Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

I just got another engine so I decided to report all the things I did to get the usable airplane engine. Entire procedure took me less than two hours (including taking pictures).

So let's start.

Step 1.
Here it is what you pay for. For $25 you got entire trimmer head with case, starter, fuel tank, and engne of course

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

Step 2.
It takes only few minutes to remove the case. Just unscrew a couple screws with hex key 5/32 and star bit T-25 (hex key 1/8 works too). Remember to disconnect ignition wires from the kill switch.

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

Step 3.
Now you need to use a little force.

First the easy part. You need to remove the muffler. It has star bit (I don't know the size), but I found standard hex key 5/32 works. It's tough so prepare for using a little more force than you did removing the case.

Carburetor is also easy. Remove air filter and under the sponge you will see two screws that you can remove with hex key 5/32. Then the black plastic carburetor's spacer also uses star bit T-25.

Unscrew two star T-25 screws holding the magneto and remove ignition assembly.

Now the flywheel. First lock the flywheel (put a screw into one of the holes on the front of the flywheel and lock it against the shaft (the front screw) with small pry bar. The using locking pliers (you can use wrench if you have) it is easy to loosen the shaft adapter.
There are many different ways to remove the flywheel. You can tap on it from the back holding the engine by the shaft. I uses very easy and safe method - simple 3-jaw gear puller does the job.

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

Step 4.
It will be easier to cut the engine if you remove the cylinder. First remove the back plate using 5/32 hex key. You need access from the back to disconnect the crank.

Two hex screws are quite tough. You need strong 3/16 hex key. I got 10 PC. COLOR CODED SAE T-HANDLED HEX KEY SET from Harbor Freight (ITEM 37861-4VGA) for $5.66. The best deal in the town.

Now protect interior of the engine from the aluminum dust. I fill the crankcase with paper towel and then tape it with blue masking tape.

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

Step 5.
Before cutting all the metal in front of the engine I drill four holes in the back and tap it for 6-32. There will go my mounting screws holding the radial mount. You need to drill long holes (about 13 mm long) so drill press is needed. Use the front of the case to hold the engine.

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

Step 6.
No the time for hacksaw . Using permanent marker I draw the cut lines and holding engine in a vise I make all the cutting. Believe me it is very easy part. Aluminum case is very soft but easy to cut (doesn't stick to blade). All cut out aluminum weights 3.8 oz (yes, I collected all pieces and put them on the scale).

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

Step 7.
I finish and polish the all cuts with sanding drum mounted on rotary tool (Dremel). It works very well and doesn't take long.

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

Step 8.
Now clean off al aluminum dust befor you remove the protection from the crankcase. Compressed air and brake pads cleaner works fine. And the engine is ready for new prop hub, electronic ignition and muffler.

Bare engine weights 23.9 oz. Original carburetor weights 6.5 oz. Prop hub about 1.5 oz. So the engine can be less than 32 oz plus muffler, radial mount, and ignition module. This is the weight of 'brand name' airplane engine of that size.

I'm going to use gasoline with glow plug on my engine. So entire ready to fly weight will be:
Engine (with prop hub, carburetor) = 31.9 oz
Muffler = 4 oz
Radial mount = 2 oz
On board glow battery = 2 oz
---
Total = 40 oz. I think it is not bad at all for the power, performance and fuel economy.

RysiuM

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

Here is the part two. It is not really instruction but shows all the components that makes the engine you can put on RC airplane.

To understand exactly what is expected weight of this engine here are all the parts put on scale.

1.Engine

Engine alone with cut all excessive aluminum. This engine will be used with glow plug, so I removed magneto parts. If you want to use electronic ignition the pickup can be easy mounted near the front bearing. Spark plug / glow plug is removed as I wanted to show it separately.

Total engine weight is 22.8oz

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

2. Carburetor

Stock carburetor (ZAMA) the one that came with the engine. Not much can be done to make it lighter unless you want to machine some aluminum of carb body. The bulky spacer is quite big and heavy. It is over 1 inch long (about 26mm) and weights 1.7oz. I believe the new spacer can be made at least 1 oz lighter. I will think about it.

Total carburetor weight is 6.5 oz

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

3. Muffler

Inverted muffler from Whackerengines is very light. I didn't include screws, but I didn't cut opening for engine's exhaust port and I didn't drill mounting holes yet. So this is 'bulk' muffler (I ordered such from Whackerengines as I wanted to decide later how I will mount it on the engine. I also have one gutted stock (original) muffler that weights 4 oz.. I opened it (it was quite difficult to do that), then I removed screens and metal dividers, and finally I drilled two 14mm exhaust holes. I didn't put any tubes do it is good only for engine testing. For flying I will use Whackerengines muffler.

