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.049 cylinder and piston for .051 Cox_ba12





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Post  Darren19 Thu May 09, 2013 5:45 am

Does anyone know if the .049 piston and cylinder will fit in the .051? I've heard they can fit? That is .049 fit the .051 tee dee?
Thanks!
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Post  JPvelo Thu May 09, 2013 7:23 am

They swap straight across but you must swap the cylinder AND the piston.

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Post  anm2 Thu May 09, 2013 8:13 am

The .049 and the .051 Tee Dee use the same crankcase. The only difference would be the piston and cylinder configuration. As mentioned above, the .051 piston is not for use in the .049 cylinder.
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Post  SuperDave Thu May 09, 2013 8:35 am

Darren:

You've gotten a number of responses as a "guest" why not join our membership and you'll probably get more as well as other benefits?

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Post  Darren19 Thu May 09, 2013 10:34 am

Thanks SD I just joined thanks!
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Post  SuperDave Thu May 09, 2013 10:39 am

A piston and cylinder must be dimenionally a matched set and not intermixed.

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Post  RknRusty Thu May 09, 2013 4:24 pm

Welcome, Darren, glad to have you on board.

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Post  Darren19 Thu May 09, 2013 5:58 pm

Thank you.
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Post  SuperDave Fri May 10, 2013 10:09 am

Darren:

FYI

The difference between a TD .049 and TD .051 is only .002" thus placing them in two different classifications 1/2A and A for competition purposes according the AMA rules.

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Post  pkrankow Fri May 10, 2013 10:53 am

SuperDave wrote:Darren:

FYI

The difference between a TD .049 and TD .051 is only .002" thus placing them in two different classifications 1/2A and A for competition purposes according the AMA rules.

SD

There are quite a few different engine pairs that do this, from several manufacturers, since it allows the same model to compete in 2 classes with an engine swap. The performance between the adjacent sizes in theory should be identical, in practice it is extremely similar or it wouldn't be a working idea.

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Post  SuperDave Fri May 10, 2013 11:12 am

And to take it a step farher the TD .051 piston has two horizontal grooves that allows contest judges to make the displacement determination.

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Post  OVERLORD Fri May 10, 2013 12:12 pm

Here's a picture of the grooved piston to illustrate what SuperDave just said.

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Post  pkrankow Fri May 10, 2013 12:17 pm

Here it is again, side by side.
https://i.servimg.com/u/f83/17/84/87/39/img_2013.jpg
.049 cylinder and piston for .051 Img_2013

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Post  SuperDave Fri May 10, 2013 1:37 pm

Yep, and if you look at an .051 piston out of the cylinder there are TWO indentifying grooves.

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Post  pkrankow Fri May 10, 2013 2:50 pm

SuperDave wrote:Yep, and if you look at an .051 piston out of the cylinder there are TWO indentifying grooves.

SD

Seeing I have never seen a 2 groove cox piston, got a picture?

What is the single groove indicate if it isn't .051?

Phil
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Post  fredvon4 Sat May 11, 2013 9:19 am

My ten .051 pistons all have only one groove...

I have seen photos of two groves but have never touched one
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Post  SuperDave Sat May 11, 2013 9:46 am

Fred:

TD .049's don't have piston grooves and SOME, but not all, TD .051's have one OR two grooves. The only TD .051 that I've disassembled that far had two.

Why? I have not a clue but Cox was known for running production variations. Regardless ANY groove was put there to identify .051's from .049 TD's on these engines.

SD
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Post  crankbndr Sat May 11, 2013 10:01 am

In my collection the only .051s with two rings are Killer Bee .051s, all NIB.
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Post  fredvon4 Mon May 13, 2013 7:40 am

Sorry to not be clear in my post. I was just stating the fact that I have a few .051s with only one groove on the piston skirt. I know there are variants out there with two grooves also indicating a .051 piston.

Side note: Because new .051 piston and cylinder sets are hard to acquire, I have had some success with fitting a well worn .051 piston into a new, but sloppy with a .049 piston, TD cylinder using Ken Cook's lapping process...since the lapping reduces the piston and cylinder I assume I have a set that is more than .049 and less than .051...grin
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Post  SuperDave Mon May 13, 2013 9:25 am

Oh what a conundrum this!

YAWN............................... Tired w/ Coffee Read Sad Goodbye

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