Now that's a bummer!

Rich

Well I certainly don't agree with that conclusion. (What you were told about having to run a flywheel...) I have a Homelite 30cc with a lot of flying time on it. It DOES NOT have a magneto, and it is all hopped up and turns an APC 16 x 8 prop at 9400 rpms!! No problems with the crank nor the bearings. A lot of the boat guys run these things in the 10,000 rpm range, again without a magneto. I have also turned a lot of 25cc Homelites some very high rpms, and I don't ever use magnetos!!

AV8TOR

Morning AV8TOR

Thanks again. I don't know if this is a particular problem with the blower engine as it has a longer shaft then the strimmer engine. What I will do is get this engine running without the damper at full RPM and walk away. If it does shatter then I will leave the flywheel on the 30cc. Have you used the leaf blower engine without the flywheel? The other question is, I was told that the diaphram on the Zama carb melts away if you use glow fuel. Is this true?

Rich

Hi, While you are on E--- Type in ecedwards_tools in the search block, he sells a lot of new old stoce carbs for $10 to $15. I just got two walbro wt540s for 15 each + s&h. They have a 13.48 venturi and accelerator pumps.

It doesn't matter if the engine came from a leaf blower. As a matter of fact, the 30cc I am presently running came from a blower, and had a long crankshaft. I cut it down to the length I needed and re-threaded it. Same with the 25cc engines. Just make sure whatever prop adapter you use is straight; with no runout, and of course balance your props. No problems....

Keith at BME engines told me that he had run some Zama carbs on glow fuel without problems. However, I did have two different Zama carbs ruin their diaphragms on Gas/Glow fuel, and they did it within a day or two even though I was running the engine dry after use.

You can shop for carbs on e-bay, then go to this site: http://wem.walbro.com/walbro/family.asp to check out whether they have twin adjustment needles, what size venturi, etc. I use an 11mm carb on the 25cc, and had been using one on my 30cc as well. However I now have the 30cc apart for a cleanup after a crash, and I am going to put a 12.7mm carb on it. The Walbro carbs have a number cast into the throat near the choke. This number is the venturi size in 64's of an inch. For example a 28 casting means:

Venturi size = 28/64" = .4375" = 11.1mm

AV8TOR

Try http://wem.walbro.com/walbro/family2.asp. that will take you to a list for all walbro carbs. sizes,exploded picts.,part # etc.

More about vibration dampers. A vibration damper is just that, a device designed to dampen harmonic vibrations. For example with a car engine, there can sometimes be certain rpms, load conditions, etc. where one can encounter a harmonic vibration in the engine. If this is encountered at an rpm that the engine spends a lot of time, like say at a common cruising speed, it can eventually cause damage to the engine. So a vibration damper is used to prevent this problem. It is usually a steel hub, with an outer ring bonded on with a cushion of rubber, but that is not the only way to do it.

This problem is also occasionally encountered in full size aircraft engines. In testing, they sometimes find that certain prop, engine, and airframe combinations can cause a harmonic vibration. In this case the owners manual and the airplane are placarded against continuous operation in the rpm range where the vibration can occur, because airplanes don't use harmonic balancers, they use props!

Now, back to our little engines. The magneto is not a vibration damper. It is a magneto, to generate a spark, and a flywheel, which provides a rotating mass and smooths the engine out somewhat, and a fan, to cool the engine in it's original installation. We don't need it to generate spark, and we have the propeller for flywheel effect and cooling, so we don't need the magneto flywheel.

AV8TOR

Well I wish I could show you a picture but alas I don't know how to put a picture on these replies[&o] The output shaft is 3 1/2" long from the bearing to the tip on this engine. Even though I like my engines on the bulkhead for CG reasons this is a tad rediculous. AV8TOR I know you said it will be ok but just from looking at it and the fact that there is only one crank bearing I do have slight concerns regarding resonance! I know the magneto isn't a damper but a big lump of aluminium is really good at soaking up unwanted vibrations. Oh by the way I have exploded race engines before due to cheap crap dampers! Learned my lesson!

Thanks oltimer2 for the addy's. I'll look them up

Rich

Well no, you wouldn't want the prop out at the end of a 3" plus extension! As I said, I cut my shaft off to a more normal length and rethreaded it, and used a reasonable length prop adapter. I think most prop adapters run more or less 2" in length, and that is enough to have extended out there without a third bearing supporting things.

Just because it was right handy here, I just now measured my 48cc twin that I made. It is exactly 2" from the crankcase, (which is very close to the front bearing face), to the prop mounting surface. My 30cc Homelite is in that bracket as well....

BTW, even the cantilevered crank engines like the Homelites have two bearings. They have a big one inside near the crank web, and a smaller one in the nose of the crankcase housing. Even the "smaller one" is a good size bearing...

AV8TOR

48cc twin made from two 23.6cc Echo engines and a custom crankcase. No "vibration damper". Two inches from crankcase to prop mounting face. RPM's from 7000 to 8500 depending on prop. You can put a glass of beer on the fuselage at any rpm, and it hardly jiggles the surface of the beer!

