PDA

View Full Version : Needle valves/ Homemade carburetors



brian Rupnow
11-27-2010, 06:23 PM
As you all probably know, I have been thrashing away for the last couple of months on an i.c. engine. I thought it would be very clever to "stretch" my machining capabilities and make my own carburetor and sparkplug as well. The sparkplug is a failure. It did work on the bench, and it did fire the engine a few times, but the Corian is so fragile that it fractures if you look at it hard. I won't build my own sparkplug again. I have however, had fair success with the carburetor, except for making the needle valve. My plan to drill through a #2-56 brass screw and insert a sewing needle has fallen by the wayside, due to the fact that #1---my machinery isn't up to this accurate of work, and #2----Neither am I. However---I HAVE A NEW PLAN!!! My new plan involves grinding a needle shaped end on a steel #2-56 screw. Again, my Chinese lathe isn't up to it, but this is the method I have come up with. The dark blue part is the spindle in my mill, with a chuck on the spindle, and a 4" "fine" emery wheel and stub shaft in the chuck. The passion pink part is a smaller chuck and partial arbor that I salvaged out of an old power drill with a #2-56 x 3/4" long steel shcs in the jaws (the head has been cut off). (I really like this second chuck, because the jaws will close enough to hold a 1/32" diameter drill). The green part is a peice of 1" x 1/2" aluminum bar with a hole in it bored to be a "good rotating fit" on the stub arbor.---It is held in the jaws of my millling vice which is not shown. Here's how I see it working---I set the angle I want by tilting the green peice in my vice to whatever angle I want the needle valve to be and lock the vice there. I rotate the stub arbor and chuck with my fingers, slowly, and I raise the quill of the mill to advance the drill chuck and grinding wheel vertically---I have a fine finger control knob to do this with on my mill. This SHOULD give me very fine control, and should allow me to turn a quite accurate and concentric needle end on the screw. I will then make a small brass finger wheel and solder it to the other end of the screw. I'll let you know how it works out. I should have lots of peices to practice on. Nobody in town had this size of screw, so I had to order a box of 100 to get one. Sure hope I have better luck with the carburetor than I did with the sparkplug!!!
http://i307.photobucket.com/albums/nn294/BrianRupnow/ASSYTOGRINDNEEDLEVALVE.jpg

rohart
11-27-2010, 06:53 PM
If you did this with the spare chuck pointing upwards under the emery wheel, then if (when) your hold on the chuck falters the chuck won't slam into the wheel - it'll tend to drop off the wheel instead. The weight of the chuck will take up the slack too, rather than your finger pressure lifting it off and on the grinding wheel.

The objection is that you'll have less control over the final length, but it's adjustable, so who cares ?

Just a thought. Good plan in general.

Why use Corian on the spark plug ? Is it the hardest insulator you can come up with ? What about casting an insulator out of epoxy ? Shame to compromise at the last hurdle.

brian Rupnow
11-27-2010, 07:17 PM
If you did this with the spare chuck pointing upwards under the emery wheel, then if (when) your hold on the chuck falters the chuck won't slam into the wheel - it'll tend to drop off the wheel instead. The weight of the chuck will take up the slack too, rather than your finger pressure lifting it off and on the grinding wheel.

The objection is that you'll have less control over the final length, but it's adjustable, so who cares ?

Just a thought. Good plan in general.

Why use Corian on the spark plug ? Is it the hardest insulator you can come up with ? What about casting an insulator out of epoxy ? Shame to compromise at the last hurdle.

I used Corian because that seems to be the material of choice on the other model building sites. It does machine nice, but its simply to fragile to live as a sparkplug. I have never made a sparkplug before, so have no prior experience. It has to be machineable but not conduct electricity, and stand up to heat (fire) down at the business end. I would think that casting an insulator out of epoxy would be fairly easy, but wouldn't it end up as fragile as the Corian?---And I'm grinding on the top side of the grinding wheel so I can see the results of what I'm doing as I'm doing it.

