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seized Medallion .049

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seized Medallion .049

Post  steve thornton on Wed Dec 06, 2017 3:46 pm

I have a Medallion .049 that, while beautiful, is seized. I am familiar with most techniques using heat to unseize engines, but am concerned about damage to the plastic carb body. Any advice would be appreciated.
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Re: seized Medallion .049

Post  Ken Cook on Wed Dec 06, 2017 4:05 pm

Steve, the plastic carb bodies can tolerate a fair amount of heat. However, it sounds to me as though the engine has had it's share of castor oil. The engine should really be taken completely apart. The shaft probably has a lot of varnished and congealed castor oil inside the case and on the shaft. I use a heat gun which can offer fair accuracy where it's pointed. I like to remove the plug and I put some oil on the top of the piston and screw the plug back on and heat it. Wearing a glove and having a prop on the shaft you can offer slight pressure to allow it to turn over. Don't force it over. Let the heat do it for you.
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seized Medallion .049

Post  steve thornton on Wed Dec 06, 2017 4:39 pm

Ken Cook wrote:            Steve, the plastic carb bodies can tolerate a fair amount of heat. However, it sounds to me as though the engine has had it's share of castor oil. The engine should really be taken completely apart. The shaft probably has a lot of varnished and congealed castor oil inside the case and on the shaft. I use a heat gun which can offer fair accuracy where it's pointed. I like to remove the plug and I put some oil on the top of the piston and screw the plug back on and heat it. Wearing a glove and having a prop on the shaft you can offer slight pressure to allow it to turn over. Don't force it over. Let the heat do it for you.

Thanks Ken, I've done this on the larger engines with great success, but have been nervous about the carb body on this TD. You're absolutely right about the gunk. I'm sure it was not cleaned after its last run. I want to be sure the conrod is loose from the crank before I try to disassemble it. I'll put some heat on it tonight and hopefully get it finished up. The engine is very clean with no scratches, and I got it an estate sale and am thinking it may have been used once and sold or traded.
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Re: seized Medallion .049

Post  Ken Cook on Wed Dec 06, 2017 5:45 pm

If you have the Cox wrench, I use it to remove the collet that retains the carb body. The older wrenches were far superior to the newer style black ones. You have to be very careful not to bugger up the threads. The spanner's tooth is not designed to hit the threads however the collet does have some taper on it. Make sure you have full contact using the wrench and don't slip. Once the collet starts loosening, keep turning and force the drive washer off of the crank. At some point your going to need to remove the backplate. That can be a real pain in the rear. At this point, I like ot firmly have the engine in my vise protected with wood or a rag with only enough pressure to retain it in the vise. I use the wrench but I place the wrench on edge and using a adjustable and firm pressure I twist off the backplate. Ken
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Re: seized Medallion .049

Post  balogh on Thu Dec 07, 2017 11:47 am

It took me some time to realize the glow head wrench actually has the function of removing the Tee Dee (and Medallion) backplates as well: the teeth of glow head wrench also sit in the diagonal recesses machined on the rim of the backplate DAMMIT!
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Re: seized Medallion .049

Post  steve thornton on Fri Dec 08, 2017 3:41 pm

balogh wrote:It took me some time to realize the glow head wrench actually has the function of removing the Tee Dee (and Medallion) backplates as well: the teeth of glow head wrench also sit in the diagonal recesses machined on the rim of the backplate DAMMIT!
Thank you Balogh and Ken. I was able to loosen it up and take it apart, the hardest part was getting the venturi loose. As a result of my retirement/relocation last year, some of my favorite tools are not "readily available," and I had some difficulty finding a wrench that was narrow enough to fit. The engine will turn freely but has a catch after passing TDC leading me to think that I need to replace the rod. I have no experience at that, but do have a tool...would love to see a video. Any ideas on that?
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Re: seized Medallion .049

Post  balogh on Fri Dec 08, 2017 3:50 pm

Steve the rod alone cannot be replaced only with the piston together..but the balljoint of the rod can be reset in the piston socket if it is loose. It takes a resetting tool sold by COX International and Exmodelengines.
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Re: seized Medallion .049

Post  steve thornton on Fri Dec 08, 2017 3:59 pm

Thank you Balogh, I have that tool, and I'll try it on an old piston/rod. Thank you for the help and experience. I'm not a real mechanic, just scrape my knuckles a lot!
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Re: seized Medallion .049

Post  balogh on Fri Dec 08, 2017 4:19 pm

Apply the hits on the tool with a small hammer very gently because excessive force may distort the piston crown out of round . Check constanly the remaining gap in the socket. If the gap disappears completely you may end up with a piston crown punctured by the rod very soon. There is no exact definition of force that you should apply so be careful. Luckily 049 piston and cylinder are still sold just in case things happen to go wrong.
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Re: seized Medallion .049

Post  roddie on Fri Dec 08, 2017 7:40 pm

Hi Steve. I've read-through this thread a couple of times.. and where its title is "seized Medallion .049"; you refer to this engine as a Tee Dee in your 2nd post. I don't know of your experience with Cox engines.. or where you got this engine. If you'll "humor me".. I used to confuse a Medallion .049 with a Tee Dee ".051".

