Pro mac 8200 questions.

[idiotwithasaw]

Ok, after reading the ipl apparently the 8200 piston is 52.4 mm. Which is an odd size. After doing some googling I found some 4 stroke pistons not sure if these would work and if not why. I have yet to try and tear it down to measure height and piston pin to crown and skirt.

 

[PogoInTheWoods]

I realize this is an old thread, and probably a long shot, but....

Did you ever come to any conclusions or pop your short block to look at the piston more closely? Looks very much like the one in my PM8200 which seems to have been scuffed and pitted the same way vs. lean scored. My theory is sloppy sealant application during assembly breaking down and getting loose in the case. You may find that piston still usable with some gentle cleaning and smoothing. The rings on mine were still free, though there was some minor debris in the lands when I pulled the rings.

Was also thinking a piston from another saw may be the ticket. 2-1/16" or 52.3875mm is what the 82cc Macs are, but that's about it for that size. The other measurements for the Mac pistons would be the keys, but the main problem there is the wrist pin/circlip issue. If it were that easy seems like someone surely would have found a solution by now.

Anyway, just fishin' around and shooting in the dark on this. My next stop is an old sled rat guy up the road that may have an idea or two. And I heard yesterday about somewhere out in California that makes hard to find pistons. Minimum production run is like six units, but they're expensive.

 

[67L36Driver]

FWIW: The problem with four smoker piston is they normally have oil control slots.

What's odd about 2 1/16" bore?

I have one for a Homelite on my bench.

 

[PogoInTheWoods]

Which Homelite? Have a pic or two and some other measurements? And what else takes 2-1/16" -- 52.4mm windowed pistons?

 

[67L36Driver]

Which Homelite? Have a pic or two and some other measurements? And what else takes 2-1/16" -- 52.4mm windowed pistons?

My bad, 2 3/16".

 

[Al Smith]

Yall need to keep in mine with the exception of the PM 610,Timberbear types most McCullochs were made with SAE measurements .Trying to match one up using metric is going to be a challenge if not impossible .
You have to remember what you are dealing with .It's not as simple as installing Chevy 2.02 intake valves in a Ford 302 engine .

 

[PogoInTheWoods]

Right you are. That 52.4mm number is rounded up from 52.3875.

 

[Al Smith]

Send me a PM with an address .I have three little rolls of lapping paper,20,30 and 100 micron and two big scotch brite pads for you .

 

[PogoInTheWoods]

What? No 300687 in an old box ya forgot ya had? LOL. Thanks a bunch, Al. PM inbound.

 

[Al Smith]

Wish I did and the saw it goes on .The only 82 I have is a toasted piston from the only saw I ever straight gassed .I can save the cylinder but I need an A grade piston I think .It's another back burner project .I seem to have quite of few of those projects .

 

[Al Smith]

So more on this piston business .First of all my background .I've installed and maintained at least 5 piston manufacturing machining lines for both Honda and Ford.About every profile ever imagined except ceramic coated .

I've seen people polish them up like a mirror,looks cool but really doesn't do much more .Smooth but not polished works better .It sheds the oil film which is the liquid bearing the thing rides on which is already thin because it's in the fuel .I won't argue about the mix ratio,use whatever floats your boat.
Now trying to save a scuffed piston .A low spot unless it's huge won't hurt you too much but a high spot will break the oil tension on an already weak mixture .Once you break the surface tension it will be metal on metal and failure will happen,it's only a matter of time .

You can do fairly well with Scotch-brite .However often it takes some sanding to get a high spot out which is where the lapping paper comes in.This works better if you use something like kerosene with it .It lessens the paper or scotch brite for that matter getting loaded up as fast .Which due to fact it's aluminum it will .Don't be afraid to use a lot of it,it's cheap .

 

[PogoInTheWoods]

Gonna try Berrymen's Dip as a pre-soak for what I think is the gum impregnation from the sealant..., when i can get the piston off the rod. That's a whole other story in another thread. Gonna try to be patient until the lapping paper gets here and go real easy with some kerosene as suggested. "Preciate the help.

 

[smokey7]

If its a concern getting the piston off the rod for you. Just stuff the case with rags and a plastic bag and go to town sanding the piston while its attached. Just rinse the piston of any. Rubbish once done.

 

[Al Smith]

With the mention of Berrymen's this might be interesting .I remember them pedaling this stuff to gas stations in the early 60's .Back then it was made in Lima Ohio,about 3 miles from me .

https://www.berrymanproducts.com/about/company-history/

 

[PogoInTheWoods]

That's interesting stuff. The Ed Roth connection is a hoot. And we both spelled Berryman's wrong.

 

[Al Smith]

I think it was called B12 or something .It would unclog the lifters on Olds engines which for some reason always clogged up.Of course the motor oils of the 60's weren't as good as todays nor were the filters .Quite frankly neither were the engines .--good old days my foot ,I lived it ---

 

[PogoInTheWoods]

For anyone following this here, my PM8200 is back together and running with the refurb'd piston. More over in the Mac thread.