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RE: Cox surestart problem please help - 1/7/2013 5:01 PM

049flyer

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Many things could be responsible for measured difference in RPM. Hard to draw accurate conclusions unless all conditions and equipment used is identical. In my case I measure to the steady Rpm not the absolute highest peak, sometimes the rpm changes too fast for the tach to register. I usually launch slightly richer than the steady rpm. My friends often launch very close to peak rpm but their engine often quits before finishing the tank.

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RE: Cox surestart problem please help - 1/8/2013 4:25 AM

Bugzidor

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Yes, I use a stock engine without any modification, except at the backplate that, I put on a carb. So, I may have some comment for you to consider :-
1. Debrist screen at the intake tube, if, it clogged, this will impac to the engine breathing, you can remove it.
2. Increase the intake tube diameter, actually, at the openning area around the spay bar. This could help feeding the fresh fuel-air mixture into the engine, to compensate a non-SPI.
Doing as above could gain few hundreds to a thousand rpm. for 6x3, but, thounsands rpm. for 5"x3"

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RE: Cox surestart problem please help - 1/8/2013 5:15 AM

Balda

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Hi,

Thanks for your tips , yes, I've heard about enlarge the air intake, should be good to try. The tiny hole at spraybar should be center or tilt a little? I've seen some argue about this, don't know which should be working for me .

Thanks

Regards,
Balda

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RE: Cox surestart problem please help - 1/8/2013 3:16 PM

049flyer

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Be careful when increasing air intake as this could affect fuel draw capability. It is my understanding that the velocity of the air through the venturi creates the low pressure that draws the fuel. Increasing the diameter of the tube may decrease the velocity and fuel draw capability.

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RE: Cox surestart problem please help - 1/8/2013 3:47 PM

Balda

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yup, need to becareful not to over do it. but before I enlarge the air intake, I think I might need to buy another piston/ cylinder set to try out first because the two sure start seems low compression if compare to my older cox engines.

balda

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RE: Cox surestart problem please help - 1/8/2013 6:30 PM

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quote:

ORIGINAL: 049flyer

Be careful when increasing air intake as this could affect fuel draw capability. It is my understanding that the velocity of the air through the venturi creates the low pressure that draws the fuel. Increasing the diameter of the tube may decrease the velocity and fuel draw capability.

Quite correct-and if memory serves me correctly, you were generally advised to open up the reed valve engines' venturi by very small increments-1/64" at a time- because of this very risk. Yes you do gain a little bit-but at the expense of fuel draw. I also recall that with the Texaco model they REDUCED the size of the venturi to improve fuel draw at the low speeds this model is usually run at~8,000rpm or less. Even the TD series instructions mentioned enlarging the venturi-but also emphasized that this should be done only if running on pressure. Pressure isn't really a practical option for reed valves-though I do know of it being done with the .15 sized Olympic.

ChrisM
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RE: Cox surestart problem please help - 1/8/2013 7:33 PM

049flyer

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Balda -

You should try the special high compression plug and head from Cox International. I have one and there is a very noticeable increase in power when using it. I have not yet put a tach to it but I think the power output with this head gets close to the TD. In fact it is best to use 2 or 3 washers with this head to keep from being over compressed. This seems ideal for your situation. You could adjust the washers based on the heat and humidity of the day as well as the fuel used. I would think that running this head with only 1 washer and FAI fuel would surprise us all. I run 2 washers with 15% fuel, i would probably start with 3 if I ran 25%.

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RE: Cox surestart problem please help - 1/8/2013 8:37 PM

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I don't think you can drill a SureStart intake far enough to experience fuel draw issues unless the engine has poor suction due to worn out parts, or parts with sloppy fits.
If the piston/cylinder has been primed with fuel and then brought up to TDC the cylinder should stay pumped for at least a few seconds with the air it compressed. Actually a real good Cox P/L set will stay pumped for several seconds.
I'm not sure if the Nelson glow plug head is as high of a compression as the TD head, but you want high compression to complement the larger intake. The Nelson conversion head pays for itself if the price of those glow plugs is still lower than the rest. I have run some Cox engines with no head shims with the 5x3 prop.
I have been waiting to see somebody come up with a way to expand a COX piston slightly to a predictable oversize. I've done it successfully once, but it's beyond my skills to get a predictably good outcome instead of "hit & miss" and hours spent when it comes to lapping the cylinder using the piston as the lapping tool.

