This post morphed into my EFCO 39cc project. It started as a question about scored pistons and jugs. Enjoy.

About half the saws I have aquired have scored cylinders and pistons. The one a stripped down today could have made a decent engine, a Homelite 42cc. To bad it is ruined. It is very low time, the top of the piston was hardly covered by carbon. You could still read the laser marked parts numbers on the top of the piston after cursory cleaning. The area around the exhaust port and less so the intake port were real badly galled. I tried smoothing it up with 400 grit paper but even the ring is damaged. The compression is poor. It is almost like somebody put dirt in the spark plug hole. The owner said his laborer told him it just stopped running.

So, is kind of thing usually from running gas without oil?

yup, see this everday.

I've seen guys sabotage equipment so they didn't have to work too.

From what I understand most oil is repelled by heat.

The exhaust is the hottest part of the cylinder, so it's the least lubricated.

That's why it's important to use the best oil and at the best ratio, to me that means 32 to 1.
50 to 1 was created to handle smog, not for engines to run longer.

The they put Carbs. on that can't be adjusted correctly so that makes them run even leaner.

It's a wonder chainsaws last as well as they do.

And yes, especially with piston damage around the intake makes me think no oil in the gas.

Many saws etc are returned for warranty, because the operator just put gas in it.
Oil? What's that? Engines run on gas don't they?

Just for yucks I attacked the jug with a hacksaw and belt sander. I got the short block assembly down to 2# 4-oz.. With the carb, muffler, hub and mount rails that should be less than 3#. It looks nice too. Can one of these scored engines be saved economically?

We are not worried about the piston/ring anymore. They are toast!

But look in the cylinder by the ports and examine the scratches. If there are deep gouges that you can feel with your finger nail the cylinder may be toast also?

But if your finger nail doesn't feel any roughness, a new piston and ring may save it

I'll put the Homelite it in the toy box for now. Thanks for the information.

I'd like to see a picture.

Can you post one?

When I ran a small motor shop, a customer brought in a lawnmower that was smoking like a fogging machine and wanted to know if I'd fix it. Did a minor check and took the air filter cartridge off and there was no filter in it. I asked him where it was and he told me he took it out because it kept plugging up. True story.

Some pics were asked for, here you go. On the left is the 42cc homelite. I pared down the extra bits for fun. Check out how trashed the piston is. Yikes! Never leave straight gas in the same area as illeterate laborers.

On the right is an EFCO 39cc. That one looks like a winner. It is ready for a beam mount, no mods. I only removed a little bit of extranious cooling fins. It has two rings and huge compression with very slow leak down. The inside is as pretty as new shiny penny. The hub came out straight first time, with in 0.002" wobble a the prop end, good enough for me!. Nottice the knurling? I did that with a regular old knurling tool. I set up the cross feed at 4 TPI and ran the edge of one wheel of the the knurling tool out from the center in back gear. One pass and done! I had been broaching radial grooves with the taper cross feed manually, a huge pain. This was about 10 second in back gear to do an equivelent job. The prop was about 1/8" of kilter a the tips. I fixed that with a file. Here is a tip, my new favorite cutting lube for aluminum is a shot of castor oil in mineral spirits. It makes the cuts really clean an smooth.

The efco sure is a nice engine. I like the soft carb mount!

I like the soft carb mount!................

Me either, I am going to try making a split ring out of aluminum that will make a flange on the jug projection. From then on it is the same as any other.

Nice work Scota. Good tip on the knurling.

The soft mount is an advantage. It allows you to mount the carb to the airframe, and iso-mount the engine. With the carb separated from the vibrating engine, you will see a lot less wear and tear on the carb. The "lack" of vibration in the carb will also let it meter fuel better!
IMHO, it is worth the effort to keep carb and engine separated as much as possible.

Huh, I'll kepp the soft mout idea in mind. Before I read that I made the carb manifold and split ring. The intake maniforld is bolted to the split ring. The split ring is afew thousands lower than the flat face of the boss on the jug. That permits a good seal. I guess the good news is that by using the split ring I did not mess up the jug. I could go ahead and use the rubber boot if it looks like and advantage.

Here is a tip for making two holes meet in the middle, like for the pulse pressure tap the carb uses. Look at the thing real carefully and make use the planned route does not come out the side. Start each side of the hole in the normal way. Put a slightly smaller bit in the drill press vice and secure it such that the bit in the chuck line up with it. Drill the hole a little alternatly from both sides using the bit shank in the drill table vice to align the work. They will meet up in the middle.

The carb should be isolated from the engine heat. You should incorporate a spacer that does not conduct heat or you will have hot start problems, or worse.

AV8TOR

I'll incorporate a phenolytic spacer. Just have not made it yet.

Progress is made on the EFCO. The ignition arrives next week.

Looking good

It runs! props, 20 x 8 6400, 18 x 8 7200rpm, 15 x 6 9200, it idles down to 1600. I have not messed with the timeng yet, it is 28 deg BTDC. The muffler is too heavy for real use. It is odd, to me that I pick up 100 rpm with the guts installed. The hub turned out nice and straight, it runs real smooth.

I had a thought for locating the magnent on the hub. Next time I will tape it in place to get the location before I drill the hole. Then I will fuss with it until the sensor is located in the middle of the ajustment range at 28 DBTDC. Once I know the exact location I will then mark it and drill.

Later that day.....

I set the plug to 0.020" gap and installed a Menz 21 x 8. The wider plug gap made it run a little smoother. I also packed the muffler full of chor boy scrub pad to keep the neighbores happy. 6100 and got the idle down to 1300. It is fun to watch it run so slow.