Stihl fs74 cc?
 

I have a Stihl FS74 from a weedeater. I know it was posted before but can't locate it, what size is the engine?
It has a cable pull throttle slide valve carb which I will replace. Also using a cdi on it.

RE: Stihl fs74 cc?
 

Post a picture of it if you can. I believe it is a 27cc. If it has four mounting holes on the crankcase it is a 25cc, if it has three mounting holes, it is a 27cc. The 27cc is particularly easy to convert.

AV8TOR

RE: Stihl fs74 cc?
 

It has 3 mounting hold on the back case. Also, a module inside the back case for ignition pickup timing. Wondering if I can adapt my cdi and advance board to use that pickup.

John

RE: Stihl fs74 cc?
 

I think it was determined in that post the FS74 was 23.4 cc if my memory serves me correctly.

RE: Stihl fs74 cc?
 

I found the post and I was wrong it is a 23.9 cc. The link is below.
http://www.rcuniverse.com/forum/m_97...tm.htm#9924295

RE: Stihl fs74 cc?
 

Thanks for the info.. I have a 60 sized Stinger it's going on when completed. converting it to my cdi.

John

RE: Stihl fs74 cc?
 

I am trying to get the flywheel off of a fs80 Stihl engine. Tried a 3 finger wheel puller until it broke one of the fingers off. Tried a steering wheel 2 bolt style pulled in the holes where the clutch shoes used to be while using heat from a torch and having no luck. Any ideas besides a hammer and chisel?

John

RE: Stihl fs74 cc?
 

Man, did you take the nut off??

I usually just wedge two screwdrivers in under the flywheel however possible, screw the nut on the crank until it is flush, and then give the end of the crank a hit with a hammer. They pop right off, usually with no heat. I can't even remember the last time I had to heat one to get it off....

AV8TOR

RE: Stihl fs74 cc?
 

I have tried that trick with 2 screwdrivers...bent them both!!
Just tried some Loosenall liquid to try and dissolve any corrosion between the flywheel, shaft and shaft key. Letting it soak for an hour before I beat it's brains out with a sledge hammer. Was going to use the center of the flywheel as a prop driver/ magnet hub if I can salvage it. Metric threads on the shaft present no real problem... Just have to get it separated without totally destroying either the shaft or flywheel. Broke a second 3 finger puller lastnight. This is getting expensive! That was a Craftsman puller that cost me $50 !!!
Hope this last try will get it off. If not, out comes the Dremel cutoff disc!
Score will be Stihl -0 John -1 !!!!

John

RE: Stihl fs74 cc?
 

Well, keep us posted, and post pictures if you can. Craftsman tools are guaranteed. They should replace that puller with no questions asked. My brother has Craftsman tools replaced all the time.

AV8TOR

RE: Stihl fs74 cc?
 

While having tension on the flywheel applied with the puller, try hitting the crankshaft smartly with a hammer. If the puller has a bolt centered on the crank, just hit that bolt head. if you have to hit the crank itself, thread a nut on the shaft so you are hitting the nut and not the shaft threads. Since you have a heat source, maybe heat up the flywheel to expand it and then hit the crank. This approach has not failed me yet. Good luck.

Richard/Club Saito #635

RE: Stihl fs74 cc?
 

Well, it's finally off!!
I used the Mapp gas torch, heated the dickens outa it and grabbed the biggest hammer in the toolbox. Whacked that sucker and it came off with a loud crack!
It was definitely rusted fast and an extremely tight press fit on the taper.
Trimmed the housing off and it's starting to look like an airplane engine.
Next is using a hole saw on the flywheel to get the center for my hub. Cleaning it all up in a bucket of solvent to make it nice and clean.
What is the size of the fs80? 24cc ?
Pictures when it's cleaned up.

John

RE: Stihl fs74 cc?
 

FS-80 = 25.4cc

RE: Stihl fs74 cc?
 

This is not the newer FS 80 motor. It was manufactured in the 70's and 80's in Japan. I am not sure about the size of this old motor, but it's in decent shape compression wise. Propshaft end is very short metric threads and a taper for the flywheel. Does anyone make a prop adapter with internal taper to fit this Stihl? Don't want to make one that way if I can get the center out of the flywheel. I have lots of 1 3/4" hex aluminum which I use to make other prop drivers. I can post a picture of the shaft and a drawing of how I might make the adapter bolt onto the hub with the metric nut inside of it.