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RE: Cox surestart problem please help - 1/8/2013 11:38 PM

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The Merlin plugs are only $5, the same as Nelson plugs, and made for the motor. I think they are pretty good although I have had a couple let go for no reason in the middle of a run. The element wasn't bent or mangled or anything, just no more glow. That was just regular longs. I think a Turbo plug might be more efficient than a Nelson at least because they are a bit smaller diameter sticking into the combustion chamber, but also because there are many ranges and brands to experiment with. They aren't cheap, and I am not sure anyone makes heads with them either. I don't like fiddling with the Cox stuff any more, they just aren't worth the trouble of plating or spending much time on IMHO. Especially with the Surestart, if you have room for a tank, you may as well use a Norvel or TD. A bigger intake hole may be worth the trouble if opened gradually and tested....

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RE: Cox surestart problem please help - 1/9/2013 2:36 AM

Balda

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HI,

thanks for all good suggestions.
I've heard of high compression heads, with good results. I will try one.
but before I try , I think my cylinder and piston having problem. both 2 Sure Start suffer from piston cylinder problem I think. I try to oil it with castor oil, and turn it to TDC, it hold its compression for just one second.

One of my friend suggest me to hold the engine's driveplate, and let the cylinder place sideway, and wait for the cylinder's weight to discharge its compression and drop. he says good engine will hold its poition forever. mine just hold for a few second.
my 2 Sure Start are new, but seems I have bad cylinder and piston.

Should I buy new piston and cylinder? anyone have same problem like me?

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RE: Cox surestart problem please help - 1/9/2013 3:25 AM

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Like CP said a good piston/cylinder should hold compression, and feel snappy when flicking the motor over, Unfortunately the later Cox quality control was not what it was or should be and many piston/cylinder sets are not really up to what they should be. Ive found the hardness of the pistons vary quite a bit too. Only way to get/make a good motor is to buy 10-12 piston/cylinder sets, adjust/reset the pistons(noteing the hardness- harder pistons require more ooomf to reset), tput the hard pistons together and selectivly fit these to cylinders to find good matching sets , if you get 5-6 good sets 3 soso's out of 12 youve done well , the rest are basically scrap.

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RE: Cox surestart problem please help - 1/9/2013 4:27 AM

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quote:

ORIGINAL: SGC

Like CP said a good piston/cylinder should hold compression, and feel snappy when flicking the motor over, Unfortunately the later Cox quality control was not what it was or should be and many piston/cylinder sets are not really up to what they should be. Ive found the hardness of the pistons vary quite a bit too.

My experience, too. I've got a Surestart that easily passes CP's compression test with flying colors. I've got others that have essentially zero compression.

I have no formal way of testing piston hardness, but I did get a batch of Surestarts that had what seemed to be very soft pistons. After resetting a lot of piston sockets, you tend to get a feel for how much striking pressure is needed to tighten the socket. The batch with soft pistons required hardly any effort to reset the rod.

It may be that you've gotten a poorly fitting piston/cylinder set - if that's the case, then there is little you can do to improve it. Some folks have been able to swell the pistons by heat treating, but I have no idea how to maintain any consistancy or control over the process.

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RE: Cox surestart problem please help - 1/9/2013 4:43 AM

Balda

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Ouch! I don't know that new Cox have low quality piston and cylinder.
My friend help me to reset my Sure Start piston last week, I can see that just 10 to 20 taps on his reset tool and done.
He reset my old golden bee and he needs hundred taps to reset it.

No wonder my old Cox engines can ran well and it last forever.

Don't know if worth it to fix this two Sure Start, or just give up Cox products and buy Norvel. If I buy a dozen of piston and cylinder set, I can buy good engines at that cost, unless Cox re- manufacture good quality piston.

What a pity that Cox engines had gone so long , since 40's with its good name , but ended with low quality piston and cylinder.

I'm interested in trying to swell the piston a little bit, but I think it's hard to control perfect heat.
Even if I can success to swell it and lap nicely with cylinder, the soft material of piston seems not last as long as older piston, hmmm... Don't know if the piston will become harder after apply heat.

Balda

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RE: Cox surestart problem please help - 1/9/2013 7:33 AM

SGC

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If you keep an eye on #bay for a No1 piston/cylinder set (theres a couple currently listed) , these are pre 1996 production as used on the first of the Blackwidows and medalions, and should have good fits.

