COX piston of irregular size

Double groove piston was used on the NFFS .051 Medallion engine. Probably made in matched sets. I remember these being for sale on ebay years ago by the seller engine049.

Thanks for the fast identification !! I tried this in the non-taper cylinder of the TeeDee050 RC the dimensions of which otherwise are the same as the 051 but it still does not fit. So the NFFS 051 Medallion must have had a tad larger bore than other 051 engines?

Or Engine 49 (Think that where my two came from) who claimed they were left over .051 NFFS and likely were not used 'cus they are too big...I just kept fussing with a very worn #5 cylinder until I got a Paul Gibeault Tap it out pinch fit

Yeah, that’s possible. The claim they were unassembled NFFS leftovers could have very well mean’t they didn’t pass the QC tolerance.

Who knows, I guess if you want to use that piston you will have to lap it in. Even regular non-taper Cox cylinders must have some sort of slight taper as you would never get a pinch at TDC otherwise.

Ron

Thank you guys..I am not particularly well equipped to take the risk of lapping a cylinder so this piston may never see the inside of an engine but stay in my parts store.

balogh wrote:Thank you guys..I am not particularly well equipped to take the risk of lapping a cylinder so this piston may never see the inside of an engine  but stay in my parts store.

Ken Cook has provided some really good Lapping tutorials. Might do a search on that.

When you get an .051 Cylinder that is completely worn try it on that. You have nothing to lose as both piston and cylinder are trash otherwise. No risk whatsoever...

Yes I may do so in some time down the road..the most worn cylinder is on my favorite old stock 051 that has run very long miles and still works fine...I would feel somehow guilty to make it a test dummy while it still works

Didn't the Killer Bee .051 use a double grooved piston as well?

I bought both the Killer Bee .051 two groove pistons and the TD .051 single groove pistons from engine 049 in person.
Neither one would fit a new or old .051 cylinder or a new TD05 cylinder in any combination.
He had a bag of about 50 of the double groove and a bag of about 500 single groove pistons that I held in my hands.
I believe that both types were made over size and were sent to R&D to avoid being scrapped.
He mentioned having two NFFS cylinders but I never saw them....
The over size pistons would have meant extra hand fitment costs to an already high cost tiny production run.
Today, I believe the NFFS "story" sold a lot of over size pistons at a super premium price .
FWIW, Steve

Steve,

I wonder if the .051 pistons were simply manufacturing rejects, or perhaps were ordered in an attempt by someone to clone NFFS engines?

Have you measured the bore of both .051 pistons, or perhaps compared the diameter to see if they were the same size?

I was tempted to buy some when that seller offered them for sale online. Now I see that he last posted here in 2012.

Bill

Bill,
I've measured the new two groove, the new one groove, and a used one groove .051 pistons and they are basically the same out to three decimal points on my new HF digital caliper.
But, from all I've read, Cox production tolerances are out to at least six decimal places and maybe even eight !!!
I believe the whole bunch of each were probably production defects.
I may try to hook up with the guy but the last I heard all Cox stuff was long gone …
Steve

Steve,

Thanks for the info.

I would like to have a sample of each piston, but if the guy got rid of them I guess I'm out of luck.

Bill

pm your address Bill
I have one of the slightly over sized 2 groove Un used .051 pistons left that I got from the guy we been discussing here

as noted they fit in a .051 cylinder but lock tight 2/3rds up to TDC

padded envelop next time in town is easy

Fred,

The piston arrived today, and I checked it in a couple of .051 cylinder. One of my piston/cylinder pairs with single groove piston was marked NEW, and the second pair was marked USED. Looks to me like they were both new sets, and the previous owner agreed.

What I think I've found is that the two groove piston you sent me fits about the same, and like both of my single groove pistons, also binds at the top part of the cylinders. What that tells me is something that I've always suspected - that all .051 cylinders were made before Cox stopped tapering their cylinders.

All the .051 cylinders  I've tested (other than a well worn example I may still have somewhere) have that same bind above the exhaust ports!

Wish I had more of these two groove pistons to check.

Larry Renger told me a trick to try on my new Venom engines, to prevent the piston top binding and separating from the skirt if I ever ran one. I didn't do any of my NIB Venom engines, because I never intend to run them. I did make note of Larry's method of hand honing the pistons.

Anyway, I did want to thank you again for your generosity, my friend.

Bill

Bill

Allow me a note from a COX enthusiast hungry for any historical anecdote of COX.
Given your obvious experience with COX engines and personal contact to icons like Larry Renger I would love to read more posts from you..did you happen to work for COX hence your acquaintance with Mr Renger?

I understand there are a few former COX employees like Mudhen (??) who also posts here but just not enough to satisfy my endless curiosity about the heydays of COX engine and model production.

Sorry for my unsolicited suggestion, I did not want to be obtrusive.

The curious Andras.

Andras,

You flatter me, my friend!

I'm no Cox expert by any means, but do have a small collection of Cox (and other) engines.

Never got to meet Larry Renger, but chatted with him a few times on an old Compuserve model forum (now defunct). I was retired, but working part time at a hobby shop, and had collected a few new Cox engines while they were still made by Cox. Larry suggested I look for a Venom engine, as they were rare, and likely to increase in value. Never found any locally, but managed to pick up one in Denver Colorado while on vacation, and a couple more from a friend who owned an R/C hobby shop in Sugarland, Texas. That's when Larry explained the problem they had with the Venom pistons, and offered a tip on how to hone a tiny bit off the top, if I wanted to run one. Mine are still NIB, and I don't intend to run any of them, but remember his kindly offered sage advice.

Had a Cox TD .010 in my youth, and later a Pee Wee .020, so I knew about the quality and reliability of Cox engines.

Realizing the vast numbers of engine types made by Cox, I knew I could never afford to collect them all, so I decided to limit my collection to control line engines no larger than .049 made from 1995 until Estes started selling them from random parts. Somehow, a few Cox engines that didn't meet my criteria, managed to follow me home anyway, and of course a pile of engine parts!

Now I'm too unsteady on my feet to fly c/l, and running engines for fun at my age is also dangerous, but I can still buy the occasional collectible engines, and parts. That keeps me happy.

Bill