JCaste

Hi all,
I recently bought from ebay this Homelite 30cc conversion, and I’d like to upgrade it. This is the first one for me, so I’ll gladly accept any feedback and advice to help me in the process to learn how to do these things. Here's the little noise-maker:




I’ve spent several hours searching this forum but despite being a rather common engine, I’ve not seen any clear ideas, numbers or how-to about how to hop up the engine. Well, I got to find some numbers and mods made to a Homie 30 by the modeller AV8TOR.
I’m not looking for radical mods; in fact, all I’ve thought of are even reversible, so if I mess things I can still go a step back. I’ll do a small review of it as well as exposing my doubts and ideas.



The engine is, to my understanding, completely stock. The conversion consists of a machined flywheel, prop hub, mount and home-made muffler (and a painted engine block, if you call that a conversion).


The prop hub, as you see it, is simple and functional, as well as the mount. To bolt the engine to the plane I will just drill four M4 holes on that mount and screw them to the firewall. I first thought of silent blocks, but after reading about them I rejected the idea. It came with a primer bulb, but doesn't seem to belong to this carb. Maybe it's useful to put it anyways to prime the engine, but at least in this carb, I have a choke so it's not that critical.


The exhaust is custom made out of an aluminium box and a machined aluminium tube which is screwed in place. It looks weak, because the thread section in both box and tube are thin and will likely get damaged in the event of a relatively soft hit (i. e. while moving the plane around). There’s a screw in the box; I guess it’s there just to seal a hole the box had from origin, but maybe comes handy if I try to make a smoke system. Now, if the muffler will just make more noise than the stock one or really help moving the gases out, I’ll know when I tach it. I have a 20x8 MA prop, so from what I've read I'll better use a 18x8 or 19x8.
A couple of things I just don’t like are the exhaust hole, which has been poorly made (as clearly seen in the pic - I hope it wont’ affect the engine), as well as the carton gasket. Also, the metal piece from the stock muffler which is still used to bolt the muffler. I haven’t tried yet, but it looks like the screws were too long so that metal piece acts like a spacer (the same happens in the carb).


This pic shows the exhaust port. The original gasket is still there, I’m not sure if I should try to remove or leave it there. But that’s not why I put the pic. When I was turning the engine by hand, I heard a whistling sound. I looked carefully and I saw, right above the exhaust port, a hole. A hole!!! That must be to relief compression, but that’s exactly the opposite I need! How can that be solved? Is it a good idea to tap the hole and put a screw? At least I wouldn’t be wasting that much compression…

The piston has two rings. I could change them in the future (Frank Bowman rings comes to my mind), I don’t know how much wear they have but they don’t look bad. I haven’t opened the engine, but what can be seen on the cylinder walls are very fine horizontal grooves and 1 or 2 fine vertical grooves; the piston looks clean, but also has some very subtle vertical grooves. I guess those few small scratches are the least I could expect from a used engine.
So, I’ve thought to change the usual things:



- Bigger carb. It seems to be one of the easiest and cheaper ways of getting more out of a stock engine. Now it has a Walbro carb with a “22” cast on it (in one of those 4 mould holes). I’m not sure what size or carb id should I look at (WA-167 it's the only reference I've seen). I want more power, but I also want an agile engine, if it transitions slowly or lags a lot due to excess air/fuel, it’s not any good. I will also need a big bore plastic adaptor. I read Carrprecision carried those two items, is that right?
Anyways, if a fellow model has a spare carb and/or adapter I could use and is kind enough to make me an offer for it, I’ll gladly look at it.
- Stuffed backplate. I don’t know how I’m going to do it, but if it’s possible with my means I’ll do it, leaving a good clearance with the piston assembly.
- Electronic ignition. There’s a CDI project here in this forum I found a while ago which looks really good, so it’s another possible mod I make. In that case, I’ll mill the front end of the engine.
- Velocity stack. If I get bored one day and want to try things… then I’ll machine one.
Maybe if there’s a good explanation available I’ll try more difficult stuff on it…

So that's all, I hope it didn't get too long. I'm open to all kind of ideas and suggestions to make this device make bit more noise and wind!

