Author Topic: Replacing bearings in a Thunder Tiger Pro .25 (Read 2674 times)

RknRusty · « **on:** August 29, 2013, 09:23:44 PM »

I did a belly buster at the bottom of an inside loop and my Thunder Tiger Pro .25 was full of dirt. I had the sense to not rotate the shaft. When I took it all apart there was dirt on top of the piston, in the crankcase and just a speck or two was visible in the bearings. I put it all in a jar submerged in fuel and shook it up and let it soak for a while. I'm pretty sure I got it all clean, and the rotating assembly seems smooth. I think it's fine for now, but I figured it would be a good idea to have a spare set of bearings in case one starts grinding itself up. I figure if one goes bad it'll be the front one.

I looked on Google, and they're easy to find at places like Boca Bearings. I'm posting this to ask if there are special tools I'll need to pull the old ones and press the new ones in place? This is the engine that's a knockoff of an OS .25, possibly an OS fsr.

Thanks,
Rusty

Steve Helmick · « **Reply #1 on:** August 29, 2013, 10:22:14 PM »

An oven mitt, a 6"-12" piece of 3/8" dowel, and a short piece of 2x4 should be all you need. I had one engine that would NOT produce the rear bearing on demand. But I finally got it out with an internal expanding aluminum plug plus a punch and hammer.

Use the kitchen oven (or similar!) to heat the case to about 250 deg. F, grab the case out of the oven (with that oven mitt) and whack the back plate area against the 2x4 on the counter. The rear bearing will drop out (it says here in fine print). Throw the crank in there and push the front bearing out, using the 3/8" dowel to tap on, if needed.

To re-assemble, reverse the order. Heat the case, drop the crank in, drop the front bearing on to align it, and push it home. Remove crank, put the new rear bearing on the crank and push it into the hot case.

Some engines (ST's) have aluminum spacers that go between the crank and front bearing. I think this practise was devised to either move the stress point on the crank, or to make up for crappy machining. If the latter, then it would make sense that the spacers would come in a variety of lengths, but they don't. Still, I had enough trouble with my early ST G.21 .29rv that the crappy machining theory was reasonable. Seizing crank (rv, less lube) and wrong length between the bearing housings relative to the steps on the crank.

Steve

frank mccune · « **Reply #2 on:** August 30, 2013, 12:01:19 AM »

Hi:

i had a very tight replacement bearing that did not want to go into the case. The easiest solution for this problem was to place the new bearing in the freezer prior to attempting to place it in a hot crankcase. It dropped right in and was a great fit after both parts became the same temperature. I use the toaster oven when my wife was not looking! Lol

Good Luck,

Frank

kenneth cook · « **Reply #3 on:** August 30, 2013, 03:50:04 AM »

Rusty, when using ball bearing engines for combat , hitting the ground is unavoidable and they will ingest dirt. I dismantle the engine, but I don't remove the bearings. I wash them out under the faucet with hot soapy water and rotate them until the grit is gone. I dry the parts with heat and re oil them. I typically run the engine immediately following as well. This just saves the step of taking them out of the case. The stock bearings work, but they can have a very limited lifespan. Boca bearings has them available if you need spares with tremendous quick service. When you reassemble the engine if it feels tight, the bearings are probably not seated correctly which can happen. Put a prop on the shaft and tighten it down tight, tap the front portion of the case with a small hardwood block directly on the bearing housing. Kinda of like seating U-joints once you pressed them into the yoke. This will generally allow the bearing to find it's happy home and all will turn smoothly once again. Ken

RknRusty · « **Reply #4 on:** August 30, 2013, 06:34:32 AM »

Thanks guys,
all that is well within my abilities. I appreciate the answers.

Rusty

Jim Kraft · « **Reply #5 on:** August 30, 2013, 06:45:19 AM »

I have tried most ways of replacing bearings, and I find a heat gun works best for me. I lay the engine back side down on a block of wood, and then heat the case till the rear bearing falls out. Then with a glove turn the engine over and tap it on the wood to remove the front bearing.

I heat the case again to install the rear bearing that I have put on the crank, and use a dowel in the hole in the back of the crank to push it in to the case. Then slide the front bearing in. I then put on a prop, snug it up good, and heat the case one more time to seat the bearings.

Not sure this is better than any other way but it works well for me. When working on Saito's, I do put the crank and bearings in the freezer over night as the bearings fit very tight in the ones I have replaced.

RknRusty · « **Reply #6 on:** August 30, 2013, 10:14:57 AM »

This is all good information. I'm a pretty good mechanic, so I'll keep all of this in mind. Hopefully the ones I have will hang in there, but the front one didn't feel 100% smooth when the crank was out and it was only wet with the residual fuel wash. I can't hear any noise or feel any roughness when I turn it with the engine assembled. I filled them with air tool oil before putting the crank back in.

