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-   -   Cox surestart problem please help (http://www.rcuniverse.com/forum/1-2-1-8-airplanes-70/11356832-cox-surestart-problem-please-help.html)

Balda 01-04-2013 08:11 PM

Cox surestart problem please help
Hi all,

I just received 2 surestart as x'mas gift. I searched for informations before break in.

I used fresh 25% Sig Champion fuel, and cox 5X3 prop. First 2oz tank I ran it really rich, and second tank I ran it rich but peak it for few second and back to rich, I continue to finished the second tank.
For the third tank , I tech it and I got 14,700 rpm.
By searching , I noticed that mine seems really low power.

I switched to second surestart, and same break in procedure. It shows 14,900rpm. Which is still a little bit low side.
I googled surestart and most of users can reach 17,000rpm. Or some even more.

I changed the prop to MA 6x3, and It shows 11,400rpm.

I owned several golden bees and I can reach around 16,700 rpm with the same 5x3 prop and those are really old engines.
I don't know what's the problem with my surestart, must be something wrong here. Any idea what's make this engine refused to perform well?<br type="_moz" />

Mr Cox 01-05-2013 07:17 AM

RE: Cox surestart problem please help
Which glowheads are you using?
The newer ones with a clamp ring have a high compression ratio, and will need several head shims to work well on 25% nitro.
The 5x3 props with safety-tips will have a higher resistance and will not spin as high as an APC 5x3 for instance.
A muffler will also reduce the performance etc.

Balda 01-05-2013 08:42 AM

RE: Cox surestart problem please help
Hi Mr. Cox,

The glow head is originally came with the surestart, its #325 type 3 fin glow head. Its low compression head I believe.
I'm using cox grey 5X3 and well balanced. No muffler used.
I mounted on blue anodised cox test stand. I will try others fuel and props by tomorrow and see how it goes.

Thanks !


<br type="_moz" />

combatpigg 01-05-2013 12:55 PM

RE: Cox surestart problem please help
Some weak Cox engines could have .....
the crankshaft too tight a fit with the case, not able to turn with very little drag
bad compression seal with the piston and cylinder
crankcase pressure leakage
loose ball socket fit between piston and connecting rod
reed valve not able to flutter freely and provide a good seal between pulses

Out of 10 Surestarts I had 4 that were real strong runners after swapping parts and checking the fit of the parts. I wish the cylinders were tapered for a snug fit at the top, but Cox did not make the Surestarts with this feature [as far as I know].

049flyer 01-05-2013 08:37 PM

RE: Cox surestart problem please help
I have several Cox Surestarts and run them all the time. I find them to be easy to start, reliable and powerful for what they are. I flew two of my planes today, both powered with Surestarts. With the Cox 5x3 prop running Sig Champion 15% fuel I get about 15,000 rpm which is plenty of power for airplanes up to about 16 oz. With a yellow Tornado 5 x 3 prop and the same fuel I get almost 17,000 rpm. You can see that two props of the same size can tach out very different. The Cox prop has a lot more blade area than the Tornado. Therfore I think your engines are about normal with that particular prop. Try the APC 5.7 x 3 prop.

One of my planes weighs 11 1/2 oz and screams straight out of my hand on launch with the Cox 5 x 3 prop and 15%. I'm almost afraid to try the Tornado prop because the plane is plenty fast as is.

I suspect you may be mistaken on the power of your Golden Bee engines or they are not stock engines. If your Golden Bees are this powerful then they are unusually strong. Golden Bees are very close in power to Baby Bees.

I suggest if you need better performance from your Surestart powered planes you learn to build lighter airplanes, 11 to 14 oz.

Balda 01-05-2013 10:01 PM

RE: Cox surestart problem please help
Hi, <div>
</div><div> Thanks all for info. </div><div>
</div><div>I plan to use one of this sure start in a trainer plane that weights 19oz. I think I need to seek for better engine. </div><div>I saw some who ran their surestart at 15,000 RPM using 6X3 prop, that's why I wonder if my sure start can perform like them.  mine only 11K ++ using 6X3. </div><div>

Balda 01-06-2013 04:00 AM

RE: Cox surestart problem please help
Hi 049 Flyer,

I'm sure not a mistake. some old golden bee really perform. please check this out,


He got 17,500 rpm peak using cox 5X3, with just 15% nitro.
mine only 16,700 rpm same prop using 25% nitro


skaliwag 01-06-2013 04:02 AM

RE: Cox surestart problem please help

Balda 01-06-2013 04:07 AM

RE: Cox surestart problem please help

Yes, my country here very humid, 85% , very dense humidity. How the humidity affect its rpm please ??


