jrjr2u

Question fof av8tor1977

When you drill the hole, do you mean at a 90 degree angle to the piston in the ring land/ring groove and the pin sticks out enough to stop the ring from spinning?
Also, I read that you used .045 gas rod... do you mean mig welding wire?
And... how can you drill a hole small enough to make that a press fit? Do they make drill bits that small?


Edit:
Actually the question is for anyone that knows!

w8ye

My Feedback: (16)

A #70 drill is .045"

THIS IS WRONG SEE BELOW

jrjr2u

Thanks
Well I just tore down my 30 and I see now what is meant
The 30cc has 2 rings and they are both pinned. One in front and the other in the rear
What puzzles me is the fact that there are already holes there for exhaust in the 25cc.
Why doesn't the ring get caught on them as they are?

w8ye

My Feedback: (16)

The Homelite 25 has a center tear drop divider that makes the exhaust port two small ones instead of the one big one like on the 30. The 25 doesn't need a pinned ring unless you take the center divider out.

w8ye

My Feedback: (16)

You must position your pins to keep the gaps away from any port

mikenlapaz

Maybe a pilot with a #70 ! [sm=wink_smile.gif] Test with a #57 .

http://www.engineersedge.com/drill_sizes.htm

jrjr2u

Yea, I plan to grind out the divider to gain some performance. But the question is why doesn't the ring catch on the openings that are there now? What does that center divider do to stop it?
The only thing I can see is it makes a narrower opening. Maybe that stops the ring from expanding enough to catch. Once the divider is taken out, the opening is wider and the ring can expand more.
Does that make sense?

Not that it matters, I am going to do it anyway I was just curious as to why......

jrjr2u

Actually, look at this chart:
http://en.wikipedia.org/wiki/Drill_bit_sizes

This says that a #70 is.026

A #56 is closest at .046

The 30cc piston pins look closer to a #51 and the pins are a tad larger than the ring groove
I bet the piston is really hard!! Not sure if my drill press will do the job or not, its a brute!

mikenlapaz

Do a test drill undersized, warm up the drilled material and see if you can insert your wire.

You piston is aluminum. you should not have any problem drilling it.

Look at the rings ends, do they have an arc ground on one side? That is for a pin. You want the rings to go back into the same ring grooves if possible. You also need to take into consideration the expansion of the ring when it gets hot, the end clearance will decrease, you do not wnt it to bind on your newly installed pin.

w8ye

My Feedback: (16)

I was trying to find the chart I was looking at to see what I did wrong but cannot find it.

I must have been reading across two columns?

jrjr2u

Aluminum... thats right! Should be ok then.
When I install a pin in a rod/piston assembly I put the piston in the oven first.
Works like a charm. Should work for this too.

av8tor1977 said in his 25cc homie hot rod thread to get a new Bowman ring made just for this application.
I would imagine that the end gap will be a little larger than normal.

Does anyone know what the end gap of a new / stock ring is?

oldtimer2

My Feedback: (19)

Send your cylinder & piston to Frank Bowman. He will build you new rings and install recessed pins so that you will have rings with minimum gap at operating temp. He did my 31cc Ryobi, it works great. He probly already has rings for your Homie made that he could give you a quick turn around. His pn # is 505-327-0696.

jrjr2u

Yea but doesn't that take all the fun out of it? LOL
Seriously, I can do this. Using a pin vise is probably the answer rather than the drill press.

mikenlapaz

Has anyone ordered things from this site? Like drill bits and pin vises http://www.ehobbytools.com/index.htm...tml&lang=en-us

Clearance; I was told 1mm per 1" inch of diameter. This has some other good points to consider.
( http://www.aa1car.com/library/ring_end_gap.htm (omitted on initial post))

I'd call Frank Bowman, he is friendly and informative. Probably has the needed ring already made up and ready to ship.

av8tor1977

My Feedback: (6)

I've done this operation a number of times and it's not hard. I recommend a pin vise in a drill press. I drill the pin hole a couple thousandths smaller than the pin, put a chamfer on the pin, and drive it in coated with a little JB Weld. No problems in many hours of flying these engines.

I also recommend that you get a ring from Frank Bowman. He will provide a ring if requested, with the notch already in it to accomodate the pin, and to provide minimum end gap. This takes full advantage of the mod and provides the most power.

I highly recommend the mod.

AV8TOR

jrjr2u

Thanks
While we are on the subject, I'm strongly considering glo/gas. Would you recommend raising the compression for this fuel?

jrjr2u

No but it looks good... reasonable prices and all.

av8tor1977

My Feedback: (6)

Hi,

Sorry, but I missed your earlier questions addressed to me. My internet connection had been down for 10 days and I've been quickly trying to catch up...

I use .045" gas welding rod for my pin. The mig welding wire is a little flexible, and .045" is not real common.

Yes, they make drill bits even smaller than that!! Use a pin drill in a drill press.

Important: You want the pin to be 90 degrees to the piston and the ring land, and it must stick up no more than half the distance of the ring land. In other words, it is recessed into the ring land one half of the depth of the ring land. This allows the notched ring to go over the top of the pin, but still not rotate.

