Radials

Posted by sassinator13@reddit | flying | View on Reddit | 7 comments

Every time I see video of people turning radials to get the oil flowing before a start, it's always in the actual running direction. Is there any reason for that, or could it be theoretically turned the other way?

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7 Comments

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wisehope9@reddit

"turning radials", I was confused about some VOR thing that.. involves oil?

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BrianAnim@reddit

I thought that too when I clicked the link.

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f1racer328@reddit

Radial engines

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wisehope9@reddit

Yep, hence the oil.

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usmcmech@reddit

Getting the oil flowing is nice, but the real hazard that they are checking for is hydraulic lock. If oil has collected in the bottom cylinders then it will severely damage the engine on start up. Turning in the direction of operation helps open up the valves in the proper sequence allowing small amounts of oil to be pushed out of the exhaust. Serious hydraulic lock requires removing the spark plugs and allowing as much as a couple gallons of oil to drain.

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sassinator13@reddit (OP)

Thanks!

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taint_tattoo@reddit

u/usmcmech has the right answer. You're moving oil from the cylinders to prevent hydraulic lock, and you want that oil out (past the exhaust valve) rather than trying to pool it up behind the intake valve - where it would then go right back in to the cylinder as soon as you bump the starter. As for lubrication and the direction of travel, think about this: does an oil pump push the oil in the correct direction for lubrication when it's going backwards? (In general, no) On engines that have a dry vacuum pump (most flat engines), turning the engine backwards can break the vanes in the pump. Not a problem, generally, with a wet type vacuum pump.