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049 crank vs. 051 crank Babe_b10
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049 crank vs. 051 crank Empty

049 crank vs. 051 crank

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049 crank vs. 051 crank Empty 049 crank vs. 051 crank

Post  Cox International on Tue Sep 15, 2020 1:30 pm

Below a message from a customer. Unsure if for a reedie or rotary valve but we have never heard of this and always assumed that 049 / 051 cranks are identical in dimensions. Of course Medallion and Tee Dee have different cutouts and the Killer Bee  / Venom crank has a balanced face.

Unfortunately, there is a difference between the two cranks, but it is so small that it can only be recognised by measurement. The .051  engines will run  with an .049 crank in it, but with a reduced performance, and this is why I am looking for an .051 crank. The difference we are talking about is approx .010” or one hundredth of an inch!  
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Post  Jason_WI on Tue Sep 15, 2020 2:13 pm

The only difference I know of is the crank web thickness from the early production runs to the later runs that had #2 stamped on the crankcase. Early engines had a thinner crank web. Can’t run a new crank in an old crankcase as it will bind up when the drive plate is pressed on. That difference was for both .049 and .051 TD engines. Diameter of crankshaft should be the same.

Edit. Found a post that shows the difference in the crank web thickness.

https://www.coxengineforum.com/t11418-number-stamped-on-td-lugs
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Post  Cox International on Tue Sep 15, 2020 2:24 pm

Yes Jason, that is correct.

Conferred with Matt from EX, Ronald Valentine and pulled the OEM drawings for Reed and TD / MD and on those, Cox refers to .049 / .051 on the same drawing(s).

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Post  fredvon4 on Tue Sep 15, 2020 5:30 pm

I agree with Jason and I have all the combinations only difference is total length from Face of crank web bearing surface to the nose...I never found a crank for sale that was specific for .049 or .051 and have used TeeDee or Medallion cranks interchangeably until I bought a few bare crank cases from Bernie and Matt

My problem was my cranks were too short and the drive plate dragged on the CC nose...too easy...face off the nose a little
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Post  happydad on Tue Sep 15, 2020 8:04 pm

Jason_WI wrote:The only difference I know of is the crank web thickness from the early production runs to the later runs that had #2 stamped on the crankcase. Early engines had a thinner crank web. Can’t run a new crank in an old crankcase as it will bind up when the drive plate is pressed on. That difference was for both .049 and .051 TD engines. Diameter of crankshaft should be the same.

Edit. Found a post that shows the difference in the crank web thickness.

https://www.coxengineforum.com/t11418-number-stamped-on-td-lugs

Jason: also I took data on the Medallion and TD crankshafts. There was a thought by someone that they were different. They are the same, except as you noted the #2 on the newer crankcases, which MUST. have the matching crankshafts and viseversa. The data is under “Medallion and Tee Dee crankcase. and crankshaft data”.  
   
   Feel free to add data. Just follow the numbering system and use the next number or make up your own. I tried to separate the Medallion and Tee Dee data.

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Post  batjac on Wed Sep 16, 2020 12:44 am

Jason_WI wrote:The only difference I know of is the crank web thickness from the early production runs to the later runs that had #2 stamped on the crankcase. Early engines had a thinner crank web. Can’t run a new crank in an old crankcase as it will bind up when the drive plate is pressed on. That difference was for both .049 and .051 TD engines. Diameter of crankshaft should be the same.

Edit. Found a post that shows the difference in the crank web thickness.

https://www.coxengineforum.com/t11418-number-stamped-on-td-lugs

Ah! Thanks for the information. I was just assembling a TD from parts a couple of days ago and couldn't figure out why, after pressing on the drive plate all the way, the crank had what seemed like excessive end play. The crankcase had the infamous #2 stamped on it.

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Post  batjac on Wed Sep 16, 2020 12:47 am

Cox International wrote:Below a message from a customer. Unsure if for a reedie or rotary valve but we have never heard of this and always assumed that 049 / 051 cranks are identical in dimensions.

Bernie, EVERYone knows there's a difference.  The TD .051 retails for $14.99 more than the standard TD .049 crank...

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Post  happydad on Wed Sep 16, 2020 2:17 am

batjac wrote:
Cox International wrote:Below a message from a customer. Unsure if for a reedie or rotary valve but we have never heard of this and always assumed that 049 / 051 cranks are identical in dimensions.

Bernie, EVERYone knows there's a difference.  The TD .051 retails for $14.99 more than the standard TD .049 crank...

