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Old Sep 20, 2012, 03:13 AM
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So this is what happened after running 5 tanks in a row for the break-in

So I got a little carried away when I was breaking in my new nitro HPI RS4 Drift. The manual said 1 tank idle and 2 more tanks running a laps or something like that. Anyways I just got a little carried away and ran more tanks after that without much of a break. Then this started to happen

-I notice one wheel starts acting funny...
-Then suddenly the car started to full throttle on it's own non-stop
-Pull string becomes IMPOSSIBLE to pull

Well I took apart the front wheels to find that there is actually a bearing missing from that side... I don't think it could come out while driving... I also think this has nothing to do with running the car a lot, but is there any explanation for this? I'm pretty sure it's a missing bearing or else they totally didn't put one in the left side.

Then I took out the glow plug to and try to unflood the engine, but it still wouldn't budge.

I took apart the motor, removed the heatsink and the pullstring. The pullstring mechanism was totally fine, and then I see the piston and bits of metal inside the actual engine...

Looks like it was keeping the piston from moving up and down. Then I took out the piston itself and found this:

http://i48.tinypic.com/2lctt0j.png

Yup. I think running 5 tanks in a row is what cause this. Lesson learned. Time to pick up a new engine.

I'd like to know more about that wheel that is wobbly due to the missing bearing if anyone has any ideas on that...

Questions? Comments? I'd love to hear them!

Thanks!
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Old Sep 20, 2012, 10:00 AM
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5 tanks in a row won't do that. even if you ran a bit hard with out heat cycles it should only loose compression and wear out too soon, not explode.
call warranty support and explain your issue.
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Old Sep 20, 2012, 10:37 AM
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Where exactly is the bearing missing on the wheel? The bearings aren't in the wheels on this car, they're in the hubs.
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Old Sep 20, 2012, 04:51 PM
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That definetly should not have happend after five tanks of fuel,i would ring customer service and state what happend,maybe you might even get a replacement engine!
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Old Sep 21, 2012, 01:00 AM
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Originally Posted by DG40 View Post
5 tanks in a row won't do that. even if you ran a bit hard with out heat cycles it should only loose compression and wear out too soon, not explode.
call warranty support and explain your issue.
You would consider the piston basically eating itself inside the motor exploding? I learned what happened when looking inside the motor more;

The pieces of the thing that holds the piston melted obviously, but those pieces blocked the throttle servo from going back to break/idle so it stayed open and just kept at full throttle until I somehow stopped it. That was pretty much the last straw for the engine.

I've posted this in other places and people have said that 5 tanks in a row in a brand new engine is understandable... I'm not the expert though! I don't think I want to tell HPI that I pretty much went on a 5 tank non-stop binge for the break-in.
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Old Sep 21, 2012, 01:02 AM
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That definetly should not have happend after five tanks of fuel,i would ring customer service and state what happend,maybe you might even get a replacement engine!
I'm hoping they can just put everything back up for me as well. Taking that thing apart was a nightmare and I tried putting an OS engine in that I borrowed from a friend, and trying to put that in was a horrible experience and didn't even work.

I just want a working nitro! I hope they can do everything without charging too much...
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Old Sep 21, 2012, 01:03 AM
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Where exactly is the bearing missing on the wheel? The bearings aren't in the wheels on this car, they're in the hubs.
Yep. They are in the hubs, that's what I meant. I took a look inside, and honest to god one bearing WAS missing. HPI said they will send over the missing bearing.
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Old Sep 21, 2012, 07:32 PM
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That's a tough one , it could happen , especially running too rich. It would diesel or misfire if run too hot and explode the motor.

The way to break in a motor is to run a half tank , shut it down , piston at the bottom. Let it cool. Then start the rest of the tank while leaning it out. Do it like this and you won't have another problem . Never lean it out more than the recommended turns on the motor.

