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Paul11277

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I fitted a new 2.5 engine to my t maxx about 6 months ago. I tend to only run my t maxx at the weekend untill i break it or the weather turns. I have had no more than 2 gallons of fuels through it and thats been very generous i think. Because i had a leaking fuel tank for the last 1.5 gallons which i didnt spot untill it stopped been a leak and became a crack.

The last time i used my t maxx it was really, really hard to start. Usualy no matter how i left it the last time it will start on any carb setting. But this time my pull start was not recoiling (winding back in). I had to turn the clutch untill it wound in and it was hard work because there is not much access when the engine is on the truck.

So got it wound back in a couple more attempts and same again pull cord was not recoiling. So i though right I'm going to leave it where it is and check my glow plug. As soon as i started loosening the glow plug the pull start started to recoil. So while the plug was out i pulled the starter a few times and it seemed fine worked every time just as it always had.

So then i checked the plug which was fine put it back in and attempted to start it. Got a few goes and same again pull cord stuck out. So i loosened the plug and let it recoil and had another go. Eventually after reapeating that same process 8 or 9 times it started. And ran fine for the rest of the day started every time and pull cord recoiling as normal.

The next day i went to use it and it worked fine but i discovered to the expense of an A arm 2 shockers a few screws and some rod ends that my fail safe doesn't work when it ran out of range at full speed into an iron fence.

This is the first time i have ever had this problem but i have a feeling that its a sure sign of something failing, it wasn't flooded and i always use after run oil and leave the piston at bdc. When my new rpm a arms arrive i shall have another go but would like to sort this out while my truck is out of action if its a common problem.

I am new to nitro engines and have not had to strip one yet. I bought my new engine from a dealer with everything fitted all i had to do was fit it in the truck so i dont know a great deal about it at all. I would have said it was seized myself or flooded but it ran and there was no fuel coming out of the exhaust indacting flooding also when i took the plug out to check it i turned the truck to empty the fuel out but there was hardly anything there at all.

But i do have to say that i dont think the 25 motor is as consistant as the 15pro i replaced. i seem to be always tunning this thing, it is much faster but seem to spend more time tunning and less time bashing.

Any help would be appreciated.:surrender
 
Sounds like the pull start one-way bearing is binding. I had the EXACT same problem on my buggy. Pullstart would turn the engine, but would get stuck out like that. You'd have to wait for it to turn the engine over under the spring's power before it'll rewind.

If it runs though, chances are your bearing just had a piece of debris in it and now it works. On my buggy it would snag up once it started after about 5 seconds. Pulled it off (with some difficulty since it clamped on the shaft) and cleaned it, now it works well.
 
Yes that could be it but why would taking the glow plug out make a difference if it was just dirt in the pull start mech.
 
Because if the one way is binding then the starter recoil spring has to over come the compression of the engine to reel in the string. By loosening the plug you take away the compression. It's also evidenced by the fact that reeling it in with the flywheel worked.
 
replace the OWB and the batteries for the fail safe. The .15 and 2.5 are the same engine just a different cooling head.
 
So if this is the case can't i put a 2.5 head on my old 1.5 engine. Surely i will need to change the carb and air filter too.
 
from what I have heard just change the head. I have not owned but the 3.3 or my favorite the picco .21 mid block.
 
A 2.5 or 3.3 head will not fit the old pro .15 engine. The pro has 4 head screws while the newer trx engines have 5.
 
TWOCANE said:
The .15 and 2.5 are the same engine just a different cooling head.
Click to expand...

The old 15 pro and 2.5 are the same engines? I'm not sure where you got your info, but it's not accurate.

The old 15 pro had an aluminum rotary carb, side exhaust and short shaft that required a shaft adapter nut.

The 2.5 and 2.5R (both also .15ci) have nothing in common with that engine other than the .15ci combustion cylinder volume. They have rear exhaust, different porting on the sleeve, different pull-start and housing, completely different crank shaft and a composite slide carb.

Now, the 2.5 and 2.5R, those at least look similar other than the head. The 2.5R's is machined and ano'd blue, the 2.5's is cast. Supposedly, the 2.5R is ported differently... but I've never compared the two myself.

I've only been around 5 or 6 of the 2.5's, 2.5R's or 3.3's. I've yet to see one that doesn't require constant tweaking to keep it from getting too hot. Except the one in my jato (old 2.5). The only reason I can think on that truck is because the engine is actually big enough for it as opposed to the maxx and revo... 2.5 just isn't enough without running it lean IMHO.
 
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I have both the trx15 pro and the trx25 and the 15pro does look very simlar to the 25r if you remove the air filter the carb and the head. But exhaust port is in a different place. I have been told i can mod the sleeve on my 15pro my smoothing out the ports making them smooth flowing to allow more of the nitro/air mixture through the port and more exhaust gas out the exhaust port. The mod does not look very hard and will gave power very close to that of the 25.

Dont know how true it is but there are vids on youtube showing the same mod so i presume it must work. But if anyone has done the mod then i would like to know if its woth the effort.
 
yhea what I meant was .15 ci is stanard and 2.5 cc is metric making them the same displacement the difference is supposed to be in the porting of of the 2.5/
 

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