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RE: Cox surestart problem please help - 1/9/2013 8:47 AM

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quote:

ORIGINAL: SGC

If you keep an eye on #bay for a No1 piston/cylinder set (theres a couple currently listed) , these are pre 1996 production as used on the first of the Blackwidows and medalions, and should have good fits.

SGC, the engines were great back then but the replacement P/L sets I ever bought back then weren't as good as the ones that came with the original engine. I figured that they sold the "rejects" as replacement parts...?
That was just my experience with 2 or 3 attempts to go that route way back then.

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RE: Cox surestart problem please help - 1/9/2013 9:33 AM

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I have been running the Surestarts for several years now and have had none of the problems you guys are talking about. I fly control line as well as RC as do my 2 flying buddies. Between the three of us we have about 20 of these things and they all run better than any of the older engines with the attached tank. Reliability is greatly improved. My pylon racer usually starts by hand without an electric starter or spring starter with only a flip or two.

The Surstart is a great engine for the price, but you have to build a plane that is suited for it.

Perhaps we need a little perspective, we are talking about a $20.00 engine, rigjt? Parts are dirt cheap too, buy a bunch of pistons and cylinder and throw the bad ones away or give them to me. I'll fly the heck out of them!

If you want to have a blast with a $20 engine and $3.00 worth of foam and balsa, get a Surestart and build a 11oz plane for it. You will not be unhappy!

It's not quite fair to expect the $20 Surestart to compete with a Norvel that costs over 3 times as much.

A too heavy plane will fly poorly no matter what engine you put on it.

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RE: Cox surestart problem please help - 1/9/2013 10:56 AM

Balda

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Hi,

I'm actually not going to squeeze the last bit out of them, just want to run it normally. 14K ++ rpm with 5X3 a little bit low but I can use it in 12 oz plane without problem. one thing I don't like is hard to start, I need to flip it for quite number of times to get it start. even primed nicely. . I removed the spring starter and plastic cam to avoid power lost.
I'm just curious that others Sure Start can do higher RPM, and mine seems a little bit lower. keen to experiment with it , thats all. Even my friend's production engine without boost port can out perform using FAI fuel, at 15,700 rpm .
whats the point they add 2 booster port but RPM lower than non booster product engine?

I strongly believe that I'm bad luck enough to have 2 bad one. I will try to buy another sure start and try again. and maybe a few sets of P/L sets to play with. If it run nicely, at least I have 2 sure start for parts. ;-)

Nice to learn a lot about Cox engines from you all, thanks you !

balda

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RE: Cox surestart problem please help - 1/9/2013 1:24 PM

049flyer

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Balda:

Remember that there is a break-in period with these engines. I would say that without an electric starter or spring starter the engine can be quite a bother until you get 30 to 45 minutes of run time on it. It also won't hold a needle setting or run through a tank wthout stopping. After the break in period all of these issues go away.

The beauty of the Surestart is that you can choke it. I usually don't even prime it like we used to with a drop of fuel in the exhaust. I choke the engine for about 6 turns to make sure fuel is drawn into the engine. Then I connect the glowplug and turn slowly by hand until I feel the bump. Ater the bump a flip or two usually has it running.

If you don't get the bump then it is either flooded or not enough fuel. This is where knowing your engine comes in. In my case it is usually flooded so I close the needle all the way and flip until it clears and then start over.

Another nice thing about the choke tube is this: remember sometimes the engine runs for a second, burns the prime and stops? If you put your finger over the choke tube before it stops the engine will catch and continue to run.

Have fun with the Surestart, it's the best $20 engine you can buy!

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RE: Cox surestart problem please help - 1/10/2013 2:02 AM

Balda

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Choke tube can be a good feature , thats why Cox named it "Sure Start" i think
Good to know that Cox engine need 30-45 minutes break in time , I was told that a couple of tanks will be settled.
I should get 20 pcs back in 2007, it was $6.90 , cheaper than a glow head.

Balda

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RE: Cox surestart problem please help - 1/10/2013 2:09 AM

aspeed

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Except then you would have 20 low compression heads which you would never want. (I think)

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RE: Cox surestart problem please help - 1/10/2013 11:26 AM

Balda

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Hi all,

I have several question before I purchase some high comp. heads and p/l set to experiment with.

1) If I'm using high comp. head, and less shim , ( over compress ) what will happen ? lower RPM? or heat up fast? hard to start?

2) what will happen if leak between back plate and crankcase? I can't see leaks but I can see uneven surface on crankcase at the edge of screw holes. I think i will sand it flat by placing sand paper on mrror surface.

