damage may have been done by the PO. What oil and ratio are you running? Remember that a richer oil ratio will result in a leaner mixture. I haven't had a two stroke for some time but raced them for many years. I'm sure there are many others on here that are more current than myself. These are just the basics. Share this post Link to post Share on other sites
mtnmanseth 0 Posted December 17, 2014 Lean pilot will give you the "hanging idle" that you are referring to. I doubt it will cause that much heat but a lean needle or main jet setting will. You may be right in that the initial damage may have been done by the PO. What oil and ratio are you running? Remember that a richer oil ratio will result in a leaner mixture. I haven't had a two stroke for some time but raced them for many years. I'm sure there are many others on here that are more current than myself. These are just the basics. Throwing in a 42 or 45 pilot jet is easy, so that will happen prior to desert outings to potentially fix the hanging idle. I concur that a lean idle probably wouldn't cause this kind of heat. Thanks. So.... needle or main. I am running Motul 710 at 40:1 ratio. GasGas recommends running 50:1 of any synthetic oil, so you're right, that is a touch leaner with the richer oil ratio. I really like Motul 710 as it's a low flashpoint oil that spooges MUCH LESS than other "racing" oils with twice or three times the heat/rpms needed to burn/lubricate. And, yeah, it's definitely confusing not knowing if this damage was done before I even owned the thing or if I did the damage. I rode Rob's brand new Husky 300 2T this summer and it definitely boosted the front wheel easier than my bike. I'm starting to consider it was suffering from a damaged piston and, therefore, lower compression from the second I bought it. Oh, geez, I can hardly wait to get it put back together and take 'er out! Share this post Link to post Share on other sites
Goofy Footer 539 Posted December 17, 2014 You trust Skeeter? Share this post Link to post Share on other sites
robertaccio 405 Posted December 17, 2014 wow the crown collapsed from excessive heat. that is hearty that it kept on going and serving you well. should feel like a brand new machine. that 40:1 ratio is fine , its really my fave ratio, just jet properly. sounds like you have it figured out. Share this post Link to post Share on other sites
Goofy Footer 539 Posted December 17, 2014 What did the GasGas specialist say about # of hours on the piston? I know it's a 2 stroke but I thought 300s lasted much longer than a 125 and even a mx ridden 250? Share this post Link to post Share on other sites
PbdBlue 46 Posted December 17, 2014 Lean pilot will give you the "hanging idle" that you are referring to. I doubt it will cause that much heat but a lean needle or main jet setting will. You may be right in that the initial damage may have been done by the PO. What oil and ratio are you running? Remember that a richer oil ratio will result in a leaner mixture. I haven't had a two stroke for some time but raced them for many years. I'm sure there are many others on here that are more current than myself. These are just the basics. Throwing in a 42 or 45 pilot jet is easy, so that will happen prior to desert outings to potentially fix the hanging idle. I concur that a lean idle probably wouldn't cause this kind of heat. Thanks. So.... needle or main. I am running Motul 710 at 40:1 ratio. GasGas recommends running 50:1 of any synthetic oil, so you're right, that is a touch leaner with the richer oil ratio. I really like Motul 710 as it's a low flashpoint oil that spooges MUCH LESS than other "racing" oils with twice or three times the heat/rpms needed to burn/lubricate. And, yeah, it's definitely confusing not knowing if this damage was done before I even owned the thing or if I did the damage. I rode Rob's brand new Husky 300 2T this summer and it definitely boosted the front wheel easier than my bike. I'm starting to consider it was suffering from a damaged piston and, therefore, lower compression from the second I bought it. Oh, geez, I can hardly wait to get it put back together and take 'er out! The only other thing that comes to mind is a leaking crank seal. That will cause the bike to run lean also. I'd just put it back together and keep an eye on it. If you still have issues or can't seem to dial in the jetting it might me worth checking the seals. Share this post Link to post Share on other sites
dirt dame 559 Posted December 17, 2014 I had an hour meter on my 2005 KTM EXC250, and I had about 250 hours (and excellent compression) on that top end, when I sold the bike. The second owner got lots of additional hours out of it before he rebuilt it. Share this post Link to post Share on other sites
mtnmanseth 0 Posted December 17, 2014 What did the GasGas specialist say about # of hours on the piston? I know it's a 2 stroke but I thought 300s lasted much longer than a 125 and even a mx ridden 250? Well, the GG forum folks say to pull it down and check on conditions/ring gap every ~70 hours. Of course, while you're in there one should replace rings (in addition to base gasket) to refresh things. Overall piston life for 300 2-strokes varies widely, between 150-200 hours for us trail riders to maybe 30-40 hours for racers and guys on the pipe ALL THE TIME. Yes, 300 guts will definitely last significantly longer than smaller bores, you're right. I have no way of knowing how many total hours are on the bike... the previous owner may have had 200 hours on it just putting around with family. Don't know. Most on the GG forum concur that the heat damage most likely due to extreme lean condition is old news... may have even happened before I bought the bike. However, it sounds like my jetting is one single step too lean for the occasional trips to sea level (Anza Borrego, Superstition, Ocotillo Wells) and I should rejet to sea level while acknowledging it will be just a little rich at the top of Pine Valley/Corral Canyon. Apparently the biggest tell tale is the few times it did the "hanging idle" after flogging it around sand dunes and through deep sand washes at WFO throttle. Now I know what to listen for. In the end, the fact that she ran as strong as she did despite the damaged piston is clear testament to how resilient and tough newer generation 2-stroke motors are. I probably got quite lucky riding it for as long and hard as I have without catastrophic engine damage, though. I loved the ridiculous tractable, electric-motor-smoothness and "lugability" before these upgrades, can hardly wait to try it out all freshed up. We'll see! Share this post Link to post Share on other sites
TrophyHunter 15 Posted December 18, 2014 It'll probably scare the begeezus outta ya and you'll have to sell it to tntmo's wife. Glad you avoided the major meltdown. Share this post Link to post Share on other sites
mtnmanseth 0 Posted December 19, 2014 Case solved! I got a call from Ron at RB Designs today (2-stroke motor mod machinist in Portland) 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 and 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! Surprisingly, I measured the bore with Spaugh's help and fancy bore gauge AND Skeeter's matched the "A" piston to my cylinder in their shop. Both Spaugh and the GG dealer said that either I started with a slightly smaller cylinder and piston (even though 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 Skeeter's adamantly recommended installation of another "A" piston because a "B" had the potential to cold seize. So... "A" it is... Share this post Link to post Share on other sites
robertaccio 405 Posted December 19, 2014 its going to feel like a different bike when you get er all back together. Share this post Link to post Share on other sites
