Rare odd cool bore 2hp?

old shed finds

Well-Known Member
#1
This engine was said to be the original engine on a 60s Arco Mini bike.... original shroud is missing. It got a crankcase breather with a louver instead of common rubber hose,it has the larger intake valve,,and most bonus the steel sleeve cool bore,Are these special mini bike Briggs engines? We never seen a steel sleeve 2hp till now.
 

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#2
What would be helpful are some more pics. If it's a 2 hp engine, I doubt it would have been on an ARCO. Correct me if I'm wrong, but my understanding is a Kool Bore is aluminum and not steel bore (makes a huge difference on the rings you use).
 

65ShelbyClone

Well-Known Member
#3
Iron sleeve means it is not a Cool Bore.

The CoolBore requires a chromed piston. I doubt the rings are any different, but don't actually know. The chromed pistons can be used in either cylinder type.
 

65ShelbyClone

Well-Known Member
#5
The Kool Bore pistons were indeed chromed. They have to be or the piston and cylinder will scuff. That's at least partly why the Chevy Vega had plated pistons too.
 
#6
I stand corrected... The pistons are chrome. There are different rings for the chrome piston. This clipping is from the Briggs 'Single Cylinder "L" Head Repair Manual'.
chrome piston 001.jpg
 
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