Tee Dee Performance Crank

I have one engine I bought off ebay that has this crank.

I dont know if it weighs less than stock when I get a moment I will check it out and compare a few things such as the intake. I would imagine the steel should be upgraded over stock.

The lightened crankshaft on the right is used in the TD050 R/C which - because of its muffler - has non-SPI design and thus a bit lower output than the normal TD049 and 051 cousins. In order to partly compenstae the non-SPI handicap COX applied the lighter crank to restore/approach the output of the cousins.

I used one of these in a tee dee .051 that I built for higher rpm. It would turn an apc 5.7X3 which was cut down to 5x3 over 22k on the bench. Unfortunately, it only had a few flights before the pin sheared off.

Thank you Balogh gooood info - hows that Speedy .010 doing did you figure out anything?

Hi fit90 I would imagine if you botch the engine in the ground while running the pin is at risk. Do you recall ever smacking it in?

I was hoping the steel was a better grade


This listing is for one Cox 049 051 Tee Dee High Performance Crankshaft.
Features:
Lightened, Balanced Design
Drilled Crankpin
New Original Cox Items

Designed For:
Cox .051 Tee Dee RC Engines
Cox .049 .051 Tee Dee Engines

Never smacked it in. I think the engine was probably turning 24k++ in flight and probably just went beyond its capabilities. I don't know if the crank was a Cox original or modified.

Last night I opened up my .051 RC and it appears to be the same crank. I dont know if it was worth drilling out the pin to save a hair bit of weight in lieu of what happened to your engine. Good to know I will have to watch how much prop weight, drag and pitch the engine swings. Perhaps only use it on a light low drag airframe to keep from shearing the steel and avoid a elect starter.

Hm. Rather interesting finds there guys. The hollow pin would really concern me. Wouldn't take much to shear it off.




Rolla

I have never measured it but I would assume the hole in the pin does not run the full length of the pin...thus the pin is not hollow in its stem where it meets the flywheel, where the bending moment on the pin from the piston rod is the highest. So the concerns regarding the reduced strength of the hollow pin leading to the pin getting sheared under some excessive load - in principle - are baseless...but again, I have never compared the depth of the hole with the pin length. And never experienced a sheared hollow crank-pin, either.

I went ahead and bought one off ebay (while the option is there) as I only have one on my .051 RC I wanted a second to have as back up and for now will install on another engine. The weight is 6.9g the hole does go deep thru the pin apparently to the flywall. Note the crank did not come in a OEM package but does appear to match .051 RC.



Without me pulling out a stock crank anyone know what the weight is??

I bought  two from the e-bay seller and one of them has a burr inside for the 5-40 prop screw threads. I am waiting on a 5-40 tap from MidwayUSA where I get gun smithing and reloading supplies.

I am currently polishing 4 cranks, 2 factory and 2 of theses so called heavy duty cranks to rebuild 4 Tee Dee .051s. Considering they are all the same weight I don't expect any performance gain. I expect the $50 is/was a poor investment except that I had a few spare Tee Dee crank cases (all all the other parts for .049 TeeDees including a left hand crank)

They are about 7dollars over priced although very rare. I plan to use 4.2 x 4 props and put this on a SPI TD .049 to explore a possible .6k to 1.2k gains in rpm after two key mods one is now completed in the photo the inside edge of the intake is sharpened on the left side.
The second arrow will be where I grind in with my dremel a small channel will angle out to speed up air / fuel into the crankcase.

Be careful not to impact the balance of the crankshaft by the asymmetrical modifications. An unbalanced crank may easily rub out the crankcase such that it will not seal along the shaft anymore and the engine can not even be started.
Once I purchased on ebay an allegeadly new TD049 with a crankcase rubbed so loose that it had to be replaced by a new one before I could start it up.

Yes watching it as I go but the flywheel was never really balanced to the crank more so for the piston. So far minimal impact however the next trick will improve dynamic balance if anything with the large intake hole the channel will offset some of that loss.

