.049 cylinder and piston for .051

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?

SD

Thanks SD I just joined thanks!

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

SD

Welcome, Darren, glad to have you on board.

Thank you.

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

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.

Phil

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

SD

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

Lieven

Here it is again, side by side.
https://i.servimg.com/u/f83/17/84/87/39/img_2013.jpg


Phil

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

SD

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

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

I have seen photos of two groves but have never touched one

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

In my collection the only .051s with two rings are Killer Bee .051s, all NIB.

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

Oh what a conundrum this!

YAWN...............................

SD