PS: I've tried to put some thumbnails, but I can't get to either do that right or hotlink the big pics. The best I got was if I put "" at the beggining, still don't know why. If someone knows how, I'll change it.

pe reivers

That narrow slit is not a big deal, and will allow better hand starting without violent kickback. At higher rpm, there is extremely little compressed gas lost, though it starts blow-down a bit earlier, and silences the engine.
The porting seems very moderate, and you can raise the central 1/3rd port part to get a timing of 155 to 160 degrees.
Also widen the existing port width to at least 50% of the bore diameter, but only the part above the transfer ports. Keep 60% as max. There is nothing to support the rings past the port.
Do not bother with crankcase stuffing if you want low end grunt. Our plane engines need not run 12000 rpm in this engine class.
Improve engine breathing without going outside the time-area port windows that belong to your target rpm. Google on Jennings and Gordon Blair. Increasing carb diameters helps up to a point, after which you also need to adjust internal porting, and/or raise rpm to get more power. More rpm needs larger ports for the same time-area data, so be careful there. You may bring the engine into rpm ranges where you rather would not be.

Edit:
I have an electronic copy of Jennings and yamaha engineering reports for the interested. These papers very much represent our tuning efforts of the sixties (when I was young). If there is demand, I can put them on my domains for reading.
Gordon Blair is quite another story. His book is hard to come by, but in my proud posession.

davewallace

My Feedback: (29)

J,
That is a nice looking Homey. There is a hole just above the exhust port that goes into the cylinder. I pull the cylinder and tap this with 10x32 tap. Then I run a bolt in until it bottoms out. Then I cut it flush and trim with a file. Be sure to cleanup any filings and reoil the bore,before reassembly. The carb venturi is small at 11/32nds(22/64ths). An 11mm(7/16ths) carb will help a bunch. You must open the carb insulator to 5/8ths to take full advantage of the new carb. These mods will give you the most bang for the effort and money spent. These engines run great with these mods, while keeping costs down. Checkout the conversion forum. This is where the answers are. Do a search on Homelite mods.

Dave

JCaste

I'm glad it's not as bad as I thought, but still those "advantatges" don't convince me. I don't want to trade some power for ease of start - even more if I'm planning to use an electronic ignition.

I'm sorry, but I don't really understand what you mean, specially the "widening" part. If you could post an image of pic or simple drawing it would be a great help! In fact, I didn't plan to grind anything, but if there's an important benefit I may try. This kind of motors have average power, they're made to run all day and weight little, but I'm afraid of spoiling the block while trying and have an expensive paperweight.
Also, what tools are required to do that? Won't I spoil the nickel (or whatever material it was) coating of the walls?

Yes, I know, I'm not making a boat engine! I read in several books that, basicly, the more power you get from an engine, the more spiky gets it's power delivery curve (= more critical to use and less overall torque). However, I read of many guys who had done that for plane engine, so I kind of assumed it helped too (after all, we kneed torque, but not a HD engine!)
The rpm range I thought of (being very optimistic and once converted) was of up to 10000rpm (no prop), with smaller props doing about 9000-9500rpm and ideal size prop turning at around 8000rpm. I hope those are reasonble limits!
And as for the carb, since I initially didn't thought of altering porting, I would have used any of the carbs most fellow modelers use for their Homelites. If I get to know what you described before and decide to do it, I'll run some numbers. Still, you always have to do some trial & error.

If it's not an effort to you, I'd like to see them, at least by mere curiosity.


I'll probably do that too. I will trim the screw so it's about a mm from the walls, I don't want it to contact the piston.
Regarding the carb, I'm looking at Walbro's site the "diaphragm carburetors".
And inside there, I saw the "HDA HD" category, but they seemed to be too big (the smallest had a 11mm venturi).
Here I found the WA series (the smallest carbs), but still no sign of model numbers and such, so I don't know what to search for. Can you help me with that? I don't even know which of those it's my current carb.
So, is the venturi size the only parameter to look for? I recall reading something like size is (number on carb)/64 (so I must find one with a 28 on it, right)?
I must be doing something wrong here, but I don't know what, and I also need to find an extra plastic adaptor.[:@] I'm getting busy by moments!
Also, believe it or not, I've been searching for several days the whole conversion forum. In fact, I chose the Homelite as it seemed to be the best choice in the 30cc range (considering power, weight and budget). But I'll search again, maybe I missed something.
BTW, do you believe milling the front end will afect th stiffness of the engine? I've not seen a single Homelite with electronic ignition that wasn't milled.
Have fun while learning!

tkg

My Feedback: (1)