Yeah I know, it's a twin and they usually have less vibration, but my Homelite singles also don't use flywheels and don't have any problems.

But hey, if it makes you feel better to run a magneto, go for it! It's all fun!



AV8TOR

I hate cutting these shafts down. I think they are harder then my chinese carbide cutting tools on my lathe! Plus I don't want to try and take this crank out of a 15 year old engine as it is press fit into the bearing and has been in there a really long time. On top of that the woodruff key is probably made out of chocolate and you know that's going to break! (mental note, don't use Homelite blower engines in the future as they have stupidly long shafts!) How about this for an idea? I'll make the propshaft 2" long and make a long nut to resemble the full size variable pitch prob hub. Thus bringing the propellor further inboard. Does this sound like a plan? I'm using 1 1/2 round 6061 for the propshaft so this should be thick enough to absorb some of the resonance.

What do you think?

Rich

P.S. Love the twin!!

Yeah, that's not a problem. Instead of using a screw on prop adapter, make a through bolt prop adapter like you said. The prop adapter will be nothing more than a spacer, with the shaft going through it.

But the crank isn't quite as hard as you think. I have cut them off with a hacksaw without much of a fight once you break through the surface.

AV8TOR

OK! 2 hours grinding and only 2 oz removed! Hmm! Maybe I will cut the output shaft down. So the crank is made out of monkey metal the same as the rest of this engine! lol!

Rich

Ah just remembered I can remove most of the front and side cooling fins from the top of the inlet down to the crankcase!

Well this is the Homelite so far. I haven't finished with the dremel yet as there is still more metal to come off! It's now down to 3lb with stock carb and exhaust. Still waiting for aluminium bar so that I can machine the propshaft and washer. I am going to order an aluminium exhaust to further decrease the weight.

Hey AV8TOR, see what I mean about the extra long shaft?!?!

First pic is just after I removed the blower and ignition mounting flange. The other three are as far as I have gotten to date.

Rich

Looking good. You've cut/dressed yours down more in front than most guys do. That's how I do mine.

That shaft is exactly how my 30cc was before I cut it down and rethreaded it.

Have fun,
AV8TOR

GOOD! I was getting a tad wary abut how much metal I was cutting off but if you say they are still reliable thats good. I will be bench testing this engine thoroughly when I finish it. On that note have you seen any ultra cheap ARFs that are suitable for this engine and that fly well deadstick or with half the engine a mile away? I'm thinking that it might be a bit risky testing it in my P47.

Rich

I'm telling you, you worry too much!! I put mine on a 1/4 scale Christen Eagle biplane without a second thought. Set up properly they are just as reliable as any 500 dollar engine you might buy.

But if you insist, try it out on a Giant Stik or something similar. I think the Goldberg "Wild Stik" is offered pretty cheap sometimes....

AV8TOR

Worry too much? Yeh! story of my life! That's why I have high blood pressure! lol! Without stress my life would be meaningless!

The same guy I bought the P47 from has a Giles G-202 67'' ARF for $79.99 so that's a possibility. I go past him on one of my routes so I don't have to pay shipping!

I like your Christen Eagle!

Rich

Ok here goes the next installment! Just finished in my workshop with the Dremel! Originaly the engine weighed in at 4lb 10oz as it left the blower. After much use of a hack saw and a dremel the weight is now down to 2lb 15oz with the stock steel propshaft, carb and exhaust! I probably could get it lighter by drilling through the fins and taking some metal away from the edges of the crankcase back plate but I think I will call it a day. I cut some of the front fins away below the manifold as these are in an area of high airflow and below the combustion line. The engine ran really cold when it was in the blower even though it was covered in grunge so I thought it would be ok if I lost a bit of metal from that area. Lets see. Next on the agenda is a light weight aluminium exhaust, new Walbro and to make the new propshaft. Pics below, starting to look more like a plane engine and less like an industrial unit!

Rich

Looks great. But now I have to tease you a bit...

A. It would weigh even less if you would cut that long shaft down to a reasonable length and re-thread it.

B. What happens if after all these weight saving endeavors, you end up having to add nose weight to your P-47?

Have fun!
AV8TOR

P.S. Just noticed after a closer look at your pic that yours has the cast aluminum back plate. They also made those backplates in stamped steel and plastic, either of which is a bit lighter.

AV8TOR

Ha!

1- If I cut the crank it will be too light!
2- If it needs nose weight I'll just use a bigger prop nut!

The stamped steel is lighter?!?!? I've got one of those! :-) Shame it's on the back of my new 30cc! Hey just think if the 30cc is lighter to start with I wonder how light I'm going to get that one!

Rich

the steel is definitely the heaviest part of these things... you can hack at the aluminum all day and not make as much of a difference as cutting off an inch of that crankshaft...

I take it the general concensus is that I hack off the end of the crankshaft then!

Rich

Are carbide bits needed to cut these utility engine shafts?
or will hss to the job?