Iseem to have caught this conversion bug and couldn't resist picking up this Stihl 066M for next to nothing. The seller said it had no spark - probably needed a coil, but had good compression. Well, it did have compression, but not great. He knew nothing about the saw or its history.

The rings are stuck and virtually welded to the piston on the exhaust port side. There is some scoring of the cylinder around the exhaust port. I didn't check the cylinder for roundness. The wear inside the cylinder is actually quite smooth except for a couple of small areas were there is some gouging (probably a couple of thousandths deep)

Anyway, is there any way to salvage this project without buying a new piston and/or block?

The last picture is a closeup of my plane tonight as Iwas packing up. It and Iwere covered with those friggin' No-see-ums (<span style="font-weight: bold;">Ceratopogonidae)</span>. Real fun having them bite the inside of your ears and nostrils while you practice your sequence flying. There were so many of them Ithought I was in Stephen King movie or something.

Thanks All

If the rough cylinder is below the exhaust port then you could be okay.

I'd lightly sand the cylinder with 600 grit just enough to break the glaze.

The piston looks rough, but there is hope.
Pull the rings off. The part that is covered my melted piston needs to be dug out.
Use the broken ring to clean out the ring grooves.

Again lightly sand the piston to find the high spots.
Take off as little as possible.
Then have the piston Glass Beaded.

Send the cylinder and piston to Bowman for a custom set of rings.
I don't remember his email address but it starts off as ringmaster@

I'm sure someone will step up and give you the rest of the address.

Now if you can afford it buy a new piston, but I have saved pistons like yours before
But they are never as good as they could be, and they were for chainsaws not airplanes.

The 066 is a great saw, Pound for Pound the best.

Gut the muffler and add 2 5/8 exhaust tubes and it will really wake up.

Good Luck

Its [email protected]

Thanks for the info! Acouple of questions:
<ul>[*]When you say sand the cylinder you mean a sheet of sandpaper and some elbow grease? No special equipment? Wet/Dry?[*]I'll have to look into the glass bead peening for the piston - not sure if it's available locally. What would be a reasonable price for this?[*]When pricing new pistons I came across some aftermarket cylinder/piston kits on EBay and Woodland International. They have NiSil cyilnders and Moly coated pistons. They run from $100-120 USD. Does anyone have any experience with these. i.e. how do they compare with the OEMparts which seem to run about $200 USD?[*]Ihaven't tackled removing the clutch assembly yet. Are they LHthreaded?[/list]Thanks again for the help

KD<br type="_moz" />

* When you say sand the cylinder you mean a sheet of sandpaper and some elbow grease? No special equipment? Wet/Dry?

It doesn't really matter because you are only going to sand enough it break the glaze on the cylinder.
A sheet of sand paper folded in 4ths works

* I'll have to look into the glass bead peening for the piston - not sure if it's available locally. What would be a reasonable price for this?

I's say $5.00 maybe $10.00 at the most. Most automotive machine shops have one.

* When pricing new pistons I came across some aftermarket cylinder/piston kits on EBay and Woodland International. They have NiSil cyilnders and Moly coated pistons. They run from $100-120 USD. Does anyone have any experience with these. i.e. how do they compare with the OEM parts which seem to run about $200 USD?

Stihl parts are really over priced. Here in the States you can only get parts from a dealership.
Check out the eBay sellers rateing. I would guess their parts would work out nicely.

* I haven't tackled removing the clutch assembly yet. Are they LH threaded?
If I had to guess I'd say Left Hand threads. It's been 15 years since I worked on one.

The cylinder didn't look that bad. I even blew up the picture. You could probally get by with just a piston.

When you LIGHTLY sand the cylinder,
Hold even pressure against the wall and rotate the cylinder back and forth while rotating it all the way around.
Just enough to get rid of some of the marks on the wall.
Then reassess the condition of the cylinder.
A new picture would be nice.

New rings from Bowman will make a big difference in the engine, even if every thing is new.

Okay so Idid some light sanding with some 600 grit, and the area around the exhaust port is better, but not perfect. It's finger-smooth around the whole port, but not fingernail-smooth at the corners, above and below. I tried to take some more pictures, but I'm having a heck of a time getting my stoopid camera to focus and get enough light in there.

Anyway, I didn't want to sand any more in case I started ovalling the cylinder.

I think I'm going to order a good aftermarket piston and a set of Mr.Bowman's rings and give it a try with this jug. If it doesn't work out Ican try one of the aftermarket cylinders as well.

I have been cruising the chainsaw forums and some guys are turning this engine at over 11K with porting and exhaust modifications! Should be a beast if I ever get it to run.

Thanks again for the help

It looks like it cleaned up nicely.
There does seem to be some metal pushed up into the exhaust port.
See 2nd picture left hand side of port, and a shadow in the exhaust port near the center.

These need to be cleaned up. They could catch a ring and wreck everything.
Simply sand a slight bevel around the exhaust port.