A good Homie 30cc with a modest amount of work will turn a 18x8 prop in the 7700-7900 rpm range. The 30 likes to rev up so prop it for 7500+ on the ground
1. plug the hole its costing you 100 rpm or so.
2. Larger carb about 11-12mm will add 200-300 rpm. Note to big a carb and to big a prop is a BAD IDEA.
3. Electronic ignition adds 100-200 rpm. You can set the timing for max power and you remove the drag form the magnets and the drag from fan on the flywheelng
These are the easy big improvents. The rest offers smaller improvements for the effort

JCaste

Tkg, those were the mods I were thinking of. [&:]
1) Tap that hole and put a screw in it.
2) Larger carb and big bore manifold. I've seen one of those online engine conversion shops carries a "big bore carb" & "big bore manifold", so I'll see exactly what they offer. I won't buy the largest carb I see because then the engine will be impossible to tune - just as well as you won't buy the biggest tyres in the shop thinking you'll have more traction and grip.
3) I'm really wanting to try the electronic ignition. The weight savings are very appealing, and the speed range should be improved noticeably.

Maybe in the future I'll try more complex mods, but so far I think that will be enough.
Thanks for your tips guys!

jrjr2u

If saving weight is a goal, which it always is with planes, then you should check out this thread and consider gas/glo operation"

http://www.rcuniverse.com/forum/m_1267448/tm.htm

pe reivers

This is how to enlarge the exhaust port. You need a dremel tool and cutting/drinding bits. When done, chamfer and round all edges.
[link]http://www.prme.nl/tuning/crankcase.pdf[/link] (see page 4, column 1 )
[link]http://www.prme.nl/tuning/jennings.pdf[/link]

av8tor1977

My Feedback: (6)

You're on the right track. Use an 11mm carb, (There's been a listing of all the carb numbers that are 11mm venturis here in the forum), electronic ignition at 28 degrees BTDC, and I use two 7/16" or 1/2" i.d. muffler outlet tubes on this size engine.

My 30cc Homelite turns a 16 x 8 APC prop at 9400+ rpms, but it has all the porting mods, etc. as well.

Have fun, it's a good engine,
AV8TOR

captinjohn

av8tor1977: We have read how your 30cc Homelite turns a 16x8 APC prop at 9400+ rpm. What we need is the port size you ended up with. You must have measured it ...right? Also the degrees of opening would be nice. We want to be right on track!!! Capt,n

mikenlapaz

Capinjohn:
"You must have measured it ...right? Also the degrees of opening would be nice. We want to be right on track!!! Capt,n "
BME posted the durations on the Don't Forget Echo" thread and implied that they might be applicable to many of the engines in that size group.

It is getting fairly dated for last post, maybe you should update it.

av8tor1977

My Feedback: (6)

Yeah, I've got the numbers written down somewhere in my files. I think the exhaust ended up at around 165 degrees, blowdown of 20 degrees, and intake of 140 or a touch more. I didn't make the ports any wider really, just increased the timing and smoothed everything up. Of course the cylinder is lowered to achieve a .015" deck height (without the squish band) for max compression. Stuffed crankcase. Crankcase/cylinder interface for the transfer ports cleaned up, etc. Carb spacer pulse port epoxied shut and the carb hole opened out to match the carb, 11mm carb, gutted exhaust with two large outlets. Frank Bowman rings. 28 degree ignition timing. Hole above exhaust port tapped and plugged with a screw.... I think that's about it, other than careful assembly and the normal tuning.

AV8TOR

mikenlapaz

JCaste; This is loaded with good idetas on stuffing the case. Some how to measure , materials to use , and how to attach. .125" to .1875" thick material and some shim stock or roof flashing .010" and a couple of small FHMS and a drillbit. (Will that stock case back self tap? if you do not have a tap?)

http://www.rcuniverse.com/forum/m_27...tm.htm#3096623

av8tor1977

My Feedback: (6)

Another mod that I keep wanting to try someday, is to fill the upper part of the backplate with something, (braze, JB Weld??), and then machine it out to unblock the transfer port in the area of the backplate. Seems like the backplate is a big obstruction to flow in that area, but only testing would confirm how much one could gain by unshrouding there, because in so doing one would unavoidably "unstuff" the crankcase somewhat.

Another thing is that right after I finished that particular engine, I found some NOS Homelite 30cc cylinders that have much larger transfer ports. I bought two of them to try. One of these days.....

Meanwhile, I'm really happy with my Homey 30cc. It rocks! My Ryobi on the other hand, just doesn't go with my motto below...

