Lycoming O-235

[LowNSlow]

Has anybody had experience of uprating the common 108 -118hp O-235 fitted to assorted Cessnas, Pipers and Airtourers to the 125hp O-235-F (or G or J) model?

Looking through the parts manual the only difference appears to be the high compression pistons - Low compression (yes really that's what it says!!) / 8.5:1 / 9.7:1 are availabe.

There are alterrnative carbs and mags in the book as well so there may be differences that can't be covered by re-jetting and re-timing but it appears relatively straight forward.......

[Silvaire1]

Do a search on the Sparrowhawk STC & conversion, which is (as you note) basically higher compression pistons. This should answer a lot of your questions.

[Big Pistons Forever]

Lycoming does not recommend this mod due to the danger of detonation. See the user tips section on the Lycoming web page.

[peterc005]

I had to recently replace a couple of cracked cylinders on an O-320-E1A.

Too the opportunity to upgrade to a higher-compression 320-D1A by getting higher compression cylinder kits, which gives an extra 10HP.

Check the specifications of other similar 235 engines to see if they came fitted with higher compression pistons.

Probably not worth it if the engine is ok, but if you need to replace the cylinders/pistons it will cost about the same for the higher compression parts. You might need an Engineering Order.

Lycoming sells kits that include a cylinder, piston, rings, gudgeon pin etc for about $1,200 each.

[LowNSlow]

peterc005, the O-235-F has the higher compression pistons.

I've been trying to find out what aircraft were fitted with the -F, G or J model engines with no success so far.

Edit: Success, the A152 Aerobat had the option of the "Sparrow Hawk Power Package" which upgraded the engine to -F spec which put the power up to 125hp and brought the TBO down from 2400 to 2000.......:(

[baron_beeza]

I realise it is an old thread but I think for accuracy we should be saying the Sparrowhawk is using basically the 'J' series specs.
The 'F' series engine does not have dynafocal mounts so would not be an easy conversion for the C152 or PA38 installations.

The link to the TCDS may not be up to date but Note 5 gives an idea of the series differences.

http://150cessna.tripod.com/e-223.pdf

[LowNSlow]

Hi baron_beeza, I was looking at the F model as my Airtourer doesn't have Dynafocal mounts. My other alternative for more power without airframe work is to fit a Continental O-240 which is a much more expensive option requiring new mounts, cowlings and prop!

After reading your link it seems that the only difference apart from the compressions is the prop flange so a new prop would be required anyway.......

[baron_beeza]

Thanks for the reply. I was doing some more reading and came across some other sites that may be handy for you also.

http://www.eaa902.org/Lycoming_Engines.pdf

Page 29 of Lycoming SSP-401 has the aircraft the various models of 235 were fitted in.
It is possibly the answer to one of your earlier questions.

http://www.stinsonclub.org/PublicTech/YahooGroup/SSP-401.pdf

There may not be a lot of them with the -F, G or J series engine fitted.