Fast Surestart Simple Mod

bakergw Tue Dec 29, 2020 2:17 am

Goodaye All,

Built a very fast Surestart the other day that somewhat surprised me. I built it from parts I had bought so quite technically what it was Im not sure. I had a Cox 049 Crankcase assembly OEM and a Cox 049 Cylinder and piston - Standard, used a Cox 049 Glow Plug Adapter, Cox 049 Backplate Assembly OEM (Grey), and the standard surestart prop and a spinner, all parts available from either Matt or Bernie. Used an OS #8 plug

To get some extra performance I made some changes that not everyone will agree with, but boy does the engine go like buggery now!!! One of my friends has a Tach so I will get him to check it in a couple of weeks. I have never so thought an engine would blow up from revving so hard.

I drilled out the backplate choke tube all the way, top down and then at the bottom into the tube with a 7/32 drill bit. I then drilled out the backplate all the way through where the spray bar goes to where the reed valve goes with the 7/32 drill bit. Replaced the reed with a mylar reed, cleaned everything and put it back together with new gaskets. Changed the needle valve setup by removing the spring, putting a washer on the needle and using one piece of silicon fuel tubing over the needle and the spray bar seal to prevent air leaks and it also holds the needle in place well. I also removed the piece of mesh in the backplate intake. Ran it on 25% Nitro with quite a bit of castor for a few tanks and quite rich. instead of 4.5 turns, the needle required 5.5 turns to start, I assume due to the extra air flowing in and therefore extra fuel. The needle was ok to adjust could run quite rich and then tune to near peak easily. I havent quite run it enough to take it to peak, but I reckon it may well break something. Lol. Maybe it wont, they might be tougher than I thought! Very Happy

Very simple mods with a huge performance change. I will get my mate to tach it later as I know lots of you are into the tach readings. Not sure of the next step, usually to get max performance the exhaust needs to be matched up with the inlet capability. Might have a look and think about that, Would like to alter the boost port setup as well, and maybe the squish band.
One very noticeable change just flicking the engine over in my hand was the extra compression was significant, which given the way reedies work and the crankcase compression makes good sense.

One thing at a time! cheers

Cheers,
Gary

davidll1984 Tue Dec 29, 2020 2:37 am

U must have no spi ?? m'y self upgrades the ventury size of the back plate for extra rpm in som of m'y engines found wit rc ring wil Not operate correct engine lean mix To mutch if try To rpm down To mutch engine stal du To fuel leaning litle air restrictions is nead To rc engines correct rpm range wit choke tube rc no troubles To rc that larger ventury egr valve for rc cars wil Not work very Good wit To large ventury modification as the gtp back plate is alredy larger

bakergw Tue Dec 29, 2020 2:52 am

Correct, it does not have SPI. SPI has pros and cons. Its not a silver bullet to performance. The really crude methods of getting performance are lots of air in, lots of fuel in, a head that can burn it properly, an exhaust that can get rid of the burnt gas properly. I just like mucking around with these motors, they are cheap enough to try things out and if you stuff up, it not like you just wrecked a $15,000 set of TZ 750 barrels . cheers

Cheers,
Gary

**Cribbs74** Tue Dec 29, 2020 2:15 pm

Gary,

There is a fine line to venturi size and runabilty. What may work on the bench doesn’t always equate to what goes on in the air. When I was building tach race engines, I quickly realized that they ran well enough on a bench, but were erratic and finicky to needle once airborne. Not sure what you are doing with it so if it’s a bench runner disregard.

While it may seem you have better compression due to crankcase sealing, keep in mind once the piston is past the transfer ports it’s just like any other engine as far as compression is concerned. My guess is you just have a good piston/cylinder fit.

Anyway, like you mentioned some of us like to see tach readings. I am one of them Wink

Not that I don’t trust your ear it’s just I don’t trust your ear. Very Happy

Keep up the good work!

