Need some help with a TRX 2.5

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Maximum_Quake_Pro.com

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I have rebuilt to new, modded, ran in my raced stadium trucks, over 30 2.5 engines personally, and being conservative on that figure too.

I once had a pallet of just over a hundred used most blown trx2.5s traded in for new ones thru Traxxas' power up program

2.5s with any run time or stored with fuel for a year or many years in it's lifetime then ran again without any service, ALL LEAK Badly.

in my time over two summers daily inside and out and trying stuff for more performance or to hold better tune thru the rpm range and running so many...

using a starting shaft and backplate for it. it will always leak here in time even if you reseal backplate the bushing start shaft sits on will leak still.

Here's what I eventually ended up with as the best things to do for all out power, holding a tad rich tune even at max rpm, lower run temps, long wear life before losing much compression.

bump start conversion, shaved crank pin, polished crank, ceramic crank and front bearing, losi new 3.4 carb, only one of the factory head shim/gasket some call them.

30percent nitro 16 to 18 percent oil, I only recommend torco after testing many other fuels if not a pure bred race application.

And sealing everywhere possible with gray block sealant like Honda and Yamaha use to seal around case halves.


if you are a occasional backyard runner and bump start isn't an option, the above is not for you.
 

littleblazer

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Let me preface this with it took all of my being not to chuck this thing clear across the effing yard.

Anyway, I pulled apart the carb, cleaned the passages, and put on the o-ring conditioner. Topped off the tank and ran it on the base settings. Ran mint. As the tank got to half I fattened it up slightly as it started leaning out. Performance came right back to excellent. It started doing the same thing again at a quarter tank so I richened it up a little more, runs perfect again... and then it ate 3 glow plugs in a matter of 2 minutes... Nailed it, went 400 feet one way turned around and started coming back, died. Dead plug. Replaced, same thing again. It looks like with the tank that low it is getting air in the line to the carb and going lean under braking? Then I guess turning around and that momentary lean mixture is killing the plug? The level in the tank is still above the seam... is this actually what is happening right now?

Also, is it possible the resonator pressure tube isn't working adequately? I don't think the mixture difference between what is perfect on a full tank and half a tank should be a full turn on the HSN.... But you fill it back up and it's pig rich again.
 

Maximum_Quake_Pro.com

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Let me preface this with it took all of my being not to chuck this thing clear across the effing yard.

Anyway, I pulled apart the carb, cleaned the passages, and put on the o-ring conditioner. Topped off the tank and ran it on the base settings. Ran mint. As the tank got to half I fattened it up slightly as it started leaning out. Performance came right back to excellent. It started doing the same thing again at a quarter tank so I richened it up a little more, runs perfect again... and then it ate 3 glow plugs in a matter of 2 minutes... Nailed it, went 400 feet one way turned around and started coming back, died. Dead plug. Replaced, same thing again. It looks like with the tank that low it is getting air in the line to the carb and going lean under braking? Then I guess turning around and that momentary lean mixture is killing the plug? The level in the tank is still above the seam... is this actually what is happening right now?

Also, is it possible the resonator pressure tube isn't working adequately? I don't think the mixture difference between what is perfect on a full tank and half a tank should be a full turn on the HSN.... But you fill it back up and it's pig rich again.
Watch closely in your fuel lines for bubbles or airgaps where delivering to carb inlet
 

littleblazer

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Soaked it in degreaser (the pipe) cleaned as much as I could with brushes then blew air through it. Readjusted all the fueling until it seemed good, light smoke at idle, nice trail running it flat out. I was ecstatic. It went through a whole freaking tank without touching the starter other than when it flipped over about 600 feet away from me. topped it off, made two passes... and burned out a plug on each. I really can't handle this freaking thing anymore. And the plugs aren't like fouled... they're melted bad. like WTF. It's going back on the shelf and I'm just sticking with the nitro sport at this point because a plug a tank is expensive. I am really at a loss here. Like if I go any richer it's a dog. I quick pressure tested it by plugging the pipe and spraying it down with soapy water and got nothing. I sprayed it with starter fluid while idling and it didn't react like it had a vacuum leak. What could I possibly be missing right now.
 

cbaker65

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Soaked it in degreaser (the pipe) cleaned as much as I could with brushes then blew air through it. Readjusted all the fueling until it seemed good, light smoke at idle, nice trail running it flat out. I was ecstatic. It went through a whole freaking tank without touching the starter other than when it flipped over about 600 feet away from me. topped it off, made two passes... and burned out a plug on each. I really can't handle this freaking thing anymore. And the plugs aren't like fouled... they're melted bad. like WTF. It's going back on the shelf and I'm just sticking with the nitro sport at this point because a plug a tank is expensive. I am really at a loss here. Like if I go any richer it's a dog. I quick pressure tested it by plugging the pipe and spraying it down with soapy water and got nothing. I sprayed it with starter fluid while idling and it didn't react like it had a vacuum leak. What could I possibly be missing right now.

What kind of plugs are you using?..🤔
 

Losi215

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Let me preface this with it took all of my being not to chuck this thing clear across the effing yard.

Anyway, I pulled apart the carb, cleaned the passages, and put on the o-ring conditioner. Topped off the tank and ran it on the base settings. Ran mint. As the tank got to half I fattened it up slightly as it started leaning out. Performance came right back to excellent. It started doing the same thing again at a quarter tank so I richened it up a little more, runs perfect again... and then it ate 3 glow plugs in a matter of 2 minutes... Nailed it, went 400 feet one way turned around and started coming back, died. Dead plug. Replaced, same thing again. It looks like with the tank that low it is getting air in the line to the carb and going lean under braking? Then I guess turning around and that momentary lean mixture is killing the plug? The level in the tank is still above the seam... is this actually what is happening right now?

