Higher Compression Cylinders on an 0-235-C1B?

[Ryall795]

I'm currently at a stage where I am going to need to have the engine in my PA-22-108 opened up and repaired (as/if necessary).

A topic of discussion that came up around the hangar has been the idea of switching out the 4 cylinders that are currently on the engine to the higher compression, less costly (parts wise) and more readily available L2C cylinders.

I've been trying to do a bit of research on this and have found information about converting the C2C to L2C, but nothing on the C1B. I'm suspecting that it would involve the same process of reaming the holes in the case for the through bolts (to accommodate the larger 7/16" bolts).

Has anyone had experience with this in the past?

For context, the aircraft is in the Canadian O-M category.

 

[Smokey]

I did a lot of research on changing a 235C1 into a later P high compression 125hp model for my Pacer. One of the best sources for data is the Lycoming table of Limits SSP-1776. There is a "Note" on the application page that reads exceptions for the 235 F,K,N,P suffixes only. So "A" is for the C suffix and "A1" is for all of the others. You would have to find all the "A1" applications to find the dimensional differences, my guess is that they are the rings, pistons etc.. Which leads you to Lycoming SI 1037 W approved pistons and rings. This has all the part numbers for cylinders, pistons and rings.

One of the biggest things I noted while digging around the table of limits (SSP1776) is that the bottom end components, main journals, crankpins, con rod big end dimensions are all the same. So... It should be within its capability to handle the increase in power over the C1b. I imagine that if you got your hands on a parts catalog for the "L" series you could determine the through bolt size. Lycoming always lists the thread and dimensions in the parts catalog. You could then cross that to the "C" series parts catalog for a comparison.

I also imagine the biggest difference in cylinders would be added fins for the extra heat. Dimensional should be the same. Another tool is to use the engine finder function on Lycomings website. For example the L2 fits the Cessna 152, which is why its economics are so good. I happened to use the P2 engine which only fits one aircraft, overseas... no parts availability, no support. But you should be good using the L2 cylinders

 

[dgapilot]

I'm currently working a DER approval to use the STC for the C2C to be applied to the C1. This will be for a Stinson 10. It can be done for any of the C series. The issue you will likely find with trying to do it on the Colt is that your 76AM-2 prop is limited to installation on an O-235 with a 6.75:1 compression ratio. If you go to the higher compression, you will also need to change props. Pretty much all the props for the higher compression O-235 engines are 70" or less, so will be less efficient. I suppose you could go with an M74DM prop, but you also need a new spinner and that prop is another 9 lbs. Recognize that the case will need to be machined to accept the heavier thru bolts, and the bolt kit alone is over $1000. So to do the conversion, you have the cost of the STC, the DER cost for allowing the STC to be installed on a different model engine, the cost of machining the case, the cost of the thru bolts and cylinder hold down studs, and cost of the cylinders and pistons let alone the normal overhaul items. When you add it all up, going with an O-320 starts to look like a better choice.

I've got the same issue with my O-235-C1 for my PA-16. Tore it down and have a cracked piston. I'm not anxious to go spend $5600 for a set of new pistons! Been trying to find some new old stock or serviceable used that are more affordable but haven't been successful. There are oversized pistons available, just haven't found standard yet.

Piston part numbers are 73851, 14B23919 or 14B28072. The ones currently in my engine are 73859, so if I found 1 of them I'd be OK. Otherwise I need a set.

 

[dgapilot]

I'm currently working a DER approval to use the STC for the C2C to be applied to the C1. This will be for a Stinson 10. It can be done for any of the C series. The issue you will likely find with trying to do it on the Colt is that your 76AM-2 prop is limited to installation on an O-235 with a 6.75:1 compression ratio. If you go to the higher compression, you will also need to change props. Pretty much all the props for the higher compression O-235 engines are 70" or less, so will be less efficient. I suppose you could go with an M74DM prop, but you also need a new spinner and that prop is another 9 lbs. Recognize that the case will need to be machined to accept the heavier thru bolts, and the bolt kit alone is over $1000. So to do the conversion, you have the cost of the STC, the DER cost for allowing the STC to be installed on a different model engine, the cost of machining the case, the cost of the thru bolts and cylinder hold down studs, and cost of the cylinders and pistons let alone the normal overhaul items. When you add it all up, going with an O-320 starts to look like a better choice.

I've got the same issue with my O-235-C1 for my PA-16. Tore it down and have a cracked piston. I'm not anxious to go spend $5600 for a set of new pistons! Been trying to find some new old stock or serviceable used that are more affordable but haven't been successful. There are oversized pistons available, just haven't found standard yet.

Piston part numbers are 73851, 14B23919 or 14B28072. The ones currently in my engine are 73859, so if I found 1 of them I'd be OK. Otherwise I need a set.

Update, I found a set of used 73851 pistons. I now have 7 so I can pick the best 4 of the bunch.


Sent from my iPad using Tapatalk

 

[RRHall]

Lycoming recently put out a bulletin dealing with 4 ring pistons in O-235-C series engines.

 

[lollyfin]

I looked into this a little while ago and was under the impression that it wasn't recommended due to the cylinder head studs being 3/8 and the higher compression engines run 7/16", due to issue of stretching. worth a look into.

Cheers

Rob