Bill736
11-27-2010, 07:51 PM
Most low speed, low flow carburetor needles are indeed slender with a long taper. However, high speed needles are sometimes rather blunt , with only a modest taper. For instance, the high speed needle in my outboard motor carburetor has no more than a 45 degree taper, if that.
If your engine is only to run under one load, at one speed, then carburetor design is easy. But, as you no doubt know, that's not usually the case.
Maintaining your target air/fuel ratio at varying speeds, loads, and throttle openings is a bit more involved, and the geometry of the jets and needles and venturi become important. That reminds me of a story, which I've never before had the excuse to tell. It involves intrigue and sabotage , carburetor style. I was working on a student project many years ago that used an Onan generator set. One day, the engine would not start. I finally took apart the carburetor, and found that the main fuel feed tube in the carburetor throat ( cut off at a 45 degree angle) had been turned around, so that air going into the carburetor blew the fuel into the carburetor, instead of sucking it out. The fuel tube was keyed in, and would only fit in two ways, the right way and 180 degrees from that, so it could not have happened from vibration or accident.
How could that have happened ? I was the only person who was known , or was supposed to have worked on the engine, and I never had the carburetor off. There was one other student present at the time, and he was certainly " Johnny on the spot" with an answer. He quickly pointed out the incorrect position of the fuel tube, even though he knew little about engines. After I turned the fuel tube around, the engine ran fine. I believe to this day that he sabotaged the carburetor, just so that he could be the one to solve the problem ! Anyway, good luck with your own carburetor !

macona
11-27-2010, 08:07 PM
I used Corian because that seems to be the material of choice on the other model building sites. It does machine nice, but its simply to fragile to live as a sparkplug. I have never made a sparkplug before, so have no prior experience. It has to be machineable but not conduct electricity, and stand up to heat (fire) down at the business end. I would think that casting an insulator out of epoxy would be fairly easy, but wouldn't it end up as fragile as the Corian?---And I'm grinding on the top side of the grinding wheel so I can see the results of what I'm doing as I'm doing it.

Most of the guys I know use teflon for the insulators in home made spark plugs.

Or you could get some macor machinable ceramic. Not cheap but wont be too bad for a little spark plug.

J. R. Williams
11-27-2010, 08:42 PM
Another good material for the spark plug insulator would be PEEK. It is easier to machine than the Corian or Macor ceramic. I used to make special insulators from the Macor and it is very abrasive and hard on drills.
JRW

lane
11-27-2010, 08:43 PM
Yes I use Teflon in all my spark plugs and they work fine.

darryl
11-27-2010, 09:10 PM
Back to the needle valve- I like the idea of using a sewing needle in the end of the adjustment screw as the valve. If it's too much hassle to drill a well centered hole down the end of the screw, maybe you just haven't hit on the right method of doing so yet-

I'd probably be drilling and tapping a piece of scrap to insert the screw into. Put a piece of rod in the lathe, drill a centered hole for the tap, then extend that hole right through with a bit the size of the needle you want to use. Tap the hole as far as you can- finishing it with a bottoming tap if you can. Then you can insert a screw as far as it will go, locking it in place with a locknut, mount that in the chuck with the screw end facing left, then use the smaller hole to guide the small drill bit to create the home for the needle. It helps before you begin drilling to flatten off the end of the screw, in case it's lopsided because of how it's made- the flat end will allow the bit to center better, and it's guided by the small hole anyway. The same jig could be used when epoxying the needle into place, keeping it straight.

Use a fuel-proof epoxy resin to bond the needle into place- what's that called- isothalic I think-

As far as the sparkplug- there must be ceramic mixtures available that would bond the parts together without danger of burning, softening, or becoming conductive. I bet a visit to a ceramics shop would be productive. Glazing might work totally fine- maybe completely adequate even without firing it to a glassy state.

Take a look at Resbond 920- heat conducting, electrically insulating, 2800 degree rating, 270 volts/mil rating

ADGO_Racing
11-27-2010, 10:29 PM
Most of the guys I know use teflon for the insulators in home made spark plugs.

Or you could get some macor machinable ceramic. Not cheap but wont be too bad for a little spark plug.

Try Glass filled Teflon. Works well in high pressure/temp. applications.

Duffy
11-27-2010, 11:29 PM
Brian, one of the members of the Ottawa valley Live Steamers made some small spark plugs, and he used porcelain. apparently he got a local potter to fire the porcelain bits with the hole already through them. I saw the finished product and it looked good. sorry, forgot his name; it was at a "show & tell" during a monthly meeting.

tdkkart
11-28-2010, 11:01 AM
My prediction says that you're gonna have a really tough time rotating the stub arbor/chuck consistently enough to give a good finish on your needle.
Somehow powering rotating the arbor is going to be required.

Just sayin', combined with been there, done that.

whitis
11-28-2010, 05:49 PM
Teflon is a bad idea. Spark plugs are supposed to reach temperatures of 932 to 1472 degrees F (http://www.ngksparkplugs.com/tech_support/spark_plugs/p2.asp?mode=nml). When heated to 680F, teflon gives off two chemical warfare agents.

