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Cox Engine of The Month
February-2024
1/2A Nut's

"RC Speed Boat Power Drive TD .020"

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Post  gvc Wed May 25, 2022 2:17 am

I have a RR1 with play in the crank.  When the piston is at the lowest you can make it go up and down slightly by “rocking” the crank.  I assume the journal is worn.  Apparently the crankcase can be re-sleeved.  I would like to find out if there is anyone out there who can do that.  Thanks
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Post  Marleysky Wed May 25, 2022 7:19 am

3 am in the morning, worrying 'bout a wobby crank? Well WELCOME to the Forum! lol!

you assumption is probably correct. do you have any other Cox 049 engines you can swap cranks and crankcases with to verify the slop in the journal? do you know the history of your RR-1? Must have been run without proper fuel/oil mixture to wear that much off the journal, usually that is where castor oil congeals, heats up and slows the RPMs down. I'm not a machinist, the closest thing I have to a lathe is a hand drill. I'm sure someone in the group could tell you if its possible to re-sleeve the crankcase. If I were going to run it, I'd find a substitute crankcase, or NOS replacement.
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Post  gvc Wed May 25, 2022 9:01 am

I did change out the crankcase with another but had to use the RR1 crank because it has that little pin used to drive the rotary valve. The wobble improved significantly. I wanted to keep the RR1 stock and use that cool gold ribbed crankcase. Thanks for the reply.
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Post  aspeed Wed May 25, 2022 3:14 pm

I bushed a few many years ago with some brass as it was just available. Made a sleeve with a thin wall and just reamed the case on a drill press. The fit of the crank was very close until it was pressed in. Then it got tight and had to be refit. Took quite a bit of time. On the old cases like yours it is very thin where the bushing gets pressed in. This wear is very common on the Bees and gives an erratic run. Foxes are pretty sloppy after a lot of running too. I have had a few Thunder Tiger .07s that were loose from new as well. I doubt very many guys have rebushed them because a new case is pretty cheap. The RR1 case is pretty rare.
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Post  GallopingGhostler Wed May 25, 2022 6:49 pm

Marleysky wrote:3 am in the morning, worrying 'bout a wobby crank?  Well WELCOME to the Forum!  lol!
Yup, goes to show @gvc fits in with the rest of us! Laughing

Wobbly Crank 2022-036

Welcome to the forum, gvc!

Marleysky wrote:you assumption is probably correct. do you have any other Cox 049 engines you can swap cranks and crankcases with to verify the slop in the journal?  do you know the history of your RR-1? Must have been run without proper fuel/oil mixture to wear that much off the journal, usually that is where castor oil congeals,  heats up and slows the RPMs down. I'm not a machinist, the closest thing I have to a lathe is a hand drill. I'm sure someone in the group could tell you if its possible to re-sleeve the crankcase. If I were going to run it, I'd find a substitute crankcase, or NOS replacement.

Personally, I don't have an RR-1, so can't contribute much regarding re-sleeving your crankshaft journal bearing surface. However, please give some time for the others to respond. Also, it would be helpful if people knew your approximate location, so they could steer you to someone.

There is another in this forum who also sells machined products for Cox and a few other half-A engines on:

https://kamtechnik.com/contact-us/

If he doesn't or can't do this service, may be he can direct you to someone who can. Popcorn

Another place to inquire is at Stunt Hangar: http://stunthanger.com/smf/index.php

Again, welcome to the forum! Thumbs Up
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Post  gvc Wed May 25, 2022 11:10 pm

Thanks for the leads. I am in Northern CA.
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Post  davidll1984 Thu May 26, 2022 8:06 am

First hello I think it would be impossible to do a buching to repair because the particularity of this crankcase would make it fragile or even detach a part of the front with the grooves this is the line in the piece it leaves very little material to machine Could be possible but not 100% sure It would be possible to make this feature on another crankcase with a swan neck and anodize gold color
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Post  davidll1984 Thu May 26, 2022 8:17 am

I have already managed to repair one with a pipe cutter I have worn out the round cutting wheel and I have place tight on the crankcase then turned a few turns, tighten and repeating until the crank turns with a small friction restriction !!!! dont cut the crankcase Wobbly Crank Img_2339
its this engine Look the front this is the result and i made it anodized
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Post  aspeed Thu May 26, 2022 9:28 am

Interesting method. I noticed on my worn ones that the wear was on the bottom of the case at the back. The front was not too bad. Maybe a short bushing at the rear would not weaken the case too much. It would have to be machined in very carefully.
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Post  davidll1984 Thu May 26, 2022 10:16 am

On the back i used the Ball reset tool tink or it was a tool box I'm not sure I remember I asked m'y self the question for a while the principle is to use a round object with a taper inside so as to crush the outline of the hole inside or it could be a punch to make holes in the leather I I don't remember anymore
Huh... I used a bit of all sorts of things until it worked lol! After the anodizing it was tight I did a polish with car polish and a dremel tool To lap the crankcase and crankchaft To mate them perfect and i have To use two thrust washer on this one One is over the wide part of the crank and one on the drive plate spline as usual but this engine did not have it was very worn I also had to install a buching in the piston conecting rod
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Post  gvc Tue Jan 17, 2023 5:11 pm