BTW, I meant to say earlier, there is no spacer like Steve mentioned between the crank and front bearing. Since that was an ST with the spacer, I'll ask a side question here; is there any relationship between Super Tigre and Thunder Tiger, other than that my TT has an ST NV & venturi?

Thanks, guys,
Rusty

Steve Helmick · « **Reply #7 on:** August 30, 2013, 08:06:06 PM »

Rusty...No relationship between TT and ST, tho I seem to recall that there might have been a lawsuit over the use of the name "Tiger". Being as it's spelled different and the engines are no way copies of ST's, I don't think there was any settlement awarded.

Steve

RknRusty · « **Reply #8 on:** August 31, 2013, 09:10:50 PM »

I cranked it up today and it lit off on the first couple of flips just like it always does. This is the most cooperative engine I've ever had. It ran smooth with no sign of bearing problems, though I don't know if you can tell trouble is coming until one of them completely lunches.

kenneth cook · « **Reply #9 on:** September 02, 2013, 08:46:21 AM »

Rusty, ball bearing engine will make a howling noise when they're really going. It will be noticeable even flipping them over during starting. The crank will feel a bit rough even lubricated. So in short, you'll have a warning unless the cage decides to depart which doesn't generally happen. Dirt is the problem and if this happens repeatedly, it will lend itself to short bearing life. Don't hose the front of the engine off with fuel like you can do with a bushed engine and re fly. It will give you short bearing life as you'll never rid the bearing cage completely of the grit. Ken

RknRusty · « **Reply #10 on:** September 02, 2013, 09:48:05 AM »

Quote from: kenneth cook on September 02, 2013, 08:46:21 AM

... Don't hose the front of the engine off with fuel like you can do with a bushed engine and re fly. It will give you short bearing life as you'll never rid the bearing cage completely of the grit. Ken

Great advice, I didn't know that, and luckily have never done it. During my post flight cleaning I have skeeted alcohol around the drive plate to remove any nearby visible grains of dirt and then always squirted some oil behind it. In the future I'll remove the drive plate and wipe it clean if I see any dirt that could get behind it. I've never had what you would call a crash where the spinner has planted, but have had a couple of belly busters that sprayed some grit.

Rusty

kenneth cook · « **Reply #11 on:** September 02, 2013, 11:41:20 AM »

Some engine have better protection due to the design of the drive washer. I just had something interesting happen as well, I had the crank hit a small rock underground and it mushroomed the threads not allowing the nut to come off. If you find yourself doinking the plane on a regular basis, placing a piece of surgical tubing over the venturi can help. Make it about 1" long so that it doesn't flop over in the wind. It will fold back over if the engine does go deep into the ground. This dork tube can prevent the engine from ingesting dirt as you found on top of the piston. Ken

RknRusty · « **Reply #12 on:** September 02, 2013, 01:05:51 PM »

Quote from: kenneth cook on September 02, 2013, 11:41:20 AM

Some engine have better protection due to the design of the drive washer. I just had something interesting happen as well, I had the crank hit a small rock underground and it mushroomed the threads not allowing the nut to come off. If you find yourself doinking the plane on a regular basis, placing a piece of surgical tubing over the venturi can help. Make it about 1" long so that it doesn't flop over in the wind. It will fold back over if the engine does go deep into the ground. This dork tube can prevent the engine from ingesting dirt as you found on top of the piston. Ken

I've seen some drive plates that have a skirt extending back over the nose of the crankcase. Mine isn't like that though. I do use a spinner and think that adds some minimal protection from dirt. Haven't thought of the dork tube. In the past I had been using one layer of panty hose on the venturi, but started leaving it off. I think I'll put it back on.
Rusty

Steve Helmick · « **Reply #13 on:** September 04, 2013, 11:36:47 PM »

The "Dork Tube" does work, and was created by some of the local Vintage Diesel Combat guys. Better, however, to avoid crashing. Having a well trimmed model and flying the pattern every flight helps a lot. No "indecision crashes" needed. There are still ways to crash, of course, such as hooking up your lines backwards.

Steve

RknRusty · « **Reply #14 on:** September 05, 2013, 06:55:12 AM »

Quote from: Steve Helmick on September 04, 2013, 11:36:47 PM

The "Dork Tube" does work, and was created by some of the local Vintage Diesel Combat guys. Better, however, to avoid crashing. Having a well trimmed model and flying the pattern every flight helps a lot. No "indecision crashes" needed. There are still ways to crash, of course, such as hooking up your lines backwards. Steve

I have a bad habit of bottoming out, though my last dirt eating belly flop was from some confusion on the second half of my horizontal 8. Flying tired. As far as bottoming on loops goes, I think I'm looking at the plane with tunnel vision instead of a wider field. Funny that I have this problem after being so used to fast 1/2A, but I was never concerned with beautiful shapes doing that.

