Crankcase Stuffing
 

I've read here the term "stuffed cranckcase" and it apparently is good for increasing RPM. I did a search, but came up with no explanation as to how to stuff a crankcase.

Would someone please explain?

I have Homelite 30cc that needs some more revs. Only 6200 rpm with a 18X8 APC prop.

Thanks.

RE: Crankcase Stuffing
 

Basically it amounts to filling the excess space in the crankcase that isn't otherwise occupied with the rotating mass of the crakshaft and rod. Some care should be used as it is possible to impede the airflow in the case. One mod that I've heard of with Homelites is adding material to the backplate until it just clears the end of the crankshaft. As I understand it the idea is if there is less room in the crank case then the mixture will be more effectively pushed into the cylinder. I seem to recall that this bit of information came from one of the boat sites. They do some pretty extreme mods for competetion up to and including water cooling.

RE: Crankcase Stuffing
 

Hi,

Yeah, you're down on power I would say. My Homelite 30cc is souped up, but it will turn an APC 16 x 8 at 9400+ rpms. I've never run an 18 x 8 on it, but it should theoretically turn one over 8000 rpms. You are definitely way down on power with only 6200 rpms.

The very first thing to do is check the condition of the engine. Any more, when I grab an engine out of my big box of used engines to convert for an airplane, the first thing I do is just go ahead and order a Frank Bowman ring for it. Even if the original ring is in good condition, which is rare, the Bowman ring is good for a power boost.

Next, are you running a free flowing muffler and larger carb? Do a search here for Homelite post done by me (and others), and there is a ton of info on hopping up these engines. As Tym1meo said, stuffing the crankcase is one hop up item to do, but all the hop ups in the world won't help a tired engine, so start with a check of the rings, bearings, and seals first.

Good luck,
AV8TOR

RE: Crankcase Stuffing
 

Av8tor,

The engine is brand new. Just a tank of gas while still in the blower. 6200 is with a Bennett muffler and 11mm carb. After running it I did notice some oily residue around the backplate. I am going to get some Yamabond and remount it. I'm neither knowledgeable enough, nor tooled enough to do any porting mods.

What materials are used for stuffing?

RE: Crankcase Stuffing
 

MFGs have playing with crankcase compression for a long time and they still can't make up their minds. If you want more power, get a tuned pipe.

RE: Crankcase Stuffing
 

Well, that explains part of it anyway. These engines take a good while to break in. They don't start sealing well and loosening up for a couple of hours, and often increase in power up to about 4 or 5 hours of use. Whenever I have a working tool I'm going to steal the motor from, I always put it to work for a few weeks before tearing it down and converting it.

Your power should increase as it breaks in. You might try either a 16 x 8 OR 18 x 6 APC prop and let it rev up a little. Those are common sizes for 25 to 30cc engines, and I really like the APC props. Use the 16 x 8 if you want more speed, and use the 18 x 6 if you want more low speed thrust.

I have never done a before and after comparison of crankcase stuffing, but I doubt you would see a significant difference without doing other mods. If you want to try, you can make a plate to attach with glue and a screw in the middle to the engine backplate. You want to leave several thousands of an inch clearance between the backplate and the crankpin. I can't remember if I used 1/8 or 1/16" aluminum plate for the last one I did. You can fine tune the clearance with extra gaskets if need be.

Good luck,
AV8TOR