David Bump

iTrader: (3)

Hey everybody, i wanted to post a thread regarding an issue with the Trx 3.3 racing engine. Racing engine? Anyway, it is a lovely engine as far as rtr's are concerned. It does a great job putting the power down in these RTR Revo's and T-maxx's, rustlers and jatos. However i notice alot of people complain about the engine not idling correctly and it stalls out and or runs hot. I have alot of experience with the Trx 2.5 and 3.3 engines, ive had about 8 of them in total. 3 of them were toasted and now my other 5 are running amazing all the time. Now ill get to the point. The 3.3's rear bearing is absolutely garbage...they go bad. Unfortunately somebody without a trained ear wont even hear the rough bearing sound within the engine while its running. 2 of the many 3.3s ive bought had the rear bearing go bad literally right after break in. Its absolutely unacceptable that an engine from a reputable company like traxxas have bad bearings right from the start. Just under a gallon the bearings go bad...Sure i have had a 3.3 in which the bearing somehow lasted 3 gallons and its amazing. usually not the case. The symptoms of a bad bearing is a bad idle, horrible rough sound and you will find yourself chasing the tune. sometimes the noise isnt so noticeable, the engine will stall out. There is also possibility of tiny pieces of the bearing to break up and get chewed up by the piston and sleeve. We all know thats not a good thing. I believe many people, including guys that do have experience with tuning and are very good at tuning make this mistake, ive done it myself. With the bearing compromised and a low idle starting to occur, guys will start to re-tune the engine thinking its the tune that is causing the poor idle. when yet its the resistance that the bearing is putting on the crankshaft and ultimately the idle itself. Because the rear bearing goes bad, i believe many people do further damage by trying to compensate for the issues the bearing are creating. it cant be fixed unless yoy replace the bearing. Honestly EVERY SINGLE TRX 3.3 should have the rear bearing replaced with a boca mx ceramic bearing....unfortunately these bearings cost 60$..however if you dont need a overkill bearing. any of these boca bearings will fit the trx 3.3 rear bearing. heres a link for you guys.

http://www.bocabearings.com/search.a....3&Feature=3.3

Its interesting how the 2.5 uses the exact same bearings as the 3.3 and yet the bearings in a 2.5 last much longer. The 3.3 EATS BEARINGS ALIVE! Get ceramics and or Bocas!

There are videos around that show how to replace rc engine bearings. I dont have any fancy tools and im able to do it without it being a huge pain in the butt. The hardest part is removing the rear bearing itself. I wont explain that here. All i will say is when you do finally put in a upgraded bearing, make sure you put it in flush, make sure you apply even pressure around the entire bearing.

I really hope this helps somebody out. I kept having issues with my first couple 3.3's and was pulling my hair out. Im very good with them now and want to help other Another thing i would like to cover is the plastic carb the trx's use. The stock carbs are very fragile. over tightening screws and high temps can harm, hinder, or destroy the carb and or the engine. Both the 2.5 and 3.3 have a sweet spot between 225-237 degrees fahrenheit. I recommend buying yourself an O.S 11k slide carburetor for the trx engines. I have 6 of them myself and swear by them. They have a all aluminum body and all of the parts are.....well, O.S Quality parts if you cant afford them, dont sweat it, just take car of you're traxxas carb. O.S11k slide carbs=100$..


Now that i run ceramics and 11k slides on my 3.3s....they last gallons with no finicky or silly stupid issues. For the newbies out there, a bad glow plug will cause a poor idle alot of times too. If for some reason you cant get a 3.3 to idle right when you know the tune is right, its either the bearing or glow plug. Also get as much air as possible to the cooling head and intake, i go overboard with my holes in my bodyshells to make sure the engines get plenty of air. it makes a huge difference. You can run much more lean and get alot more speed when you run without the body on, obviously because its getting much more air and can stay cool while being at the perfectly lean spot. Keep that sexy body on though and make sure the holes are biiig. I hate to state the obvious but i figure i would help everybody! Much love and keep bashing and racing those 2.5's and 3.3S!!!!

proto20

Very nice write up, I run the trx 2.5r and have no issues with them other then what you already covered. Once taken care of they are a dream to run.

I do not tune off temp though. I typically see the temp around 240-260 when they are at their prime.