There are many reports of pet birds being killed by teflon cookware. In one incident, dozens died at the same time. Even at 464F, it can kill rats.
http://tuberose.com/Teflon.html

brian Rupnow
11-29-2010, 07:14 PM
My box of 100 shcs arrived today.---Yep, had to buy a box of 100 to get one!!! Actually, I'm rather excited about this. Having never built a carburetor before, (Yes, thats it in the picture with a screw turned in full depth) I am anxious to make the needle valve to see if it works. I had no idea what to do with the other ninety nine #2-56 x 3/4" long shcs, but my friend Colin (The other model engine guy in Barrie) said he would buy half of them. Then I remembered that I borrowed a 1/4" brazed carbide boring tool from him and promptly managed to break it.---He will be GIFTED with half of them.
http://i307.photobucket.com/albums/nn294/BrianRupnow/100screws001.jpg

Dragons_fire
11-29-2010, 08:47 PM
Where did you order your 2-56 shcs from? i use 2-56 and 4-40 all the time, but cant afford to buy them from the hobby shop, so i order 100 at a time from digikey, but they had a little flathead slot and i would rather have socket head.

brian Rupnow
11-29-2010, 09:03 PM
Where did you order your 2-56 shcs from? i use 2-56 and 4-40 all the time, but cant afford to buy them from the hobby shop, so i order 100 at a time from digikey, but they had a little flathead slot and i would rather have socket head.
I buy them at Brafasco or Fastenall in Barrie.

brian Rupnow
11-29-2010, 09:03 PM
Well, we have proof of theory at least. A very crude set-up, and I didn't cut the head of the screw first, so its not 100% concentric to the chuck, but I think when I have time to do a little more refined set-up work its going to do fine!!! (And yes, I know that grinding wheel is uglier than old sin, but this was just a quicky "try-out".
http://i307.photobucket.com/albums/nn294/BrianRupnow/grindingneedlevalve001.jpg
http://i307.photobucket.com/albums/nn294/BrianRupnow/grindingneedlevalve002.jpg

brian Rupnow
11-30-2010, 08:58 AM
Well, based on this mornings results, I would say this was a complete success!! Tdkkart was correct----It took some RPM at the needle to really get things cooking properly. I clamped my Dremel in the vice, turned it on "mid range" speed and set the mill in reverse at high RPM. I slowly raised the quill so as not to burn the needle. it turned a very nice tapered point. I then took the dremel out of the chuck and dressed the turning needle against the side of a "fine" oilstone.
http://i307.photobucket.com/albums/nn294/BrianRupnow/grindingneedlevalvewithdremel001.jpg
http://i307.photobucket.com/albums/nn294/BrianRupnow/grindingneedlevalvewithdremel002.jpg
http://i307.photobucket.com/albums/nn294/BrianRupnow/grindingneedlevalvewithdremel003.jpg

brian Rupnow
11-30-2010, 09:34 AM
And of course, every self respecting needle valve needs its own knurled brass finger knob with a visible notch so I can see how many turns open it is. The End!!!!
http://i307.photobucket.com/albums/nn294/BrianRupnow/needlevalveincarb001.jpg

Duffy
11-30-2010, 11:51 AM
Brian, (and Dragonsfire,) for itty-bitty fasteners, try Micro-Fasteners in New Jersey. the are on the web. Great selection, very good prices AND they ship USPS.

Paul Alciatore
11-30-2010, 12:14 PM
Just a side thought. And I know it takes the fun out of making your own. But for an alternative source, model aircraft engines use needle valves and they are subject to breakage so hobby shops stock or at least used to stock replacements. A good shop should have a small assortment of replacements available for different sized engines. Most of them have a very fine taper. But you would have to take whatever size screw thread that comes with them.

Dragons_fire
11-30-2010, 04:10 PM
ill check when i get home, but i think the cox049 engines have a 2-56 thread on the needle. I have piles of them at home and i think the hobby shop i used to work at carried lots of them which means they are probably a fairly well used part.

