Other than knowing the brand, what's the secret to identification of any particular engine? I can see measuring the bore and stroke by taking the engine apart, but what if there's no other markings on a motor? I just got a Stihl engine out of an older FS-40 line trimmer, but it sure doesn't have the rail and rear mounting holes like the other Stihl motors I've seen on this site. It looks noticeably smaller than the Poulan 30cc I found. Is there a book or manual that has the info to determine exactly what critter you have on your hands?

I e-mailed Stihl for info on engines to find out CC'S, thats one way before stripping apart. Echo has a great site that you can down load the manual which gives you RPM, CC's ect..., I'm all eares on this post.

figuring out the bore and stroke can be done by taking the muffler off and the spark plug out on most engines if you have a caliper, with the plug out at TDC go from the spark plug sealing surface or wherever there is a good point of reference, set the depth gage thing of the caliper down the hole and to the piston and zero the caliper, go down to BDC and that will be your stroke, with the muffler off, zero it normally and lower the piston near BDC and put the base of the caliper at the piston and use the depth gage to measure to the other side of the cylinder

that's how it works, most of the other engines are just identified because they are something common, the exact identification of the engine doesn't matter really if you are making your own parts, and even if you're buying your parts there's a good chance you can find something that'll work if you find the threads on the crank, most engine mounts are over rated anyway...

You more than likely have a 22cc or 25cc.The only other way is to do as stated and check to see what the actual ccs are.
I use a popsicle stick.Find stroke as stated.use a pencil to mark the stick at the spark plug opening.[TDC,then BDC]
Use stick to measure bore.Insert stick and tap piston against stick and cylinder wall[top of piston].
Then heres your math equation,remember in school we said we dont need this stuff.
Divide the bore in halfWe will say your bore was 32mm and your stroke is 30mm.Use a clear plastic ruler to measure MMs.
Heres your equation[16x16x3.14]- [3.14-this is PIE rounded down].===803.14
803.14x30======240942this means your engine is a 24cc actual,closely.we only use the first 2 numbers.
Now the best kept secret is that most of the people answering the ID this engine question that seem like where the magical engine gurus is just that we have so many different engines from so many manufacturers sitting in our homes,sheds,garages,basements,shelves,closets[i have 5 in my bedroom closet right now].I have 4 on my shelf next to my lathe but ran out of room.That all somone has to do is ask about an engine and one of us will run out or over to our stash and answer all the mysteries there are so we can help out our fellow modlers.This is what i tell my wife,im providing an invaluble service to all the newbies who would be lost and confused with out me.Now this is a terrible addicting sickness but one wich somone must do.After you do your first engine conversion and you fly it,look out!

Yep, you sure are right Buck. I started out with a lowly 16cc Echo on a Big Stik. I loved it and never looked back. Now I have 5 airplanes flying conversion engines, my friends and family have engines flying converted by me, I've sold some, and I must have 20 good engines waiting to be converted!! (Nope guys, it's my prized collection and sorry, but I don't want to sell any.)

Your formula is correct, but I use "(bore x bore) x stroke x .7854". If you measured in inches, this will give you cubic inches. To get cc, divide by .061. Same result, different method.

AV8TOR

I'll measure the bore and stroke tonight (thanks for the tip on measuring the bore through the exhaust port!!!). It cleaned up real nice and the compression is good.

Any guesses?

BTW - if there is any interest, I want to ask my inlaws for a list of the abandoned power equipment they have on hand. Perhaps I can help find a good home for some of the engines and help my inlaws recover the $ they have in the repair? Anyone interested? They said it's mostly line trimmers, not so much the more expensive saws and blowers...

Wow, nice engine rear intake and exhaust. This makes mounting in cowled planes great. The Ryobi has the same setup but is not that great of engine. Did you say this is a Stihl? FS40. Looks Like a Ryobi 28 or 31 cc.

Yup,think i had one once.I think stihl came out with a cheaper curved shaft trimmer just for lower income population.I had one thinking it would be some great engine to convert and when i dismantled it thats what i found,a long shaft ryobi 31cc.sold it.
I kind of jumped to the gun when he said stihl without a pic.I have 2-22ccs.128cc.And 225.4ccs.
OOOOOPS,make that 5 engines next to my lathe,not 4.Not addicting my arse,i dont even remember what i have and its right next to me.

Ryobi, huh? It has the letters "ST" inside a big letter "C" on the lower right front of the crank case - wouldn't that mean "Stihl Corporation" or something like that? Also on the front of the crank case is a "5" with some dots on/around it and a raised "19". The jug has a "B" cast on the lower front corner and on the back a "11" on the left side of the exhaust port and the "95" on the other side. The carb is a Walbro, it has "Stihl" on one of the plates, "62-118" on the choke plate, and "WT 160B L" on the side.

The stroke came out to 1.300". It was harder to measure the bore since the exhaust port is split down the middle by part of the cylinder liner. I tried to measure it the best I could and got 1.350" on the diameter. That would work out to 30.49cc. If I was off on the bore by even a little (say it was 1.30 instead of 1.35) that could change the numbers by 2cc or so.

Even if it's a Ryobi, it's a lot lighter than the junk Poulan 30cc I got from a Weed Eater, and the compression is much better. There's no scoring on the piston or cylinder. I'm still going to use it. What's so bad about the long shaft? If you can't make a long spacer, can't we cut the shaft shorter and re-thread it?

It's a Ryobi! Stihl FS 36-44 are Ryobi's. Metric screws, different muffler, carb and reed back plate but Ryobi's....Bob

Hey farley,how ya doing,got snow yet?
NG,farley has a repair shop,he knows his stuff.Anyway,theres nothing wrong with the long shaft other than your right.You would just use a short hub,put prop on,then use a nut and washer on top.Or cut crank and rethread.Theres just to many shortshafts around that are easier and mine have 2 rings.[not thatr it maters much].Ive attached a pic of one of mine i sold.Converted to cdi ign.
Your also right about the ccs.Your so close at 30.49 that its a 31cc.If you want to use it let me know i have a hub setup already made for that engine that im not going to use.PM me if you need it.