New to these engines, curious about how to tweak them and care for them!

RknRusty wrote:A Tee Dee glow head will always run better on any Bee engine. It's higher compression, so you may want to adjust head gaskets and/or nitro content to suit the engine. Trial and error in that department.
Rusty

'Bout how many shims would you suggest as a starting point when running 24% nitro?

RknRusty wrote:

Here are some of my opinions, not all necessarily facts. Some may have been answered, but just consider it my extra 2 cents:
1.It's been said by performance guys that the big opening of the old style cylinders is overkill, and the slits work just as well. But give me the choice, and I'll take the wide port. Old style SPI is made with a lower opening on the port, so the piston skirt clears it at TDC.

There is more than one way to achieve SPI. With the newer slit exhaust, all exhaust decks are the same height. A shorter piston skirt(something you can modify) clears the port allowing the same amount of sub induction. Do not put a short skirted piston in an old style SPI cylinder because it will then have too much induction and the performance will falll on its face.


Here is an explanation I wrote explaining what happens with SPI:
https://www.rcgroups.com/forums/showthread.php?1538781-Sub-Piston-Induction-anyone-understand-how-it-works

A good read for sure, makes me a bit more comfortable having the ports opened up without risking getting SPI. My engines are throttled via a choke tube throttle and, per Cox Intl, SPI renders said throttle pretty ineffectual. Kind of a shame, because SPI is a huge power boost, but having an engine I can throttle(and even shut down) from my transmitter is higher priority for me than all-out max Bee performance.

Reading that thread, you mentioned that the new TD cylinders Bernie's producing don't have SPI, yet are more or less equal in output to the SPI-enabled #4 cylinders. Perhaps it'd be worth my time to put some of Bernie's TD jugs on my engines to see if they'll buff power a bit while retaining the throttle?

3. Unless you want to run more than 21k RPMs, a Bee crank is fine. They will run a little faster because they are lighter.

Ahh, good. I'm probably turning something around 16,500 or 17,500 on my Spear and closer to 14,500-15,500 on the Sportster(Spear runs 5x3 three blade props, Sportster has a 6x4 wood prop, both run the same 24% fuel). Really need to get a tach though, find out for sure.

Be sure you use 5-40 prop bolts that reach deeply into the nose. Short screws can make the splined tip break off easier. I like the black oxide hex bolts.

I'm using the bolts and spinners that Bernie includes with the engines he sells for now. FWIW they take 6 or 7 turns to tighten down a prop, so I imagine they're going quite a ways in there.

5. I can only guess, but it seems logical that a 5 fin head would be good for a pusher.

Mm. Definitely something to keep in mind. I'd like to run higher power heads on those two(And they're the ones that need it most!), but thermal issues take precedence and if they wanna run hot with the 3-fin standard glow heads I don't have much of a choice but to swap to the 5-fin Texaco heads. I'll pull the heads and check 'em after each flight for the first 4 or 5 runs, look for the signs of overheating. Excessively dark discoloration around the element, external discoloration, and of course if they start misfiring or dying mid-air there's an issue to be sorted.

I don't anticipate any thermal issues on the Sportster. It's a tractor configuration with the engine in a nice little air channel. Running it for 20+ minutes at wide open throttle on the ground didn't even overheat it, so if anything, it's probably a bit over-cooled. Def gonna toss a TD head on that one.

6. Drone props are made for electric motors and usually have thinner hubs. The e-props cannot endure the cyclic pounding that an IC engine will subject them too. I say stay away from those.

Really limits prop selection these days, especially multiblade props of which I'm quite fond.

I hope I didn't re-answer too many. I skipped a couple due to no experience. Hope that helps.
Rusty

Oh it definitely does!

The TD cylinders Bernie sells are SPI..they are made from slit exhaust non-SPI cylinders by removing the middle bar and lowering the exhaust port bottom for SPI timing.

balogh wrote:The TD cylinders Bernie sells are SPI..they are made from slit exhaust non-SPI cylinders by removing the middle bar and lowering the exhaust port bottom for SPI timing.

Quite correct. Thanks, Andras.

JennyC6 wrote:
'Bout how many shims would you suggest as a starting point when running 24% nitro?

Two.

... My engines are throttled via a choke tube throttle and, per Cox Intl, SPI renders said throttle pretty ineffectual.

That's mistaken. Mufflers interfere with SPI because they feed exhaust gas back into the crankcase. A choke tube throttle doesn't directly affect SPI or visa versa. Sub Induction is only effective only at peak or near peak RPM. That's when you want max power. But that's irrelevant when you throttle back and don't even want peak power

...you mentioned that the new TD cylinders Bernie's producing don't have SPI

I don't think I said that. As Balogh said, they cut out the slit bar AND lowered the exhaust deck so the long skirted piston can open the SPI gap. I did say the Cox slit exhaust cylinders were all the same, meaning a regular long skirted piston won't open an SPI gap. Rather they used a short skirted piston to achieve SPI. It's easy to shorten a skirt with a file and a drill press if you need to. Just keep in mind, there is a fine line between an effective gap and too much gap.

