TampaRC

Can the stock piston/cylinder/glowplug on the choke tube engine be replaced with the TD piston/cylinder and hi comp plug ? With positive results? What about adding Bernies Killer Bee back plate on top of that? Then where will I be performance wise?


Q #2 Lets say I have a TD .051 with a worn cylinder and piston. Can Iinstall an .049 TD cyl/piston?

fit90

Yes, you can use both a Tee Dee piston/cylinder and a Killer Bee backplate on a Sure Start. Both should yield a mild increase in performance. But, allCox engines respond to different parts differently so running the engine after the changes will be the only way to tell. I suggest making only one change at atime so you can quantify your results.

Yes, an .051 piston/cylinder can be replaced with an .049

aspeed

A single port piston liner can be used on a Tee Dee but it will be slower if that is what you may need.  An .051 piston cyl. will vibrate on a reedy case though.  I guess the counterweight isn't enough for the little extra weight of the piston.  The low compression heads are a waste of money unless you are using crazy big props like 7" .

BMatthews

You CAN run that combo but due to the limitations of the reed style intake and the extra length of the choke tube style intake you will likely not see any RPM gain over the more simple two bypass flute style cylinder.

The increased compression may or may not work out. You'd need to try it. If the increase in compression combined with the less than true "small prop" Tee Dee style RPM results in firing too early you'll simply beat up the engine and not see a gain in RPM.

For example even with a Tee Dee the high comp head needs a fairly free running prop. The one time I ran my own Tee Dee for a lot of runs on a model using a 5x3 prop it ran like crud for the first few flights. Eventually it darn near stopped. Seems I'd been getting so early ignition that I busted the seal on the plug. I replaced it with a regular straight cone style plug and it ran much stronger and smoother immediately. Never looked back and have not seen a need to try another high comp head for the sort of flying I do.

Oh, I tend to run at LEAST 25% nitro for my 1/2A engines all the time other than on my Tecaco models where it's 5%.

TampaRC

Wow, more variables than I thought....thx guys

aspeed

Just experiment, and buy a tachometer, it is cheap entertainment/education.  If the reedies are overcompressed they usually flutter back and forth.

TampaRC

I have tach,  before I buy a bunch of parts I was hoping to hear of proven results.

aspeed

If you have a TD, toss the reedie stuff.  It is just a poor design.  A TD cyl and head in a TD will outdo any reedy.

fit90

Mr. Matthews,

I hope you don't mind but Ipassed this along to another Cox engine user at coxengineforum.com. He had a problem that I thought your post might help him to solve.

Thanks for sharing your insights,

Bob

gcb

The TD head not only has more compression but also has a "squish band" around the combustion chamber for higher performance. My question is does the Nelson plug/Galbreath head set have a squish band?

George

ffkiwi

Yes-quite a wide one. I'll post some pics later

ChrisM
'ffkiwi'

ffkiwi

Here's the comparison:

ffk

aspeed

Looks like someone needs to do a run off of the B Bee head, TD head, Merlin, Galbreath, Norvel and Mecoa head.

ffkiwi

A lot of work, by the time you fiddled gaskets, nitro %, props etc-and then the result would only be valid for the particular engine used for the test...........then for the Mecoa and Galbreath heads the additional variable of what brand and heat of glowplug to use (ditto for the Galbreath-there are 3 Nelson plugs and two Nelson inserts-and that's before you start looking at the Merlin range!)
For more general trends you'd have to test across several engines-and different models-and I would expect results to be variable.

ChrisM
'ffkiwi'

skaliwag

My Feedback: (1)

Did anyone mention temp, humidity, Hg?

aspeed

Ya and then you have to find someone that has all of the heads to try at once. I am just going with the Merlin because they are cheap and work.  The Nelson ones have too big of a flat for the little motors IMHO.  I think a Turbo would be better because of the smaller hole needed and again, they aren't $5.

gcb

To amplify what ChrisM said, when Norvels were new kids on the block someone switched heads on a TD and NORVEL and both engines gained RPM. Go figure.

Sooo, as previously stated in different words, you may be better off just picking a plug and tuning for your setup.

George