AV8TOR

pe reivers

you can use JB-weld filled with aluminum powder or glass balloons for that. Mix two batches, one without the filling, and one with the glass balloon reinforcement (putty). first wet the surface with the normal mix, then apply the putty. I think that would be a larger gain than the stuffing of the case since we want more power in the 7000 to 8000 range, not 14000 and up like the boat guys.

jrjr2u

Sounds like the Homie 30 is not a lot more powerful than the 25..... 200 rpm's maybe??

av8tor1977

My Feedback: (6)

I've done several of each.... I found the 30cc to be quite a bit more powerful. They are harder to find, but worth it to me...

The 25cc engine is not bad though. Look up the thread "Non machine shop Homey" or something like that. Without too much work I got one to turn an APC 16 x 8 prop around 8700. You have to pin the ring and take the bridge out of the exhaust port to really get anywhere with the 25cc. With these size props, a few hundred rpms is really noticeable in performance, and it's a decent horsepower gain.

They are good engines for the price, which is often "give away". Another thing that is cool is that you know you can rev the hell out of them, because the boat guys run them over 10,000 rpms without significant reliability problems. I would take one over a Ryobi any day. The Ryobi is good for scale airplanes that you don't want the engine parts sticking out of the cowl however, like my big Tiger Moth.... .

AV8TOR

JCaste

I'm not finished reading the thread (many threads to read, and too little time!), but I'm not particularly interested in mixing fuel or running glow. I prefer to use just gasoline and oil. By the way, I bought some time ago an oil specially made for chainsaws and such, I don't know if it's of some good or not for those conversions - I think, though, I may be better than a common 2-stroke oil. I also plan to pour some castor oil on the mix, it's a good product and gives it that "racing smell" I love so much!

Thanks for the links and pic! A new and interesting addition to my virtual library!
I'm just a bit confused about the position of the transfers in the pic. Assuming the black line represents the stock exhaust port and red lines the modded port, there are no transfers there. They are, in fact, about 85º apart, so unless I grinded a lot they are not affected by the port modding. Anyway, I'm starting to think those "radical" mods will be put into practice in a future engine. I have waited many time to have a working gas engine, so I prefer to s tick to the tested stuff for now.

I found the thread! LIST OF 11MM CARBS HERE!!
There's an overwhelming amount of carbs there, even if I only count the ones with 2 needles by Walbro (all the smallest series of diaphragm carbs are in the link). There must be some differences! I'm sure a series of carbs is better suited for our use, for example. So choke, yes or no? What about the primer? I don't think I'm going to need them, but the weight is neglectable and they may come handy some day. Well, I think I'll toss a dice or two and pick up one or go for the WA-167 I've heard about.

Regarding the exhaust, I've made a simple calculation about the exit area. My pipe has an ID of 16mm, with area of roughly 200mm^2. The resulting area for yours are 97mm^2*2=194mm^2 (7/16) and 127mm^2*2= 254mm^2 (1/2). Maybe a bit on the low side? However, I still think factors like exhaust shape are possibly of more importance than that. I can try to make several mufflers using the "box" or "mousse can" techniques, or go ahead, buy some equipment and custom weld my own, but that will be when I finish many of the things on my to do list! There's a certain exhaust noise I'd like to have in my planes! - if you think about it, it's kind of a signature!

Nice link Mikenlapaz! I'm searching now for the other one, the Echo thread. Let's see what I can learn from there!


Can you further explain the "cylinder lowering", "transfer ports cleaned", "gutted exhaust", etc. (if it's not a secret engine modding!!) In a few days I'm reading many new stuff for me. BTW, I found some Homelite 30cc info you posted in previous treads. I post them here since you posted them before in a public place, but if you like me to remove them for some reson just let me know.

"�* My highly souped up Homelite 30cc turns an APC 16 x 8 prop at 9400 rpms. It hauls my 12 + pound Ultra Lite Stick 120 around with great aerobatic authority. I'm sure it would be good at hovering if I propped it with more diameter and less pitch but I like the way it flies now as I'm not really into 3D. "

"�* Hi,

Here's the stats and a pic of my Homelite 30cc . It turned an APC 16 x 8 prop at 8600 with only an opened up muffler and a slightly larger carb. Then I modified it...

