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So here is the deal I ran the rex low on oil over Tday and now I think I have a rod knock. I am going to be tearing into it and have a few questions. First lets me just say that I ride in a variety of terrain and altitude. Everywhere from Glamis to Northern Arizona and hopefully a week long Paiute trail trip this summer. Reliability is my major concern and I also don't want to have to tune it every time I ride. So these are my 3 options. Option 1 rebuild it back stock with maybe a cam mod. Option 2 standard bore kit with cams (exhaust will have to come later). Option 3 is go all out with the 840 kit again exhaust will be later. I don't want to debate the power difference between the 3 options I understand all of that. All I am curious about is tuning the 840's I have been around don't seem to do altitude changes very well what about a standard bore does it have the same problems. Ok lets hear it and thanks for all of your help. :00000004[1]:
 

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me to i bet my crank and rods from having low oil thought it was not that bad but but brought it to my guy vforce john putting a st bor in it
 

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:confused: I hate to hear you let it run low on oil. That will take one down FAST. All I can recomend is CHECK your oil OFTEN. OK as far as engine kits go , since power isnt the factor (840 wins). Since you have a 08 and change altitudes alot I would go with a standard bore. BUt , you will need to jet it as much as the 840. There just not as finackey as the 840 in dialing them in. I would invest in two air/fuel gauges and permantely mount them in your dash. I know were you can get them for $150 each & reliable. You can just mount one & get a extra Bosh O2 sensor$35 and manually switch the plug to the gauge. That way you can check front and rear cylinder. But I would leave it hooked to the front during riding, because that cylinder seems to show a lean condition first. All this sounds complicated , but its not. It takes about 15 min to jet one ( if your changing major alttitudes) . Also if you do it like I say it will only cost you about $200 and you should only have to do it once for each place you ride. Write down what jets , screw turns , needle position for each ride location. Then when you know your going prejet it to what worked last time and just watch your air/fuel gauge. I bet you will never have any issues. As far as that goes you can do that with a 840, but it cost more to build a 840. So if money is a issue do the standard , get a air/fuel gauge set up, and a YFZ oil brake so it doesnt run low on oil;) Oh, and enjoy the power:D
 

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I feel your pain, I'm currently putting my engine back together after running it low on oil. It wiped out the crank and both rods. Our stories sound really similar because I figured since its already apart, Its going back together with the 840 kit. Almost there, I can't wait.
 

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I feel your pain, I'm currently putting my engine back together after running it low on oil. It wiped out the crank and both rods. Our stories sound really similar because I figured since its already apart, Its going back together with the 840 kit. Almost there, I can't wait.
Hey if you don't mind how much do you have in parts minus the 840 kit? Trying to figure out my best route and not quite sure how to go about it thanks.
 

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I'm my second engine! First one went down because I sunk er and the second........you guessed it, low on oil. I run the fst 840 with stage 3 cams in my four seater. I just went to colorado this summer and rode the 840 at 14, 6?? feet. I made it just fine. Yes very low on power and rode in low the whole time but so did my friends who were on fuel injected riggs. Razors and Brute forces. If you are rebuilding do yourself a favor and go with the fst 840. You will not regret it.
 
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