MLAToolbox
11-30-2010, 06:17 PM
Brian, In regard to making your needle valve, a method I've used works well. Mount a block of wood on the compound or cross slide with the grain parallel with the lathe axis, and with the top surface at center height. Chuck your stock with, say, a half inch overlapping the block, then file the end of the stock any taper you want. The stock will tend to imbed itself in the wood and the wood will steady it. Finish with emery paper or by stoning. I used drill rod or music wire and it made a nice point, perfectly symetrical, as far as I could tell. Anyway, it worked well in the engine, no galloping or uneven metering. It was sweated into a drilled screw, but that's another thing. I forget the details, except that I was able to drill the hole and it worked. Andy L.

brian Rupnow
12-12-2010, 12:41 PM
Well, the carburetor works quite well, as evidenced by the running of my Kerzel engine. The throttle is rather useless, as I was warned it would be----It makes no real difference to engine RPM as it is slowly closed, right up untill it is totally closed, and then the engine just dies. The needle valve wants to unscrew itself and change settings while the engine is running due to vibration, but a bit of thread locker helped that. It still can be turned with fingers, but no longer adjusts itself. It seems to be quite sensitive, adjustment wise, but again, as I have no previous experience with buillding carburetors, I have nothing to compare it to.

dp
12-12-2010, 12:53 PM
Well, the carburetor works quite well, as evidenced by the running of my Kerzel engine. The throttle is rather useless, as I was warned it would be----It makes no real difference to engine RPM as it is slowly closed, right up untill it is totally closed, and then the engine just dies.

It sounds like you have some air going around the carb, Brian. Possibly sucking by the intake valve stem. You can test that by dripping oil on the valve stem. It will momentarily seal the stem without keeping it from working, and if air is getting in that way the rpm will drop. I suspect the reason the carb only kills the engine is because that also cuts off the fuel. Enough fuel is getting into the engine to burn the air coming in through other paths right up to the point when the fuel path is cut off completely.

Another test of this can be done by putting a ring of clay on the head around the intake valve and sliding a cigar tube or capped pvc pipe over the entire valve. That will cut off the air flow if it exists and air will have to come in via the carb.

BTW, I don't see this as a problem but it would be interesting to understand what is happening there.

neonman
12-12-2010, 01:06 PM
Brian, just got hooked up to this thread. I saw your picture of the needle valve grinding setup on the previous page of posts, I like the idea. I was wondering if you have ever tried a method like this for grinding valves? Getting valves not to leak seems to be a much harder thing for me to do than making needle valves. You could use a xy table on the drill press to feed the valve into the stone

For needle valves, i carefully turn a piece of stainless down to near dia, turn up the speed and use a 4" fine cut file to make the taper.

neonman

brian Rupnow
12-12-2010, 01:35 PM
Neoman---I don't know if you have followed my build of the Kerzel hit and miss engine which is running concurrently with this thread or not. I had a dreadfull time getting the valves to seal on that engine, and after three different attempts I was only succesfull after building a pilotted valve seat chamfering tool, cutting the seats by hand using that tool, then lapping the valves with 350 grit lapping compound, followed by 600 grit lapping compound, followed by toothpaste. I turned the valves from drill rod on my lathe---no grinding.

brian Rupnow
12-14-2010, 03:05 PM
Since the throttle I had built into the carburetor didn't seem to have any positive effect on the way the engine ran, I decided that it was just an impediment to good airflow, so I removed it and made up a pair of brass plugs which I loctited into the sides of the carburetor body. Jury is still out on the net effect of this, but there are only really 3 things to be adjusted which influence the way this engine runs, now that the compression is good. ---Ignition timing, valve timing, and needle valve setting. By removing the throttle, I have eliminated a couple of places where the carb might have been sucking air around the throttle shaft.
http://i307.photobucket.com/albums/nn294/BrianRupnow/throttleremoved001.jpg

darryl
12-15-2010, 01:37 AM
You guys who build spark ignition engines- I'm just wondering if any of you have used the piezo igniter modules to supply the spark. There would have to be a sort of hammer that whacks it with the right timing for each power stroke, but I can think of a couple ways of doing that- one even gives some advance according to rpm. They seem pretty rugged, but who knows how long they can take the hammering- could be for a good long time. They are very small and simple, and can be had for a buck from any dollar store. With it you get some butane, a handle, etc (looks exactly like a barbeque lighter) :)

Just a thought.