3) someone mentioned that place toothpaste in between crank case and crank shaft and spin it using drill to polish inner surface to mirror finish. will this increase RPM? roughly how much increase in rpm?

4) Other than trying to change the glow head to high comp. I want to keep others as original as possible. i'm thinking of adding choke tube throttle just for experiment. one of my friend mentioned that the air intake at back plate measured 4.56mm but the intake on the throttle just 4.00mm, which will lower its power even at full throttle by several hundred RPM or even a thousand rpm. is that true? if it is true, why manufacturer not drill it bigger to match with the backplate size? can we modify it by drill it from 4.00mm to around 4.5mm to gain a little more air into engine?

Sorry for a bunch of silly question but I'm keen to know more about Sure Start and wish to experiment with it.

Balda

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RE: Cox surestart problem please help - 1/10/2013 3:57 PM

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Balda

Hard to say what (if any )modification might get you a predictable increase in RPM

I usually get a 500~600 RPM increase by just barely increasing the venturi opening

Galbreath head and nelson plug has always increased my RPM

Merlin head and plugs seem to the same to me but last noticeably longer than Cox heads

Increase or decrease of head shims has dramatic effect and depends a lot on weather and fuel

I generally use Sig Champion 25% nitro mix for all the Cox reedie.049/.051s and 35% on my medallions and TeeDees

Smoothing the crank case back on 400 or 600 sandpaper on flat glass is good idea

Also using 2-56 tap on each of the four screw holes to make sure your screws are not bottoming out before you get good seal

Do NOT try to use tooth paste in the crank case bearing as you don't want to reduce or remove the hard anodising in that area

Use progressively finer grits from 800 to 12,000 then very fine polish and cloth to mirror finish the crank ( I use a MicroMesh kit designed to repair plexiglass windshields). Polishing the crank bearings does not take long. Wash well in hot soapy water and then wash it again

When polishing the crank bearings, you do NOT want to reduce diameter much if any- just get it mirror scratch free, use a good magnifier

Polishing the crank does nothing if the fit is already too loose,,,,,BUT almost always yields an increase in RPM on well fit parts. I polish all my cranks and then mix n match with cases to pair up the best fits

Watch e-bay for the "lots" of sure starts. There is always a offer for three or four sure starts that are about $17 each-I know shipping to Singapore kills the savings

Find a copy of Paul Gibeault's mouse race instructions. In it are very good hints and instruction on making a Cox motor sing

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RE: Cox surestart problem please help - 1/15/2013 6:41 PM

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Just perusing this thread got me wondering if Balda got one of those Estes Sure Starts that was possibly made with a mishmash of parts from who knows what years in their parts inventory. Also I was wondering if Balda was using FAI (zero nitro) fuel.

Warren Leadbeatter, a Cox 049 engine collector and flyer has this blog article in E-Bay, explaining how to successfully hop up the Surestart:

http://reviews.ebay.com/Cox-Surestart-Hop-up?ugid=10000000005390559

The $6.99 US cost he mentions was a few years ago, when Estes was selling them on clearance prior to liquidating their entire Cox engine parts inventory.

It sounds like to me that as long as one doesn't overdo it, probably won't experience fuel draw problems, but YMMV.

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RE: Cox surestart problem please help - 1/15/2013 11:12 PM

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Sorry to stray off the subject matter on this thread. I just opened a new surestart from its bubble pack to clean for a grace airplane i just completed. When i took the backplate off i noticed that the backplate is split (cracked) on both sides of the venturi where the spray bar goes thru. So i take it that this assembly is junk right!

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RE: Cox surestart problem please help - 1/15/2013 11:35 PM

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quote:

ORIGINAL: glowtime Sorry to stray off the subject matter on this thread. I just opened a new surestart from its bubble pack to clean for a grace airplane i just completed. When i took the backplate off i noticed that the backplate is split (cracked) on both sides of the venturi where the spray bar goes thru. So i take it that this assembly is junk right!

Well glowtime, I'd say that common sense prevails. Does the cracking seem more than superficial (possibly allow changes to fuel/air mixture or atmospheric air outside the engine to bypass the venturi throat and dilute fuel/air mixture)? Then it's broke. Depending on how badly cracked, you might get by with some RTV sealant, but it looks like to me it might need replacement.

Fortunately, tank back parts abound and you should be able to get a replacement for reasonable cost.

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