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Cox Surestart RPM and run time.

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Old 03-12-2009, 02:45 AM
  #1
Lost Glider
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Default Cox Surestart RPM and run time.

This information was obtained last summer, with a Cox gray 6 x 3 prop,
and Omega 15% with 4oz castor oil added to the gallon.

16 Surestart engines
Start 14,700 - 13,100
After warm-up 14,100 - 12,100
.125 oz fuel 58" - 1' 37"

Toss out highest and lowest then average 14 Surestart engines
Start 13,893
After warm-up 12,879
.125 oz fuel 79.5 seconds

More recently one engine was run with a Top Flight nylon 5.25 x 3 prop, 16,000 rpm.

Randy
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Old 03-12-2009, 08:00 AM
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Default RE: Cox Surestart RPM and run time.

Thanks for all that testing Randy. Am understanding you that rpm's dropped after the engines ran for a while? Were those tall backplate NV's rotating from vibration? I personally prefer the Cox 5x3 or an APC 5.7x3 on reed valve engines (using 6" props on TD's).

David
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Old 03-12-2009, 11:36 PM
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Default RE: Cox Surestart RPM and run time.


Quote:
ORIGINAL: rainedave

Thanks for all that testing Randy. Am understanding you that rpm's dropped after the engines ran for a while? Were those tall backplate NV's rotating from vibration? I personally prefer the Cox 5x3 or an APC 5.7x3 on reed valve engines (using 6" props on TD's).

David
Yes, highest RPMs after starting and tweaking, then they tend to tighten up and slowdown.

This raises two questions:
#1 Too much castor oil?
#2 Engines just need more runtime to achieve optimum fit between piston and cylinder?

I keep adjusting the needle valve, but a hot engine will never achieve the same RPM that it did when first started.
I don't see the needle valve self adjusting. I'm going to get some hotter fuel and NOT add Castor oil.
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Old 03-13-2009, 02:41 AM
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Default RE: Cox Surestart RPM and run time.

I don’t know how to adjust a Cox engine, but I’ll think you have set the needle a little too lean, if the settings are familiar to other engines.
Try set the mixture more rich (1/8 to 1/6 of a turn), and keep an eye on the RPM. Now it shouldn’t drop in RPM after short while.

In Denmark you can buy special Cox fuel.

Here is a link concerning Cox 049 fuel + tips.

http://www.modelgeeks.com/Uwe/Forum....t-fuel-for-049

Use castor!
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Old 03-13-2009, 03:07 AM
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Default RE: Cox Surestart RPM and run time.


Quote:
ORIGINAL: Lille-bror

I don’t know how to adjust a Cox engine, but I’ll think you have set the needle a little too lean, if the settings are familiar to other engines.
Try set the mixture more rich (1/8 to 1/6 of a turn), and keep an eye on the RPM. Now it shouldn’t drop in RPM after short while.

In Denmark you can buy special Cox fuel.

Here is a link concerning Cox 049 fuel + tips.

http://www.modelgeeks.com/Uwe/Forum....t-fuel-for-049

Use castor!
I do back it out to run rich then lean it out again but they never hit the same high rpm that they did when they were first started. This makes me think too much castor oil, it's just getting to thick in the cylinder. I have never had one cease up.
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Old 03-13-2009, 11:00 AM
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Default RE: Cox Surestart RPM and run time.

I've never had castor oil effect the way my Cox engines run. I use at least 20% and sometimes more.

You do need to use at least 25% nitro, 35% being even better. Cox's just don't run very well on 15% nitro.

I think the large - 6" - props are bogging them down. Again, the APC 5.7x3 is ideal for reedies.

Traveling NV settings have always been a problem with Cox engines. It's not a bad idea to put a piece of fuel tubing them.

Here is all the info you'll ever need for reedies:

http://www.rcuniverse.com/forum/m_3747940/tm.htm

David
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Old 03-14-2009, 04:16 PM
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Default RE: Cox Surestart RPM and run time.

Well. It still sounds like lean settings. You should aim for a steady top RPM, and not just a short peak performance. I can set my engines the way you write, and they will drop after 30 second = too lean. The engine shouldn't go straight to the max RPM, but slowly (approximate 10 sec.) take the last 3-500 RPM - and stay there

You could give it a try.
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Old 03-14-2009, 06:18 PM
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Default RE: Cox Surestart RPM and run time.

FWIW I ran 2 Sure Starts today...in my basement.

I don't think they are officially "broken-in" yet, but I ran ea. one 4 times before tach readings. (a 1oz. tank, and ran half a tank thru then cool down, and did that for two tanks ea. engine )

Temp. 53 degrees...
25% nitro and 20% oil (half-n-half syn./castor ) mixed myself.
5x3 Cox black "rubber duckie"

Got 16,600 out of one, and 16,700 out of the other.
The one that did 16,600 is pure stock, and the other is mod. with a drilled out backplate, no screen and the mylar reed. Makes me wonder if mod. them is worth bothering with?

I peaked them to their max for the tach reading, then richened approx. 300-400 r.p.m. down and they would run the rest of the 1oz. tank out at that (stable ) r.p.m.
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Old 03-15-2009, 02:30 PM
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Default RE: Cox Surestart RPM and run time.

You can get close to KillerBee performance from Surestarts if you buy a large enough stock of engines to mix and match until you luck into some good P/L sets. After working the internals to mimic the KB's as much as possible, they are capable of surprising performance.
After going through all these gyrations, it would make more sense to just look for a TD or KB on the auctions.
I've recently tached 20 of these engines with 6x3, 5x3 and 4.2x4 props and the readings were all over the place from engine to engine.
If the engine bogs down after being peaked out, lap the crank. If you can, cut a relief notch like the KBs have on the crank journal.
The bottom ends need to be detailed and evaluated to minimize friction. The bottom ends need to pass a "prop flick test" before reassembly can go any further.
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