Ron

bakergw Tue Dec 29, 2020 2:47 pm

Goodaye Ron,

You are right on all points. Laughing

My ear is not what it once was, when I was young I could hear the slight change in a Yamaha TZ GP Bike and pull the clutch just before the rear wheel locked as you throttled off at the end of a straight. Usually piston seize up, sometimes crank mains, but you could hear and feel it just before it translated to a very disappointing moment. Laughing

Those that couldnt do it, usually gave the sport away broken in spirit and body!!! Old Bugger

I hope to fly the modded surestart in the next couple of days, my intent it to fly all of my engines, and with all engine based sport bench running and theory goes out the window when you actually use them. Thumbs Up

Thats the fun part of the building and mod challenge. I reckon its going to be ok in the air, it needles well on the bench right through the range. But it might turn out to be an in-flight dud. Laughing

I will keep learning though as I go. cheers

the piston and cylinder are definitely a very good fit, I went through lots of parts to get the best fit I could for this engine. My little hand-grenade Laughing

Cheers,
Gary

bakergw Tue Dec 29, 2020 3:08 pm

Hey Ron,

Now youve mentioned it, I probably will get a surprise when I finally get the motor tech'd. Ill probably find its only doing 17,500 RPM HaHaHa. Problem might be, that Ive never heard a Cox truly screaming and think mine is, when its probably pedestrian. Clapping

Wouldnt be the first time Ive made a goose of myself. Or last!! Old Bugger

Cheers,
Gary

balogh Tue Dec 29, 2020 3:30 pm

Gary

If you post here a video on the engine run, you do not have to wait a few weeks until your friend tachs your engine, because e.g. I could tach it with a totally reliable audio tach app on my Android phone, or you can do the same if you download RPM Gauge from Google Play on your Android phone providing you have one. Parallel handheld tach measurements proved identical readings with RPM Gauge and Hobbyco handheld..

I do thst often for a CEF mate Iceberg here see e.g. below

crankbndr Tue Dec 29, 2020 7:15 pm

I have never seen one blow up, I have tried to blow a few. They are pretty tough. The racers probably had them come apart. Come to think of Kens probably wrecked some. A video would be cool. Popcorn

**Cribbs74** Tue Dec 29, 2020 7:41 pm

One of Fred’s let go on me during a tach race, but it didn’t come apart. I’ve never had one do that, need to try harder!

aspeed Tue Dec 29, 2020 8:11 pm

I've had TD cranks break, sometimes it goes through the case. The older TDs were weaker. I think the bigger bore on the Surestart might still be a better runner than with a Bee, because of the greater chance for air leaks in the Bees. For sure get a video. It is pretty easy to get a tach reading from that.

bakergw Wed Dec 30, 2020 2:00 pm

You blokes crack me up! Laughing

Great morning laugh. the dedication and application made to trying to indirectly blow up an engine through maxing the performance to the point it breaks. When I first read this forum I never thought taking a tach reading would be something I would ever be bothered doing, but Im slowly getting sucked into that adventure as well. Surprised

But, I am not going to start collecting old motors from Ebay and junk/antique bits and pieces and fairs when I drive through country towns!!! Nope, Nope, I am not going to end up there! Laughing

Take it easy.

Cheers,
Gary

aspeed Wed Dec 30, 2020 3:44 pm

Fairs, no. Swap meets are always fun though. Always meet like minded folks. This year was a bad one for that with the Mexican beer disease.

bakergw Fri Jan 01, 2021 2:59 pm

Goodaye All,

Ran my modified Surestart in my rat yesterday. Well, unfortunately Ron was correct. It was absolutely useless in my plan!!! As soon as my Lad let go of it to launch it and it started moving the engine just died. Even tuned a bit rich it did it. Later today i might try it again, with no muffler and using a known good fuel tank. Probably open it up this morning and check reed valve, spray bar etc. make sure there is no rubbish in there etc. But it did pretty much as Ron said it would. Still, Im ok with that, it was worth finding out for myself. Laughing

Ive never been different and a bit late to change now Old Bugger

I will keep working it over time. I would never have made such a huge change to a motorbike race engine inlets without changing the outlets either, but regardless, plus marks to Ron, it did exactly what he said. Cool

Take it easy.

Cheers,
Gary

aspeed Fri Jan 01, 2021 3:10 pm

An opened carb just needs pressure feed. Either a bladder or crankcase pressure is fine. Crankcase is a bit tricky on a reedy but possible. If it was running strong before you let it go, the reed and needle system is likely ok.

