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OK Cub .049 diesel -- pix and notes

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OK Cub .049 diesel -- pix and notes

Old 03-05-2008, 08:12 PM
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lildiesel
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Default OK Cub .049 diesel -- pix and notes

Here's the "new" wee beasty almost right out of the packing. I did, of course, put a 7x3 Rev-Up on it and flip it over a few times before picture time. Next the little Cub is shown between a Webra Picollo 0.8cc and a Cox .049. The Webra is the third version of the Picollo released in the early 60s and the first engine I ever bought for myself NIB in 1969. The Cox is a rebuild of an R/C Golden Bee with the Davis HD crank, hex prop driver, and a plastic backplate from the 90s.

The first thing of interest is that while it is a front intake engine, unlike most other Cub B models it is beam mount only. The only other Cub variant I've heard of that was beam mount only is the Cub .049X, but I've not found a picture or drawing of one yet for comparison. The other difference is the brass section where the nose of the crankshaft is bushed. I've found no mention of that on any Cub variant.

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Old 03-05-2008, 08:32 PM
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Default RE: OK Cub .049 diesel -- pix and notes

Here I've taken off the head to show the top of the contrapiston. The contrapiston is flanged on top and so cannot drop down into the cylinder. The small piece is called a "bump pad" and is fitted inside the contrapiston between the compression screw and the top of the contrapiston. The engine was not fitted with this piece when it arrived, and the bump pad shown is filed down to size from a Cub .075 diesel part. Without the bump pad fitted the compression screw goes right down and there is no compression adjustment available. With the bump pad the compression can be adjusted and the contrapiston clicks up nicely with a flip of the prop.

The second shot shows the contrapiston and the neoprene 0-ring used for the compression seal. The 0-ring is 1/16th inch wide and 7/16th O.D. and 5/16 I.D. It will be replaced with a Viton 0-ring before running.

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Old 03-05-2008, 08:47 PM
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Default RE: OK Cub .049 diesel -- pix and notes

With the contrapiston out of the cylinder it can be seen that the contrapiston is slightly domed and that the piston domed as well. Removing the cylinder reveals a piston and connecting rod with a wrist pin. The piston can be move up the tapered bore but not completely through. The taper must stop where the contrapiston fills the cylinder at full compression.

When flipping the engine with the contrapiston in and the head on there is a nice diesel "plop", noticeable compression change with half turn adjustments to the screw, and the contrapiston clicks up with the first flip. With the head off, flipping the prop will shoot the contrapiston four or five feet across the room.

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Old 03-05-2008, 08:57 PM
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Default RE: OK Cub .049 diesel -- pix and notes

That's a neat engine. Hope it runs good for you. I still haven't attempted to run my Deeil. Been busy lately working on airplanes instead.
Old 03-05-2008, 09:14 PM
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Default RE: OK Cub .049 diesel -- pix and notes

Removing the backplate shows the crank pin and the counter balance on the shaft. Note that there is an indentation in the crankcase above where the backplate screws in and where each of the mounting lugs meets the case. With the backplate on a standard Cub B fuel tank fits over the backplate with the excess gasket material on the outside making the front seal. A 1" 2-56 screw and a fiber washer would complete the tank installation if that is how the engine was shipped from the factory. All the pictures and drawings of other Cub .049 diesels show the radial mounting and beam mounting together on the crankcase. Clearly the nose of the crankcase and the beam mounting only will need an inquiry with the OK Engine Museum or perhaps access to a copy of the company's history.

So far I have not pulled the drive washer to see the entire crankshaft. I assume it is has the same rectangular intake hole just milled across the shaft like other Cub B crankshafts I've seen in pictures. Unless I find some explanation of the brass section at the front of the crankcase on the internet or in print, I suppose curiosity will make me pull the drive washer and remove the crank and see what's going on with the front bushing.

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Old 03-05-2008, 09:48 PM
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Default RE: OK Cub .049 diesel -- pix and notes

The last thing of interest can be seen on the bottom of the crankcase. The brass section of the case is fitted at a point where it obscures final numbers of the "PAT'D U.S.A 2179..." in relief on the casting. Whatever has been done with the front bushing to put on the brass section clearly involved machine work to the casting. As the King of Siam would say, " 'Tis a puzzlement."