This is more for the Flying discussion though. I'm off to practice right now, so I'll update that post this evening. And if I get time to fool with the camera, maybe I'll have a video of some much improved pattern flying.
See y'all in the funnies,
Rusty

RknRusty · « **Reply #15 on:** September 10, 2013, 09:31:17 PM »

I see Boca has choices of ceramic, stainless steel and chrome steel bearings. The Chrome are the economy bearing. Always on a tight budget, I'm wondering if the $19 bucks I save by getting the economy Chrome rather than stainless is worth the savings. This is an engine that gets a few flights once or twice a month. They don't say which ones are OEM.
Rusty

kenneth cook · « **Reply #16 on:** September 11, 2013, 01:25:07 PM »

The economy bearings Boca provides are superior to what is already installed in the engine. They last just fine as long as you oil them prior to storage. Ken

RknRusty · « **Reply #17 on:** September 11, 2013, 01:28:14 PM »

Thanks, Ken. I'm going to order a set of spares.
Rusty

RknRusty · « **Reply #18 on:** October 16, 2013, 10:36:39 AM »

I could hear some noise resonate through the Monokoted wings when I turned the prop. And the front one seemed a little hitchy when I turned it with my finger with the crank removed. So I went ahead and removed them and put the new ones in. I used Jim Kraft's method and it went pretty easily. At first the new ones were a little stiff so I re-heated the case and knocked on it, loosened and re-tightened the prop and it feels good. They aren't completely loose but I think it's because they're packed with grease. Flipping the prop is quiet and smooth and it'll spin for 5 or 6 seconds. Oddly, the old front bearing doesn't have the little roughness that I felt while it was in the case. I haven't mounted and cranked it yet. If y'all think my description sounds like it needs more atention, I'll take another look before I fire it up.
Thanks for the help.
Rusty

Quote from: Jim Kraft on August 30, 2013, 06:45:19 AM

I have tried most ways of replacing bearings, and I find a heat gun works best for me. I lay the engine back side down on a block of wood, and then heat the case till the rear bearing falls out. Then with a glove turn the engine over and tap it on the wood to remove the front bearing.

I heat the case again to install the rear bearing that I have put on the crank, and use a dowel in the hole in the back of the crank to push it in to the case. Then slide the front bearing in. I then put on a prop, snug it up good, and heat the case one more time to seat the bearings.

Not sure this is better than any other way but it works well for me. When working on Saito's, I do put the crank and bearings in the freezer over night as the bearings fit very tight in the ones I have replaced.

Brett Buck · « **Reply #19 on:** October 16, 2013, 10:56:19 AM »

Quote from: RknRusty on September 10, 2013, 09:31:17 PM

I see Boca has choices of ceramic, stainless steel and chrome steel bearings. The Chrome are the economy bearing. Always on a tight budget, I'm wondering if the $19 bucks I save by getting the economy Chrome rather than stainless is worth the savings. This is an engine that gets a few flights once or twice a month. They don't say which ones are OEM.
Rusty

I have only used the cheapies and they seem to be fine to me. They really are a lot better than the originals.

Brett

RknRusty · « **Reply #20 on:** October 16, 2013, 01:12:10 PM »

Quote from: Brett Buck on October 16, 2013, 10:56:19 AM

I have only used the cheapies and they seem to be fine to me. They really are a lot better than the originals.

Brett

That's what Ken says too. The only difference from the originals I can see is that the inside of the original front bearing was open, and both sides of it are sealed on the Boca bearing. The rear bearings were open on both sides and identical looking, and that's where I could see the new one was packed with some blueish heavy grease.

Rusty

Brett Buck · « **Reply #21 on:** October 16, 2013, 01:43:34 PM »

Quote from: RknRusty on October 16, 2013, 01:12:10 PM

That's what Ken says too. The only difference from the originals I can see is that the inside of the original front bearing was open, and both sides of it are sealed on the Boca bearing. The rear bearings were open on both sides and identical looking, and that's where I could see the new one was packed with some blueish heavy grease.

Probably should remove the rear shield and wash the grease out of it before installing it. Put light oil (like Air Tool oil) to replace the grease.

Brett

RknRusty · « **Reply #22 on:** October 16, 2013, 02:13:28 PM »

Quote from: Brett Buck on October 16, 2013, 01:43:34 PM

Probably should remove the rear shield and wash the grease out of it before installing it. Put light oil (like Air Tool oil) to replace the grease.

Brett

Ahh crap... not you, Brett, thanks for the tip.
I'm fixing up the Shoestring tonight. If I have time I'll do it, If not I'll take my heat gun to Hville and do it there.

Rusty

RknRusty · « **Reply #23 on:** October 16, 2013, 09:32:34 PM »

I did it. It spins more freely now too with the air tool oil. Glad you caught that. I went to Boca's website and they recommended it too. I'll crank it in the morning.

Rusty