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Flats machined on COX cylinder top fin, for the wrench Empty

Flats machined on COX cylinder top fin, for the wrench

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Flats machined on COX cylinder top fin, for the wrench Empty Flats machined on COX cylinder top fin, for the wrench

Post  balogh Tue Oct 26, 2021 7:05 am

As we all know, old-stock - especially thin wall - COX cylinders came without the flat milled in the top fins to accommodate the COX wrench, so the cylinder removal was with the wrench slipped into the 2 exhaust openings. A rather brutal and obtrusive operation, often ending up with a non-repairable cylinder burred at the exhaust ports..

Later cylinders, many of the stepped walls, but all thick walls had the flats milled  in the top fin in the COX factory. The top fins on these cylinders - especially 049 size - are - at least visibly - thicker than the old stock cylinder top fin, so one may wonder if the flats are machined as a DIY at home in the thin, top fin of a thin wall cylinder, will the thinner top fin be strong enough to take the torque from the wrench, or surrender and get dented?

Any DIY experience with milling the flat into old stock cylinder thin top fins?
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Post  TexasWade Tue Oct 26, 2021 9:51 am



Haven't messed with it on an 049 yet, but I did do it on my .09 before making a throttle sleeve as you can see here.  I also don't really like wrenching through the exhaust ports, be even more importantly, you'll need the top cylinder flats with a sleeve as I had or any kind of muffler.  I didn't notice the top fin being thin when I did it, but that wouldn't worry me since I don't think those things need to be assembled actual gorilla torque  Wink .

I would think that even if the cooling fin was a bit thin it would still be fine, just be sure your wrench engages properly.  Maybe tape up the thickness so it can't fall in between the fin and glowhead or whatever?

I'm thinking that once I get my RC carb thing sorted out I might turn my attention to a muffler setup of some sort.  Whenever I get to that point, I'm going to need wrenching flats at the top of my .010 cylinder too.  Maybe the .020 also, I'll have to see about that one after it arrives.  Shoot, maybe the 049 that's also on the way.  I might just have myself a cylinder cutting party one of these days!
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Post  balogh Tue Oct 26, 2021 10:43 am

Thanks, TexasWade,

yes, indeed, the lack of flats on the top fin becomes a serious issue if you want to add exhaust throttle, or muffler to the cylinder, making the exhaust opening inaccessible for the COX wrench..how did you mill the flats on the 09 cylinder? Your exhaust sleeve looks very professionally machined, that I cannot think of doing myself, not having a lathe or similar milling machinery...I have 09-s and 049-s waiting to mill the flats on them, but I am not equipped with very sophisticated tools...I can think of simply raw-cutting them with a fine hand-saw, then adjust the exact distance between the flats for the wrench by filing away the rest. Maybe temporarily slip a thin aluminum plate cut from a beer can or similar,  in between the fins such that the saw and the file should not damage the fin below the top one...I guess the cylinder material is mild enough so the above should not be a problem?
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Post  TexasWade Tue Oct 26, 2021 12:13 pm

Thanks!  I made that sleeve on the manual lathe and mill.  Lapped it to fit the cylinder OD pretty well, but obviously not perfect because the engine was still amazingly able to breathe with the ports completely covered!   If I were to do it again, I'd leave the sleeve slots a bit shorter to allow more overlap so it could seal up better.

When I cut my cylinder, I laid it flat in the machine vise... now, that's a vise with very flat, hardened jaws that stay nice and parallel.  I would not recommend trying this with a typical workbench vise!!  I cut one flat, flipped the cylinder over and rested that flat on top of a thin parallel, then cut the second flat.  Very simple stuff if you have a milling machine...

pics to hopefully make my explanation clearer...
Flats machined on COX cylinder top fin, for the wrench Cylind11
Flats machined on COX cylinder top fin, for the wrench Cylind10

If I had a few to do, I'd probably want to find a collet and grab the cooling fin right below the one I'm cutting, and stand the cylinder vertically.  Main thing is, we don't want to squash that booger out of round!

I think I've read that the Cox cylinders were made from 12L14 steel, which would make sense.  That is some great cutting steel!  Easily cuts to a nice surface finish and you can really crank up the cutting speeds without burning up the tools. Mills, drills turns files and sands very easily.  

