Tapered piston?

The tapered cylinder/piston is one of the distinctions of a TD .049-.051 that make it a "contest" rather than "sport" engine" like the Medallion.

Bernie:

My 1973, Santa Ana produced TD .049, I believe, has both a tapered cylinder and a tapered piston.

At what point in TD production change in this aspect?

Thanks,

Hello Dave & All,

A most excellent discussion which has prompted me go into my personal "Cox reference files" .
From a Dale Kirn letter to me dated 7-1-85: "For all out racing I prefer the Tee Dee pistons as
they have a double taper.
The Tee Dee cylinder bore/hone is also tapered. but neither the Babe Bee or Black Widow are.
They have a straight taper.

Dale's hand drawn piston diagrams showed:

1. On Babe Bee's there was no taper from 1979 to present.
2. the old style babe Bee (prior to 1979 I imagine P.G.) had a single taper.
3. The Tee Dee had a double taper

I hope this has been of some help.
p.s. somehow the text comes out a little off, when I post this....?

Cheers, Paul (aka Mr. Mouse)

SuperDave wrote:Bernie:

My 1973, Santa Ana produced TD .049, I believe, has both a tapered cylinder and a tapered piston.

At what point in TD production change in this aspect?

Thanks,

BTW, to answer the initial question. Yes, All Cox pistons can be used in ALL Cox cylinders. BUT.... how well they perform is the question. My take...you never REALLY know until you run them. As this letter states, too tight fitting & too loose fitting always runs / starts poorly, but there is a lot "in the middle" worth trying out...

Dale Kirns 2nd letter to Paul dated 9 Dec 93:

Dear Paul - You have put together a very informative article - esp. on the engine & fuel areas. I added a little note on the last page about the importance of castor oil. I never use less than 10% castor oil in my fuels.
In 1979 cox made a major change in the cylinder & piston sizes (except for the Tee Dee series).
1. Cylinder:
a) went to 2-slit exhaust to prevent a fire from starting from over priming
b) eliminated free port on 2-slit exhausts.
c) "loosened" tolerances on I.D. hone

2. Piston:
a) finish grind - no longer has a "taper" at the top.
b) "loosened" tolerance on O.D. of piston

Unfortunately, the Black Widow has both of the "loosened" tolerances in all engines. If both are on the "right" end (cyl I.D. on the small and piston O.D. on the high) you can have a fairly good engine. But the other way - very loose fit/poor compression/ hard restarts/ poorer performance. In defense of Cox doing these changes it was because the bulk of their engines went to "first time users" who didn't know anything about a 1/2A engine. "Rich" and "Lean" was a term they did not understand. So, by fitting the piston/cylinder on the "loose side" - and leaning the engine to max power (when new) it was less likely to stick.
Apparently, it cut down on a "few" returns, but mainly it cut manufacturing costs. Seems that is always the bottom line.
Good luck on this venture, Your off to a good start.
Keep 'em flying,
Dale Kirn
"and now you know the rest of the story...."

Well there you have it.
Thank you, Jim

I have read about ordering several sets of piston/cylinder and assembling mis-matched to get several tight fit sets to select from.

This also allows selecting front/back exhaust port alignment since this supposedly improves performance.

The downside is some parts get selected as out of range and never used.

Phil

I myself don't recommend switching these parts from one to another. Yes, it can be done but as Paul states performance can be trial and error. Having a good set of calipers on hand is a must and knowing how to use them. If for instance you do find that a piston does indeed fit one cylinder better than another, you still should fit that piston to the cylinder. I've lapped in many pistons using mild polishing compound and Brasso for fine polishing. This is done with the piston upside down in the cylinder. It's really not going to do any harm to the piston sleeve to slightly relieve the fit of the skirt and the bottom portion of the cylinder. This will allow the fitment to stay good on the top end and it will allow for a slightly higher rpm range.

Making a lapping tool is extremely simple as it only requires a piece of K&S 3/8" brass tubing about 4" long. Wrap some Scotch tape around the brass tube and you have just made this very helpful tool. One to two wraps is all that's required. Insert the rod down through the tube and the piston will wedge easily onto the brass tube. Watch that the tape doesn't slide down. Insert the tube with the piston skirt upside down and raise it up to the exhaust cutout. Put a few drops of your polish of choice and begin to rotate in a up and down fashion. This needs only a little polish and it also has to be taken out, cleaned off and re applied. Take your time and be patient. Eventually you will remove shiny spots on the piston and scratches as well as both parts are being fit to each other. Afterwards an extensive cleaning needs to be done and a old toothbrush that has it's sides beveled allows it to get down into the cylinder using soapy hot water. All polishing compounds MUST be removed. If you have a bore brush like a Davis Diesel brush this will place swirled micro scratches into the cylinder walls and will allow for oil retention and break in procedure once again. After the bore brush, another soapy water wash followed by a heat dry. I lap and fit the piston so that when the top of piston is placed in a dry unoiled cylinder it hangs and sticks at top dead center. When you touch the piston it should fall right out in your hand. This takes practice and experimentation and I don't recommend doing this to an engine that your currently running until you achieve the feel required for this black magic. Most of us have several parts and old engines and this is where this should be tried.

