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· Sears tinkerer
94 Posts
Discussion Starter · #1 ·
Anyone ever broken a piston? I removed the head on my SS12 to clean carbon to see if that would help my low power under load situation and I discovered that there was a 1/2 to 3/4 inch section of the piston missing.

i almost have the engine all the way down (still working on the pulley) and will be ordering a piston and ring kit to get her back on her feet.

Any tips or hints for a successful rebuild?

· 20,000 +posts!
20,933 Posts
Only engine I had with piston damage was a '79 Chevy 250 six,its #6 piston lost chunks at the edges and the top ring was exposed,at 117,000 miles..I think a combination of lean mixture from the "Varijet" 2 bbl carb and the "camelhumper" intergrated cylinder head design noted for being prone to preignition and pinging is what blew the piston..

The only small engine I saw with a blown piston was an old wisconsin I found in a scrap pile--its piston was snapped off right at the top ring groove,and the head of it was stuck at the top of the bore!..I thought it had a broken connecting rod when I saw no movement of the piston looking in the spark plug hole,but when I took the sump off,I saw the rod and the rest of the piston was intact,and the motor wasn't junk!...the cylinder wasn't scored either,I got a new piston (65 bucks!:eek:) and honed it lightly and reassembled it,and it ran great again..

I'd hone yours only enough to get a good cross hatch finish on the bore,avoid temoving much metal if at all possible,if your using "standard" size piston and rings..and lap the valves while your in there too,and ensure the stems on them aren't worn or the giudes aren't sloppy..usually not much else goes bad on the HH Tecumsehs..

· Registered
42 Posts
You know the old HH engines were pretty high compression
mixed with carbon buildup it gets even higher. Detonation probably burned the
piston away a little at a time.

Ive got my old hh120 and I had to convert it to points using hh100 parts
unfortunately I lost my compression release doing that and its a PITA
to start, I have to use the booster to get it to spin over.

These old engines were designed for leaded fuel and octane back then
was higher.....

I love the old thing, it powers through the lawn in 3rd gear wide open
with no troubles at all, its a beast....

· Registered
107 Posts
Right now its just not moving. What kind of puller would work best?

I have removed all the set screws and have soaked with WD40 first, then Liquid Wrench but no luck yet.
I find PB Blaster works better, give it a try with a good puller.
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