I have an 82lb. MG TM. What is your opinion of putting an aluminum Machette prop on there? I currently use the 3 blade nylon prop. My concern is that the alum. prop weighs twice as much (6oz. vs 12oz.). Is that extra weight going to bog down or put too much stress on the motor?

The additional weight of the Alu prop will not affect the motor operation. The diameter and pitch of the prop will, but not much. The most common cause of motor burn out is getting the prop full of weeds, or stuck in the mud, and then giving it full throttle. A motor with the prop stalled (can't turn) will smoke in just a few seconds.

I have a 55 lb 12v motor that I put several props on in search of a little more speed, and it took a prop from a 9.8 hp gas motor to get the full throttle current up to 50 amps, the max the motor is specified to draw. And the boat didn't go any faster when drawing 50 amps. But that is a different story.

Just be careful trying to make salad out of weeds. Be careful using the throttle to clear the prop. It can get very expensive. :-/

I doubt you will tell too much in performance loss unless you use the top end speeds of your trolling motor religiously.  I used to have a machette but plastic and it did help some.  The 4 blades mostly just help by giving the weeds less space / time to get between your blades. Your still not weed proof though. As sneaker mentioned, you still need to be careful and check it once in awhile.  I find that if the weeds are wrapped on my unit very bad I'll just pull my prop slightly  out of the water and hit it on a higher setting, usally clears them right off.  Or sometimes even reversing your prop in another direction quicly while giving it more speed can clear it in the water w/out pulling it up.  If it would happen to be a stern mount style then simply throwing it into reverse will clear most of it.

madbass, you may want to delay the purchase of the Motor Guide aluminum prop for the new one being introduced at the Classic

I'm getting one as soon as they are available.

I am thinking of getting one too for my 109# MG.

I had talked to a few pros at the bass masters classic a few years ago that had changed theirs to the metal props. they said it gave them more power and steady power. mainly in current. The blades don't flex as much as the nylon ones do

If I am right there is no pitch or size differance between the 3 blade nylon and 3 blade alum. props, just material