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Lesson learned the hard way.

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Old 01-18-2004, 09:49 PM
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sovietspyguy
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Default Lesson learned the hard way.

Well, I guess I was one of the ones not informed of the dangers of running an engine at WOT while holding it off the ground. I was driving a friend's car around the street and it seemed like something was binding up in the drivetrain, so I pick it up and give it a few blips to check. Then for some reason, I decide to hold down the throttle for a few seconds. All of a sudden, CLINK and all I hear is the wheels spinning. So, I start wondering what happened...I'm fairly positive I wasn't running it too lean. I try pulling the pullstarter, nothing...won't budge. I try turning the flywheel, still nothing. No movement whatsoever. I'm driving this to my girlfriend's house you see, and I didn't want to carry it the remaining mile. I prayed it was a flooded engine, although after trying the flywheel, I was in some serious doubt. Unfortunately I had decided I wouldn't need the glow plug wrench and left it at home to lighten my load.

So here I am stuck with a car that doesn't run, a mile from my house and an equal distance from my girlfriend's...

I get to her house and her dad finds me a wrench and pulls out the glow plug. Full of hope, I tug on the pullstarter. Nothing. It may as well have been full of epoxy. So then I start thinking that the one-way bearing has probably blown (though after taking apart the engine I realized that would've been impossible as the shaft it rests on doesn't even move). "Well that's easy to replace," I thought to myself. After getting home, I decide to pull the engine apart. I was a little wary as this was the first time I'd ever done this, but it (and the following rebuild) was a success. I get the pullstarter off, and the one way bearing.....works perfectly. Well damn. Now I knew it was serious. So, with my promises of replacing anything I broke still bouncing around in my head...I take off the backplate...

Holy #$@!, is all I could think to say.

Turns out that the engine either turned so many RPMs or got so hot that the conrod MELTED and was torn in half. The crankcase was FULL of metal shavings, as the pictures will attest to. I call my LHS and ask if they have the parts in stock...and they don't, so I have to wait a week (turns into 2) for the parts to be shipped. To add to that, although the sleeve looked in perfect condition, the only way to obtain a new piston was to purchase a set including it and the sleeve. Total cost? 70 dollars. All because I held it off the ground for 3 seconds. After getting the parts and reassembling everything I took it out and prayed...and amazingly, it started on the second pull. This is right after putting in a new sleeve and piston. Broke it in and it runs perfectly. After giving it back to my friend I talk to him an hour later, and he broke the front right swingarm (which I spent an hour sanding and cutting to make it fit onto the MT2, since I had to order an MT swingarm) doing jumps on the PAVEMENT.

ARGH. But now it's in his hands, so oh well.


So in case you ever feel yourself getting the urge to throttle your car off of the ground...pull 70 dollars out of your wallet and ask if it's really worth it!
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Old 01-18-2004, 09:51 PM
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Default RE: Lesson learned the hard way.

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Old 01-18-2004, 10:00 PM
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Default RE: Lesson learned the hard way.

Boy. Thanks for learning the lesson for me.
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Old 01-19-2004, 05:04 AM
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Default RE: Lesson learned the hard way.

for some reason with my first nitro car that i got 4 years ago i decided in sit it up on a couple of brick and let full throttle for a whole tank after a 4 month i got it and it still runs to this day without replacing any put of the engine other wise being extremly hot nothing else happed
musted of been a falty conrod
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Old 01-19-2004, 09:44 AM
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Default RE: Lesson learned the hard way.

I have seen a con rod snap... but never look melted like that...

and yeah... holding a car off the ground and giving it full throttle is a not so good idea. things go wrong when the RPMs go off the scale.
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Old 01-19-2004, 09:59 PM
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Default RE: Lesson learned the hard way.

Well, I think you did a great job fixing it up again! Thx for the info!
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Old 01-19-2004, 10:13 PM
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Default RE: Lesson learned the hard way.

I did the exact same thing saturday with my 1/8 buggie, I had just put a new carb in it and it wasnt running right , so i sat it on the starter box to adjust the needles. When I revved it wot for like 3 or 4 seconds it went bang and locked up , apon taking it apart the bottom of my piston was crushed and there was metal everywhere. I think its almost cheapre just to buy a new engine, parts are like 75 bucks but a whole new engine is 119
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Old 01-19-2004, 11:00 PM
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Default RE: Lesson learned the hard way.

yep... over revved your engine.. damn that's a new hpi t-15 engine too!..
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Old 01-19-2004, 11:18 PM
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Default RE: Lesson learned the hard way.

that is exactly what i did to my TRX .15 engine, when i switched to .21

the piston blew into pices [>:]
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Old 01-20-2004, 12:27 AM
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Default RE: Lesson learned the hard way.

Thanks for the graphic demonstration for the people who dont believe

Too bad it cost you so much!

Live n learn eh?
Take it easy
ram
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Old 01-20-2004, 09:36 AM
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Default RE: Lesson learned the hard way.

I recently did something similar to my Evader ST. I made a [link=http://www.rcuniverse.com/forum/Engine_Rebuild%25/m_1439983/tm.htm]post[/link] over on the Stadium Truck board.
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Old 01-20-2004, 10:19 AM
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Default RE: Lesson learned the hard way.

I wouldn't kick youself to hard, that looks like more than a few seconds worth of engine wear to me. Maybe holding it off the ground for a few seconds was the finial nail in it's coffin, but I dont think it was the only cause. It looks to me that cod rod was loose for some time before it finially broke.

How much time did you have on that engine? For that Con Rod to be melted and have all those shavings like that it would have to have been streaching for quit a while, not just a few seconds.

I've broken con rods before from over reving. The have allways just "snapped" not melted down. One more funny thing, all the rods I've ever boken were broke down at the crank, not the piston side. That piston was getting HOT! baby.
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