Also, is it possible the resonator pressure tube isn't working adequately? I don't think the mixture difference between what is perfect on a full tank and half a tank should be a full turn on the HSN.... But you fill it back up and it's pig rich again.
You’re not gonna love this man, but if your engine is running good then randomly eats 3 plugs, that’s not amazing. Could be a sign of bearing failure, rod failure, or some other kind of issue. It’s really hard to kill plugs that fast unless there’s something major league wrong. Maybe someone else can chime in with a better, or different opinion, but I have a feeling something let go in the engine is literally killing your glow plugs.
 

littleblazer

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You’re not gonna love this man, but if your engine is running good then randomly eats 3 plugs, that’s not amazing. Could be a sign of bearing failure, rod failure, or some other kind of issue. It’s really hard to kill plugs that fast unless there’s something major league wrong. Maybe someone else can chime in with a better, or different opinion, but I have a feeling something let go in the engine is literally killing your glow plugs.
They're melted like a lean out though, and they fail the same way too... Wide open right past then as I brake and make the u-turn, just before I get on it again boom, nothing. I wouldn't normally be picky about it but the fact it is so consistent when it happens almost makes me think you may be right though...
 

cbaker65

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Soaked it in degreaser (the pipe) cleaned as much as I could with brushes then blew air through it. Readjusted all the fueling until it seemed good, light smoke at idle, nice trail running it flat out. I was ecstatic. It went through a whole freaking tank without touching the starter other than when it flipped over about 600 feet away from me. topped it off, made two passes... and burned out a plug on each. I really can't handle this freaking thing anymore. And the plugs aren't like fouled... they're melted bad. like WTF. It's going back on the shelf and I'm just sticking with the nitro sport at this point because a plug a tank is expensive. I am really at a loss here. Like if I go any richer it's a dog. I quick pressure tested it by plugging the pipe and spraying it down with soapy water and got nothing. I sprayed it with starter fluid while idling and it didn't react like it had a vacuum leak. What could I possibly be missing right now.

What kind of plugs are you using?..🤔
They're melted like a lean out though, and they fail the same way too... Wide open right past then as I brake and make the u-turn, just before I get on it again boom, nothing. I wouldn't normally be picky about it but the fact it is so consistent when it happens almost makes me think you may be right though...

Yes ,Losi 215 is right ,what he described could cause premature detonation an burn up plugs on top of bleeding
fuel out of bearings ,check for wetness around the flywheel & chassy!..👍
 
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littleblazer

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What kind of plugs are you using?..🤔


Yes ,Lois 215 is right ,what he described could cause premature detonation an burn up plugs on top of bleeding
fuel out of bearings ,check for wetness around the flywheel & chassy!..👍
Flywheel is dry as is the case and clutchbell. Chassis is damp but I spilled fuel while filling... it doesn't have anything flung out so to speak. 3232x plug.

I pulled the cooling head off... there appears to be a perfect minus in the top of the piston and there doesn't seem to be much pinch. I may tear it down completely tomorrow and check but for now, I've wiped the chassis and we'll see what it brings.
 

littleblazer

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The os .21 is looking mighty nice right now...
 

littleblazer

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Pulled it apart, pinch is good, nothing odd with bearings or metal bits... just not seeing much. There is a bit of varnish on the rod but nothing to write home about.
 

cbaker65

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Pulled it apart, pinch is good, nothing odd with bearings or metal bits... just not seeing much. There is a bit of varnish on the rod but nothing to write home about.

Did you check for slop or play in the piston rod ,on the crank an in the piston?
That is where the first things start to break down as those parts take the beating ,
those get sloppy ,an causes pre detonation an can snap a rod!
 

littleblazer

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Did you check for slop or play in the piston rod ,on the crank an in the piston?
That is where the first things start to break down as those parts take the beating ,
those get sloppy ,an causes pre detonation an can snap a rod!
Yes, no real feeling of anything... No movement on the crank pin and no real slop on the wristpin end either.
 

gandalfnz

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Dude, brand new engine from Jenny RC is less than a $100 usd.
Rip that engine out, save it for spare parts, and break in a new one.
They run great when properly broken in, I have 5 and they all vary in running temp, but so far I have never had to replace a TRX.
Oh, and for a bit extra, you might as well put at 3.3 in it, its a straight bolt on.
 

cbaker65

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Dude, brand new engine from Jenny RC is less than a $100 usd.
Rip that engine out, save it for spare parts, and break in a new one.
They run great when properly broken in, I have 5 and they all vary in running temp, but so far I have never had to replace a TRX.

I remember Jenny ,I had bought stuff from them years ago!..👍
Yes, no real feeling of anything... No movement on the crank pin and no real slop on the wristpin end either.

Also ,make sure that all the proper shims are on the head!..👍
 
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littleblazer

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Dude, brand new engine from Jenny RC is less than a $100 usd.
Rip that engine out, save it for spare parts, and break in a new one.
They run great when properly broken in, I have 5 and they all vary in running temp, but so far I have never had to replace a TRX.
Oh, and for a bit extra, you might as well put at 3.3 in it, its a straight bolt on.
It had a 3.3, was a bit uncontrollable with it even with the long chassis... then it launched a rod. The 2.5R was perfect for one tank lol. A friend told me to grab a dynamite .19... I'm tempted to give up on this mill regardless at this point. Maybe it'll eventually make it's way into the nitro sport...
I remember Jenny ,I had bought stuff from them years ago!..👍


Also ,make sure that all the proper shims are on the head!..👍
Just the one copper shim, should've miced it but didn't but it was there
 

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