ptulmer

My Feedback: (5)

I took a Cox Surestart head down to the lathe. The result is a head with LESS volume than a TD! The only problem with the setup is that I turned it just a tiny bit too much and will have to shave about 1/64" of the threads off. The post-thread depth in the cylinder is very small, so this should work by turning the head down less. You can see I also took the bottom fin off, too. Anybody else tried this yet? How did it go for you?

combatpigg

My Feedback: (3)

That's a pretty neat trick! How did you get it chucked up? How did you get it square? I don't understand where you came up with a problem, as long as you cut enough heat sink away to allow the squish band to seat against the head shim, it should work.

ptulmer

My Feedback: (5)

The only problem is the surestart cylinders aren't threaded all the way down. The next one will be a little better because I won't turn quite as much down. There's enough meat on the tip to make these heads usable.

Squaring it up was simple enough. The front of the chuck and the top of the fins are close enough tolerance. I merely tightened it down on the top, thick fin and checked everything out. Plenty square for the job! It seats perfectly in a TD cylinder.

vicman

My Feedback: (10)

Chuck, when I get the right deal you have a most excellent lathe set-up package in the mail. Patience will be a great virtue.
Obviously Patrick has a dial indicator and knows how to use it.[X(]

ptulmer

My Feedback: (5)

Vic, yes to both. In this case, we're working with a gasketed surface, so absolute perfection isn't necessary. Close to perfection is, but in machining "close" will let you get away with a lot. I try to determine what tolerance is necessary on whatever I'm doing and work accordingly.

combatpigg

My Feedback: (3)

It will be interesting to hear the final results, could be a screaming mod! I've been reading through some early 50s HOT ROD magazines.....very interesting stuff. They considered high compression for the flat head engines to be 8:1. They also figured that anything above 30% nitro would melt the pistons . It took a couple of 22 year old chemical engineering students from Southern Cal, about 10 years later to show the old "experts" how to run and win with 90% nitro.

I'm getting an itch to toss this airplane stuff in and build a rail!!! [>:] A street legal rail, head lights, turn signals, windshield wipers, etc., but still look like a rail.

injunnut1

ptulmer,
That head will run like stink, especially if you up the nitro and add some propyl-oxide to your fuel, but don't expect it to last very long! About 10 years ago we used to turn the Cox #325 and the older # 302-1 plugs down like this for 1/2A Free Flight Nostalgia competition flying .... they darn sure do work, and work well! And yes, the lower head fin must be removed, that is unless you would rather turn some material off the top of your cylinder, either way will work well. Don't figure on hand starting tho ..... at the higher compression set-ups like this an electric starter is a must, or a stock Cox spring starter will work as well also (on the Cox reedies).

Donald Garry

ptulmer

My Feedback: (5)

CP, if I can resist that 68 Corvette that was offered to me cheap, you can resist this urge... Now, why am I resisting...?

Injunnut, glad to hear this works! I'll report back with some readings on the SS I'm modding.

gcb

A couple of observations:

A squish band is not usually flat but tapered toward the center a few degrees. Looks like you did this.

The TD head has a small lip between the cylinder head and the squish band. For that reason, it has a very narrow gasket. Did you turn down your gasket to match? Or perhaps it's not necessary for your setup.

Threads on the TD plug do not run to the bottom of the plug, re: the cylinder threads do not run to the seat.

Great work. Keep us posted on how it works.

George

ptulmer

My Feedback: (5)

The TD cylinder had several gaskets in it. I guess I used it for storage at one time or another. You're right about the threads being almost the same on the TD cylinder. If you mean it should be taper to a high in the inner side of the seat, the TD head I had wasn't tapered that I could measure, so I didn't do it. Maybe Injunnut could tell us if what the steps should be and I can avoid tossing some as a scrap.

gcb

You are correct. Got out the old eye loupe and re-checked. Apparently I was just seeing the radius where the squish band meets the cone. Guess my glasses need glasses for real close-ups.

Keep me honest.

George

injunnut1

ptulmer,
You're doing fine ..... don't worry about squish-band taper, or better yet try one with the taper and see for yourself? The R&D / Testing that YOU are doing and the conclusions that YOU will draw from those tests will far out weigh any of the at-large armchair theorists' rhetoric!<GRIN>

Donald Garry

combatpigg

My Feedback: (3)

That's right, DUDE, you're in "cut and try land" now. Are you're ears good enough to hear preignition? some say it is a bacon frying sound.........I don't know. If you are getting healthy increases in fuel demand after doing a mod.......then you have done some good, you have increased HP. so if you have to open the needle up to maintain a good mixture, then you have increased the engines' ability to use fuel. some of the most dramatic results come from playing with .049s, VS working over larger stuff.

