Cox Engines Forum
You are not logged in! Please login or register! Guests are limited to posting in the "General Questions (Guest Posting Allowed)" section only. Becoming a member is fast, easy and FREE!


The disappointing OK Cub Babe_b10
Log in

I forgot my password

Search
 
 

Display results as :
 


Rechercher Advanced Search

Cox Engine of The Month
November-2019
jmcalata's

"Pee Wee .020 throttled combinated"



PAST WINNERS
CEF Traveling Engine

Win This Engine!
The Traveling Prop
Gallery


The disappointing OK Cub Empty
World of Aviation

The disappointing OK Cub

Page 1 of 2 1, 2  Next

Go down

The disappointing OK Cub Empty The disappointing OK Cub

Post  rsv1cox on Wed Jul 10, 2019 7:53 am

Not to paint all Ok Cubs with the same brush but this one let me down after having high hopes.

It just looks right, integral metal fuel tank, great compression and a nice needle valve feel with just the right resistance and no slop. But as mentioned in another post it would not run past about, my guess 250 rpms on Cox 35%, you could almost count them. Full range of the needle made no difference. Full rich 250, full lean 250. Not dieseling or four stroke as normally seen, just running like one of those old time hit and miss engines.

Any idea's?

The disappointing OK Cub P7070015
rsv1cox
rsv1cox
Top Poster
Top Poster

Posts : 4665
Join date : 2014-08-18
Location : West Virginia

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  Kim on Wed Jul 10, 2019 8:32 am

I'm sure you've already thought of it, but has it got anywhere decent compression?
Kim
Kim
Top Poster
Top Poster

2019 Supporter

Posts : 6789
Join date : 2011-09-06
Location : South East Missouri

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  Marleysky on Wed Jul 10, 2019 9:12 am

My guesses:
1- dirt or debris in fuel line, spray bar hole clogged, not allowing full fuel flow, or the tip of the NV is broke off inside the spray bar?
2- the rust on the splines of the prop driver makes me want to think there is rust or castor goo causing friction on the case to crankshaft mating surfaces between the drive plate and intake opening.
3-cylinder to head seal leaks. Do you have another Cub to swap heads or glow plugs with?
Clear our the passageways for the fuel, and air, then make sure you’ve got a good hot glow plug. gotta be one of three things choking the RPM’s ....but you know that!
Marleysky
Marleysky
Diamond Member
Diamond Member

2019 Supporter

Posts : 2407
Join date : 2014-09-28
Age : 67
Location : Grand Rapids, MI

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  gkamysz on Wed Jul 10, 2019 9:31 am

These little engines can't really run at such low speed. Was it maybe bouncing back and forth, not making it through TDC?
gkamysz
gkamysz
Gold Member
Gold Member

Posts : 133
Join date : 2018-02-22
Location : Chicagoland

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  fredvon4 on Wed Jul 10, 2019 9:49 am

IIRC Bob's tach is times 10 display so I assume 2,500 rpm
fredvon4
fredvon4
Diamond Member
Diamond Member

2019 Supporter

Trusted Seller
Posts : 2922
Join date : 2011-08-26
Age : 64
Location : Lampasas Texas

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  fredvon4 on Wed Jul 10, 2019 10:57 am

and I would be wrong
fredvon4
fredvon4
Diamond Member
Diamond Member

2019 Supporter

Trusted Seller
Posts : 2922
Join date : 2011-08-26
Age : 64
Location : Lampasas Texas

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  smooth_bill on Wed Jul 10, 2019 2:12 pm

I have never had any of those Cub metal tank mounts, but I would suspect the tank screws are leaking fuel into the engine crankcase in some manner. If fuel were being drawn from the spray bar/venturi surely the needle valve would be effective?

A similar problem was caused by the red tank mounts on a Cub 049A I worked with. A tank mount screw had perhaps been screwed into the crankcase without the tank, or too long a screw used, as the screw hole had been punched through into the crankcase. This allowed fuel from the tank to leak slowly along the case screw channel and directly into the engine. The engine was difficult to start, and would run very rich when it did start, but shortly flood to a stop!

Bill
smooth_bill
smooth_bill
Gold Member
Gold Member

2019 Supporter

Posts : 118
Join date : 2012-02-19
Age : 82
Location : Beaverton, OR

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  rsv1cox on Wed Jul 10, 2019 5:37 pm

Thanks guys, yes, great compression. Except for the rusty prop screw and alignment peg it looks new and never ran so I did not disassemble it other than checking the needle valve.

Times like this is wish I used the movie option on my camera and had a youtube account. Almost signed up last week but they ask to many questions.