So, here we are at the end of our little bit of Vintage Engine Porn for the evening. I'm waiting for Viton O-rings for the contrapiston seal and the backplate gasket as well as a package of 5-40 1" binding head screws. The engine arrived sans prop screw and washer and is wearing those taken from my NIB mid 90s Babe Bee. The 5/8th inch screw from the Babe Bee seems a bit long and only screws 1/4" into the nose of the crank while the reed valve Cox crank takes about 1/16" more. I don't know if the engine originally just had a screw and washer or a spinner and screw, but a Tee Dee spinner and 1" screw will mount a thick hubbed (3/8") wooden prop to the engine. Some of the other dimensions on the engine match or are very close to those of a Cox .049. The flats on the diesel's head allowed a Cox wrench to be used for removal with the cut out used on the flats on the top fin of a Cox cylinder.

I look forward to reading your comments and absorbing any experience that some of you guys might have with either the Cub .049 or .075 diesels. I understand that the McCoy .049 and .09 diesels used a similar contrapiston design with an O-ring. Anybody who has run or owned a McCoy should chime in as well. Any help before I try to start this engine in a week or so will be appreciated.

PS: I bought this engine because I wanted an 1950s American made diesel to go in a Keith Laumer designed plane when I finally get a chance to build one. It ought to look good in the nose of a Buttons or a Twin Lizzie.

PPS: The contents of the above posts were not created under the influence of 50% ether blend. But they sure do make me want to mix a pint can and start flipping.
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Old 03-05-2008, 10:01 PM
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Default RE: OK Cub .049 diesel -- pix and notes

Due to the light construction of the small cubs and Mc Coys they dont stand up too well to small or oversixed props , probably a 6x4 or 7x3 would be about right, also use fuel with high (40-45%) ether as this will keep the compression down and the load off. also the higher ether will make it easier to start/tune.
Re the crankcase , my guess is its been repaired, not a bad thing if they got the fits right as some of the cubs were too loose.
Stewart
Old 03-05-2008, 10:45 PM
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Default RE: OK Cub .049 diesel -- pix and notes

Thanks for the input. The fit of the shaft seems very good. When I grab the prop driver and apply side forces there is no discernable play. If that is a home repair, the original owner or whoever did it was very good. As for fuel mix, I'll go with the high ether homebrew I use to get my Picollo started with a few flips. The spring starter it came with didn't survive the couple of years of hard service I put it through in my early teens.

ORIGINAL: SGC
Re the crankcase , my guess is its been repaired, not a bad thing if they got the fits right as some of the cubs were too loose.
Stewart
Old 03-05-2008, 10:53 PM
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Default RE: OK Cub .049 diesel -- pix and notes

I have one that does 11,500 on an 8x3 MAS which I think is pretty impresive!! Also it only is about 2 OZ's and doesn't need a motor mount...


Woops!!! EDIT! Mine is an .074. Sorry for the miss info.
Old 03-05-2008, 11:15 PM
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Default RE: OK Cub .049 diesel -- pix and notes

Never having gone the diesel way, could you tell me how the Davis HD crank is different than the standard Cox crank? Surely the pin must be the same size or the smallish rod end would not fit unless bored out thus making it weaker.

I like the Cub. Is there a diesel kit for one available these days? I have a few Cub 049s both reed and front rotor types however mine have both type mounts, radial and beam.

Robert
Old 03-05-2008, 11:57 PM
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Default RE: OK Cub .049 diesel -- pix and notes

Here's a quick, dirty, and slightly soft focus picture of the Davis HD crank pin. You can see where the part of the crank has been reshaped to relieve stresses around the crank pin. I'd have to pull the drive plate off to do a side by side comparison and get a better lit picture. BTW, Cox produced a similar HD crank for either the Killer Bee or the Venom.

This is the first Cub I've ever owned. As a kid I got to mess around with a few belonging to friends who didn't have a lot of a lot of luck with them, but at about age 10+ or so without much help we all struggled. One Cub was mounted in a RTF control line plane: wish I could remember more.

edit: that picture is awful! i can barely see where the reshaping is either side of the pin. Can anybody put up a better one to show the differences from the standard reed valve crank?

ORIGINAL: build light
Never having gone the diesel way, could you tell me how the Davis HD crank is different than the standard Cox crank? Surely the pin must be the same size or the smallish rod end would not fit unless bored out thus making it weaker.