Below; a Medallion .049 photo:



and below; a Tee Dee .051 photo:



They look similar.. because of the red carburetors. A Tee Dee .049 has a black carburetor; which distinguishes it as a Tee Dee engine. Most all Tee Dee engines have black carbs.. except for the .051, .050RC and the some Tee Dee .010's.

If this engine is by chance; a "higher-performance" Tee Dee .051.. there may be a "taper" in the cylinder-bore at TDC. I'm however NOT SURE about that.. but it could explain the "catch" or tightness that you felt in the piston/bore-fit. I just wanted to mention that.. because resetting the ball-socket joint; although possibly needed.. would have no effect on that.

I'm not an "engine-guy".. so please excuse me if I've misrepresented/misinterpreted anything.

EDIT: The morning after.. Embarassed SORRY.. Rolling Eyes after reading your avatar.. you obviously know which engine you have.
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Ball socket

Post  Mike1484 on Sat Dec 09, 2017 2:00 pm

Setting the ball and socket on these small motors can be a challenge . I wonder how Cox did it at the factory . I'm sure they didn't set them by hand , perhaps they used a press and die .

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Re: seized Medallion .049

Post  balogh on Sat Dec 09, 2017 2:10 pm

I wonder too. In principle the gap could gave been  set in the factory  with a press with all dimensions and material thicknesses known. Indeed almost all COX engines even the smallest 010-s  have a quite fine balljoint play as new. I had a brand new 09 though that had a very sloppy fit that I had to reset before the breaking in run.
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Re: seized Medallion .049

Post  steve thornton on Sat Dec 09, 2017 4:20 pm

Sorry for the confusion Gents, I was thinking of the Medallion I have on my desk while typing! It is a TeeDee and with the glow plug removed it spins freely for a few turns, then gets the "click" at the top. The reason I was trying to clean it up in the first place was to sell it (I have 6 more), and now I'm thinking I may sell it as is rather than take a chance on messing it up, as it is a really nice little engine otherwise. I have a couple of old weak engines I could practice on. Thanks for the help guys!

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Backplate now

Post  steve thornton on Mon Dec 18, 2017 1:23 pm

I have read all the great advice you guys have offered and it worked just fine...and now I don't want to sell it! lol!
I have another that I cannot get the backplate to budge.  Filed the notches square, and still cannot get it to move even with heat.  My question now is what causes these buggers to get so tight?  Is it heat, I cant imagine being able to get them that tight with any tool?
Steve
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Re: seized Medallion .049

Post  balogh on Tue Dec 19, 2017 2:29 am

Though heat conductance of aluminum is very high and you cannot avoid the quick equalization of temperatures of mating aluminum parts, but if you blow heat on the crankcase only and try to loosen the backplate as quick as possible so that the two aluminum parts should have a bit different extent of expansion, that may work. Other than that, the castor gunk solidified between the threads will keep the backplate kinda glued in..though the heat will melt the gunk a bit too. So I would use a hair-dryer with its cone blowing hot air only on the crankcase bottom and - maybe pressing an ice cube to the backplate in the meantime - try to remove it instantly after the heating.


The concentrated cooling of a hot COX head by either squirting a few drops of fuel on it or blowing cool air on it when the engine is hot has the same effect...you typically cannot loosen a COX head when hot unless you suddenly cool it to contract a bit more than the steel cylinder it holds ...
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Re: seized Medallion .049

Post  KariFS on Tue Dec 19, 2017 3:57 am

I sometimes clamp the tool in a vise, so that the tool protrudes just enough to make contact to the slots in the backplate, then push&turn the engine against it.

Andras is right, heat helps, and you can also heat the crankcase and cool the backplate simultaneously. Maybe a piece of ice in the "bowl" of the backplate while heatinh the crankcase?
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Re: seized Medallion .049

Post  roddie on Tue Dec 19, 2017 8:12 am

Do you have any aerosol-spray dust-Remover? That product gets freezing cold. The cans usually come with an extension-tube. Maybe heating that area of the crankcase; followed immediately with a shot of the spray to the backplate might be enough to do the job. Have your wrench ready.. because you won't have much time to work before the temperature equalizes between the two parts.
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