Have I broke my engine on break in?!
 

Hi guys just a slight concern, i finished building my Acme Condor buggy yesterday. Im new to nitro but have swatted up on breaking in the engines for the first time and know how important it is that this must be done properly. Despite this i had a slight issue. I started my engine, got it idling nicely (I had to blow gently through the back pressure pipe to keep fuel going into the carb for a bit) anyway was idling for 3/4 of a tank, the wheels were free to spin as it was off the ground. Then all of a sudden the plastic flywheel which the engine turns to move the drive shafts was stripped of 4 teeth, obviously this created a section for the flywheel on the engine to run freely. the engine revved its absolute nuttts off and cut out. I know this is bad during break in but i couldent do anything to stop it!!!! i was just wondering the chances that the engine is ok? i have no way of testing it until i install a new flywheel. Also how much grease should i put in my diffs? i put quite a bit in but they seem stiff. i stripped them and WD40'd them, put them back together and was told this was bad as this actually strips grease!? must i do it again and regrease?!?!? arrrrgh

The Flywheel that spins the drive shafts is called a "SPUR GEAR".. The engine reved like it did and died because it ran out of fuel.. Repair the Spur gear reset gear mesh, and continue break-in of engine.. It isn't good for an engine to rev free when new, but it is unlikely to kill it.. IN other words don't worry about it too much..

I would check all the bolts that hold your engine in and threadlock them, no way a gear should strip during run in unless the engine has moved.

Normally it shouldn't be necesaary to use thread lock on the engine screws. You can get a lot of problems next time you will have to get them out.

Yep
 

You should be fine. But It sounds like you may need to richen the needles on the engine a bit, even at full speed the engine should not spin too fast during break in.

ACME....isn't that the brand that Wile E Coyote uses?

Cheers
 

Cheers guys, my new hardened spur gear should have arrived when i get home so im gonna be straight on getting it installed and meshing the gears properly then trying to fire the engine again (in the dark) =S. i have a feeling my teeth were stripped due to the gears being to stiff or engine moving slightly. i have stripped my gears and regreased then since. im not sure why my engine wanted to spin on tickover tho =S. I checked i had a 1mm gap in the carb and the engine was factory set at this point.??

As someone stated you need to check your gear mesh or something moved therefore check your center diff's and motor mount screws. Read up on setting gear mesh very important.

Might be running your LSN too lean. Your wheels shouldn't be spinning when they are lifted off the ground. You want the engine to idle fast enough that it doesn't cut out, but not much higher than that. Read up on the engine break-in in the first post of this thread http://www.rctech.net/forum/offroad-...ng-engine.html. You are actually currently breaking in your engine with too narrow of an idle gap and running your LSN too lean. As for your spur gear stripping, you likely had the mesh set too loosely. This allows the metal pinion gear on your clutch bell to spin freely enough to chew up your plastic spur gear.

Another piece of advice: If ever your engine revs up out of control for some reason and you need to stop it (seen this happen when someone's receiver battery got disconnected mid-race), use either a thick rag, handle of a screwdriver, or an exhaust occluder (if it came with your kit) to plug the exhaust tip of your pipe. This will make the engine safely stall rather than it over-revving and toasting your engine.

Cheers guys, usefull advice. When running in my engine it was quite inconsistent, as is not rotating, rotating on and off . I had my radio switched off so any servos should not have moved, the LSN was left at factory settings. It was visually about 1mm gap between the needle and the sleeve it slides into which i thought was fine. I believe winding this in makes it run more lean or am i wrong? Also the carb had a 1mm gap also which was recomended? Any views?

Seriously, read the link I posted in my last post. It talks about setting your idle gap to 2.5mm, forcing you to run your LSN needle richer so the engine doesn't idle too fast, thus allowing you to saturate your engine with fuel and more importantly, the caster oil that's in the fuel. The 1mm idle gap is for when you have your engine broken in.

Cheers zao, still not installed my new spur gear it has not yet arrived, gutted. Hopefully on it tnyt tho so will continue to break my engine using the info given. Cheers