The real best way is to take the motor apart first , remove all the metal filings , then wash it nitro fuel . You will be amazed at all the bits you will find in there. Get some associate green slime and coat all the rubber gaskets with it . This stuff will seal any air leaks and will lube the seals. Set all the needles as per running the engine then give them a half more turn open for breakin.
Then you should be good to go.
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Old Sep 21, 2012, 07:47 PM
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Nitro tuning

Nitro RC Engine Tuning 2 (useing a HPI- Savage 25) (3 min 5 sec)



Nitro RC Engine Tuning 1 (useing a HPI-Racing Savage 25) (4 min 47 sec)
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Old Sep 30, 2012, 10:08 PM
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Originally Posted by jombo View Post
That's a tough one , it could happen , especially running too rich. It would diesel or misfire if run too hot and explode the motor.

The way to break in a motor is to run a half tank , shut it down , piston at the bottom. Let it cool. Then start the rest of the tank while leaning it out. Do it like this and you won't have another problem . Never lean it out more than the recommended turns on the motor.

The real best way is to take the motor apart first , remove all the metal filings , then wash it nitro fuel . You will be amazed at all the bits you will find in there. Get some associate green slime and coat all the rubber gaskets with it . This stuff will seal any air leaks and will lube the seals. Set all the needles as per running the engine then give them a half more turn open for breakin.
Then you should be good to go.
Great pro tips there! Thanks a lot!
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Old Oct 01, 2012, 10:32 AM
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That's a tough one , it could happen , especially running too rich. It would diesel or misfire if run too hot and explode the motor
Just a little correction... glow/nitro engines run just like diesels do, there's no timing of when they fire (like a spark engine has), they just compress under heat (glow plug) until it explodes, so I'm not sure what you mean by "it would diesel or misfire"?

I don't see how running too rich would break the piston like this, in a 2 stroke engine more fuel = more oil, so it's not like a full scale engine (not mixed fuel) where running too rich will wash the oil off the cylinder walls and lead to damage. I would bet on running too lean causing damage like that long before running too rich.
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Old Oct 04, 2012, 06:52 PM
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Just a little correction... glow/nitro engines run just like diesels do, there's no timing of when they fire (like a spark engine has), they just compress under heat (glow plug) until it explodes, so I'm not sure what you mean by "it would diesel or misfire"?

I don't see how running too rich would break the piston like this, in a 2 stroke engine more fuel = more oil, so it's not like a full scale engine (not mixed fuel) where running too rich will wash the oil off the cylinder walls and lead to damage. I would bet on running too lean causing damage like that long before running too rich.
nope i got it right .
if run too rich , it will hydraulic the piston and put too much pressure on the pin and shaft. if run to lean it will predetonate the fuel early and blow the piston to kingdom come . it needs to be just right
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Old Oct 04, 2012, 07:12 PM
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^^ You said it would diesel, which is totally different than hydrolocking.

I've never seen a glow engine run so rich that it hydrolocks, usually they will stall long before there's that much fuel in the cylinder. The only time I've seen damage from too much fuel is if it's flooded during start up.
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Old Oct 04, 2012, 09:26 PM
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^^ You said it would diesel, which is totally different than hydrolocking.

I've never seen a glow engine run so rich that it hydrolocks, usually they will stall long before there's that much fuel in the cylinder. The only time I've seen damage from too much fuel is if it's flooded during start up.
i have.
yes , when i say deiseling it means it sounds like a deisel engine , hence running too rich . what happens is it will spirt out oil and unburnt fuel , then it will hydro lock and blow its self apart.
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Old Oct 06, 2012, 05:31 AM
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i have.
yes , when i say deiseling it means it sounds like a deisel engine , hence running too rich . what happens is it will spirt out oil and unburnt fuel , then it will hydro lock and blow its self apart.
Nope, it will not.... Combustible fuel/air ratio will be typically something like 1:10 by weight, which by volume (fuel in liquid state) would be very roughly in the area of 1:100.... that is NOWHERE NEAR the amount of liquid needed to cause hydraulic lock. Not even if you take down that figure to let's say, 1:50 due the oil content and an extreme rich mixture.

You will also never get the engine running rich enough to have it spit out fuel in liquid form. The fuel will have evaporated before it exits the exhaust port.
The exiting gasses will also blow out the excess oil that might have collected in the combustion space every cycle again.

Although it is true, that running too rich will cause a higher compression ratio due to more oil present in the combustion space, even that, is nowhere near enough to cause hydraulic lock.

What caused the damage to your engine? No idea, but not hydrolock.

Brgds, Bert
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