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Motor problems, need some tuning help

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T-maxxJared

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I have been having some problems lately that I have been chasing, and can't seem to figure them out. The truck fires right up on the first start up of a session and idles great, runs good off-idle and in mid range, but when I take it up to the point in the top of the rpm range where it should just about be hitting 2nd gear, it just cuts off. No spitting or sputtering, just cuts off. Then, when you try and restart it a couple seconds after, it will spin the motor over and sound like it is on the verge of starting for about 15-20 seconds, but not start until after this. I was messing with the tune at the track yesterday, got frusterated, and then decided to stop and try again today at my shop, so I went back to the base line break in tune because I thought this would have been a lean setting on the hsn, 4 turns out on the hsn, and the lsn is flush with the metal that surrounds it. The glow plug is brand new, and the air filter was just changed. I can't figure this one out, and I am hoping I didn't tear up my motor, but I have a bad feeling.
 
I have let it cool down for a minute, and if you are looking at the back of the truck forward, I can roll the flywheel over with my fingers fairly easy clockwise, but not counter clockwise.
 
Thats the first thing I thought was that it was lean, but the carb is set to break-in settings, so maybe there is an air leak somewhere? I already have a new piston and sleeve that I was going to put in, but I will check everything out first before I go that route. I am going to take everything apart that is a possible suspect for an air leak or something blocking it and inspect, clean, and put it all back together, and see how it goes from there.
 
Last edited:
T-maxxJared said:
Thats the first thing I thought was that it was lean, but the carb is set to break-in settingsQUOTE]

With the hot humid weather I have I had to richen the carb from factory settings. 4 1/2 on the hsn and 1/2 turn out from factory settings on the lsn.
Click to expand...
 
as far as the flywheel spinning okay one way and not the other is normal (the one-way hooks up when it is spun the wrong way)

are you getting okay compression?

which glow plugs are you using?

My recommendations:
pull the motor completely apart and clean w/nitro clean
while apart take the piston and CAREFULLY push it throught the sleeve (if it gets tight towards the top with about a 16th of an inch from being flush:
|------ |
|.........|
|.........|
|.........|
|.........|
....| |
....(o)

if this is true for you then your piston/sleeve is fine
(personally I wouldn't install the new piston and sleeve until you must, that is an expensive replacement on a maxx)

carefully reassemble to traxxas specs and after run the hell out of it.

good luck!
Mike
 
So what you are saying maxxbasher is if it does get tight, it should be ok, and if it doesn't get tight, then the piston and sleeve are done? Thanks for the tips, I really appreciate it!
 
if you roll the flywheel and it doesn't feel hard at the top of the stroke it's done....also check it when it's hot too those 2.5s like to just flame out at temp but feel OK when cold.....if you don't feel the "pop" when it's hot, it's done......and did you open the P/S package yet? if not I'd suggest giving it back for a refund and get a new mill.....when you change the P/S you should also do the conrod....and once you add that up your only 20 bucks shy of a new mill....
 
I was thinking about a new motor, but I don't know, I still have a truck that I can't drive well and this motor going so quickly is no ones fault but mine, I do practically zero maintenance on it, and thats why I think it went in 2 gallons. I would like to keep it and just fix it again and learn how to drive the truck well, and then go for not just a better mill but one of the best ones. I have learned my lesson on engine maintenance and after run significance, so I will take a lot more care this time and hopefully get more than 2 more gallons out of it. I still have the piston and sleeve in the package but I think I am just going to put it in and go from there, run it and learn some more driving for a while, then go to a bigger/more powerful motor.
 
how much was the P/S?
and did you get a conrod too?
if not you can do yourself a favor and just get your sleeve pinched for 25 bucks...I got a local guy who does good work......I'm going to see him tonight if you want to meet him.....about 7:30-8...if you just want to revive it that's much easier on the wallet than the whole replacement....hey I got 3rd saturday in the B-Main...you missed it
 
The piston/sleeve was $57, and the guy at the hobby shop and a few things I have read online said that the connecting rod can be re-used if it is in good shape, so I hope it is, otherwise I am going to return the piston/sleeve and just buy a new mill, because you are right, in that case it will only be a few dollar difference. They wanted $20-something for the connecting rod. I think I saw a few scratches in the bore of the sleeve when I took the head off the motor last night, so I think I am just going to replace the piston/sleeve, but if it wasn't for that, I would strongly consider getting it pinched. With a new piston/sleeve or just a pinched sleeve, I take it you have to break in the motor all over again, and can you expect the same life out of the motor as you could a well taken care of all-brand-new motor?
 
oh yeah and congratulations on the finish, you made it through one. I am going to enter my truck in the monster truck class not this coming saturday, but the one after. Our goal is just to finish, and beat whoever doesn't.
 
^^^ yeah I aim for the mud and if I hit the grass I feel better....LOL....unless you take a micrometer and measure the conrod new and used you really don't know if it stretched or not.....it usually the bushing that gets oval shaped and lets the piston go higher up than it should.....when it's pinched you don't have to break it in the same...the piston and sleeve are already mated together....it just makes it a little tighter......most people only get about 4-5 gallons from a 2.5 if it's their first mill and they really do everything right....I know one guy that got 7 from one but he is on point w/ that mill.....I ran mine to death in 3.5 gallons but I'd run it at 260 dry.....it goes pretty quick like that but it dies quick too.....also for a quick fix I added castor oil to my fuel once just so I didn't have to rebuild it...kept it from flaming out for a few days but I toasted the mill big time when it went....snapped the conrod in half and jammed up in th ecase.......not recommended but will get you running for a while longer.....IMO the 2.5 is a mill you want to spend as little as possible on rebuilding it......good learning engine (cause it makes you actually have to trouble shoot it) but not something meant to last....
 
and that was the 3rd time I finished all my runs......I'm at about 40% finishing rate now...woohoo
 
What would you recommend to replace it with that will work with the ez-start and not require any chassis conversions, etc.? It doesn't have to be a firebreather or anything, just durable and cheap.
 
well I would recommmend the O.S. 18 just because it's an OS and they are very reliable well made engines....but not cheap...200 bucks....then there's the Fantom .18.....decent mill but it's close to the OS in price...might as well go OS at that point.....then there is the P2....unreal power, cheap, BUT every time mine cooled down I had to retune it to run again...as long as you keep it at temp it runs great all day long......SICK POWER.....hard to tune....the siro I've never had either but I hear it's awsome....Very expensive...like 300 bucks.....I beleive they all fit the EZ start system......the aftermarket mills are either cheap and cheap or expensive and quality for the maxx anyway....when you get into Big Blocks there are more mills available at all kinds of prices/quality levels...
 
yeah, I can't throw down 200 bucks on a new mill at the moment and I have already paid for the piston/sleeve so I think I am going to go that route for now and save the new motor for down the road somewhere.
 
I tend to lean more towards the cheaper engines too.....I say get your pinched and hold onto the P/S set replace it down the road adn do the conrod then too.....save the P/S and later before you do the rebuild get the conrod and wristpin.....it won't be a chunk from your wallet all at once that way.....and you'll get a little more life from the existing P/S in there...if you blow that set you won't be as pissed either.....My RG was doggin guys w/ WS72s last night....Mills Pond doesn't let them wind up enough to kill me.....
 
ok, sounds like a game plan. if you can, give me a call anytime today about seeing the guy that pinches the cylinder, I am going to pm you my number.
 

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