You could maybe put a tight-fitting wooden dowel in your cylinder and then drive a wood screw into the end of the dowel to lock it up, and with that setup you ought to be able to file that flats you need.  I wouldn't try to match the flats to a wrench though.  Cut your flats only as deep as the cooling fin minor diameter, then get a piece of sheet steel and cut a notch to fit.  As a bonus, if you can find a piece of steel the right thickness to just barely fit between the second fin and glowhead, there will be no chance of it going anywhere except where you need it.
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Post  balogh Tue Oct 26, 2021 12:22 pm

Great points and demonstration, thank you TexasWade..

Regarding the sealing of your exhaust sleeve, you can reduce the blow-by if you place a fitting O-ring into the groove under the exhaust ports. I added that with the purpose of retaining spent castor from flowing past the muffler neck and accumulating in the engine cowling. Your sleeve may leak the most near the cutout edges but there is some leak at the stepped neck of the 09 cylinder too.


Last edited by balogh on Tue Oct 26, 2021 12:31 pm; edited 1 time in total
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Post  Levent Suberk Tue Oct 26, 2021 12:30 pm

Hi Andras, you can make flats on cylinder as you already described by cutting and filing. Other than this can you find a nylon -or semi rigid plastic- bar to insert exhaust slits instead of making flats? Nylon bar do not burr exhaust slits.
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Post  balogh Tue Oct 26, 2021 12:35 pm

Thanks Levent for the idea! I will have to try the saw and file method in lack of more precise tooling, and will do first on an old cylinder.

I need the flats most in situations when the exhaust ports are inaccessible for the wrench like when adding an exhaust throttle ring or muffler to the cylinder...
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Post  Levent Suberk Tue Oct 26, 2021 12:37 pm

I need the flats most in situations when the exhaust ports are inaccessible for the wrench like when adding an exhaust throttle ring or muffler to the cylinder...

I didn't think that.
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Post  Levent Suberk Tue Oct 26, 2021 12:42 pm

Perhaps firstly you want to make an aluminum template for top of cylinder to score and cut them parallel. Reed shape I meant.
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Post  balogh Tue Oct 26, 2021 1:28 pm

Yes Levent, or just use the opening of the wrench as a cutting pattern to be scratched on the top fin. Most top fins have a small shoulder though the diameter if which is the same as the wrench opening
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Post  TexasWade Tue Oct 26, 2021 1:43 pm

Try this!

Should be super easy to make, just carefully shape the dowel to fit as closely as possible inside your cylinder, then saw a slot in the end so it will expand easily with a screw installed.  Glue the opposite end into a block of wood as shown.  Install the cylinder on dowel, clamp both the block and the file down to your bench, and you've got it.  Take a few strokes, flip it over, and while you're flipping it check your progress and brush the fillings out of the way.   The block will keep your flats parallel, having the block and file clamped down will keep your flat at the height you want (one fin or two??), and the dowel will flex enough for you to stroke the cylinder against the file while also holding things square.    As long as you don't get in a hurry you should have great results.

Flats machined on COX cylinder top fin, for the wrench Cylind14
Flats machined on COX cylinder top fin, for the wrench Cylind13
Flats machined on COX cylinder top fin, for the wrench Cylind12

Hey, also I just thought of an improvement.  Screw a stop block down to your bench, or clamp or whatever you can do with your setup... then when you lay down the tool, push it up tight against the stop block.  Will keep your block-to-file distance consistent while you're flipping things over.
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Post  Levent Suberk Tue Oct 26, 2021 5:50 pm

Andras, if you want to try saw and file to make flats, then you can check whether flats are parallel with a vernier caliper. Just an idea Very Happy
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Post  rsv1cox Tue Oct 26, 2021 6:03 pm

This is the Cox engine that causes the most problems when there are no flats cut on the top of the cylinder. Slit cylinder unfriendly to the Cox wrench as there is no way to remove the glow head if the cylinder unscrews with the glow head. Note the tool marks indicating that the previous owner used pliers.