Maybe my 250 rpm's was a bit low, but it was running and did so for about a minute and a video would confirm this. It was eager to start with lots of good feeling pop, you know what that is like but when running it would not change rpm's through the whole NV range. Curious. First time I have ever seen this.

rsv1cox
rsv1cox
Top Poster
Top Poster

Posts : 4665
Join date : 2014-08-18
Location : West Virginia

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  Mark Diedrichs on Wed Jul 10, 2019 5:58 pm

Dude, Why struggle? Use it as a doorstop and go with Cox power! We all know it works!!!! Just teasing,Mark
Mark Diedrichs
Mark Diedrichs
Gold Member
Gold Member

Posts : 304
Join date : 2017-11-11
Age : 67
Location : fairfield ohio

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  rsv1cox on Wed Jul 10, 2019 6:01 pm

Mark Diedrichs wrote:Dude, Why struggle? Use it as a doorstop and go with Cox power! We all know it works!!!! Just teasing,Mark

It's the challenge Mark. Read my Cox misadventure...….
rsv1cox
rsv1cox
Top Poster
Top Poster

Posts : 4665
Join date : 2014-08-18
Location : West Virginia

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  Mark Diedrichs on Wed Jul 10, 2019 6:16 pm

I hear you Bro, I once had a weedwacker that I wouldn't let beat me!!! All about the challenge, Mark
Mark Diedrichs
Mark Diedrichs
Gold Member
Gold Member

Posts : 304
Join date : 2017-11-11
Age : 67
Location : fairfield ohio

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  getback on Wed Jul 10, 2019 6:18 pm

i go with number 2-3 anyway stopped up NVA can bee just a tiny piece of crap messing with you bad !! Been there done that ! 4th of July Flag
getback
getback
Top Poster
Top Poster

2019 Supporter

Posts : 6339
Join date : 2013-01-18
Age : 62
Location : julian

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  ticomareado on Wed Jul 10, 2019 6:43 pm

Getback is prolly right, though there are a number of things that a hard core Cub guy can do with these engines. Nostalgia F/F guys like to hop them up and get some pretty impressive results in terms of power to weight ratios.

http://www.flyfreeflight.com/Site/OK_Cub_Rework.html

The design itself is sound as it is based largely on Ray Arden's .099. The problems arise from inconsistent QC practices and metallurgy.
ticomareado
ticomareado
Platinum Member
Platinum Member

Posts : 869
Join date : 2013-10-03
Location : NC

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  aspeed on Wed Jul 10, 2019 8:57 pm

I got a load of 4 or 5 a long time ago when there was a sale. It said they were for display or collection. I guess that is all they are good for. Two would not run at all. I sold the one before I knew and felt bad about it. They were all new. After reading lately, I have heard there is a bad seal at the needle valve where it screws into the housing. Maybe check over the needle valve, blow though and see if it opens up enough after a few turns or whatever. I should go over mine too. The one that ran seemed to run well enough to pull a plane.
aspeed
aspeed
Gold Member
Gold Member

Posts : 344
Join date : 2013-01-18
Location : Leamington Ont. Can.

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  Oldenginerod on Wed Jul 10, 2019 9:55 pm

smooth_bill wrote:..... I would suspect the tank screws are leaking fuel into the engine crankcase in some manner.

These tanks don't have any screws into the case. Only mounted on external lugs. The screw-in backplate could possibly leak, drawing fuel straight into the case. Bob, just try again using an external tank and leave the mounted tank empty.
Also, use a small prop. These don't like to lug.
Some of the Cubs didn't have the port in the crank ground out properly. Is this the first model .049 (pre-"A"/"B") or is it an .074? These tanks only fit those two models.
Honestly, I've never had much success with the first model .049 even when everything seems ok. .049B was a much better engine.
Oldenginerod
Oldenginerod
Diamond Member
Diamond Member

Posts : 2746
Join date : 2012-06-15
Age : 57
Location : Victoria, Australia

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  Surfer_kris on Thu Jul 11, 2019 1:23 am

rsv1cox wrote:
Maybe my 250 rpm's was a bit low, but it was running and did so for about a minute and a video would confirm this.  It was eager to start with lots of good feeling pop, you know what that is like but when running it would not change rpm's through the whole NV range.  Curious.  First time I have ever seen this.  

Sounds like it might just have been rocking back and forth...

What prop-size did you use?
Surfer_kris
Surfer_kris
Diamond Member
Diamond Member

Posts : 1636
Join date : 2010-11-20
Location : Sweden

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  rsv1cox on Thu Jul 11, 2019 6:35 am

Thanks all for your responses.

For now I have retired it to a display stand but intend to remove the tank and see what's up.  I also need to run some Remoil spray through the NVA and blow it out with compressed air and try again.  Just got fed up yesterday with balky engines after a rewarding day with the Testors/McCoys the day before.

I do like this engines design, the only one I have with that style attached tank.  Although the top mount hole is nearly impossible to get to.

The disappointing OK Cub P7100010
The disappointing OK Cub P7100011
The disappointing OK Cub P7100012

A couple of years ago I sold on ebay 40-50 engines mostly Cubs, Wens, and McCoys.    The extent of my Cub collection now.  I usually keep the propeller with the engine as received.  I know I ran one of the .099's just to see what they were like but I don't think I ran any of the others.  I know I never ran the diesels.