Sanding the cylinder out of round is not your problem.
Sanding through the cylinders coating is what you needed to be concerned about.

So clean up that port and spray the walls of the cylinder down with WD-40.

You will be amazed with the power of this saw. It's a Hot Rod in stock form.

Keep us updated ....

Okay - you asked for it...

Iset about trying to get the crank out of the case by splitting it open. Turns out it's not that easy. The bearings are press-fit into the case, and there are two very-clerverly concealed dowel pins that need to be tapped out. I kind of wondered why the guys on the chainsaw forums were making such a big deal about splitting the crankcase on these engines....

Anyway, Stihl makes a whole range of special pulling tools and jigs to extract the case halves from the bearings and crank - VERY expensive. I am off to pick up a gear puller or two, and then I'll machine some flanges that Ican attach to the case via the screw holes around the crank and pull them off. Sheesh!

Also pulled the carb and had a look. It's a Walbro WJ48 - 19.05mm venturi. Interesting scoop above the diaphragm. Should Iplug that off and tap it for a nipple or leave it alone?

Ilearn and learn and learn... Just not fast enough to keep me out of trouble.

KD

I was thinking you could cut it down without splitting the case.

Iwish I could do it without splitting the case but I was going to use the crank as a mandrel to machine the prop adapter. I decided to do it that way after failing so miserably with one on an Echo 50cc short block a few weeks ago. Also, so much crap has fallen into the case from me monkeying around (the whole thing is caked with sawdust and chain oil) I need to give it and the bearings a good cleaning. I figure it will be easier to machine the halves in my mill too.

And then there's the fact that it now needs a new center gasket, thanks to yours truly

KD

Piston is shot get a new one.
Jug looks like you are already through the chrome in a couple places, its not worth putting time and money into it.Get a new one.

Hard to beat the new head/piston for cheap on eBay. Still a good deal for a 90cc engine.

I ordered a new cylinder and piston kit from Bailey's Online for $119. Ithink I'll still get Bowman rings for it. The Ebay kits are cheaper but Bailey's has an excellent reputation for backing up what they sell.

Use the stock ring set, its designed for the piston and is compatible with the chrome. They are designed for proper sealing and long life.Using aftermarket parts is asking for trouble.

And Bowman rings are designed for improper sealing and short life? This is news to me.

Trouble is my middle name, Mister.

Actually, using OEMparts from Stihl would cost almost $400 and they're only available through dealers. Kind of defeats the purpose of the exercise, no? From what I read about the aftermarket kits on the chainsaw forums, they work great for most people who use them. Apparently the most common problem is the rings, which aren't manufactured with the same Q.C. as the other parts. This is my thinking vis-a-vis getting Mr. Bowman's help.

Thanks for the feedback

Have in the past bought a head assy for a 3120 Husky, is everything needed, looks great, assembles great and has compression like no tomorrow. The chances of it wearing out on a plane are slim, more likely to crash it first. Am looking at some heads for the 090 Stihl on eBay, cannot beat the price at $129 for such a big engine.

Here is a man who has never owned a Bowman ring.

Bowman's the best!!

AV8TOR

Never owned a bowman ring never will.

I have a freind who owns a stihl dealership, his favorite saying is "you can pay me now or pay me later" your call"

You are second guessing a large company with vast resources and experience.

Most of us trust Bowman Rings more than what came in the engine. I have used them for about 10 yrs and never had any problem with them.

His work is the best

I doubt Stihl even makes their own rings. They are most probably out sourced to specifications from the lowest bidder

Then you will never know what your missing.
But you will hear about it.

I don't know how or why but Bowman rings just perform better.

If it works for you more power to you, but you can hardly go wrong with the factory parts.Over the years seen too many claims that failed to live up to expectations, makes you skeptical of everyone. Seen it in dirtbikes, boats, cars, snowmobiles, lawn tools. If the factory is willing to use the parts that they do and put a commercial warrenty on it , then thats what I'm going to use and recommend.

The problem with being closed minded is you miss out on some real cool stuff.

But on the other hand it's okay to be narrow minded if your right.

Life is a balance, isn't it.

I'm not closed minded, prove that these things last longer, seal better, then I'll beleive it. You read a bunch of ballyhoo on the internet and it becomes gospil? hardly. Must be a west coast thing, no one here runs em.

But back to the main topic. If a salvage motor is damaged beyond what you want to spend to fix it, why not move on and find a better one? I don't bother with conversions if the motor is of need of major repair to start with.

Did you miss this post from the moderator?
"Most of us trust Bowman Rings more than what came in the engine. I have used them for about 10 yrs and never had any problem with them."

He is not on the West Cost, he is from Ohio.

Bowman him self is from the Mid West

And Gospil is actually spelled Gospel.

Spend the $12.00 and see for your self.

Has anyone reading this ever wore out a set of Bowman rings?