Was on my second flight today and the engine sputtered and died in the air. Brought it in and notice the prop wouldn't turn through the compression stroke. Even if you forced it. I removed the top of the engine and there were small metal shavings on the top of the piston. The glow plug was toast as well. I cleaned out the cylinder and it fired up again but there was a small knocking sound every now and then and didn't seem to run as smoothly. Any idea what happened? I'm hesitant to take it all apart but if I have to do it I will.

what fuel are u using?

10% Omega.

It sounds as if your bearing cage has failed.

Don't run it (or even turn it over) until you change the bearings!

And use a replacement bearing that has a polymide/polymer retainer.

A good place to get such bearings at a give-away price is [link=http://www.rc-bearings.com]RC Bearings[/link]

For instructions on how to change the bearings, [link=http://www.rcmodelreviews.com/bearings.shtml]look here[/link]

I recommend you to check the rear bearing. I have seen the same thing several times in my club.

Well, this happens when I read RCU and watch TV at the same time ... when I started to write, there was no answer.

When I take the bearings out, what am I looking for? Broken bits or wear and tear? Probably a silly question but I'm curious.

First you want determine where the metal shavings came from, and that should be pretty easy once you have opened up the engine. You really should not have run it again once you found metal in the top of the engine, that may have sent it to the graveyard. Hopefully the sleeve and piston are not badly scored from the debris running around in there and you only need a new set of bearings.

Mike

All the TT PRO46's I saw came with a polymide caged rear bearing. They would swallow the cage every once and a while

Look for no cage on the balls of the rear bearing

All of my TT .46 & .40s have metal cages in the stock form. I had the cage come off on one of mine after getting over 17K. Now I change them out before ever running them with PSpecs muffler bearing. www.pspec.com
When you pull the back cover off you will see bits of the cage in the case.

Same here, I've *never* seen one come with a polymide retainer as stock which is why they sometimes grenade like that.

Fortunately, the TT46Pro is a *tough* beast and we've had two cage-failures (stock bearings) in our club with no permanent damage to the engines involved but with lots of shrapnel in the chamber and some very light nicks on the piston.

Thanks for the help guys. It sounds like it is the bearing so I'm going to order some new ones this week and try to install them this weekend. I'll post pics of what I find.

You only need to replace the rear bearing.
http://www.pspec.com/details.asp?ProdID=77&category=7
Here's the link to performance specialties. Look under accesories.

The front bearing is pretty safe, I've only had one go bad after a mid air.

To change the bearing you need to dis-assemble the whole engine, use a little heat from a propane torch and bang it down on a bench it will fall right out. I'm sure there are plenty of threads here in RCU about how to replace bearings, it's pretty simple.

Be sure to inspect your piston and sleeve for scratches. Also pay attention to which way the piston and rod assembly face when you take the engine apart. I know my .40s will only fit one way but can't remember the .46 it was a year or more ago.

Since the front bearing is just a couple of bucks it makes good sense to change it anyway. Can't hurt and also means you won't have to use a puller to remove the prop-driver, you can just tap it out like I show in my video.

If you *do* tap the crankshaft out you do need to change that front bearing because the balls may be brinelled by the force of the tapping.

Whatever, I change the rears on all of my .40s for 424 planes with out a bit of issue.

I've ordered replacement front and rear bearings from RC Bearings (link above). I'm going to follow the videos posted above to help me change them. Do I need a propane torch or is sticking it in the oven just as good? Trying to keep costs down.

The oven will be fine as long as you don't stink up the kitchen and get in trouble with others in your home.

Yep, the oven works fine too. [8D]
I just use the torch to keep from going upstairs. When I do the people who live up there ask me to do stuff or tell me to be quieter.

Cool. I'll let you know how it turns out.

You will be disappointed at how easy this turns out to be.

Haha.. I'm kind of excited to take it apart, never played with an engine before. I just hope it runs afterward!

As long as you use proper tools you'll be fine. It is also a good thing to mark things so that you can put them back in the same direction, e.g. the piston and conrods are often symmetrical but have been run in by now so they should go back the same way as they came out.

Have you taken it apart yet to see if the piston sleeve assy are scored up? If they are tore up I would just toss the motor and buy a new one. By the time you buy a bearing and sleeve assembly you could have a whole new engine for a little more.

I haven't done anything with the engine yet as I haven't had time. I'll be sure to examine all the parts as I take it apart but when I had to top off at the field I didn't see any scoring from that angle, just metal shavings sitting on top of the piston.

The order in which you do the work is of some importance.

After removing the liner, piston and connecting rod tap the crankshaft out with a wooden block before heating the case. If you heat the case first the rear bearing will probably come out on the crankshaft. It can be very difficult to get a rear bearing off of as crankshaft. So, you want to tap out the crankshaft while the case is cold, leaving the bearings in the case.

Then, heat the case to remove the bearings.

Put the new rear bearing on the crankshaft and place them in the freezer (along with the new front bearing if you are replacing it).

Re-heat the case and press the cold front bearing in place. Then, push the cold crankshaft with the rear bearing on it into the hot case. Finally, put the prop drive on and tighten down a propeller to make sure the bearings and crankshaft are fully seated.

David