The disappointing OK Cub P7100013

Oh yes Chris, I think the prop used was about a 6/3.
rsv1cox
rsv1cox
Top Poster
Top Poster

Posts : 4665
Join date : 2014-08-18
Location : West Virginia

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  GWILLIEFOX on Thu Jul 11, 2019 8:16 am

i WOULD CLEAN OUT THE SPRAYBAR AND MAKE SURE THE DISCHARGE HOLES ARE NOT PLUGGED.  MAKE SURE THE SCREW IN REAR COVER IS SNUG.  I GOT 5,800 TO 13,800 RPM ON MY USED CUB.  MY TEST RESULTS ARE ATTACHED.  THE SHORT STROKE 049B IS WAY FASTER THAN THE LONG STROKE CUB.

One day I realized I had an HKG plug in my Cub instead of an Arden.  While I was putting the Arden in, it occurred to me it was a long, not a short plug as is common in .049s.  But as the Cub was first, there was no long plug to put in it.  So I sorted out some props and plugs and went out to run them.  I used Cox 25% nitro fuel.  You can see the Arden plug worked noticeably better than the OK Long or Fox long plugs.

I also ran an .049B on a couple of the props.  It was at least a couple of thousand RPM stronger than the Cub on any of the props.
The disappointing OK Cub Cub_pl10
The disappointing OK Cub Ok__mi10
GWILLIEFOX
GWILLIEFOX
Gold Member
Gold Member

Posts : 299
Join date : 2014-12-23
Age : 76
Location : Beaver Falls, PA

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  Surfer_kris on Thu Jul 11, 2019 8:33 am

If it has a good piston to cylinder seal and a good glow plug, it should run. Smile

I still thinking that it didn't actually turn over, only rocked back and forth?
This can easily happen if the compression ratio is too high. Perhaps try with less nitro and a different prop.

The needle looks very blunt or perhaps even too short? You can check the operation by blowing through a fuel line and listen to the "hiss". There shouldn't be any air coming through when the needle is closed, and if you open it until you hear a slight "hiss" you have a good (enough) starting point for the needle setting.
Surfer_kris
Surfer_kris
Diamond Member
Diamond Member

Posts : 1636
Join date : 2010-11-20
Location : Sweden

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  Surfer_kris on Thu Jul 11, 2019 8:34 am

If it has a good piston to cylinder seal and a good glow plug, it should run. Smile

I still thinking that it didn't actually turn over, only rocked back and forth?
This can easily happen if the compression ratio is too high. Perhaps try with less nitro and a different prop.

The needle looks very blunt or perhaps even too short? You can check the operation by blowing through a fuel line and listen to the "hiss". There shouldn't be any air coming through when the needle is closed, and if you open it until you hear a slight "hiss" you have a good (enough) starting point for the needle setting.
Surfer_kris
Surfer_kris
Diamond Member
Diamond Member

Posts : 1636
Join date : 2010-11-20
Location : Sweden

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  Surfer_kris on Thu Jul 11, 2019 9:05 am

If it has a good piston to cylinder seal and a good glow plug, it should run. Smile

I still thinking that it didn't actually turn over, only rocked back and forth?
This can easily happen if the compression ratio is too high. Perhaps try with less nitro and a different prop.

The needle looks very blunt or perhaps even too short? You can check the operation by blowing through a fuel line and listen to the "hiss". There shouldn't be any air coming through when the needle is closed, and if you open it until you hear a slight "hiss" you have a good (enough) starting point for the needle setting.
Surfer_kris
Surfer_kris
Diamond Member
Diamond Member

Posts : 1636
Join date : 2010-11-20
Location : Sweden

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  Marleysky on Thu Jul 11, 2019 9:21 am

Geez Kris, I don’t mean to nag, but you’re beginning to sound like my ex-wife!!  Laughing

Yes Honey, I heard ya the first time.....
Marleysky
Marleysky
Diamond Member
Diamond Member

2019 Supporter

Posts : 2407
Join date : 2014-09-28
Age : 67
Location : Grand Rapids, MI

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  Surfer_kris on Thu Jul 11, 2019 9:40 am

Marleysky wrote:Geez Kris, I don’t mean to nag, but you’re beginning to sound like my ex-wife!!  Laughing

Which part is that, the too short needle or the rocking back and forth... lol!
Surfer_kris
Surfer_kris
Diamond Member
Diamond Member

Posts : 1636
Join date : 2010-11-20
Location : Sweden

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  ticomareado on Thu Jul 11, 2019 10:15 am

Sick, sick, sick is all I can say.
ticomareado
ticomareado
Platinum Member
Platinum Member

Posts : 869
Join date : 2013-10-03
Location : NC

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  rsv1cox on Thu Jul 11, 2019 10:39 am

ticomareado wrote:Sick, sick, sick is all I can say.

But funny!  Smile

Thanks Bill, I will bring out a few of those Cubs and swap needles and glow plugs around when I try it again.

Anybody got a Cub just like this one? Picture?

Bob
rsv1cox
rsv1cox
Top Poster
Top Poster

Posts : 4665
Join date : 2014-08-18
Location : West Virginia

Back to top Go down

The disappointing OK Cub Empty Re: The disappointing OK Cub

Post  Sponsored content


Sponsored content


Back to top Go down

Page 1 of 2 1, 2  Next

Back to top


 
Permissions in this forum:
You cannot reply to topics in this forum