049flyer 01-06-2013 06:50 AM

RE: Cox surestart problem please help
Humid air is less dense than dry air. This means less power from your engine. That being said, expecting good performance from a 19 oz airplane powered by a Cox Surestart is too much to ask unless it has a wing like a glider. You will not be happy with the performane of this plane.

You need to build planes that weigh less than 16 oz. For high performance you should build planes less than 12 oz.

I have a friend that I fly with who just built a 9 oz plane powred by a Surestart. What a hot rod!

Most of the older planes found in old magazines were designed around the radio gear available at the time and are therefore much too big. I usually shrink them down about 10 or 15 percent. They come out lighter and fly much better.

049flyer 01-06-2013 06:58 AM

RE: Cox surestart problem please help
I have tried the high compression head and special plug from Cox International. You will get a bit more power, just bolt it on. There are other things you can do for more power but I haven't tried them. You might contact combatpig on this forum, he is more knowledgable about getting more power out of these engines.

But the real problem is your plane is too heavy. Use smaller, lighter stuff to build planes. A light plane flies well even when the engine is running poorly, a heavy plane usually will not fly at all on a poor engine run.

Do either of these engine have a throttle? Throttles decrease power.

049flyer 01-06-2013 07:09 AM

RE: Cox surestart problem please help
Concerning the Golden Bee on youtube. Do you KNOW if the engine is completely stock? After all these years it's very possible that the piston and cylinder have been changed. Cox made several 5 x 3 props, one of which is very similar to the Tornado prop that I have used that turns 17,000 with the Surestart. What atmospheic conditions were present when the video was made? Cold dry air is best for more power. Has the tach been calibrated for accuracy.

Don't believe everthing you see on youtube.

MJD 01-06-2013 07:26 AM

RE: Cox surestart problem please help

15k on a 5x3 Cox prop sounds low for Sure Starts or Babe Bees.

Balda 01-06-2013 07:50 AM

RE: Cox surestart problem please help

Thanks for info.

I'm not sure my cox Golden Bees are stock or not, I bought 3 of them used , from the bay.
3 of them from the same seller, can't tell much about the parts used. but one thing for sure, Its non SPI .
I have Cox 1702 glow head, its high compression. I will try it out . thanks for the tips.

my cox 5X3 prop not the safety tip type.

Yaeh, I searched around and I think 15k rpm seems a little bit low, but I need to try again when humidity drop .


aspeed 01-06-2013 08:35 AM

RE: Cox surestart problem please help
The single bypass port cylinders along with the low compression heads will rarely be fast.  This included Babe Bee and Golden Bee, and the older Surestarts.  The twin port and TD twin port with the relieved edges on the bypass ports are quicker.  Likely the good numbers on the internet have those cylinders in.

fredvon4 01-06-2013 02:49 PM

RE: Cox surestart problem please help
I think you can find bits from Cox International

or ExModel engines

for things to get you surestart hopping

Compression ratio (adding or removing head shims)
Better plug (Merlin or Galbreath with Nelson plug)
Dual bypass port cylinder from a TeeDee
Sub Port Induction Piston and cylinder
Open back plate intake diameter and install a Texas Timers Fine thread needle valve and run on bladder presure
Killer bee crank shaft
Mirror polish the crank to remove all drag

By the time you do all this you should just by a hot rod motor from one of the fellows above

For the 19oz plane you are planning I recommend a Norvel BiG Mig RC .061 for around $70

http://www.nvengines.com/index.php?page=shop.product_details&amp;flypage=fl ypage.tpl&amp;product_id=23&amp;category_id=1&amp; option=com_virtuemart&amp;Itemid=65<br type="_moz" />

Balda 01-06-2013 06:13 PM

RE: Cox surestart problem please help
Hi ,

I checked my surestart cylinder , Its dual bypass port and dual boost port. My Golden bee have 2 bypass.
I noticed that golden bee have slightly more compression than sure start, especially when its still hot after run, surer start virtually lost its compression.

I found that most of 1/2a RC plane kit that advertised as "designed for 049 engines" but weights 20oz. Kits manufacturer should come out with something more lighter.
I have bigmig pre-revlite engine in my other plane,
its a good performer.

I love Cox engines because it looks special, with its own character.
I'm not going to put any hop up parts yet,just want to know more about its power range, I can see some tested Sure Start with good performance but some just like mine.

