I have a t-maxx and im wondering if i should stay with the stock engine or should i get a different one and what kind should i get if i get a different one?? It has the nitro TRX3.3 on it now

As long as it works, stick with the 3.3. I'd hold off on upgrades until something breaks, then you get an idea of what parts are going to break. The 3.3 has gobs of power, and there should be no reason to upgrade.

The engine has a bad rattle and no power and it wont idle.. Theirs slop in the rear crank bearing and in the piston pin but its in the piston not the rod.
Thats why i was thinking on upgrading.

Do you think it would be better to rebuild what i have?

There are two ways. If you don't mind putting time into it, tear it down and inspect everything. Get the schematics off Traxxas' website and write down the part numbers of the parts you will need to replace and price them out. Make sure the replacement part cost doesn't exceed what the engine is worth, or if it's close and you don't mind paying, just buy the new 3.3 and keep your old one for parts. You can get a new 3.3 for around $150-$175. Either way, start with removing the engine. It's going to have to be repaired or replaced.

You'll notice that the engine components between models have the same part number.

Here's the 3.3 exploded view:

http://traxxas.com/sites/default/fil...y_051221_0.pdf

Assembly:

http://traxxas.com/sites/default/fil...s_070403_0.pdf

Model 4907 parts list:

http://traxxas.com/sites/default/files/4907_parts_1.pdf

Model 4909 parts list:

http://traxxas.com/sites/default/files/4909_parts.pdf

Thanks for your help and parts list. I will go through it all and see what everything cost

You can get a new 3.3 on E-bay for about $110 with shipping but if you get a new engine I would go with a OS .21tm it is more reliable and a better engine but will coust you about $220 on e bay but worth every penny

I was looking at those and thinking about getting one.. i had an OS .18 that was awesome. i had it on a Losi XXXnt then put it on an HPI.. I know the 3.3 runs good but i want something that is going to last. Im very picky and take great care of my RCs. thanks for your input.