Here is an example with the channel in place. Because the piston was lightened up the owner decided to remove area off the flywheel to compensate but offset for the intake weight loss in conjunction. Thinking deeper the piston location where mass is best suited hence the deg of offset.

FYI the Medallion crank is 7.1g (per my scale) there is a .2g difference between the TD crank.

I am replacing that crank from a previous upgraded engine TD on the outside will now be a complete TD.

I don't think that the crank web mods will do very much at the usual revs that a cox engine can take (i.e. around 20-22 krpm). You'll need to make careful notes though in order to see what works and not for you, but those mods are mainly for high revs I believe.

One mod that that does work well at our regular revs, and also for RC engines, is to improve the front end of the crank. There is often a lot of dead volume there that comes from saving money/time in the machining process, rather than optimizing for the engine. By filling this volume with epoxy (e.g. JB weld) you can improve the flow through the crank and also increase the crankcase compression, thus aiding the scavenging.

Just take a look at any of the high performance engines (below is a crank from Rossi) and you'll see what to do.
This mod will give you a few hundred rpms, in general, and it improves throttling too. I've done it on my Cox 05RC, and a few other engines too. The worse case I have ever seen in any engine is on the Fox .15BB, there the crank is threaded so far that the threaded prop stud is visible inside the crank...

RE above: We see the Medallion crank is heavier than the TD crank by a micro bit... TD crank is shorter and has a larger amount removed for the intake

1/2A Nut, sounds like you are trying to make a TD from a Medallion. If true, be careful as the Medallion crank and case are longer than the TD...what happens is the TD crank in a Medallion case is a few thou too short and the drive plate hits the nose of the case. I fixed this years ago simply by reducing the nose length on my disk sander then beveling the the front nose hole slightly to remove the swarf.

Surfer_kris, Exactly what I was planning, don't know if on the small crank it will make much difference but since I am building up 4 TDs I plan to add the intake "ramp" to one of the old and one of the new cranks Leaving one of each basically stock and see. Then I will add on a "improved venturi" (opened to .145) to each engine one at a time to see.

I plan on these to be on light combat planes and want max power but still easy starting

Currently I have 2 Medallion .049s, 4 TD .049s, and 3 TD .051s and spare parts enough to build up two more TD in .049 or .051

Good info Kris and Fred all this should be good reading for those checking in.

Yes I normally use a phenolic thrust washer this one didn't have enough gap so it went without / pic shown of the finished gap after using a aluminum carb body.

JB weld will stick and stay, the ramp trick has been done by many. So far I have only done the first mod mentioned with pic. I will run it up to get a base reading then add the ramp and channel and see what gains are made. Since the pin is bored out this one will only get small, (thin airfoils) light low drag props. SPI .049 cylinder gets the simple throttle sleeve to keep the rpm down during break in and till ready to take a tach reading or to launch to reduce stress on the pin. I want to try a bored out venturi shown in pic as there is less obstruction over a RC carb. I have two different aftermarket NV will try the Kern Kraft after break in and a base reading is done with the stock NV.

I won't use a 1/2A elect starter due to bored out pin.

The medallion engine comes with a bare aluminum prop thrust plate. I may source a bare aluminum carb body to replace the red one purchased (as this is a .049) for an all aluminum look.

Fred if willing let us know what gains you see once done.

FYI you can get the fine thread NVA assy from Texas Timers for $15 plus modest shipping and Hank Nystrom the owner is super fast filling orders  

http://www.texastimers.com/

I also buy his fine thread retro fit NVAs (for reed style back plates) and sleeve them into my .049 Aero Norvel engines to run on pressure bladder, so far the JB weld has held up to 35% nitro.

I think with proper prep/clean/prep/clean the small dab of JB as a ramp inside the .049/.051 TeeDee Crank window will hold without problem.

