36cc baja 5B oil swap

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Ides28 said:
i would go through everything. tank breather ok? servos moving normally, adjusted properly? air leak somewhere? air leak on lines? air filter clogged? gaskets ok? the plugs ngk not no name brand? motor suck in dust from anywhere? (this will have eaten your piston and cylinder) try running with the choke on? nice consistent white/blue spark? head clogged with grass and overheated and died? both carbs don't have leaks on the throttle shaft? the hpi baja motor manual is a must have. it's not the oil that did it, that's good oil, and smokeless still smokes in my expierence. if you do everything you can think of (and you know what you're talking about if you have snap on tools and racing engines) and no improvement i'd start thinking about a new piston and cylinder. i've had several top ends go on me for whatever reason. 36cc, is it a rovan? welcome to the world of gas engines, is why i run electric now. gas is cooler, but has extra 10 systems that can go wrong and are hard to diagnose lol.
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It is rovan 36. It did suck in some dust/dirt. I ordered a new complete 2 ring top end and a single ring piston and ring....if it the correct size I will have a kit small enough to do comp test on these motors tonight....we have a few of them and my oldest son is experimenting with building his own with porting and polishing and so on..... his first build the skirt cracked on the Piston he's currently running his second building it's running very strong
 
oh wow so you really do know what you're talking about then. i had that same motor i swear. i'm pretty sure all it took to ruin a perfectly good motor i had one time was to have a slight gap on the air filter. one half hour run on a baseball field and i needed a new top end. you did get a new cylinder too right? you actually know better than i do but i had a motor that i went through everything, then did a compression test and it was never lower than 85 psi but the motor was still gone. they're weird (or maybe it was my cheap compression tester). do you know about oneil brothers racing? they sell a long block kit that they say puts out 8hp for around $300
 
Ides28 said:
oh wow so you really do know what you're talking about then. i had that same motor i swear. i'm pretty sure all it took to ruin a perfectly good motor i had one time was to have a slight gap on the air filter. one half hour run on a baseball field and i needed a new top end. you did get a new cylinder too right? you actually know better than i do but i had a motor that i went through everything, then did a compression test and it was never lower than 85 psi but the motor was still gone. they're weird (or maybe it was my cheap compression tester). do you know about oneil brothers racing? they sell a long block kit that they say puts out 8hp for around $300
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OBR YES. My son did his first build with one of there blocks.....and yes I ordered a complete top and in addition to a separate piston and ring and wrist pin. And yes I've been around Motors a while I've been building race engines for probably 15 years and have very good luck so far building them so yeah it worked out good so now I want to get Dibble into these two strokes
 
50 lbs of compression......so what should I see on 38cc? Also have lone 29 30.5 and 32 cc anyone tell me what I should see across the spectrum.
 
Pull the head off and found this. Also found the ring gap to be around .125. Has anyone file fit rings in these. I like to have mine around .012 give or take depend on cylinder finish. Based on what I see guess it is time to start building. Sitting here typing and decided to take the ring off the piston.....yup found the issue........one end of the ring is gone. That explains the ring gap.....and low compression
 

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Seandonato73 said:
They aren't file fit rings like a gas car. You can check, but there's little to do about it that doesn't involve loads of tedious filing.
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I guess maybe I am thinking about it to much....it's not like a you have 5g's in parts......just realized the new piston kit as it is called does NOT come with a ring. Your kidding. Smh
 
Seandonato73 said:
Yeah... there's a surprising amount of nothing that comes with a piston kit....
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Got it all back together with the upper complete kit I bought as well. Only issue now is gotta hold WOT and pull for 5 min to get it to start and won't idle. 1 3/8 low and 1 7/8 high. Went both ways and not much change.....I know its loading up just gotta find out why.
 
Rcnut24 said:
I'll give that a try.....thanks
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that didnt work. fired once with choke and would't fire after that. how critical is the white inslator between the carb and intake. also lining up the holes for the pulse from crank case. can they be blocked off?
 
That insulator is extremely critical, I throw the composite ones out as they all warp due to the heat. I use the obr aluminum/nylon ones so I don't run into air leak issues. Take it off and put it on a known true flat surface and check to see if it's warped, if it is throw it out and get a new one or lap it to get it flat again. These are maintenance items that are rarely mentioned and don't reuse intake gaskets but im sure you know that.
 
Rep732 said:
That insulator is extremely critical, I throw the composite ones out as they all warp due to the heat. I use the obr aluminum/nylon ones so I don't run into air leak issues. Take it off and put it on a known true flat surface and check to see if it's warped, if it is throw it out and get a new one or lap it to get it flat again. These are maintenance items that are rarely mentioned and don't reuse intake gaskets but im sure you know that.
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I want to be sure we are talking about the same thing......Composite intake.....replaced with aluminum one......block,gasket,aluminum intake,gasket,white plastic spacer,gasket,carb....I measured the white spacer.....bolt hole ends..... .018 the center hole .017
 
@Rcnut24 uh yea, the thing that sits on the cylinder that the carb bolts on to. Your definitely over thinking all of this, take it off and put it on a flat surface and shine a light at it. If it's warped chuck it.
 
just pulled on it for 25 minutes and it fired twice.......
Rep732 said:
@Rcnut24 uh yea, the thing that sits on the cylinder that the carb bolts on to. Your definitely over thinking all of this, take it off and put it on a flat surface and shine a light at it. If it's warped chuck it.
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the aluminum intake???? that shouldn't be warped...The one that came on it was in the trash before the gas hit the tank
This is what is have.
 

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