Homelite 30cc - older design with small transfer ports.
Weight with muffler - 2 lbs. 14 oz. (More cutting/grinding on this one than my Homey 25cc, and this is with prop adapter but without prop or spinner.)
Muffler - Stock, square, gutted, with two brass 1/2" i.d. outlets added.
Carb - 11mm Walbro, manifold ported to match, external pulse line.
Ignition - CH Ignitions electronic set at about 28 degrees presently.
Cylinder - Quench or Squish band removed, cylinder to head clearance set at .020"
Port timing - Exhaust 165 degrees, Intake 148 degrees, Transfers 120 degrees (22 degrees blowdown). All ports cleaned up and entries in crankcase smoothed.
Crankcase- stuffed to .020" crankpin/backplate clearance.
Rings - FRANK BOWMAN'S!!
RPM - APC 16 x 8 = 9400 (Possibly more with tuning and more run time. Also, with this port timing, a tuned pipe would probably give 800 more.)
Test conditions - 4200 feet altitude, temperature 78 degrees, barometric pressure 29.75"

Please also note that while I did modify the transfer port timing, I did not alter the size and I think this would also help. I'll do that on the next one for sure, or use a later model cylinder with the larger transfer ports.

I like it!
AV8TOR"

Those numbers belong to another thread (don't remember which modeller):

"�* Here are some numbers from my 30cc homelite . I did not alter the exhaust port and just used a little thinner head gasket, wa-167 carb. The rest of the mods are described at the top of this page. The thrust # comes from a digital fish scale and are approximate.
zinger 20x6 7600/16lbs 12oz
top flight pp 18x6 7600/16lb
top flight pp 18x8 7200/16lb 2oz
apc 16x8 8900/ 16lb
zoar 18x6 8100/17lb 5oz "

Well guys, I thank you again for all your help; all my old questions are nearly solved. I'm learning a lot of things and I'm sure that will pay off soon. For now, I'll keep reading and trying to put into practice all that has been said, and then come back with my results. I'll ask one more thing, so I don't lose my bad habit of asking: how much traction can I expect the engine to have? I'd like to have a rough number so I can resize a project I'm designing accordingly.
Also, if someone has one of those big bore carbs for spare, I'd gladly buy it. I've sent an email to Carrprecision but after 2 days or so I still got no answer, so I'm not quite sure they want to do business overseas. Perhaps they don't like to be asked about their products. Who knows.

Have fun!

pe reivers

Not the position, the height should be looked at as reference to rework the port. Leaving the lower part of the port untouched reduces the fresh charge shortcut to the Exhaust port.

captinjohn

If I had a good milling machine I would start by milling the crankcase to about 1/2 way and make a 3 piece case. The new back half would incorperate a better way to mount engine and at the same time give a person a chance to rework the passage ways in the bottom for best performance. I am with Pe Reivers on not trying to stuff the case to much if it does not help in our RPM range. Capt,n

tkg

My Feedback: (1)

A WT9 works on a 30cc homie nicely. Its 11.1mm and has a choke. I used one on my 9000rpm 25cc.

av8tor1977

My Feedback: (6)

ONE of these days I'll put that tuned pipe on Terry....

AV8TOR

JCaste

Just a quick question guys, is there a prop size you recomend for the engine? I went to the LHS today and they only had a 18x6, so thinking it was way too little pitch I ordered the 18x8. Is this prop OK for -mostly- pulling power? I plan to use it on a big autogiro, so I certainly need more thrust than speed. I can also try to use a MA 20x8 and check my tach, I think it will be too big for the stock engine, but at least I'll get some numbers.

Captinjohn, are you talking about custom making the crankcase? If so, that mod will have to wait till I have acess to a mill.

Pe reivers, I've been reading a bit more your papers and they're really interesting. I have a question though, have there been any important changes in what is there written? From what I've read in other sources, it seems like most things haven't changed at all, but I might be misinformed.

av8tor1977

My Feedback: (6)

An 18 x 8 is a little "over propped" for a Homelite 25cc, especially without much in the way of hop ups. I personally like a 16 x 8 on my planes with the Homelite. An 18 x 6 works well for a bit more thrust at the expense of pitch speed. I would think offhand that an 18 x 6 would work well in an auto gyro. I like APC props better than the other props of around the same price....

AV8TOR

pe reivers

The old homepage with the SPitfire, Supertiger and Ryobi work is indeed quite stationary, because lack of time and the need for a modem connection. Still there are lots of things in there.
My prme.nl pages are updated frequently.