advice on piston and cylinder for old Stihl 051AV

[edbee]

I recently purchased a Stihl 051AV (89cc) saw. It isn't running as it needs a coil and the piston appears to be worn out: smooth but with some vertical lines visible when I removed the muffler. I plan to get a new cylinder and piston for it but am wary as it sounds like there is some junk on the market (I am relatively new to this, this'll be the first chainsaw I have ever rebuilt.)

For the cylinder and piston: any particular vendors anyone can recommend who tend to have better quality items? (I am in Canada but often have stuff shipped to Washington State as that is pretty close to me and saves crazy shipping prices.)

Thanks in advance!

 

[Cliff R]

Did you do a compression test on it?

I've seen P/C's torn up 100 times that bad that cleaned up and worked fine without replacing any of the parts. Minor scratches to the piston don't tell us the condition of the cylinder bore and rings. It may be just fine and not need the piston or anything else replaced......

 

[Vintage Engine Repairs]

Take the head off and measure the skirt to cylinder wall clearance. More than 0.14mm change it out. Under that and leave it. Also measure ring end gap. Anywhere between 0.2mm - 0.5mm and you’re good.

 

[89HD]

I’m working on the same saw right now, I think you can clean up that cylinder and piston, maybe put some new rings in.

 

[edbee]

Thanks for the feedback everyone. I'll do a compression test and also measure the piston to cylinder wall clearance (and inspect the bore) and then decide what to do.
I definitely will need to buy a coil. I bought this as a non-running saw as it had no spark. It came with 2 coils and 2 chips and I was able to get a good spark by mixing and matching ignition parts so I thought that the ignition was sorted but then once I put the saw back together... no spark again. Unfortunately, the "good" coil has an intermittent open circuit in the primary winding. I see there are replacement coils available on eBay for around $35 USD but I am a bit hesitant as one of these 2 coils that came with the saw was "brand new" (bought by the previous owner just before he gave up on the saw). If anyone has had good luck with any particular aftermarket coils, I'd be happy to learn which brand or vendor.
Thanks again.
PS - not sure if one can upload videos here so this is a youtube link to testing the ignition (note that in the video the spark looks intermittent but in reality it was consistent during that test)

 

[89HD]

When you put it back together did you have the air filter base grounded?
Piece #19 in the picture

 

[edbee]

When you put it back together did you have the air filter base grounded?
Piece #19 in the picture

Well, that is an interesting question. I wondered about that piece, #19 in the diagram. It was connected to the air filter base but the hole at the bottom end didn't really line up with anything to bolt to so it was just sitting against the case. I don't think that was an issue for me though as I believe that would only have to carry any current if you put the kill switch in the 'off' position, and I disconnected the kill switch altogether when I was testing (after assembling the saw). Although, wouldn't the carb studs go into the cylinder so they would ground the air cleaner base?

 

[Mad Professor]

The Stihl 1111 series is 050 051 075 and 076.

Not sure how many parts they share that will swap out? Others here might know.

 

[89HD]

You do need something to ground that base it’s insulated from ground because of the intake block studs for the carb do not go thru to the cylinder.
The bottom end of that #19 goes between the tank and cylinder shroud.
Give it a try again, those coils are usually pretty good it’s the triggers that go more often