Need Engine Help
 

I was driving my T-Maxx in my front yard earlier today. Mind you i am a complete newb when it comes to R/C but i am very good with internal combustion engines. I build and restore muscle cars. I think thst i overheated the engine. I was driving an i noticed a tiny bit of smoke from the top of the head and a loss of power, it felt like the engine had almost no power. I quickly shut it down and let it cool off. I stripped the engine and examined all of the parts. The engine looked fine, a little bit a what looked like a burnt piston but residue came off easily. The tolerances looked good, no warping. I spun the flywheel and it still had compression. The engine will nto start though. I changed the glow plug also. Does anyone know why my engine will not start.

RE: Need Engine Help
 

First thing you need to do is buy a temp gauge. Are you using the easy start to crank it or are you using a glow stick? Sounds like your engine is ok. Maybe your easy start its not getting hot enough to ignite the plug. Try a diffrent plug and make sure your getting fuel.

RE: Need Engine Help
 

When you said it still has compression, how did you check that? One of these motors can feel like it has compression but not have enough to start or run well.
The easy way to check is to try to turn the engine over by turning the flywheel with one finger only. If you can easily turn it over with one finger then you do not have enough compression. These engines rely on a tapered piston sleeve for compression, not rings. When an engine is new it can be VERY dificult to turn one completely over by hand, even with the motor out and grabbing the flywheel with your whole hand.
When you lose compression on these motors they have a real hard time drawing in fuel and of course with less preasure it's hard for them to fire as they rely on the preasure to ignite the fuel.
If I had to guess, I'd bet that low compression is going to be your problem.
You might try to repinch the cylinder sleeve or just replace both piston and sleeve (usually $35 - $60 for parts)
Good Luck
Dave

RE: Need Engine Help
 

I think that my problem is the head. I did not attach the head securely and i saw fuel spitting out from the sides. I am going to re-attach the head and tighten it down more. Hopefully it will then start, if not rebuild time.

RE: Need Engine Help
 

When my cooling hed started smoking, i just richened up the needle settings and ran way better. The burnt look on the piston is just carbon build up which is normal. Sorry i couldn't be more of a help!

RE: Need Engine Help
 

Yes, well, that would be a loss of compression I guess :D
Don't forget to tighten the head in a cross pattern and a little blue loctite won't hurt either.

RE: Need Engine Help
 

i got it started. Now i need to tune it. I have a temp gun. Where do i meaure the temp from and what temp should i tune it to.

RE: Need Engine Help
 

lol measure the temp of the tool box. man i hate temp guns just me. good for some bad for the new guys. set yer lsn flush or leave it a lone if oyu never touched it from the box. turn the hsn all the in. NOT TIGHT STOP WHEN YOU FELL IT GET TO THE BOTTOM. now from the bottom turn it out 4.5 - 5 turns out and start her up. will it start/ idle by itself? no then turn hsn in 1/8 turn (lean). repeat until it will idle. you should be in the ball park @4.5 turns. now notice any spitting out the exhaust, alot of smoke when you apply the throttle, or engine dieing? yes lean it 1/8 turn. what you are shooting for is smoke heavy too rich. mild smoke is good truck will run but not up to max potential. light smoke yer right there. and where i like mine is light smoke just noticeable, i run mine right there just before it starts pop and spudder. from i have read the trx2.5r runz hotter then normal.

hate to see what the temp is but hey i ran my first gen tmaxx (.15trx)like that for hell 7-8 gallons before it quit.

now once you get her running then take temps with the gun. but you gotta get it running first

RE: Need Engine Help
 

I agree - temp guns should not be used to tune engines.

Once you get it running, run it normally for a while, maybe a few high speed passes. With the body ON, use your temp gun to spot check the temperature. Only check the temperature to make sure you're not exceeding the maximum operating temperature. Depending on ambient conditions (temp, barimetric pressure, altitude, etc), your engine temperature can vary significantly.

Tune based on smoke and performance. Make your tweeks between real runs, not sitting there idling or reving the engine with the wheels off the ground. Use the pinch test for the low speed needle, or if you notice it bogs on acceleration, lean out the low speed needle.

I tune for performance, then richen it out a bit to make the engine last longer. Then run the hell out of it, check the temp, if it's pushing the max limits (230-300 F, depending on engine), I richen it up a bit more. Make sure the body is on for the temp readings and you're running the car - you want to simulate the cooling effects of real running. If you run too rich your engine will be extremely cool and you'll be blazing through tanks and decreasing your plug life.

If you can't accelerate out of idle, even with a new plug, you probably have lost some compression.

Don't F with the mid range adjustment (it's the LSN seat) if you have one - just leave that at the stock setting.

RE: Need Engine Help
 

Actually, a temp gun is very handy for setting your low speed needle. After everything is fully warmed up and you have the HSN set where you want it, make a few fast passes, bring it in and shoot the head temp. Count down 10 seconds and shoot it a second time. If it's dropped off 6~8 degrees your LSN is where it should be, if it's gone up or stayed close to the same, your LSN is too lean, and if it's dropped more than 8 degrees it's too rich. This is much more accurate than the pinch test. Think of all your adjustment needles as a clock face and never turn them more than an hour at a time when tuning, a little goes a very long way here. Also, make sure you get the chassis heat saturated before doing final tuning.

A good way to check your piston/sleeve seal is to bring the engine up on the compression stroke and hold it there, then put the exhaust port almost in your ear. If you hear a frying or gurgling sound, it's time to think about a new p/s set. The best way to check for a worn engine is to see if the piston will push through the top of the sleeve. If it won't you still have some pinch left and you should check for a good seal as described above. If the piston will push through the top of the sleeve, you have lost all pinch. Most engines will still crank in this condition, but will flame out once warm.

The dark spot on the piston crown is not actually carbon, it's more of a burnt oil glaze. If the fuel you use contains dye, the stain will be a darker shade of the same color. If your fuel does not contain dye, the stain should be a nice golden yellow color. If it's black you are running too hot a plug. If you have a blackish looking skid mark in line with your exhaust port you have run the engine too lean. This will also show as signs of metal transfer from the roof of the combustion chamber and edge of the piston. Metal transfer looks like the parts have been sandblasted with a corse media. The problem here is the places where metal has detached itself will become hot spots, and if it's bad enough will cause detonation.

Last but not least. If you have a mid range adjustment and after doing all the usual adjustments to the HSN, LSN, and idle screws you are still not getting what you want, remove the carb and looking in from the bottom adjust the mid range until the hole(s) in your spraybar are centered in the throat. Do this with the slide or rotory valve fully open. You will then have to retune everything else, but you should get a better idle, more crisp off idle response, smoother mid transition, and much better overall acceleration.