The losi 3.4 carb also works great at a much cheaper alternative.

I run Avid bearings and keep both seals in for the front bearing.

I do not run the 3.3 due to their issues with rod issues. After everything is set and done to make a reliable 3.3 you are at a price of a picco/nova drop in. Not really cost efficient.

Here is a vid of one of my 2.5's in my track oriented revo. Moves it just fine and this setup is very conservative. Stock clutch etc. Only real difference is a sirio crank.

I have a youtube channel (proto2o) with tons of videos of my trx trucks running and showing what a proper tuned trx can do.

Megatron1

A good 3.3 engine to buy is a 3.7 mod by rb mods
You can get it with ceramics and all the juicy engine mods. Losi 3.4 carb or a picco 7.5 carb take your pick but your looking between $250-$325 depending on how far you want them to mod it. The outcome is a fantastic basher or drag engine. The kicker is rick brake will tell you his engine takes a full gallon to break in and for timings to kick in. Im on my second 3.7 mod and its a little beast.

Morris400

I'm wondering if this could be an issue on my 3.3. I'm having a hard time getting my 3.3 to prime. I have to blow in the pressure line to the tank to get it to prime. Pulling the pull start and pluging the exhaust won't get enough fuel to the carb.

I'm running a losi 3.4 carb as well. And I've replaced the tank and fuel lines and completely tore down the engine and cleaned it out. Maybe the bearings are on its way out. I've got about 2 gal through it.

timjs

Over the years, I have owned maybe 8 or 9 3.3 engines.
I'm not sure where Traxxas gets their bearings, but in every single 3.3 I have had that failed, it was the rear bearing. It's no exaggeration that the rear bearing is not up to par. I have had very good luck with Avid steel and ceramic replacements. For all I know, the steel may very well be the same exact piece Traxxas uses! But, bought from Avid, none have failed on me.
The stock carbs are okay but I don't really like them. I prefer a short needle carb over a long needle, but the Traxxas carb is a SUPER short needle. Makes the transition from low to high metering very abrupt.

Carry on!

WheelNut

iTrader: (5)

Its not really surprising that the bearings in a TRX3.3 would fail. The bearings are too small for the loads they are put under, which is why the bearings in 3.5cc buggy engines are way bigger and hold up a lot better. The crankshaft in the TRX3.3 is TINY, as are the bearings. The reality is that the TRX3.3 has 50% more displacement than the engines it's block was originally conceived for: 2.1cc or .12ci.

cbaker65

Lol...see what your saying ,ran across that on the Ae 8.0 engine!

The 8.0 engine is nearly twice as big as a 4.6 engine ,The rod thickness
is pretty much the same.

A rod takes a lot of punishment especially on an engine that hsnt been broken
in yet an is under a lot of stress due to tight pinch ,compression & heavy amount of fuel!

Megatron1

im a 3.3 kinda guy myself and i did the same thing trashed them junk bearings and installed ceramics. Im at 4 gallons in my stock 3.3

David Bump

iTrader: (3)

RB Mods traxxas 3.7 is pretty pricey, its really not a 3.7 either. its basically just ported and polished, its still a 3.3 though. It is sad that almost literally every single traxxas 3.3 has rear bearing failure. Sometimes you can get lucky enough to finish break in with the stock bearing, sometimes you cant finish break in with it. Its interesting because the 2.5 uses the exact same bearing and they seem to last a long time in the 2.5's. I dont have cod rod issues though, not yet anyway and ive put tonsss of fuel through mine. i dont tune by temp, i tune by performance, smoke, and temp combined. I truly believe 225-235 is the best temps for both traxxas engines, anything over 245 and they seem to lose power, especially low end grunt. perhaps its difference in environment, but they run flawlessly at 230 all the time. They will also last forever with the rear ceramic, premium carb upgrade, and pre-heating before starting. you can get a super hot heat gun on ebay for like 15$. well worth it..

David Bump

iTrader: (3)

Id like to hear some more peoples input on their experience with the trx 3.3 engine and problems or accolades they have had with them

timjs

Sure. I've owned many 3.3 engines over the years. Most if not all that I can remember had rear bearing failure. So from my perspective, yes they have bearing problems.
I eventually got in the habit of putting Avid bearings in my 3.3 engines, but it's been quite a while since I've dealt with another Traxxas product.