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Tortrons GN


tortron

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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?

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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

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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

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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

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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...

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