**Cribbs74** Fri Jan 01, 2021 3:31 pm

bakergw wrote:Goodaye All,

Ran my modified Surestart in my rat yesterday. Well, unfortunately Ron was correct. It was absolutely useless in my plan!!! As soon as my Lad let go of it to launch it and it started moving the engine just died. Even tuned a bit rich it did it. Later today i might try it again, with no muffler and using a known good fuel tank. Probably open it up this morning and check reed valve, spray bar etc. make sure there is no rubbish in there etc. But it did pretty much as Ron said it would. Still, Im ok with that, it was worth finding out for myself. Ive never been different and a bit late to change now I will keep working it over time. I would never have made such a huge change to a motorbike race engine inlets without changing the outlets either, but regardless, plus marks to Ron, it did exactly what he said.

Take it easy.

Cheers,
Gary

Sorry Gary, I was hoping I was wrong. Pressure may be the way to go as Aspeed suggested. We would never improve if we didn’t fail along the way. You are on the right track.

Ken Cook Fri Jan 01, 2021 3:57 pm

11/64" is pretty much the max you can open the venturi when running suction.

bakergw Sat Jan 02, 2021 2:17 pm

Thanks Ken, I keep forgetting about the suction/pressure need as this didnt exist as a problem with my yamaha TZ race bikes and engines. Their fuel tanks were significantly above the inlets (when I was upright on it Laughing

) and generally carrying at least 15Litres of fuel and therefore the gravity effect provided a nice no problem fuel flow. It makes perfect sense when brought up to me now. As a kid I flew my enya 2.5's mounted in Dominator and Warlord wings with muffler pressure and never considered why, other than the "big kids did it" Laughing

I have several of my almost standard reed 049 engines running on the bench and in flight nicely with pressure via the standard 049 muffler. So I should try this engine with the modded back-plate and venturi out on pressure with a known good tank. I might mod a crankcase for pressure as well to compare against muffler pressure. I need to use a muffler anyway as I fly on school ovals and local district Ozzy rules footy ovals and dont want to get kicked off for being too noisy when there is a way to prevent it. So many options! Lucky the parts are so cheap we can afford to try out things just to see for ourselves. Ive watched the pressure bladder videos and understand them but not yet ready to cross that line. Smile

Cheers,
Gary

Ken Cook Sat Jan 02, 2021 3:28 pm

Gary, the plastic Cox used on the Sure Starts is also iffy. It's not uncommon for the backplate to crack where the needle valve passes through. I have some new in the bag which show signs of splits. Take a close look at yours as well. The crack can also cause air leaks. This can offer issues to a venturi that's stock due to air leaks. I personally haven't tried this but it's been mentioned . With the crankcase off, looking directly at the needle valve in the venturi behind the reed assembly, take note of the jet hole in the spraybar. It's been said to optimally obtain better fuel draw, locate the hole slightly off center. I highly doubt that would help your issue because you have a venturi size that equates to a TD .09 which is almost twice the size needed for a .049.

Now on another note, I see you mentioned the Warlord. I assume this is the British combat plane? I just built a Warlord which is now powered with a wonderful Enya 2.5 diesel. I love this thing. My son is very good with diesels, he puts this thing through it's paces. I can't remember the manufacturer of the kit but it was from about 1971. It was to say the least a challenge to build as it was very unorthodox compared to American kits.

Here was our first flight the tank had to be adjusted higher which stopped the burping. It flies much better than I ever thought actually especially since it's built like a tank.
https://www.facebook.com/513140418756097/videos/214695249594746/?__so__=channel_tab&__rv__=all_videos_card

bakergw Sat Jan 02, 2021 3:47 pm

Goodaye Ken,

I have checked the back plates thanks!. I did see the thread and am very watchful of the backplate now to make sure they dont cause me problems. So far I have been Ok. I bought six of them and none of them has cracks yet thankfully. Yep, the turning the spray bar off centre might help possibly, but I think the mod I made is beyond that alone solving it. Very Happy

Yes, it was the british Warlord combat plane my mates and I used to fly in the 70s with enya 2.5s glows and then I got a gold head Taipan 2.5cc bearing glow head engine with tuned pipe for my wings. it was an awesome combo, but I cant find the taipan anymore unfortunately. We modified the Warlord design and built them ourselves from hobyshop balsa. We basically simplified the constuction. It was good enough for us Smile

We tended to fly home built Dominator' more so than the Warlords, dont know why. Probably fashion. Laughing

Cheers,
Gary

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