Guys,

I have this old chainsaw that won't run (probably just a problem with the sparkplug), so it's an excuse to convert (what for, I don't know, it's just another engine).
Is is worth it? From what I gather around this forum, it seems to be a bit of a pig for conversion...

http://www.mccullochservice.de/image.../800lserie.pdf

Any input is greatly appreciated. Thanks! [8D]

I've had a 835 and a 838 for a few years as chain saws. The engines run nice and should be good in a model airplane.

I have a couple McCulloch weed whackers converted which work nice as model airplane engines and the chainsaws have even better timing.

The saws have a plastic case with a engine unit that is easily removeable. The carb is of generous size with dual needles, so should not need replacement.

I have found that the engines really wake up to take all the baffles out of the muffler.

Looks like it will convert easy enough, and at 35cc it should do pretty good on the 120 size planes

Is timing the only difference between the Saw engines and the Strimmer engines? If converting to ECDI would the timing be set the same, and at what degree BTDC? Thanks.

Sincerely, Richard

he means port timing, saw engines have more favorable exhaust port durations than trimmers.

They usually have larger ports too, and often come with a suitable carb so you don't have to look for a larger one.

What I often do when I am considering an engine is look around on the internet for a "blow up", (diagram) of the engine. That way I can see how it's made as far as whether the crankcase is part of the saw or not, where does the carb mount and exhaust exit, etc., to see if it is a good candidate for airplane conversion without even having to disassemble it.

The "crankcase being part of the saw" isn't always a deal killer though. If it is otherwise a good engine to convert, those often make the lightest engine but they require a lot more work cutting the engine out and coming up with proper mountings....

AV8TOR

I have a Mini Mac and though the engine is made and runs a lot like the others, The carb is in the wrong place.

Took it out, and it looks neat after all the years of work, with what seems like a small play on the conrod. Mind you i haven't opened it up.

Also, compared its weight with the Homie 33 I took a year ago from a brand new saw (it is still unrun), and it will be lighter than the homie once the excess aluminium and crank is cut.

the one down side I see is that it has roller bearings on the crank not ball bearings, but if you make/buy a thrust bearing it would probably be fine.

The muffler most likely has an inner baffle plate that can just be removed?

Hmmm, how would I put a thrust bearing there? Doesn't seem to have enough space for one on the crankcase to be a bolt-on substitute.

Yeah, the muffler had a baffle

Okay, opened the crankcase up.

It's filled with dirt inside, and the piston leaks quite a bit past the ring. It's a no-no this one...dang[:'(]

I've taken .020" brass shim stock and cut washers to place between the front bearing and crank, but if you go to your local hardware store they usually have the little bins and usually some bronze thrust bearings in there but the closest they had was twice as thick as the space I had available.

If the bore and piston look in decent shape there's always a frank bowman ring, should wake it up, ring land might just need freshening.

I decided to give it another chance then.

Cleaned the bore really well, took out all the crap inside (including left over gasket sealant, must be cheap in Mexico, where it had been assembled), did the same for the lower half of the crankcase.
The rod and its bearings took the same treatment, removed the ring and gave the piston ring skirt a touch of 600 grit sandpaper. All decarbonized the best I could.


The crank is composed, on both sides, of a thrust washer, needle bearing, and a brass covered crank seal. Just made sure the crank travel on the prop side was just enough to keep the crank hitting the case on the inside.

Assembled it with gasket sealant (just a touch) and threadlock on the crankcase bearing surfaces and screws.

I gotta say, even though I lubed it up with chain grease (had it at hand), this little guy has some kickass compression![X(]


EDIT: Forgot to add, the weight as is is 1914 grams [:-]

mac motors are putting out more hp than most motors and are built better than most