...I'm using the bolts and spinners that Bernie includes with the engines he sells for now. FWIW they take 6 or 7 turns to tighten down a prop, so I imagine they're going quite a ways in there.

Okay. I'm just saying... I feel better using all the threads. But Albert Einstein said, "Imagination is more important than knowledge." Lol

I re-read the whole thread and some my prose was redundant, sorry. I missed the ball socket reset question too. After break-in it's frequently necessary, but I never mess with it after that. The metal all gets work hardened and I usually only manage to mushroom the piston crown after that. Some people apparently have a more deft touch than I do.

So you're saying I could still throttle down to a nice low idle and even shut the engine down entirely via the choke tube throttle while running an SPI cylinder?  I've been looking into every other option but SPI to get more power out of these because my understanding is they don't throttle very well with SPI and the choketube throttle combined due to that extra air getting sucked in at/near TDC.

I'm not overly concerned about it on the Mini Sportster as even without SPI, without a TD head, that thing's gonna have more power than it needs. But the Spear's a heavy ol' pig, 40-odd inch wingspan and likely somewhere around 800-900 grams fully fuelled, with two engines pushing hard as they can. They're the engines I want to hotrod the most. If I can coax more power out of them without sacrificing throttling by putting SPI cylinders on them I will do exactly that!

Hey, C6,
I've never tried, but the choke throttle and the SPI don't seem to me like they are mutually averse to each other. I bet an old style exhaust restrictor throttle would most likely throw a wrench in the works, and I bet that's where the mistaken assumption came from. Many 2-stroke motorcycles, boat motors, yard tools, etc. have SPI combined with intake throttle bodies, and they idle fine. But like I say, I'm only applying my knowledge of engines, and have no hands-on experience or proof. Just my educated guessing.

Try and see. I bet it works fine. At least fine for a tiny Cox engine. From what I gather, they never have had the most reliable idle anyway. I think that may be due more to lack of inertia in the rotating assembly. And any, even the most negligible air leak in the engine will likely cause a big idle problem. A heavier prop might help it idle slowly, but that may not match up well with your thrust needs.
Rusty

From running my own engines, I can attest that they idle surprisingly well. I can leave them sputtering along at 5500-6000RPM for 30 seconds, suddenly floor it, and they ramp right up like a champ. They're nowhere near as responsive as something larger from OS or Saito, but just the same, these little guys throttle surprisingly well. Especially my Mini Sportster, with its 6x4 solid wood prop, and you can see, hear that in the video of it I posted most recently.

A little more inertia would certainly get the numbers down more, but I'm just happy if itt'l idle on the tarmac without trying to buzz off on me until I want it to.

FWIW it's not a true carb by any stretch, and indeed, if one removes the choke tube from the engine they'll run just fine as a tankless non-RC 0.049. Same needle, mixer, et-al. Not like the RC Tee Dees which did have a true carb on them instead of an open venturi.

So I decided, on a whim, to pull the jug off one of my 0.049s and have a look at the piston socket endplay. Found it to be absolutely atrocious! I didn't measure it but I'd say the rod could move a good 16th of an inch in and out of the piston...side note; the engine still ran fine, I can't imagine how bad the socket must be before they start acting up.

Since I bought the reset tool when I bought my first two engines, I decided to remove the engine from the airframe, pull it down, and reset that piston.

* It takes a LOT more force than I thought. I ended up having to whack the everloving *$($ out of the poor thing with a 2lb mini-sledge to swage it back in. 4-6 blows too. Tapping it on my knee with a screwdriver, with a jeweller's hammer did nothing. Whacking it with a 16oz claw hammer on the kitchen floor only served to wake up everyone else in the house. Ended up going outside to my workbench at 12:30AM to finish the job! I initially expected it'd just be a little tappy-tap-tap with a jeweller's hammer, but no, had to go all 200lb gorilla on the thing. Needless to say, the other two engines I have are getting their resets done tomorrow afternoon after I get back from work, but I will pull the jugs and inspect now.

* I knew they were small but holy balls these pistons are TINY. Need to buy a totalled reedie off eBay for a keychain.

* Can't remove these cylinders at the exhaust port, have to use the flats at the top. Slits are too small for the wrench to fit in there. Isn't too big a deal now but makes me worry I might break a cylinder when these things get some time on them a few years on down the road.

Jenny the symptoms of a sloppy joint can be more severe than just bad exhaust etc timing because sooner than later the small end of conrod can punch a hole in the piston top that is a lethal consequence.

I made it a rule to always check the balljoint fit before putting a new engine in service and set it if needed. My experience tells me that later pruduction run slit exhaust engines got less attention in the factory than old stock ones and the sloppy joint is not a rarity with these even when new.

Good news is the 1st or 2nd setting is final because the swaged cup work-hardens.