Flats machined on COX cylinder top fin, for the wrench P1011917
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Post  aspeed Tue Oct 26, 2021 8:14 pm

I have used a milling machine with a 5C collet indexing head. The old style cylinders would need a split sleeve to hold properly. A file or Dremel with a cutting disc may get the job done too. Got a pic of a cylinder here. Don't know the history of the fail. I like the picture though. The case on the TD had a rod go through and it was soldered up successfully. Just some parts Flats machined on COX cylinder top fin, for the wrench Uglytd14
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Post  TexasWade Wed Oct 27, 2021 9:52 am

Wow, that's some kind of supermod there!  I like that prop driver and whatever is going on under the needle valve body.  Shocked

I believe that particular cylinder will be approved for removal with vise-grips Thumbs Up
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Post  aspeed Wed Oct 27, 2021 11:02 am

I made the prop driver, the spline cuts itself when installed if it is the correct diameter. The brass sleeve around the plastic body is to keep the pieces together when it splits. It may also have a plug washer on. IDK. That case is actually pretty good working order. I will likely use the broken cylinder to machine other cylinder bypass ports some day. I wonder if the cylinder broke from a crash or from tightening it too hard with the top cut cylinder for the wrench.
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Post  ChaseBanner Wed Oct 27, 2021 1:05 pm

@balogh wrote:Great points and demonstration, thank you TexasWade..

Regarding the sealing of your exhaust sleeve, you can reduce the blow-by if you place a fitting O-ring into the groove under the exhaust ports. I added that with the purpose of retaining spent castor from flowing past the muffler neck and accumulating in the engine cowling. Your sleeve may leak the most near the cutout edges but there is some leak at the stepped neck of the 09 cylinder too.
but sometimes the stress of getting em to run will make you grow older. oh and having daughters as well
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Post  Lukemiester Wed Oct 27, 2021 3:02 pm

@rsv1cox wrote:Flats machined on COX cylinder top fin, for the wrench P1011917

That really hurts to look at lol
Why would cox even make a cylinder like that?
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Post  rsv1cox Wed Oct 27, 2021 3:44 pm

There is an explaination for the added metal "slit", but it escapes me at the moment. As a kid I thought it was meant to keep the seeds and trash out of the port as I was always landing in the weeds. But I think it has something to do with strength. Cox brought it to market before thinking it out as it was impossible to remove a stuck glow head. The later engines with the milled top grooves cured that.

It could be made to look like new if I removed the finish cleaned the scratches and gun blued it.
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Post  balogh Wed Oct 27, 2021 4:13 pm

Bob I think the slit exhaust was thought to be less susceptible to throwing flames from an overprimed engine.
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Post  rsv1cox Wed Oct 27, 2021 5:09 pm

@balogh wrote:Bob I think the slit exhaust was thought to be less susceptible to throwing flames from an overprimed engine.

Sounds reasonable Andras, but I have checked Dannels/Sitter, on-line, wiki, etc. and can find nothing verifiable relating to it. Unless I find something different, your explaination stands.

Bob
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Post  balogh Wed Oct 27, 2021 5:20 pm

Bob, Dan Sitters Cox Model Engine Handbook explains on page 11 the slit exhaust was subsequent to the use of a steel mesh welded to the exhaust ports to stop occasional flames from the overprimed cylinder. Because spot welding the mesh was problematic, COX introduced the slit exhaust design in 1977..

Flats machined on COX cylinder top fin, for the wrench 16353710
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Post  rsv1cox Wed Oct 27, 2021 5:24 pm

@balogh wrote:Bob, Dan Sitters Cox Model Engine Handbook explains on page 11 the slit exhaust was subsequent to the use of a steel mesh welded to the exhaust ports to stop occasional flames from the overprimed cylinder. Because spot welding the mesh was problematic, COX introduced the slit exhaust design in 1977..

Flats machined on COX cylinder top fin, for the wrench 16353710

Darn Andras, I just read that exact page a moment ago and missed it. Going to reread now.

Bob
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Post  rsv1cox Wed Oct 27, 2021 5:29 pm

Ha, impatient me didn't read down far enough.

Flats machined on COX cylinder top fin, for the wrench P1011923

Thanks Andras
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Post  balogh Wed Oct 27, 2021 5:33 pm

I love all COX engines, but somehow old stock open exhaust cylinders have more appeal to me..I came to know COX engines in 74 or so with stepped wall open exhaust cylinders and the contour was reminescent to a panhead engine of Harley Davidson choppers  that I guess Peter Fonda and Dennis Hopper rode in Easy Rider,  a cult film behind the Iron Curtain back in the 70's.

Besides that the hand matched excellent piston to cylinder fit was also abandoned with the slit exhaust cylinders, at least neither of the new Surestarts or new Texacos I have with slit exhaust have the sharp fit and compression, let alone the TDC pinch of my used thin wall ole stockers...
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