Ring end gap for these little motors is spec'd at about .003", and that is a very tiny gap. Frank Bowman actually recommends zero end gap for these little guys. Can't argue with him, as his rings really work great! Every used engine I ever pulled apart had excessive ring gap. That's a big power killer. You must use a properly notched ring with the pin to eliminate having an excessive gap. Once again, I strongly recommend getting a ring already notched from Frank Bowman. His rings are about $9.00 I believe, and he'll send you one quickly. It's the cheapest and easiest hop up there is!

I am now running all my engines, (four "gassers" presently flying), on the Gas/Glow system. Yes, I do recommend raising the compression as much as possible. Minimum deck height should be .015" or so.

Have fun,
AV8TOR

jrjr2u

That wasn't so bad. The old drill press worked great!
I used a piece of a gas welding tip cleaner for the pin - .047 and a .046 bit with our old buddy JB
Worked like a charm!
Bowman ring on the way

av8tor1977

My Feedback: (6)

Good for you! Here, check out this thread:

http://www.rcuniverse.com/forum/m_26...tm.htm#2677889

I also did one recently that I didn't even stuff the crankcase nor lower the cylinder and it turns an APC 15 X 8 at 9000+. It would turn a 16 x 8 at around 8500. All I did was leave out the base gasket, raise the exhaust port about .025", take out the exhaust bridge and pin the piston like you have, and put a free flowing muffler and 11mm carb on it. (When I leave out the base gasket to lower the cylinder, I use Yamabond sealer to seal the cylinder/crankcase interface.) Sometimes you can get away with this without taking out the squish band in the head area when you do this, and sometimes you can't. It depends on manufacturing tolerances. Check your deck clearance by inserting a piece of solder into the cylinder in such a way that when you turn the engine over the piston smashes the solder flat against the head area. Then measure the solder thickness and that's your deck height. The minimum is .015". Make sure the solder reaches all the way to the cylinder wall when you do this, so that it measures the clearance at that squish band area which is at the very outer circumference of the head area.

I also have a Homey 30cc that has all the hop up tricks I could think of done to it. It turns an APC 16 x 8 at 9400 rpms. That's a bunch of power for an engine I paid $15.00 for from an old blower!!

You're going to like that Frank Bowman ring, and his service. His rings break in fairly quickly, but even so the engine is going to gain power until it has at least a gallon of fuel run through it.

Have fun,
AV8TOR

jrjr2u

I read that thread, in fact I did a search for homelite and read every thread!
Thats where I got the ideas. Anyway, I figure I will machine the squish band out too if I can find some pvc the right size. Right now my deck clearance without the base gasker is .035. I blueprinted it, at least I hope I did it correctly. My results were Intake - 156 Exhaust - 126 Trans close -->Exh close - 20 with no base gasket or sealer.
I will touch them up a bit when I get to it.

I just spent 2 days reading and absorbing the 1000+ posts in the gas/glo thread. Amazing! I have an adapter coming and will be doing that too!!

Just got some coroplast in so i'm building a plane now....

Also, I picked up a 16cc Kioritz. I wonder how much I can get out of that?

av8tor1977

My Feedback: (6)

Wow, congrats on all the research. That's a lot of reading!

I did the Echo 16cc once. It really is a bit heavy for the power it makes but would be ok for a Cub or something like that, especially if done on Gas/Glow to eliminate the weight of the ignition system. I did mine several years ago with ignition and some minor hop ups. It flew a 10 lb. aerobatic plane ok at sea level, a bit underpowered at the 4200' elevation I moved to later. (An engine loses about 2 to 3% power per thousand feet of elevation.) If you do it on Gas/Glow let me know how it turns out. I think I might still have the pieces to put another one together if the urge strikes me....

It uses basically the same crankcase and crank assembly as the 21 to 25cc Echo engines; that's why it weighs quite a bit for it's displacement.

Have fun,
AV8TOR

jrjr2u

Thinking ahead.........

Do you think these specs would be close for that 16cc Kioritz? (overpowered is ALWAYS good )


Clipped Wing Cub

REQUIRES: Engine: .60-.90 2-stroke or .90-1.60 4-stroke engine Prop, Engine Mount, Fuel Tank

SPECS: Wingspan: 86" Wing Area: 1300 sq. in. Wing Loading: 25 - 27 oz/sq ft Airfoil: Semi-symmetrical Fuselage Length: 67 in. Weight: 14 - 16 lbs

Balancing may require thinking outside the box.......

av8tor1977

My Feedback: (6)

Way too much airplane for the 16cc, especially if you like power.

The 16cc would be better on a Cub that weighs no more than about 10 lbs. ready to fly if you want to do any more than just get it in the air and back down again. (no aerobatics)

AV8TOR

Antique

My Feedback: (4)

You need a little ring gap..SuperTigre found that out a while back...
And I think some of the very early G26s had the same problem, no gap, the ring expands and tightens up against the cylinder wall, makes heat, expands more, seizes the engine...I think the old rule of thumb minimum is at least .001 for every inch bore size...