caleb93 Posted February 5, 2018 Author Report Share Posted February 5, 2018 I never did get anything to work with the other ignition system, just went to the kokusan. The piston was installed backwards. The little pins that live in the ring lands to keep the piston rings from moving about were facing the front of the bike towards the exhaust port. The cylinder has two wear grooves exactly where these pins are and most importantly where the ends of the rings were who caused the wear. The exhaust port is also chipped where these wear lines are. If the piston were flipped the ends of the rings would live in between the intake ports and have a solid surface to ride on through the whole stroke. So I just want to know if that came from the factory and went these 14 years or if someone else put it in backwards. I guess it doesn't really matter because I get to fix it... 1 Quote Link to comment Share on other sites More sharing options...
d2w Posted February 5, 2018 Report Share Posted February 5, 2018 How badly is your cylinder scored/grooved by the pins? Can this damaged be honed-out and still leave you with the bore plating? Since you have the cylinder off the bike perhaps you should show a machinist and get their opinion? I like to think that GG would have an assembly process which ensures that pistons are installed with the correct orientation. But, as you say, you'll never know and it doesn't matter. But now you do know what was the likely cause of your troubles and that you have corrected it. Quote Link to comment Share on other sites More sharing options...
sectionone Posted February 5, 2018 Report Share Posted February 5, 2018 Before I open an engine for the first time I look for any evidence of someone opening it up before me. Rounded bolts, scraped off gaskets, marks from removing seals, etc. I doubt a backwards piston would last 14 years. It will cost about $300 to get the cylinder welded and replated plus the cost of new piston. If you have any up and down play on the rod you should have the crank bearing replaced and while your doing that, replace main bearings and seals. Another $500 or so. Up and down play on the rod will toast a new top end, side to side play is normal. I guess totally rebuilding the engine will cost about $1000. Quote Link to comment Share on other sites More sharing options...
miner Posted February 6, 2018 Report Share Posted February 6, 2018 Could running 91 RON fuel instead of 95 or 97/98 RON blow a hole in the piston? Quote Link to comment Share on other sites More sharing options...
caleb93 Posted February 7, 2018 Author Report Share Posted February 7, 2018 The cylinder had a decent groove in it from the most recent eating of the ring. I was able to do a cylinder exchange and they think they can fix it so more power to them. I am going to to as sectionone advised and update to the new mains and seals since everything is apart anyways. I was actually advised to not replace the big end bearing since it has no play so I guess I'm leaving that. Miner, it is unlikely that the octane killed it, it was never detonating especially because the 1mm spacer was installed for whatever reason. Oni nou explained it all very well. Anyways the bike should be going in a week or two with a forward facing piston so that's nice. Thanks to everyone for the advice and for helping me come to the reason for top end bits coming apart! 2 Quote Link to comment Share on other sites More sharing options...
d2w Posted February 7, 2018 Report Share Posted February 7, 2018 (edited) Forward facing piston? I think you want the arrow facing to the left if you're in Europe and to the right if you're in North America. It may be a struggle to do so though. Edited February 7, 2018 by d2w 2 Quote Link to comment Share on other sites More sharing options...
sectionone Posted February 8, 2018 Report Share Posted February 8, 2018 How much did it cost for the cylinder exchange? I assume it is from Jim. I just had my YZ welded and replated and it cost me $320 with shipping plus $100 for new piston. Quote Link to comment Share on other sites More sharing options...
caleb93 Posted February 9, 2018 Author Report Share Posted February 9, 2018 280. Yes from Jim. Another 170ish for Piston. They come in a set from Jim as the cylinder is matched exactly to a specific piston to get the clearances just so. 1 Quote Link to comment Share on other sites More sharing options...
caleb93 Posted February 12, 2018 Author Report Share Posted February 12, 2018 Got the bike back together tonight and wow! The top end is so so much quieter and pulls way harder. I guess that makes sense looking back now but I just thought the noise was a Gas Gas thing. Anyways once again thanks for the input from everyone! 1 Quote Link to comment Share on other sites More sharing options...
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