Heading to town in a few for new JB weld as my tubes are over 5 years old. Plan to photo document the builds this afternoon and hopefully get some bench time on each engine tomorrow or Saturday

Shaweet Fred, this is getting juicy look forward to your documentation.


This weekend if not sooner I plan to fire up my converted engine and do throttled controlled rpm rich break in.
Will list static tach readings as I go into the mod stages.

May use the APC 4.2 x 2 on the bench to keep the load down and to simulate unloaded flight rpm if with a 4P.

Well not really, once done with this post I will mix the JB and do the "Ramp" mod to 1 each of the crank styles.

I plan on testing on the bench with a Green 5" x 3.5"P well balanced prop, 25% Sig champion fuel with a good oil package for these Iron engines.

All engines will start with Doug Galbreath adapter heads for Nelson plugs (standard heat range) All P/Cyl sets are .049 from Bernie and each has the same ball socket slop and dry drag as per Paul Gibeaults Mouse race engine prep article. (If you have not read this down load, you are missing a lot of great and proven information, Paul Gibeault is referenced all over the interweb as a expert in this field)

https://www.coxengineforum.com/t753-the-revised-2011-gibeault-mouse-race-program?highlight=mouse

Eventually I will post bench RPM, and in-flight performance results---- but only for the base line set up.

I was a test officer for the Army and know the math for all the variations and do NOT intend to write a 150 page "Tee Dee Modifications Test Results Document" - TDMTRD. I did that for 11 years in USAOTC and got paid well for it. (Thank all you tax payors! grin).

Variables include: Cox standard head/Cox High Comp Head/ Nelson NL05  base line standard and/ Nelson NL07 Hot plugs. Prop dia and pitch. Venturie inner diameter (.110" to .145"). Fuel Nitro % range 10% to 35% on hand with the correct lube package for theses engines, and the ability to mix any ratio I desire. Probably will play around 40% to see if it really matters.

My Test horse aircraft is a Jeff Dawson combat design close to a Larry Driscol "Lite Hawk" that I built a tad heavy (7.9oZ with TD) but can safely fly without a figure 9 ending...Grin

4 sets ready for JB and assembly (-) the one buggered crank



Problem crank with burr, notice the case hardened screw from Berni has 1/4" of the threads buggered up...I will chase with a new 5-40 tap once it arrives.



The "heavy Hawk" Fred built

Nice layout looks like some fun Fred!

I went ahead and fired up my engine 3.5 turns out with a wood tarnado 6x2 very light prop low pitch perfect to break in the engine and avoid any high rpm. The lil beast didn't want to turn slow lol I had to choke off the exhaust throttle all the way and add another half turn just to keep the thing tame. So far 2 rich runs about 3 mins each will do a couple more for good measure take it apart clean and look for black aluminum goo. I may end up filing down for a thrust washer. I don't really like flipping these snarling things just too snappy on 30% nitro 25% castor blend. So far I have found the aftermarket aluminum carb bodies to seal well they come with a rubber O ring in the front and a rubber gasket for the back end. So far no bad vibrations from mod 1 or from the vintage prop I didn't bother to balance it during this break end period as I intend to use a APC prop in the end.

I used two shims and a cox high compression head, look forward to some tach readings this weekend.

Exhaust ports with a vintage new old stock OEM thick walled TD cylinder





This engine will be a back up / alternate open exhaust speed engine for my original design the 1/2A Skorch.
Tatone muffler and RC carb with a Kustom Kraftsmanship pressure tapped backplate-  TD .051 / 5 channel sport / speed plane with flaps.

Is this the 051 engine whose crank you have lightened? I am looking forward to your tach readings.
On the aftermarket aluminum carb body, did you buy that from COX Int'l? I have never seen these come with O-rings.

The speed-plane is a beautiful deign, it resembles the ones with 010 and/or 020 engines you posted in another topic...I gather this is RC, and not CL?