John

RE: Stihl fs74 cc?
 

This is a link to a picture of my FS80 engine I am converting. The shaft has a taper and I need a prop driver made for it. Any ideas?

http://db.tt/WFLlRTzs
http://db.tt/svMmZu3U
http://db.tt/ovmbmLVo

RE: Stihl fs74 cc?
 

Yeah, that's not like the newer 25.4 nor the 27cc engines. I like how the fins are rounded on yours. Looks like a model airplane engine!! ;)

Let us know how it runs, and good luck,
AV8TOR

RE: Stihl fs74 cc?
 

I am no authority on the making of prop adapters, but it looks like you need a two part adapter. One part fits the taper of the shaft and is held by the threaded end o the shaft and a nut. Then the second part is bolted to tapped holes in the first part. The second part is internally threaded either with one central bolt or four bolts spaced radially out from the )center. The prop is bolted to that (those) tapped hole(s). Some of the Chinese engines have this arrangement, and maybe one of those prop adapters might fit your engine? I think CRRC or CRCC engines had a problem with their 45cc engine adapters. Maybe search here for a thread on those engines for some pictures and things to avoid (like sharp corners with no stress relieving radii).

Good luck.

Sincerely, Richard

RE: Stihl fs74 cc?
 

I have made single piece adapters with cranks like that, you just have to take the key out and run a taper when machining the adapter and have internal threads to capture the stud sticking out and continue them through for the prop bolt. When I do that I machine the taper a little shallow so it is more of a press fit, and it hits the outside edge first and not the inside edge. It would take some careful measurements to get that one right though...

I have my McCulloch 32 machined that way along with my Pioneer 52cc, the Mac has a few gallons through it while the Pioneer only has a couple tanks.

RE: Stihl fs74 cc?
 

Maybe I can use the old flywheel for the taper part of the 2 piece adapter. It's extremely hard to cut thru it though and not ruin it for the intended purpose. Tried a regular hole saw and it started chewing it up really bad. Guess maybe I should drill a series of holes in that circle to part it off from the rest of the outside part. Done that with Macs before and a few Ryobi's. Still not an easy task later to true it up to use it. Planned to make the prop driver part and use 3 bolts and an aligning recess to keep it perfectly centered and the 3 bolts to mount it. Did it with 2 bolts on my Shindaiwa 20 cc and worked perfectly. Ran that one yesterday with a 15-10 and it was turning in the high 9,000's. Really a little screamer and it's going onto my 60 size Big Stik. Weighs a little over 1.5 lbs with gutted stock muffler and my CDI and timer board.
Well, guess I'll drill a bunch of holes then and machine off the rest on my lathe. Alot of ideas to ponder here.
Thanks!

John

RE: Stihl fs74 cc?
 

I've long since abandoned trying to duplicate the internal tapers when machining once-piece adaptors. It's not ncecessary. Just machine the large diameter carefully (tight fit). let the adaptor locate on thatit's good enough. Bore the full diameter all the way deep enough to completely extend beyond the shaft's taper. Or one can step it down in diameter, just make sure no part of the internal steps touch the taper. Then, after carefully making sure the adaptor will work as machined, do the final assembly and fill the cavity with JB weld. It will work fine.

RE: Stihl fs74 cc?
 

So, are you using a dial indicator and moving the hub as the JB dries to make it straight? Making straight prop hubs is my nemisis. They never seem to run smooth unless I have it to a couple of thousandths and use a balanced prop.

Tapers are not a big deal. set your crank between centers and use a dial indicator to set up the compound feed. Put sharpie marker on the crank taper to check you progress. It will rub off of the tight spots during a trial fit. Do not remove the hub from the chuck until all the boring is done.

I have thought of machining the outside of the hub, on the crank, in the lathe with the steady rest on the bearing. Then use a stud made of all thread that is glued in place with JB and pushed in to exact alignment. Is this the only way to get it perfect?

RE: Stihl fs74 cc?
 

Sounds like you are doing everything right. Mine come out well and all I have is a cheap small Harbor Freight lathe. I even did two of those BME twin 23.6cc engines on this lathe, machining the cranks, prop hubs, everything. They run so smooth you can set a drink on top of the airplane and run it through the rpm ranges and it barely jiggles the liquid...

Maybe get your center bore, taper, and threads done, then install the blank on the crankshaft and finish machining it into a prop hub with it mounted to the crank??

AV8TOR