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Enduro Engine - 2 stroke Cylinder, Piston, Tranny, Bearings, Clutch, Pipes & Silencers, etc.


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  #11  
Old 12-17-2014, 04:02 PM
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hamilton hamilton is offline
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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.


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  #12  
Old 12-17-2014, 04:20 PM
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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!
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  #13  
Old 12-17-2014, 09:50 PM
Moto7man Moto7man is offline
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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.
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Last edited by Moto7man; 12-17-2014 at 09:51 PM. Reason: Grammer
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  #14  
Old 12-18-2014, 07:19 PM
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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!

Quote:
Originally Posted by Moto7man View Post
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...
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  #15  
Old 12-18-2014, 08:50 PM
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That'll do it.
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  #16  
Old 12-19-2014, 02:39 AM
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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.
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  #17  
Old 12-19-2014, 09:18 AM
Moto7man Moto7man is offline
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Quote:
Originally Posted by mtnmanseth View Post
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.
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"If you stop eating donuts you will live 3 years longer. It's just 3 more years that you want a donut."
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"I think best when I have a wrench in my hands." Soichiro Honda

"Dreams are messages from the deep."
-Unknown Sardaukar
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