Q: I have several wide deck cylinders (for a Lycoming) 360 but the deck is a little bit thinner than normal and the deck looks like it is milled or radiused around the attach nuts area on the deck.
I’m not sure where I got them from, but are they early style wide deck? Can I mix with other thicker wide deck cylinders?
Are Lycoming pistons marked for weight class anywhere and maximum gram difference between? Could you recommend any SL or SI regarding this?
Jahn Mueller, via email
A: Hmm, wide deck cylinders with a thinner flange thickness from a Lycoming 360 series engine and looks like the area has been milled and radiused (I’m not certain this is a proper word, but you know what I mean). Jahn, that sure sounds to me like it’s a narrow deck cylinder configuration.
From your description, it seems to me that the cylinders with the thinner flange and different machining are narrow deck and are used with a cylinder hold down plate (some people call them banana plates). This was the combination of components used prior to the introduction of the wide deck cylinder design.
The cylinder hold down nuts used to attach narrow deck cylinders using the plates were the internal splined barrel nuts. Wide deck cylinders with the thicker flange use a regular hex nut to attach the cylinder to the crankcase.
A quick check of the proper parts catalog for the narrow and wide deck models of the Lycoming series may provide the answer. I’d suggest you refer to Lycoming Parts Catalog PC-106 for the narrow deck configuration and PC-306-1 for the wide deck configuration.
There is one absolute in this entire situation and that is the two types of cylinders you mentioned cannot be interchanged.
With regard to the piston weights, many Lycoming pistons will have a large letter “S” stamped following the specific part number. This indicates this piston is compatible for use with all pistons of the same part number.
It’s been my experience when I’ve had the occasion to weigh Lycoming pistons that they are all very close in weight, which allows certain pistons, like the part number 75089, used on certain Lycoming 360 series engines, to be manufactured to a mean weight allowing them to be interchanged with any like part number piston.