Engine Bearing replacement- a how-to

[WayneBrown]

It has been a recurring question, so here's a how-to copied from a PM.
Thanks to Rastaman for the inspiration to make this a tip in the newbies section!

Rastaman wrote:
Hi LameBird,

Would like to seek your advice. I have R50-V2 with OS Hyper engine, just started with helis about 5 months ago. The heli and engine are only 4 months old, so far I ran about 3 gallons through it. When I first bought it I ran it in properly with about 5 tanks running rich and just hovering. The past week I heard a noise in engine, never heard before, I can only hear it when engine is idling, like a metal grinding sound. Couple of guys at my field said they think it is my engine bearings. I am just learning so I can't do any 3D flying, all I do is hover. Is is possible for my bearings to go so quick?? I took the engine out but I have no idea where to start, can you tell me what to look for? Are there any instructions on how to id bad bearings, how to take them out and replace them?? I saw a couple of paragraphs on Raptortechnique but I'd like more information. Appreciate if you can guide me!! Thank you!!

Derek
I'll be glad to walk you through this.
Bearing failure is pretty normal, and can happen almost immediately even in a new engine. To check the bearings, remove the glowplug, and turn the motor over by hand. You are looking for a rough, notchy feeling.
Anything other than silky smooth is suspect, and should be investigated further. If you need to disassemble the motor, start by removing the head, carb and backplate. You may notice small metal filings in the crankcase after you remove the backplate, this will confirm a bad bearing.
To disassemble further, The cylinder liner may or may not slide out when you turn the motor, if it does not, turn the motor until the piston is at its lowest point and try to pull out by wedging a finger inside..use no metal tools here! If it won't come out easily, don't force it, instead place in an oven at 350 for 10-15 seconds to allow the block to expand away from the liner. It should now pull out easily.
Rotate the motor to nearly top dead center, and remove the connecting rod from the crankshaft, scratch a mark on the rod with a hobby knife to identify one side for later reference..
Now the block should only have the bearings and crank in it, remove the crank, and place motor case back in the 350* oven for 1-2 minutes. Place a piece of scrap wood on the counter, remove the motor from the oven and attempting to hold the block square to the wood Slam the block rearwards against the wood. If all went well, the bearing will drop out, if not repeat the oven heating and try again. It sounds elaborate, but it's pretty simple. Just don't overheat the block, and don't use metal tools to pry or bang on the block. Once the bearings are out, installation is pretty much the reverse, I heat the block (actually never let it cool down) place the new (rear) bearing on the crankshaft, and shove it back in the crankcase. A wood dowel about a pinky finger diameter is good to tap the crank with, to make sure the bearing seats fully, but you can improvise here, just keep in mind that you need to be gentle but firm..
The front (small) bearing should have simply fallen out during this, if not when you first remove the case from the oven to remove the rear bearing, use a pen/pencil through the case to push the front bearing out..
Replace by simply pressing the bearing in with your fingers before you try to install the rear bearing.
Now you have a block with new bearings, and a crank installed, replace the piston and rod, note there is a gap in the ring, and a small pin in the piston, line these up and install the cylinder, noting there is a notch on the rim, and a pin in the case, slide the cylinder in and place pin in notch. Rotate crankshaft down and the cylinder will follow, place your thumb over the cylinder and push fully into the crankcase.
FYI: the piston ring will compress when you push the cylinder down over it, there is a beveled edge at the lower portion of the cylinder. Pay attention to the pin and gap in the ring so you don't break the ring by having it misaligned.
Bolt the backplate, carb, and head back on and reinstall into the chopper.

Hope this helps!
-Wayne

[ChrisLaFollette]

What you forgot which I think is important and hopefully wayne wont get mad at me for posting this:

When tightening the head back on, tighten each screw a turn or two into the block so the head wont come off, now push down on it firmly with one hand and tighten one screw down so it just touches the head of the engine, now do another screw directly across from the first one, now pick another bolt and keep criss cross tightening them so they are all just against the head. Once they are all against the head VERY EASILY take and tighten one of them up snug ( dont be too tight but be snug ) and then tighten the rest in a criss cross sequence. The reason for the pushing down on the head and all of this is that if you tighten the crap out of one and then do the rest, the head could be on the engine completely sideways which you dont want.. :smokin: .. so do as I said and all will be well. Good luck with changing the bearings and I will say the information wayne gave is good except he forgot to tell us what the mark on the conrod is for... :lol: I usually dont mark mine as the piston has a half shaped moon cutout on the skirt on the bottom on one side and on most engines that goes torward the rear bearing so the piston doesnt touch the bearing at BDC (bottom dead center). If you want you can take and put a small x somewhere on the rod or mark it with a permanent marker and write BACK on it or something to remember which way it goes when installing it back into the motor. Nothing on the engine has to be tightened up gorilla grip tight (dont get me started on my gorilla grip issues and me stripping my SZ-H crankcase :hammer )... just take it easy on all the bolts but tighten them up firmly. As for sliding the liner back over the piston/ring while installing it back into the engine, press it against the ring lightly and turn the liner a little bit as to make sure the ring is catching the pin in the piston, push on the liner and give it a little spin and itll slide over the ring and piston, just slide it down and into the engine and align the pin in the block with the notch in the liner. Hope this helps somebody!

[Janek]

WARNING, dont' forget to ask your better halves permission to use HER (or his :shock:) oven.

And for the love of God, don't forget the scrap of wood when "slamming the block rearwards".

Either of these oversights will leave you short of your manhood :lol: :lol:

[Rcer22]

Very informative. I myself like to clean the rust stain from the bearing seat before installing the new bearing. Also make sure there are no chuncks of metal left in the engine before putting it back together.

[ChrisLaFollette]

If I usually have the engine torn down enough that nothing would melt or warp if it got hot in the oven, its usually stripped down enough to clean with carb cleaner, which I do. :)

[Finless]

Here is a tip for you people that hate rust!

Go get a set of Abec-3 STAINLESS bearings..... I put a set in my OS 91 which always seemed to have a rust problem.... Been a year now no issues... VERY worth the extra you pay for stainless.

Bob

[Rcer22]

What do you think of the ceramic bearings?

[Dave]

Stainless or ceramic sounds like the way to go. Where would one get these for an OS 91????

[Rcer22]

Hey Just so you know. I installed a set of ceramic bearings in my 37. The bearings went after 1 gallon of fuel taking the engine with them. :( I never run hot and I don't do any 3D. :? The motor didn't need 100% power to fly and have good power. 85% was enough and I used after run after flying. So go figure. :? Use them at your own risk. :!:

[vera]

I need a booster... does the front bearing go in from the front or the rear?

[Rcer22]

Your kidding right? :shock: Just incase you aren't the front bearing goes in from the front. :!: :twisted:

[vera]

Nope, not kidding. I never removed the bearings. I replaced a broken crankshaft once but the bearings stayed put and I didn't try to get them out. The big back bearing obviously comes out from the rear but it seems like the small front bearing could go either way. Maybe it's obvious if I gawk at it long enough. Anyway thanks for the info.

[Rcer22]

TIP!!
When you install the front bearing put the crankshaft in the engine first. This way when you slide the front bearing in it will slide in straight and true. The shaft will act as a guide.

[brunobl]

> "does the front bearing go in from the front or the rear?"

The front bearing goes in from the front. The rear bearing is slipped in from inside the crankcase (rear).

[fogger]

if the wife won't agree to the use of the oven, a heat good quality 2-temp gun can be used instead. They can get things surprisingly hot on high, so be careful.

-Fog