Engine air leak...

Discussion in 'RC Onroad Forum' started by vette_7t9, Jan 3, 2005.

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  1. vette_7t9

    vette_7t9 Member

    Ok my OS 15 engine has an air leak!! Me and my dad investigated it, took apart the entire engine. We didn't think any of the parts appeared to be so worn out they can cause an air leak, since the engine is fairly new too. We did however find that there was a leak from the bearing thats near the flywheel, if you know what i mean. The bearing that holds the crankshaft on the end of the engine thats connected to the fly wheel. So we put some grease on it to stop the leak, and the engine started fine. Halfway through testing time, the engine seemed to run erraticly so i put my finger on the exhaust to stop it. BUT the engine just kept running!! So i pulled off the gas line and it died. My question is: is it the bearing that needs to be replaced? Or is there something else leaking?? The engine has gone out of control before, screaming like #@$% and i had to run over to it and stop it. Is it because i used to have a 1 speed tranny and i keep gunning the engine? I need help!
  2. dj6666969

    dj6666969 Active Member

    hmm from the sounds of it if that bearing is letting air by then it might have to be replaced.
  3. rockn82

    rockn82 Marx Brother

    Sounds like you need a new Exhaust Coupler. Or an exhaust gasket. If your exhaust is leaking then your engine will not get the correct amount of fuel. Causing the engine to idle eradically. Especially if you put your finger over the exhaust and the engine did not stop then you have a leak somewhere in there that is letting the exhaust escape from other places.
    Check that and you will find your problem i can just about guarentee it.
  4. vette_7t9

    vette_7t9 Member

    Cool. Ok i asked my auto teacher and he said it might be a problem with the crankshaft bearing seal. The bearing that seals the crankshaft to the engine block and can be seen on the outside with flywheel removed. I cant figure out a way to replace it......maybe i should take it to my local hobby shop to have it replaced.
  5. dj6666969

    dj6666969 Active Member

    if it is the problem they are presure fit into the block... in a old rc caraction mag they replaced them and they had to put it in a oven for a few mins so it would heat up and then you can tap it out of there, that is the only way I nknow of maybe there is a bearing puller or soemthing?
  6. rockn82

    rockn82 Marx Brother

    Trust me fix the leak in your exhaust and you will be fine... If it is the bearing (which I more than highly doubt) then your better off just getting a new engine. Especially if that one wore that quick, then there is something wrong with the engine. Probably out of balance.
  7. rockn82

    rockn82 Marx Brother

    By the way it is impossible to completely seal the rear bearing on any RC engine. There is a tolerance of +/-.001" and that leaves air to get in. So sealing the bearing with grease will, yes, make a difference, but not one that matters.
  8. vette_7t9

    vette_7t9 Member

    So there might be something wrong with my exhaust gasket and coupler??
  9. vette_7t9

    vette_7t9 Member

    but im also pretty sure its the bearings fault cuz it wouldnt even draw fuel up, but wen i greased it i could start it......im confused now.
  10. rockn82

    rockn82 Marx Brother

    That front bearing will always leak. HPI and some other companies even make an oil catch that fits around the front of the engine so that any oil doesn't get on your brakes (for racing). Here is a link:
    http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXN379&P=7

    The engine doesnt draw fuel the exhaust gas causes pressure in the tank and that pressure pushes fuel to the engine.
    Take your coupler off and check it for leaks. Also check the gasket from the engine to the header and finally check to make sure you have no leaks in any of the fuel lines. Ususally fuel lines will break right at the connection so you have to look close and be sure.
  11. vette_7t9

    vette_7t9 Member

    Oh ok. I'll see what i can do. Maybe this weeekend i can find some time. Is anyone living in the mississauga ontario area and can gimme a hand with this? I am a semi beginner with nitro engines. In fact, a few weeks ago was the first time i took apart a nitro engine, pistons, sleeves, crankshaft and all besides bearings.
  12. vette_7t9

    vette_7t9 Member

    Ok.............something strange i found. when i put my thumb over the carb(my thumb is clean) and pull the pull start.....the engine draws in fuel like magic. I just cant draw fuel in when finger on exhaust. I saw this site taht recommended to use silicone sealant that is O2 sensor safe to seal the engine and any leaking areas, much like how a mechanic will use silicone to seal leaks in a real engine. Should i try it??
  13. rockn82

    rockn82 Marx Brother

    When you put your finger over the carb it acts like a choke, so yea it will suck fuel because it will not be able to suck air. Sealing the engine with silicone will not help you. Try it if you want but your only gonna end up with a mess and make it hard to work on your engine when you do have to pull it apart. Get a new exhaust coupler. Get new zip ties for sealing it. That will solve your problem. Just do it. It is only a %5.00 fix.
  14. vette_7t9

    vette_7t9 Member

    oh my goodness....i should thank HPI so much. Yes i tried sealing my engine. Yes i tried the new exhaust coupler. Yes i even made a new gasket for the exhaust header. But none of that seemed to cure my engine. I began observing the engine, and noticed that there was a hissing air leak noise whenever the engine is turned to a specific position. This baffled me for ages, i didnt know whats wrong. BUT TODAY I'VE FIGURED IT OUT. I feel like a million bucks!!! what had me baffling i shoulda seen the first day i began fixing my engine. I got bored and started reading HPI Racing websites engine horror stories. I saw the pics of horribly damaged internals, and decided to compare my own with those, just for kicks. WELL THERE IT WAS. my crankshaft had extreme scratches and gouges. This indicates there was dirt getting inside the engine. And yea...i hav to admit, i ran the engine without the filter a few times out of convenience like during break in =O which is extremely bad! i learned a lesson the hard way. If i performed a very thorough parts inspection in the beginning, i wouldn't have needed to buy sealant, gasket maker, and thread lock hehehe. Ah well it feels good to kno whats wrong, so atleast now sumtins out of the way.
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