I somewhat resolved the wobbly crank by using a crankcase from my parts box. Thanks for all the responses.
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Post  gvc Tue Jan 17, 2023 8:50 pm

I have to post a 5th time before I can use the for sale/wanted forum so this is it.
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Post  Michpatriot Sun Jan 22, 2023 12:45 pm

Well I bought a new in box Venom 2 from a oldtimer fellow C\L fanatic, and was intending to use it to power my girls Man Win trainer. Straight out of the box I noticed that the crankshaft was very wobbly, you could see with a prop on it that the prop tips would move 1\4" side to side. It was like a joystick, not to mention the thrust slop. I ponder it for a few days and concluded that maybe the Venom was manufactured loose for more power..boy was I wrong! I should have gone with my gut feeling to find another crankcase and crank even though it was brand new. I decided to start it, and on the third rich tank.it locked up..broke the connecting rod right where it connects to the ball in the piston..Crazy! Never in 30 yrs flying nitro have I seen a broken connecting rod.
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Post  aspeed Sun Jan 22, 2023 12:54 pm

I have had/seen a broken rod that went through the case of a TD, a rod that wore through the top of a piston in a swap meet motor, broken cranks at the crank pin.... Later cranks had a thicker web in the TDs and I believe the reedies too? Maybe your piston/rod socket was loose?
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Post  HalfaDave Sun Jan 22, 2023 6:44 pm

Hi All,
I had a pull start Cox Sanblaster rig,
To put on my new RC (Heathkit) equipment.
Good Luck,
Dave
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Post  Yabby Mon Jan 23, 2023 3:53 am

broke a controd on a piston where it connects to the piston. TD at absolute full cry on 42 foot steel tent pegged DAMMIT! Plane was a write off engine seemed surprisingly ok, quick cleanup disassemble on launch table and clean and into another plane. To my surprise started perfectly, ran great! Launched plane, flying around, all was good, and then silence. The engine just stopped. Paranoid Huh...
Had a look, didnt turn over so good anymore.

Wobbly Crank Piston10

Cant really blame Cox for that one though. lol!

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Post  getback Mon Jan 23, 2023 5:42 am

Hi Gvc , there was a guy on here that did a repair on the journal with a valve guide from i think was a Porsche , so you said you were looking for someone I would try engine machine shop they do this work as in replacing guides and could possible turn on down on a lathe and press in in for a FEE ! Don't cost much to find out and beeing in CA. in am sure there are some good shops out there   Small Cox Logo And I would have sent that Venom back for a refund off of eBay as soon as i seen the slop ! Happy New Year  Wow here is one for sale Bid > I would ask him what he means about the Bad crankshaft , Maybe the pin us broken the shafts very seldom wear out.  https://www.ebay.com/itm/266096417685?


Last edited by getback on Mon Jan 23, 2023 6:02 am; edited 1 time in total (Reason for editing : add on)
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Post  gvc Thu Jan 26, 2023 10:35 am

Thanks getback - I contacted the seller with the RR1 parts, you guessed it, the crank pin is broken off. Thanks for the lead. I may bid on the parts and hope that the crankcase is better than mine.
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Post  gvc Thu Jan 26, 2023 10:42 pm

Here’s my RR1 with a Babe Bee crankcase. It’s a strong runner with none of the finicky reed valve issues. It is a little hard to start requiring lots of primes.Wobbly Crank 7002f210
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Post  getback Fri Jan 27, 2023 5:07 am

Nice looking engine , may try a new/difft. glow plug and see if it starts easier . Those parts only come around ever few years from what i have seen ( just keep that I mind ) Is that old castor at the front drive plate ? Good luck if you decide to bid . Small Cox Logo
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Post  gvc Sat Jan 28, 2023 9:09 pm

I suppose it is baked on castor oil. I bought the engine used and was disappointed with the worn crankcase. I think the buyer sold it in good faith and worked with me a little when I pointed out that the engine was unusable.
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Post  GallopingGhostler Sat Jan 28, 2023 9:22 pm

gvc wrote:
gvc wrote:Here’s my RR1 with a Babe Bee crankcase.  It’s a strong runner with none of the finicky reed valve issues.  It is a little hard to start requiring lots of primes.Wobbly Crank 7002f210
[...]
I suppose it is baked on castor oil.  I bought the engine used and was disappointed with the worn crankcase.  I think the buyer sold it in good faith and worked with me a little when I pointed out that the engine was unusable.
In salvaging the situation restoring the engine to a great runner, I'd say that now you have a story teller. That hybrid engine, uniquely customized by you, restored to fine running condition is a potential winner for the next COX ENGINE OF THE MONTH CONTEST as is. But, you could possibly highly polish the Babe Bee crankcase to a mirror finish, and send chills up @fredvon4's spine. Very Happy
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Post  Michpatriot Sun Jan 29, 2023 8:37 am

Awesome setup you have there!
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Post  getback Mon Jan 30, 2023 6:20 am

WOW it fetched a pretty good price >> https://www.ebay.com/itm/266096417685 Small Cox Logo
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Post  gvc Mon Jan 30, 2023 10:30 am

I’ll say, I was stunned. It looks like I should be happy with the Babe Bee crankcase. Here’s another, I wonder if it will go for the asking price?

https://www.ebay.com/itm/115514154846
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