Was looking at the exploded schematic for my OS .40 engine last night. And noticed the piston doesn't have a piston ring. Am I missing something? How do you get any compression without a piston ring.
signed a dumb new flyer
Newbie Engine Question
Sep 19, 2003
3 Replies
There are both ringed and non-ringed engines on the market today. Typically, a non-ringed engine is of the ABC type or something similar. ABC means Aluminum, Brass, Chrome which corre- sponds to aluminum piston and chrome plated brass cylinder (some engines are ABN; aluminum, brass, nickel).
Anyway, with ABC type engine, the cylinder is usually "choked" meaning it is slightly smaller in diameter near the top, resulting in a some- what tight fitting piston. As the engine warms up the cylinder expands just enough to allow a tight enough tolerance between the piston and cylinder that a piston ring isn't required. Ringed engines have a little more space between the piston and cylinder.
Hope this helps.
DS
On non ring motors, the cylinder sleeve is tapered at the top of the sleeve. Thats how it gets its compression.
The piston is a very close fit in the bore. The oil from the fuel forms a seal between the piston and cylinder.
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