These same procedures can fix those buggered cylinders from the wrenches as well and were probably all guilty of that experience. Ken

Hello Bernie, my father is a machinist of 50 years experience. Unfortunately, he suffered a career ending accident prior to retirement with a milling machine. Although disabled, he's quite sharp when it comes to metallurgy and how things are made. Although my career choice wasn't the same as his, he's passed many of his traits onto me. I have several styles here as I have all his tools now. When I have a problem with an engine, he's my go to person and we take it from there. It gives him something to do and I certainly benefit from his work. He has many styles of manual and digital calipers, from Starett to Mitutoyo calipers just to name a few. If I have a mix of parts, he clearly defines what's going to work and what is headed for the trash. Ken

FYI: In the picture posted by Paul Gibeault, he's the guy on the right.

Paul and "Mudhen" (Mud) are Cox authorities "par excellance" and we're fortunate to have them posting on our forum.

Ken,

Your dad must have some pretty skookum tools. We also have a good caliper here but it only resolves to .0005". After that tooling costs go up exponentially

SuperDave wrote:FYI: In the picture posted by Paul Gibeault, he's the guy on the right...

Oh, I'd been thinking Paul was the guy on the left.

Rusty:

Paul Gibeault is the more diminutive guy on the right. The larger man in the blue shirt?
I dunno.

Isn't this another reason Paul is known as "Mr. Mouse"?

Cox International wrote:I am curious as to what type of calipers you are using Ken. Even calipers in the $200 range only resolve to .0005", which is a huge tolearnce for a piston fit on a Cox engine. Cox OEM tolerances are 20/millionth of an inch - that is until they began "loosening" their tolerances to 20/100,000 of an inch.

Also, keep in mind that, somewhere in the 80's (?), cylinders and pistons were no longer matched anyhow.

My pretty much plain vanilla 0-1" c-clamp vernier caliper reads to 10th's (.0001"), but even that (as you correctly observe) wouldn't be close enough to do any select fit/blueprinting.

You'd also need an air gauge for the cylinder ID, which is a pretty specialized piece of equipment and would require a purpose made mandrel very close to the spec ID.

My reference as to measuring was in regards to checking used pistons and not just in one spot. Were talking about used pistons here. I'm not manufacturing engines here. Even the engines manufactured were not always within the tolerances claimed. If this was the case, every engine would be running absolutely the same. What was really quite incredible for the time was the honing machines that Cox used and the speed they ran. This basically brought the cost of manufacturing down and yes it separated the need for piston sleeves to be hand lapped. Basically one person had a feel for a part slightly different then another and this is true when using high precision instruments. I merely was explaining on how to take a box of crap and make it viable once again. Setting aside pistons that are worn out and fitting them to used cylinders. It can be done as I've done it. Most of this knowledge isn't new and I take no credit in what I'm suggesting. Combat flyers like Richard Lopez and other flyers were doing this stuff back in the late 70's. Certainly when one suggests that it can't be done is just a fallacy.

Rather than lap the piston and sleeves in, guys were running these engines and placing a bit of Lusterox into the cylinder and running the engines full bore on 70% nitro and clipped down props. This is how they were polishing the piston sleeves. If the engine sagged and started to overheat it was taken apart and the procedure was done as I stated in my other post. This was how they were getting the high rpm's from these engines. You can feed an engine all the nitro you want, this doesn't mean that it's going to sustain the rpm's. Generally, the engine will seize and gall. I have a chart which was posted in early model mags that suggests what rpm's you should be hitting on suggested props and nitro prior to lapping in a piston. These procedures can be done by anyone on this forum with a little practice. Seeing that Bernie was looking for certain ideas and information to place in his magazine, I just gave you some pretty good hints and tips. If one feels or doesn't believe what I claim to be true, then don't heed the advice given. I can honestly claim my advice is proven and not something I made up or read. Ken

lousyflyer wrote:Tapered cylinder needs a tapered piston.

Once again I have inserted my foot into my open mouth.

lousyflyer wrote:

lousyflyer wrote:Tapered cylinder needs a tapered piston.

Once again I have inserted my foot into my open mouth.

No. You simply stated what you believed to be correct. And, it is a quirky theme as many modellers think what you thought. As I initially said... misconceptions ...

Ken,

Why don't you write an article about what you have posted for our quarterly magazine?

If we get this by tomorrow around noon Pacific time, we can include it in tomorrow's newsletter. Alternatively, our next publication will be 3 months later and we would love to get your contribution.

That certainly would be a good idea but I'm currently bailing water from my cabinets due to this storm. I'm fortunate to still have power, for now. Water is quite problematic here. Ken

Right, that "little wind" on the east coast Perhaps for the next edition then...

Cox International wrote:

lousyflyer wrote:

lousyflyer wrote:Tapered cylinder needs a tapered piston.

Once again I have inserted my foot into my open mouth.

No. You simply stated what you believed to be correct. And, it is a quirky theme as many modellers think what you thought. As I initially said... misconceptions ...

If you start reading about making your own engine ONE way to fit the bore and piston is to use compound and the piston and cylinder with a means to rotate to lap them to each other. The result is a matched tapered fit, with the exact dimensions determined by measuring afterwards, if one were to be concerned.

There is rarely only one way of doing anything. However with this way it would be unlikely to exchange piston and cylinder between two different engines made to the same dimensions and plans.

Phil

Ken Cook wrote: That certainly would be a good idea but I'm currently bailing water from my cabinets due to this storm. I'm fortunate to still have power, for now. Water is quite problematic here. Ken

Stay safe Ken! We were ordered to leave McGuire AFB and head inland. Which is odd because in my 18yr career we have always sheltered on the base!