Total muffler weight is 3.7 oz

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

4. Radial mount

My radial mount is made of piece of 6061 aluminum 3mm thick. First I cut it rough with hacksaw then I mounted on my lathe. First I cut the center hole, and then holding it from inside I cut the outer circle. The top part doesn't need to be round so I cut the top part flat with hacksaw. This mount still can be lighten up without weakening it, but the save may be 0.5 oz or less. I didn't bother. Four aluminum stands off and four screws are also included in the total weight. It is difficult to see it on the picture, but on stand-off is 2mm shorter. It is how it fit the engine. Three are 15mm long, and the shorter is 13mm long. Hole is 4mm for 6-32 screws and outside diameter is 8mm.

Total radial mount weight is 2.2 oz

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

5. Prop adapter

The prop adapter is a little different that you can buy from Whackerengines. The main difference is that the front part included 5/16-24 high grade steel screw. The prop must be drilled to 12mm to fit on the hub but the prop nut goes on the hard steel. I didn't like the common solution, where you screw the prop with the bolt using the thread in aluminum. With my solution you can tighten the prop without stripping the thread in aluminum. The back side doesn't need to be so wide, but as I don't have a flywheel I wanted some kind of shield in front of the shaft bearing.

Total prop adapter weight is 1.5 oz

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

6. Glow plug with adapter

Glow plug in glow plug adapter. The adapter is made of gutted spark plug, that has been turned inside to 8.5mm ID with small step 1mm long to 9mm OD on the piston end.. Then I turned aluminum plug 6.25mm long 8.57mm OD with 1mm step to 9mm OD at one end. The plug is threaded for glow plug 1/4-32. Now the plug was pressed into the gutted spark plug, and then again re-threaded (the plug compressed a little). I had to shave it a little from the connector's end on order to fit the glow extension.

Total glow plug with adapter weight is 0.5 oz

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

Summary:

Now let's add all parts together:

Engine = 22.8oz
Carburetor = 6.5 oz
Muffler = 3.7 oz
Radial mount = 2.2 oz
Prop adapter = 1.5 oz
Glow plug with adapter = 0.5 oz
-------------
Total = 37.2 oz

My scale shows 37.5 oz. This is because of rounding with scale accuracy +/- 0.1oz.

If you want to go with electronic ignition you need to add 0.5oz for spark plug instead of glow plug and all the weight of the ignition module. Other than that it is the same engine.

RysiuM

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

do you have any performance # for this engine?

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

This is the same engine described in the tread[link=http://www.rcuniverse.com/forum/fb.asp?m=3082557]Poulan 25 from FL trimmer [/link]. On MA 16x6 (classic) it turned 7300 with magneto idling to 1800rpm. With glow plug i went to 7400 rma with idling 1600rpm. I have also [link=http://m.modelersinc.home.comcast.net/poulan.wmv]test run video[/link] over there.

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

How did you set up the throttle linkage on the Poulan since the carburator is not in the best of position ?

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

There are many ways too do it. Most of gasoline engines have the same problem (including "RC engines"). The way I did with my Poulan you can see [link=http://www.rcuniverse.com/forum/fb.asp?m=3109524]in this post[/link] (look at two left-bottom pictures).

EDIT:
I apologize for linking forth and back - I hate it too. ;)
So just to keep this thread more on the information side I copied here my pictures of throttle linkage.

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

Really nice work Rysium. Now we have a good thread to refer all the newbies too. Well done.

AV8TOR

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

Nice RysiuM,
were did you get the linkage? Are there plans to port this engine? Stuff the case? maybe test a bigger carb? Did you run a compression check? Did you degree the motor?
Mine is on the bench. I have a Carr Precision prop hub and mount. Same muffler as yours. Hope to have in together in a few days. I've been following your posts in the glow/gas and I know the mix works on a homelite.

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

Did you use the carb that came with the engine without mods?

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

dirtybird Check out post #13 for a number of good ideas on how he dealt with the original carb.

RysiuM , Again thanks for taking the time to furnish us with so much infomation on your conversion.

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

I don't see anything on the carb in post #13. In post #19 he shows a lot on the carb but he is showing it in the gas - magneto configuration. It also seems he has adjustable jets. The ones I have do not have adjustable jets.
I also wonder if he used that carb with glow fuel. If so how?

RE: Step by step converting Poulan 25cc FL trimmer ($25 on e-bay)
 

This is ZAMA carb that came with the engine. It has limited adjusting on Hi and Lo needles. However it os not good carb for glow fuel unless someone knows how to modify it. I was not able to adjust it porperly running on 50-50 gas-methanol fuel. Even with 30% methanol the transition was not as good as on pure gasoline - and I was not able to find a Hi and Lo needle setting for it. Finally I decided to run it on 10% methanol - 90% gas fuel. The engine has the most power of this mix and transition is still good.