PT, Can't you picture this, a single seat, 60s style slingshot dragster, fendered, bumpered and carrying enough signal lights and junk to be street legal? I think it would be a good rod to either go with a 383 stroker kit, or go the other way with a 302 Z/28 type motor.

ptulmer

My Feedback: (5)

I can picture it with a 429! Here's a picture so far. When I took the threads up a little, it went to the bottom, but leaked down like heck. So, I tried the taper idea. No difference. Finally, I pulled the whetstone out and lightly ran it around. No difference. The light bulb is a little dim at this point, but it's coming on. I stuck the TD head on it and no difference! So, flat, tapered and whetted probably all work fine, but darn this is one LOOSE engine! I stuck it on the TD and the piston hit the friggin plug! The TD head is relieved to let the piston up! You can see it in the picture. 1st head it the TD, 2nd is mine and the 3rd is a standard SS. The TD head has a deeper cup than the cut down SS head, giving the modified head less volume.

combatpigg

My Feedback: (3)

Hmm, The difference between deck heights of COX engines is all over the place, that is why making custom heads that are set for kill isn't a one size fits all issue. KK used to sell liner shims. now that they are out of the picture the other approach to adjusting deck height would be to mill the top of the piston. I have no idea how thick the top is, but am willing to bet it is too thick already A holding fixture is what you need to make, basically a bushing that fits the piston snug, with a split in it, which allows the bushing to clamp the piston with out distorting it. just remove material that is under the squish band, leave the middle part of the dome alone. you will be the first guy ever to have domed pistons in a Cox .049 [8D].

BTW, if I went the 429 route, I would just buy an old beater pick up truck for a couple of hundred, then have the engine and trans rebuilt, and have the rear end narrowed enough to leave me with just enough room to sit between a pair of M&H RACEMASTERS.

KidEpoxy

429 truck?
get some 4banger station wagon, carve the backseat into FireWall2 and mid engine it.... and leave the 4banger transaxle engine in it.

sit at traffic lights gunning the 4banger next to a 5.0Pony or SportLuxury, then kill it & hit the open header 429 just before SmokinTime![X(]

combatpigg

My Feedback: (3)

Good idea KE, but you would want to pull the [oink] front drive assy and throw it in a lake, then put a straight axle under the front end, with a pair of leaf springs that can handle the return to Earth from a bumper scrapin' wheelie.

KidEpoxy

"...pair of leaf springs that can handle the return to Earth from a bumper scrapin' wheelie...."

Canard? A full flying cannard for pitch control might supress the wheelies


All these machining threads make me think
1. Man, I need to get a lathe
2. Man, I need to get a place I could put a lathe

I was just looking at the balloon bladder aluminum stopper too... and was considering how to go about it without a lathe- but that kinda talk belongs in that thread, not here.

So is PT gonna cut the valve notches into his domed piston just for looks too? What they hurt in compression they help in lightening the piston, right?

combatpigg

My Feedback: (3)

The other piston mod that Clarence Lee or Glen dye would subscribe to are oil retension grooves cut towards the upper part of the piston skirt. gotta get back to my rail plans, this airplane stuff is too distracting. there's always the old AA/ FUEL ALTEREDs to consider, pretty barbaric engineering, but BAD ***** looking machines [X(]!!!

Big Al-RCU

Kid,
You are right. In this hobby you really do NEED a lathe. After many years I finally got a Sherline lathe. It’s small enough to use on the kitchen table and store on a pantry shelf but still able to handle most anything within the size that we modelers are likely to run into and the projects discussed in this forum The downside (aside from the upfront cost) is that you will find so many more uses for it that machining projects may become a hobby of it’s own.
Al

DICKEYBIRD

Cool project CP. At your warp-speed building rate, you'd only be away from the planes for what, maybe 2 or 3 weeks at the most?

When you get through, you can help me with my little pipe-dream. An old fat-tired bicycle with a 5 hp. Briggs grafted on and a skinny little tank configured to look like a pseudo board track racer from the early 1900's. It'd make a great little neighborhood putt-putter (or should I say tapocketa-pocketa-pocketa-pocketa-er?) I figure we could replace the pedal crank assy. with a reduction jackshaft running on sealed bearings with a big pulley on one side and a small sprocket on the other to drive the rear sprocket. I had the math around here somewhere that said it could be possible to gear it down to around 25 mph tops which would be about right. Do the old loose belt/idler wheel/hand lever trick for a clutch. Graft on a 1 1/2" straight pipe to get'er sounding cool.

Then I'd hafta mount a modified SS glowhead on the bars as a cigarette lighter to keep this on topic.

KidEpoxy

5hp pocketa-pocketa-pocketa Hit & Miss?
just slap about 8 Surestarts on it, worm drive spur pully to bigwheel? Maybe 100:1 on the worm then belt reduction...

The ultimate in geared 049.... hmm maybe that could swing a 22-12 as a slowflyer, or the impeller from a 20" boxfan from walmart

combatpigg

My Feedback: (3)

DB, to get your project going, the very best folks to deal with is MANUFACTURERS' SUPPLY........contact them at 1-800-826-8563 and have them send you a catalog. The BRIGGS engines are designed to run at 3600 rpm, so figure your sprocket needs from the stuff that is in the catalog.

ptulmer

My Feedback: (5)

Shoot, I'm putting this engine back together and forgot which way the hole in the needle assembly went. To the rear, right?

ptulmer

My Feedback: (5)

Err... that'd be the front of the engine... towards the reed, right?