which engine do i need....pls help...thanks..

If you buying a new motor, i would just stick to the basics. http://www.ebay.com/itm/5309-Traxxa...Accessories&hash=item5ae29cb44d#ht_1442wt_952

this motor is most likely what you have in yours right now. unless its 2.5 but even if it is. the flywheel, clutchbell, and your starter will fit on this engine. So i would say this is the most cost effective way to replace your motor.

what exactly happend to replace your whole motor... you could just rebuild it if its just been worn out. after about 3-4 gallons your engine is about done.

If you do want to try the rebuild route ebay is also a good cost effective way.
http://www.ebay.com/itm/Traxxas-TRX...Control_Parts_Accessories&hash=item45fc69969d

Also multi shaft is for bump starting witch i dont think is possible for the revo. I would just stay with basics. get the one i listed in the first link.

I have the new revo 5309 and mine uses the ips shaft engine tra5407. To tell you the truth i dont even know what the difference is other than it looks like one dosent have a shaft for the clutch bell.

Here is an idea of what you get if you got a multi shaft. http://www.buytraxxas.com/popup_image.php?pID=2572

I would just get the IPS shaft. its going to save you alot of headache.

thanks man that exactly the reply i was hoping for....
the reason for the replacement...well...i had several threads on this forum trying to figure out just that...the motor would start and would run as long as you held it wide open but would die as soon as you let off the fuel any at all...i tried all sorts of stuff...i tuned on it for days...i swapped out the sleeve and piston...tried changing the carb...best i can tell the bearings are damaged

Well if youve replaced all those things you should have power. There might be some drag on the drive train thats making it hard for it to spin. But i would atleast check the bearings before buying a whole new motor. but i mean a whole new motor is nice aswell.

Just check those bearings for if their really hard to move.