tony5oh

Hi,i am new here but have some questions i need knowledgable answers too.first off my experience with 2 stroke glow style nitro's is limited,with that said my experience with 4 stroke gas engines (american v-8's) is quite vast.i'm a gear head and find rc stuff quite interesting.i recently purchased a losi ten t that i was happy with @ first.i purchased an os 25xz engine and os exhaust and installed it in my truggy,i also purchased an ofna starter box to start it with,i had to change the polarity on the motor to get thecorrect rotation.i have attached some pics of the install.now for my dillema,the engine starts and runs very well but i notice times when @ idle the engine burbles and the truck actually starts to move in reverse.any amount of throttle and the engine dies.i phoned the tech guy @ os and he said it is impossible(although he did admit only imppossible because he had never seen it him self).i could understand if the starter box was rotating in the wrong direction,it's not.when on the box looking @ the front of the engine it is rotating counterclockwise.i also asked about glow plug heat range he told me that would have no effect on the rotation of the engine,which i already knew.what i was trying to find out is if this plug is holding too much heat and is firing the mixture before it is totally compressed (pre-ignition?) and forcing the piston,rod,crank back down in the opposite direction.can plug heat range be juggled around to have the same affect as ignition timing on a 4 stroke?.the gentle man @os engines answers to my questions i felt were very narrow minded as his responses were it's the truck not the engine,he claimed it was probably a stripped wheel hub(s) ***?,the tranny ,it's a single speed forward only.when this engine runs right it rocks,but occassionaly it will sputter and run in reverse rotation ( @ idle only,and only when its warm above 210).sorry for the long post.
summary to my questions
-how does glow plug heat range affect the performance of the engine?
- couldincorrect carb adjustment do this?
-has anyone else experienced this?
thanks

Argess

Running in reverse isn't that common, but it's happened to me several times. Usually when it's cold out and the engine fires, starts to stall and then picks up as the piston bonces back off the compression stroke. Something is causing the misfire....bad fuel possibly, bad glowplug maybe. Try turning your idle screw in a bit to raise the idle. Maybe that way it will have enough momentum to keep running the right way until you can troubelshoot it some more.

downunder

With plane engines it's fairly common for them to start in reverse when hand starting. This is caused by overpriming and the mixture fires too soon which kicks the piston down before it's reached TDC. This kickback is more powerful than a hand start so it continues to fire in the wrong direction. Sometimes it can be made to fire the correct way by quickly opening the throttle for a moment. The extra flood of air leans the mixture enough to restore the correct ignition point.

I suspect with your engine that the idle mix may be too rich and when an engine is idling it begins to get a build up of fuel in the crankcase because, with the throttle closed, there's very little air coming through to cause turbulence which normally sweeps up any small amounts of fuel. This is the reason why an engine can bog down if the idle mix is too rich because opening the throttle gives the extra turbulence which sweeps up the pool of fuel making the engine far too rich for an instant. In your case it may be so rich it's overcoming the flywheel inertia causing a kickback, especially if you have the idle set for very slow revs. To check idle mixture, let the engine idle for about 20 seconds or so then pinch the fuel line to stop any more fuel getting into the engine. If it's too rich then the engine will be running on the buildup in the crankcase and as that slowly gets used up the mix will begin to lean out and revs will rise (sometimes considerably) before dying off quite quickly. If OTOH the revs start to drop as soon as you pinch the line then the idle is too lean and I'll have to try to think of some other reason it's running in reverse .

tony5oh

thanks for the tips.argess i have noticed that if i pick the idle up a bit it's okay.i may have to engage the clutch @ a higher rpm.when it starts on the box i have to turn the idle up slightly and the clutch wants to engage (tires are not loaded against anything),as soon as this happens the momentary shock seems to make it want to run in reverse.downunder i took your advice as well,seemed to be a little better when i leaned it out some but still having same issue as i stated to agress.has the same clutch as the 3.4 engine,and i tried a cooler glow plug didn't help made it worse

Argess

The odd thing about a car engine running in reverse, is that for pull starts, or in my case, a roto-start, the starting shaft will be rotated in reverse by the crank and the OWB should lock up and work against the roto-start or pull start. Although I'm not sure, I would assume the OWB would have to be slipping for a car engine to start in reverse. This could be why it's not so common.

With a starter box, the scenario is more like an airplane starter and I can see it being a more frequent occurence, although not as common as flipping a propellor by hand. DownUnder's description makes more sense that my misfire theory, but all in all, these engines are basically symetrical in design and can run in either direction. Fuel swirling from the crank would be one difference from one rotation to the other, but not enough to keep it from running in reverse.

In my Savage, the vehicle won't move in reverse due to a OWB in the tranny, although there's a tiny bit of backwards movement. The sure sign is it won't go forward. Shut it down and restart and everything is fine.

Edit: Oh....I see you responded while I was typing the above. Wish I could offer more insight, but I can't. I'd suggest a heavier flywheel, but I take it everyting used to work OK, so it appears tuning as per DownUnder is your best bet. Oh.......you might try some new fuel. Sometimes old fuel will allow an engine to run at idle, but die when you apply the throttle. I suppose if you were to let off the throttle at the same time it was starting to die, it could flip back and run in reverse.

Shabbernigdo

Ihad this problem with my GXR28 when i was trying to break it in. Once i leaned it out some it hasent done it since.

downunder

That's true except for the inlet timing in the crankshaft (which I bet you knew but forgot about ). I don't think it applies to any car engines but for plane engines that have a removeable crankshaft housing, the housing can be rotated 90 degrees to the right, looking from the front of the engine, and this reverses the intake timing allowing the engine to run in reverse as well as it did the normal way. Actually if the crank timing is open for 180 degrees then timing is identical when reversed but even a fair difference in the open amount doesn't seem to make any really noticeable difference.

Piston ported and reed valve engines can run equally well in either direction but they're hardly high performance .

Argess

Yes, I forgot....I only thought of the flaring at the crank fuel outlet....[sm=red_smile.gif]

I didn't know about the removeable crank housing in (some) airplane engines though. Interesting info.

tony5oh

THANKS FOR THE HELP GUYS.CLUTCH SPRING WAS BROKE.FIXED THIS,WAS ABLE TO TURN THE IDLE UP SOME,LEANED IT OUT A LITTLE AND EVERYTHING APPEARS TO BE WELL .SO FAR NO MORE RUNNING IN REVERSE.

Argess

Too funny....today my Savage started in reverse again. Hasn't happened for a long time. It was cold, so I probably flooded it a tiny bit (so too rich like DownUnder and Shabbernigdo say) and OWB was slipping a bit.

kyledean

my t-maxx bb runs in reverse and it has the 4908 tranny and that makes its foward only, and i took it out lastnight and it ran in reverse i didnt know what to think really never had it happen to me is it possible that the motor could be broke and runing the wrong way any help guys?

downunder

Your engine will be fine because there's nothing in an engine that can break and make it run in reverse.

Snook Man

kyledean

the diffs cant go in uside down but the could go backwards would that hurt to have the front on the back or outher way around?

Snook Man

The diffs can absolutely be installed upside down (A very common mistake on a TMaxx). It does not matter if they are installed Front or Rear, just that they are oriented correctly when installed.

buttdud1122

wouldnt that mean to add a shim? i thought if it was misfiring like that, a shim will do the trick...