flyingbrick Posted November 4, 2020 Share Posted November 4, 2020 Ummn.. How you do the calc? Because I can't get an output that makes sense. 77mm stroke and 9500rpm? Edit, I get 1,462,893...... Edit. Because a 535 BMW diesel has a mean piston speed of 889,101mm/min.. @Guypie your numbers all seem too low? Quote Link to comment Share on other sites More sharing options...
tortron Posted November 4, 2020 Author Share Posted November 4, 2020 No need to do the math it's a GN just mang it Like I did just now. Cold start new start 0-8000rpm to warm it up 3 Quote Link to comment Share on other sites More sharing options...
keltik Posted November 4, 2020 Share Posted November 4, 2020 5 hours ago, SOHC said: I wouldn’t recommend it, needle roller big end bearings don’t like high rpm The big end bearings on my GN have had nothing but max RPM abuse since I've had it and they are absolutely fine getting a little bit knocky. Its still an amazing engine IMHO. More usable rev range than a Lifan 125 and the 5 speed makes them possibly the best shitty 125 you can buy. Have also heard stories/read somewhere that having a greater piston to wall clearance means the piston heats up more as it cant effectively transfer heat into the cylinder walls through the oil layer around the skirt. Then the wrist pin thermal mass causes the piston to expand non-symmetrically and things get all scuffy on the sides. I don't think your issue is too much clearance, too much abuse or too lean....I think it has to be crappy oiling to the piston. I'm assuming these things don't run a piston squirter oil jet? Have you been running the same rod/crank for all of the big bore kits? 1 Quote Link to comment Share on other sites More sharing options...
tortron Posted November 4, 2020 Author Share Posted November 4, 2020 Yes same crank and rod, there's no other available They don't have squiters, it's just a splash sort of low pressure thing. I only think that's a problem because no one who messes with these engines does anything to the oiling, think had considered options Quote Link to comment Share on other sites More sharing options...
tortron Posted November 4, 2020 Author Share Posted November 4, 2020 And again I'm pretty sure the piston was too tight to begin with. After honing the cylinder again, and rubbing the piston on a stone to smooth it off, it came in just above the minimum clearance Quote Link to comment Share on other sites More sharing options...
keltik Posted November 4, 2020 Share Posted November 4, 2020 Bit of schmoo stuck in the rod perhaps? Quote Link to comment Share on other sites More sharing options...
tortron Posted November 4, 2020 Author Share Posted November 4, 2020 Possible my rod has some cheese in it yes, but I do change the oil and filter way more often than required. The pin never has any marks or discoloration on it, underside of piston never had burnt oil on it Quote Link to comment Share on other sites More sharing options...
M.H. Posted November 4, 2020 Share Posted November 4, 2020 9 minutes ago, tortron said: And again I'm pretty sure the piston was too tight to begin with. After honing the cylinder again, and rubbing the piston on a stone to smooth it off, it came in just above the minimum clearance Too tight and probably not a very round piston or bore Quote Link to comment Share on other sites More sharing options...
tortron Posted November 4, 2020 Author Share Posted November 4, 2020 I wouldn't disagree It's pretty round for a China bore, pistons are very cheap. I have tested a ring at multiple points in the cylinder and it's within spec. I think the pistons are hit and miss, but choose to ignore 1 Quote Link to comment Share on other sites More sharing options...
keltik Posted November 4, 2020 Share Posted November 4, 2020 And since your cam hasnt turned to custard, we can assume the plastic oil pump is pumping 1 Quote Link to comment Share on other sites More sharing options...
SOHC Posted November 4, 2020 Share Posted November 4, 2020 wile its running squeeze Jiff into the carb for extra piston to bore clearance 1 Quote Link to comment Share on other sites More sharing options...
tortron Posted November 4, 2020 Author Share Posted November 4, 2020 People didnt even do that back in the 30s, its some kind of weird meme just run it with no air filter Quote Link to comment Share on other sites More sharing options...
keltik Posted November 4, 2020 Share Posted November 4, 2020 14 minutes ago, SOHC said: wile its running squeeze Jiff into the carb for extra piston to bore clearance Once bought an engine from a wrecker and it ended up having oil consumption issues. So they got me to take it to their closest authorised 'mechanic' for inspection. He told me the best fix was to "put a little jiff down the carby to scuff up the rings a bit".....and this was on a 2008 Subaru. /thread derail 3 1 2 2 Quote Link to comment Share on other sites More sharing options...
Guypie Posted November 4, 2020 Share Posted November 4, 2020 1 hour ago, flyingbrick said: Ummn.. How you do the calc? Because I can't get an output that makes sense. 77mm stroke and 9500rpm? Edit, I get 1,462,893...... Edit. Because a 535 BMW diesel has a mean piston speed of 889,101mm/min.. @Guypie your numbers all seem too low? I just did stroke length x rpm but thats probably 50% what is should be cause I'm a dum dum and 1 rotation =up and down Also, sorry for spamming all over your loverly GN thread Tori, carry on as you were... Quote Link to comment Share on other sites More sharing options...
SOHC Posted November 4, 2020 Share Posted November 4, 2020 Didn’t you just buy this bike? Is it still under warranty? Quote Link to comment Share on other sites More sharing options...
SOHC Posted November 4, 2020 Share Posted November 4, 2020 Didn’t you just buy this bike? Is it still under warranty? Quote Link to comment Share on other sites More sharing options...
tortron Posted November 4, 2020 Author Share Posted November 4, 2020 nnay it was one year and its been over that 1 Quote Link to comment Share on other sites More sharing options...
tortron Posted November 4, 2020 Author Share Posted November 4, 2020 why would that matter? 1 Quote Link to comment Share on other sites More sharing options...
SOHC Posted November 4, 2020 Share Posted November 4, 2020 1 hour ago, tortron said: why would that matter? Take it back lol 1 Quote Link to comment Share on other sites More sharing options...
tortron Posted November 4, 2020 Author Share Posted November 4, 2020 warrenties dont really work like that, i had hoped to get a new one when they repaired the frame 1 Quote Link to comment Share on other sites More sharing options...
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