<br type="_moz" />

ffkiwi 01-06-2013 07:40 PM

RE: Cox surestart problem please help
A standard 'as manufactured' Golden Bee should have a single by pass cylinder-the only internal difference (apart from the stunt venting on the larger Golden Bee tank) was the reed opening ID of 11/64" vs 9/64" for the Babe Bee. So yours is not standard! 'Aeromodeller' found fairly close performance between the Babe Bee and the Golden Bee on the dyno when tested-their examples producing 0.056BHP at 13,000rpm for the Babe Bee and 0.0625 BHP at 14,000rpm for the Golden Bee. These are fairly typical figures for the time-and by comparison the later Black Widow with twin bypass and a hi compression head produced around 0.08BHP-about the same as a Medallion 049. It was much later (into the 90s) that further development of cylinder, and lighter pistons in tapered liners produced near TD levels of performance from the reed valves-in the form of the original Killer Bee 049 and 051s.
AM provided a range of prop rpm figures extracted on KK Record Nitrex fuel which would have been 15% nitro content, and quote 14-15,000 for 6x3 props-of the narrow blade style. They also show the Golden Bee as capable of turning the DC 5-1/4x3-1/2 prop at 17,600rpm so figures of 17,000 on a 5x3 are quite feasible. [NB this prop seems to be a copy of the Topflite 5-1/4x3 and is very flexible, so I doubt its stated pitch is accurate, and it always turns up high revs so I suspect it is more truly about a 5-1/4x 2!]

The Golden Bee was typically about 1000rpm faster than the Babe Bee on the same brand and size props in the prop rpm table

Typically in the 1960s for reed valve Mouse Racing, the first thing you did was fit a TD 049 cylinder set and high compression head to your Golden Bee, the second thing was loosen up the shaft fit, (using wet and dry and jewellers' rouge) and the third thing was playing around with reeds (this was well before mylar, teflon and stainless steel reeds were options)

AM suggested that the Golden Bee seemed happiest in the 15,000-16,000rpm range whereas the Babe Bee was more comfortable around 12-14,000rpm. All in all this suggests 6x3-6x4 props........of which there are any number of choices available............


049flyer 01-06-2013 08:23 PM

RE: Cox surestart problem please help
Just returned from a short evening flying session. I had time to tach my Surestart as well as my buddy's Surestart:


Stock Cox Surestart

Temperature: 55 degrees F.
Humidity: 33%
Fuel: Sig 15% 1/2a fuel - last of the quart so not very fresh.
Prop: Cox dark grey 5 x 3
Elevation: 500 ft above sea level

Rpm recorded: 15,500 steady RPM

Buddy's Surestart under exact same conditios EXCEPT using Powermaster 25% 1/2a fuel. Rpm recorded was 16,500.

Therefore it seems to me that your engine is performing normally under your conditions of higher humidity and temperature.

I agree with a previous poster's suggestion that a Norvel .061 would be a better choice for a 19 oz airplane.

Balda 01-06-2013 10:43 PM

RE: Cox surestart problem please help

thnaks for the numbers

15,500 - 16,500 on 6x3 seems good, mine only 11,400 rpm using 6x3. What a huge difference compare to your country humidity. My elevation just 25m above sea level. Humidity today 78%.

I will try to run it in one of my friend's factory in this coming Sunday. His factory equipped with humidity control device that limit humidity under 40~%.

Thanks .


<br type="_moz" />

Bugzidor 01-06-2013 11:01 PM

RE: Cox surestart problem please help
I'd run my .049SS, here in Bangkok, with a home made muffler and carburetor, APC 5.7"x3", Byron 15%(10y. old).

Balda 01-06-2013 11:03 PM

RE: Cox surestart problem please help

thnaks for the numbers

15,500 - 16,500 on 6x3 seems good, mine only 11,400 rpm using 6x3. What a huge difference compare to your country humidity. My elevation just 25m above sea level. Humidity today 78%.

I will try to run it in one of my friend's factory in this coming Sunday. His factory equipped with humidity control device that limit humidity under 40~%.

Thanks .


<br type="_moz" />

Balda 01-06-2013 11:25 PM

RE: Cox surestart problem please help
Hi bugzidor,

Yes, I have seen you using cox engines for years, especially your own throttle control. Your country seems close to me, but you can perform well.
May I know is your sure starts are stock one , or you modified , or you match from parts?

I just want to find out if my sure start having problem , or just normal.m


<br type="_moz" />

049flyer 01-07-2013 05:16 AM

RE: Cox surestart problem please help
Sorry everyone but there was an error in my numbers, I have just changed it. The prop was 5 x 3 not 6 x 3. Typing on a tablet computer is a pain sometimes!

Balda 01-07-2013 08:27 AM

RE: Cox surestart problem please help

No problem, tablet always give typo problem.

I just came back from one of my friend's house, tested his old production engine with #0 cylinder, wihout any modification.
He used pure methanol and 22% castor. without nitro. yes, its 0% nitro.
Impressed to see 15,700 RPM with Cox 5X3, and Master Airscrew 6X3 teched at 13.400 RPM.

This proved although hulidity can slow down its RPM , but not that much. Just wonder how his twin bypass without any booster can outperform my newer Sure Start.

<br type="_moz" />

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