Make sure you place the tool cup on hard surface so that the hammer taps be centered, and rotate the tool for a uniform setting. Hard taps will not only make the joint over tightened but can end up in a mushroomed piston top which is again near lethal unless you can lap the piston but then the compression will never be like before.

I second Balogh's comments.  The tool anvil must be on a solid surface, preferably steel.  The back of a bench-vise works fine.  With a solid surface you don't need to whack it so severely.  Just multiple even taps as you rotate the tool.  I managed to crack the skirt on a brand new piston while resetting once.  Ya need to be gentle and persistent.

I see no real need to remove the cylinders from the crankcases unless the piston is too tight to come out of the top.  If you must remove it, try a little heat on the crankcase first and the use the correct slot on the tool across the flats of the cooling fins to loosen it.  It's sometimes easier with the head in place because it can help to stop the tool from slipping.

Just one rule.  NO PLIERS!!

balogh wrote:Jenny the symptoms of a sloppy joint can be more severe than just bad exhaust etc timing because sooner than later the small end of conrod can punch a hole in the piston top that is a lethal consequence.

Yeah and that's why I went ahead and reset mine. It still ran fine but I don't need any viewing windows punched into the piston crowns.

I made it a rule to always check the balljoint fit before putting a new engine in service and set it if needed.

From what I've gathered...mostly from this thread...they generally need one shortly after break-in and then are pretty good from there on out. And since I'm not trying to set any speed records with any of mine, they should be good for a good long while.

Just wantin' to have some fun with foamboard planes and old school glow power~

My experience tells me that later pruduction run slit exhaust engines got less attention in the factory than old stock ones and the sloppy joint is not a rarity with these even when new.

I'm not sure how that compares with the ones Bernie's selling. I bought all of my engines brand new from him, throttleable RC Rangers. First impressions on them are that they might as well be brand new, I honestly wouldn't be able to tell one of them apart from an original Cox production engine that's still new/sealed package on a quality basis.

Make sure you place the tool cup on hard surface so that the hammer taps be centered

Ended up using my toolbox, which is one of those huge 7' long rolling models with a stainless steel workbench built in. Nice and solid.

, and rotate the tool for a uniform setting.

As I did the job, I'd pause every 2-3 taps and re-check the endplay, so it got rotated around in that process. Never put in the same angle.

Hard taps will not only make the joint over tightened but can end up in a mushroomed piston top which is again near lethal unless you can lap the piston but then the compression will never be like before.

Didn't get any mushrooming. There are some cosmetic rings in the piston top from the way the tool Bernie sells is designed but no mushrooming and no damage to the wear surface. Compression is great, no burrs or anything like that.

Oldenginerod wrote:I second Balogh's comments.  The tool anvil must be on a solid surface, preferably steel.  The back of a bench-vise works fine.

Yeah the top of my toolbox ended up doing the trick nicely. Cornwell, designed to do work on 1:1 engines atop the thing.

 With a solid surface you don't need to whack it so severely.  Just multiple even taps as you rotate the tool.  I managed to crack the skirt on a brand new piston while resetting once.  Ya need to be gentle and persistent.

Mm. Ramped up the force until I started getting progress and didn't apply more force once I reached that point. Was basically holding the hammer head directly.

I see no real need to remove the cylinders from the crankcases unless the piston is too tight to come out of the top.  If you must remove it, try a little heat on the crankcase first and the use the correct slot on the tool across the flats of the cooling fins to loosen it.  It's sometimes easier with the head in place because it can help to stop the tool from slipping.

You can get the big-end off the crankpin with the cylinder in situ? Noice. Will have to put some fuel line on my forceps jaws and try it out tomorrow. Don't wanna scratch the rod ofc~

Just one rule.  NO PLIERS!!

Yeah I didn't buy two wrenches when I bought my first two engines to have a wall decoration! Knew from the moment I decided to start getting into these engines that they needed special tools so I made sure I got them all. Have two standard repop wrenches, a 0.049 reset tool, a crankshaft removal tool, and a crankshaft installation tool.

Jenny the parts Bernie sells are guaranteed new.

As the COX piston design evolved I saw some modification of the already 2-piece pistons (piston+rod):

The old-stock  pistons did not have a totally smooth and flat top, some concentric circles and a center part protruding from the piston top were visible..my assumption, is that this center part with the ball joint cup inside the piston was made separately, and contact-welded into the piston.

I found these old stock pistons with very good ball joint fit, and thick enough never the get punctured by the rod small end.







The newer pistons seem to have a smooth flat top, as if the cup inside were machined from the parent material of the piston itself. I managed to puncture a few of these pistons with the sloppy ball joint fit not set early enough..Of course this is not to mean these pistons are inferior to the old stock, just to underline that regular check of the ball joint fit will prevent mechanical failure.

Got the other two engines in my fleet reset. No problems doing either one. More of a pain to get them off and back on than it was to actually do the job.

One engine I took the cylinder off, one engine I just nudged the piston up and out the top. Much easier than I thought it'd be.