Black_Moons
12-15-2010, 05:32 AM
darryl: As most piezo lighter elements iv had brake after 2 years or so when I was a smoker.. Lets say, 20 cigs a day, 30 lights (say 30% failed attempts), 30 * 365 * 2 = 21,900
At an idle of 2000rpm, That means you'd get about 11 mins outta an igniter. Not a great life.

brian Rupnow
12-15-2010, 08:43 AM
There seem to be two distinct schools of thought on the shape of the needle. One school is saying you don't need a iong taper, that a blunt needle will do. The other school is telling me it must be a long taper. Keep in mind gentlemen that this is for a "fixed speed" carburetor which was never intended to be throttled. I had added the throttle just to see what effect it would have, but basically, it had no effect so the throttle ws removed. I have my engine running reasonably well, but there is only one spot where the needle valve setting seems "just right" for this engine, and a tweak of 1/4 turn in either diretion will make the engine shudder and die. Today, because it is a relatively easy thing to do, I will turn a much longer tapered needle and try it, just to see if it does make any difference to the engine behaviour or not.----Brian

Black_Moons
12-15-2010, 10:10 AM
Needle taper/position adjust the mixture over the 'midrange' of throttle.. When its attached to the slide of the carb. The jet sets the WOT setting (When the needle is nearly clear out of the main jet), And the idle circuit.. sets idle :)

Hence, the taper angle is kinda pointless for a fixed throttle engine as its not moving in and out of the main jet passage except when manualy adjusted, And then its not moving along with anything else, so its just.. how much you feel like adjusting it.

While there could be something else 'special' the taper does, I am not aware of it and have never read anything hinting at it.

Technicaly, you could probley do without a needle at all, Just a precise main jet. Its just you'd have to drill it out to the exact precise size you need, insted of turning a knob untill it runs just right.

PS: Air temp, engine temp, fuel, etc can require minor adjustments in fuel/air mix, So its likey best to keep the needle adjustable, Or have a choke for starting/cold weather conditions.

brian Rupnow
12-15-2010, 10:17 AM
Needle taper/position adjust the mixture over the 'midrange' of throttle.. When its attached to the slide of the carb. The jet sets the WOT setting (When the needle is nearly clear out of the main jet), And the idle circuit.. sets idle :)

Hence, the taper angle is kinda pointless for a fixed throttle engine as its not moving in and out of the main jet passage except when manualy adjusted, And then its not moving along with anything else, so its just.. how much you feel like adjusting it.

While there could be something else 'special' the taper does, I am not aware of it and have never read anything hinting at it.

Technicaly, you could probley do without a needle at all, Just a precise main jet. Its just you'd have to drill it out to the exact precise size you need, insted of turning a knob untill it runs just right.

PS: Air temp, engine temp, fuel, etc can require minor adjustments in fuel/air mix, So its likey best to keep the needle adjustable, Or have a choke for starting/cold weather conditions.

On these carbs there is no idle circuit. There is one .035 diameter hole in the tube which delivers gasoline into the venturi, and the needle valve that controls how much gas gets admitted to that hole.---Nothing else. No choke---no accelerator pump---no idle circuit---no throttle----nothing.

dp
12-15-2010, 11:00 AM
In this implementation the needle only determines the ease with which the optimal fuel flow can be set.

More complex carburetors have tapered needles attached to the throttle linkage directly or indirectly via volume-driven diaphragms. They also have low-speed circuits, idle stops, and accelerator pumps. None of that is needed in Brian's engine as it is throttled by controlling the exhaust valve.

About the only choice one has in this design is to drizzle the fuel from a feed tube at the top where it unavoidably meets the air stream, or to let it well up from the bottom where it meets the air stream after a fashion.

Black_Moons
12-15-2010, 11:19 AM
On these carbs there is no idle circuit. There is one .035 diameter hole in the tube which delivers gasoline into the venturi, and the needle valve that controls how much gas gets admitted to that hole.---Nothing else. No choke---no accelerator pump---no idle circuit---no throttle----nothing.

I know, I was just compairing it to a conventional carb and what the needle does in one of those.

PS: 0.035" Seems a little big for such a tiny motor. Not sure how it compairs exactly but my 50cc motor only runs a 0.028" main jet. And while the needle compensates for the jet in this design, it does so by reducing vacuum the jet is exposed to, and that may compermise its ability to atomize the fuel.

Lew Hartswick
12-15-2010, 11:22 AM
S U Carbs anyone? :-)
...lew...

Deja Vu
12-16-2010, 11:28 PM
Today, because it is a relatively easy thing to do, I will turn a much longer tapered needle and try it, just to see if it does make any difference to the engine behaviour or not.----Brian

I suspect that instead of the 1/4 turn either way the needle will have a wider degree of usefull adjustment. .....maybe 1/2 turn from optimal position...or more.