The Helpful Mark

batjac:  I have an extra TD .049/.051 crankshaft. Which do you need? The new or the old? I would have to measure mine, but I think I added it to the data on file. PM me if interested.

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049 crank vs. 051 crank Empty Re: 049 crank vs. 051 crank

Post  batjac on Wed Sep 16, 2020 4:46 am

Happydad. I appreciate the offer, but I'm going a different direction with the new rebuild. See forthcoming build thread.

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049 crank vs. 051 crank Empty Re: 049 crank vs. 051 crank

Post  davidll1984 on Wed Sep 16, 2020 8:35 am

Jerobee tee dee crankchaft  is litle difrent from m'y mesurment Front bearing surface larger Windows port litle difrent like angle is difrent and crankchaft is plated for use of flyweel on cars. cars engine difrent from for pusher type tee dee its crank fit n2crankcase loose litle Not axial play just back an forward if engine run and y place m'y finger on ventury is flyweel get suck in is let me tink of m'y Reed engine damage on m'y tigermoth engine is dieselised rc now run nitro conecting rod get push of the track inside crankcase on low rpm just in flight Not statick lets say is wy use of egr valve is Good for rc cox engine carburateur on rc plane only Huh...

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Last edited by davidll1984 on Wed Sep 16, 2020 10:43 pm; edited 1 time in total (Reason for editing : Ad info)
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Post  gkamysz on Wed Sep 16, 2020 10:09 am

Which dimension was in question here? Was it just tolerance observed? I have 4 cranks in front of me, and all 4 have different bore sizes for the intake passage. Tolerances for sure, but the Medallion crank is definitely a larger nominal size. Why would Cox bother with a larger bore on a Medallion crank when the flow limit is the intake window?
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049 crank vs. 051 crank Empty Re: 049 crank vs. 051 crank

Post  Cox International on Wed Sep 16, 2020 2:27 pm

Below is a copy and paste of the last two emails exchanged and that should put this matter to bed  lol!


Bernie, I owe a huge thank you for your powerful mail –why? Because it made me think again.
I had misread a Peter Chinn review, which in fact said the increased capacity of the .051 came from an increased BORE, and somehow I read stroke.
The .051 that I am working on, has a reduced performance and noticeably, no sub piston induction, so maybe I went to the Chinn article with a preconception. Be that as it may – I feel I owe you an apology for putting you to all that work, and maybe an explanation of how it came about.
I am very impressed with the depth of your knowledge.
With my best regards, (deleted).
.

From: Cox International - Support [mailto:support@coxengines.com]
Sent: 15 September 2020 18:29
To: Deleted
Cc: sales@coxengines.ca
Subject: RE: Cox .051 crank

Deleted,

We are unsure if you are referring to TD / Medallion or reed valve engines but it does not really matter. However, perhaps send a few pics of your 051 engine and the 049 crank / 051 crank that you are referring to and also indicate where your 049 crank and 051 crankcase originated from?

When we purchased the remaining Cox inventory over 10 years ago, we also inherited over 4,000 drawings and there is no such thing as a standalone .051 crank drawing. Of course the Killer Bee / Venom crank has a different faceplate but the bearing surfaces are the same. The Tee Bee and Medallion cranks have different intake cutouts but the bearing surfaces are the same. This morning I did the following.

• Callipered the cranks of .049 Babe Bee, 049 Killer Bee and 051 Killer Bee – All three identical @ 2167”
• Calipered the cranks of 049 Medallion and 051 Medallion – Both identical @ .2809”
• Calipered the cranks of 049 Tee Dee and 051 Tee Dee – Both identical @ .2809”
• Conferred with our competitor; who is hugely knowledgeable re. Cox products – Got the same answer
• Conferred with Ronald Valentine; who manufactures complete Cox engines – Got the same answer
• Posted on the Cox Engine Forum; lots of very knowledgeable members there – Got the same answer

We are even attaching screenshots from the respective drawings; from which you can see that Cox referred to .049 / 051 in the same drawing(s)

Here are a few possible scenarios:

• Your 049 crank and / or 051 crankcase are R&D rejects (there are lots of those out there)
• Your 049 crank and / or 051 crankcase are worn past OEM specs

Simply put, there are no cranks specific to .051 and you will not find one. However, will you be able to get a good fit? Yes, by either replacing the 049 crank and / or the .051 crankcase; depending which part is outside of OEM specs.

Cheers
Bernie
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