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Old 03-06-2008, 04:57 AM
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Default RE: OK Cub .049 diesel -- pix and notes

Robert,
Heres a DD killer crank (diesel) then a std and car crank, notice the car crank is heavyer all over but still break through the crankweb under diesel use. The DD crank has a MUCH thicker crankweb to withstand diesel pressures and high RPM/high nitro use.
Stewart
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Old 03-06-2008, 08:07 AM
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Default RE: OK Cub .049 diesel -- pix and notes

Thanks for the pics and explanations. I've never run a diesel (other than years in a tractor seat) and always enjoy reading posts by folks who have the experience.
Old 03-06-2008, 10:13 AM
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Default RE: OK Cub .049 diesel -- pix and notes

I had contacted Herkimer late last year. They said that due to lagging sales, they have no intention of reproducing any further bigger or smaller glow engines, or diesels.

Guess we gotta go with what we got now.


Wm.
Old 03-06-2008, 06:53 PM
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Default RE: OK Cub .049 diesel -- pix and notes

The only Cub I've seen with a crankcase back like that is the .09. IMHO, someone did some extensive work on that engine, probably as a labor of love.
It appears to be milled off. That front piece is probably a bearing surface to remove wobble.

I had a Cub .075 diesel. It was a bit hard to start if you under-propped it, at least to my unexperienced hands (mid 1950's). A few years ago, after forty years or so of non-use, I ran it and gave it back to the guy I bought it from...back in the day.

I don't remember mine having a "bump pad" but it's been years since I took a Cub diesel apart.

Good luck with it.

Oh yes, I do have some McCoy diesels... one beam mount .049 and .09, plus two radial mount .049's.

George
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Old 03-06-2008, 07:27 PM
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Default RE: OK Cub .049 diesel -- pix and notes

That sounds interesting and likely, since I can't find anything like it in the references to which I have access. It's really nice to think that somebody else loved this engine and took really great care of it.

ORIGINAL: gcb
The only Cub I've seen with a crankcase back like that is the .09. IMHO, someone did some extensive work on that engine, probably as a labor of love.
It appears to be milled off. That front piece is probably a bearing surface to remove wobble.
Old 03-10-2008, 10:16 PM
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Default RE: OK Cub .049 diesel -- pix and notes

The 5/16th I.D. 7/16th O.D. Viton O-ring fits the contrapiston nicely and seems to provide a better seal than the one that was in there. At least as crudely and subjectively tested --when I flip the prop over with the head off the contrapiston doesn't shoot off across the room as before, instead just raising up a bit in response to the compression. I lubed the O-ring with a bit of pure silicon spray and it went on easily. When I put the contrapiston back in the cylinder it took a little turning in addition to pressure to get the O-ring into the bore. I wonder if the fit of an O-ring with a 1/4th I.D. might be better or if getting Viton quad rings would improve the seal appreciably? Something else to investigate after first attempts at bench running.

I got the OK Engines newsletter/parts list in the mail today. Clearly this is the end of the line for OK 1/2As. Seems like they are down just to assembling rear reed valve versions with or without tanks. I've seen a picture of the tankless rear venturi reed valve engine and it looks sweet & cute in a Thermal Hopper early 50s fashion. Anyway, I'm ordering sets of the diesel specific spares that are still available (unfortunately there aren't any piston/cylinder sets available or I'd get one to build a "new" diesel) and some stuff that is common to all engines like wrist pin, con rod, &etc. Also a couple of aluminum spinners from the Mohawk Cub since they'll look more appropriate than a Tee Dee spinner and three different lengths of velocity stacks to try on the carb opening (might make a difference for fuel draw or swinging an 8/3).

Here's a picture of a Mohawk Cub showing the OK spinner and velocity stack.

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Old 03-11-2008, 09:42 AM
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Default RE: OK Cub .049 diesel -- pix and notes

Is that tube actually called a "Velocity stack"? I always assumed it was just an extension to allow you to choke the engine while it was in an RTF.

George
Old 03-11-2008, 11:20 AM
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Default RE: OK Cub .049 diesel -- pix and notes


Looks like a stack to me and since it comes in three different lengths with smaller bores than the carb it seems to be intended to perform as one. Why would a simple choke tube extension change the diameter and length of the air intake? And besides, "velocity stack" sounds much better than the very prosaic "carb insert" listing on the parts sheet.

ORIGINAL: gcb
Is that tube actually called a "Velocity stack"? I always assumed it was just an extension to allow you to choke the engine while it was in an RTF.

George

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