Replace stock O235 engine with O320-E2G AirModsNW STC
From Bondline
Bob Steward suggested I create a page here in an attempt to describe my process of performing the engine upgrade from the O235-C2C that our AA1x models came with to the more appropriate O320 engine. I started with a core that I purchased from Gil Alexander. I'm told Gil did me very well in selling me this core. It's an O320-E2G, which is the stock engine for the Cheetah. This worked out best for me as I wanted to use the STC available from Ken Blackman AKA AirModsNW. There are three STCs available to choose from to perform this modification. If you are considering the upgrade gather as much info as possible on all three before making your decision. Each has its positive and negative sides. Each owner needs to weigh the pro and con of each for them-self. My decision was made on recommendations of others who had used Ken's STC and by my A&P after describing the process involved and each of the STCs. Since my particular A&P/IA had never performed an O320 conversion on a Grumman AA1x before (C&P brand yes, just never an AA1x) I wanted to go with the one that had the most documentation provided with the STC. For the engine I chose new ECI Cerminil cylinders. I picked Winchester-Aero Services for the overhaul of the engine. This STC limits the HP to the stock 150HP pistons and since the crank did not pass the AD inspection, it's my understanding I would not have been allowed to use it in my engine with the 160HP pistons. I was told by several reliable source gurus on the GG that I'd never miss the 10HP. They were right; going from 108HP to 150HP has been such a dramatic increase in power it's like I'm flying and entirely new airplane. I intend on uploading photos of the project as I put this article together. So keep an eye out for updates.
Day 1: Removal of the old O235 engine. Removal was a fairly simple process. It is a REAL good idea to keep track of every nut bolt and screw as well as making GOOD documentations of what wire came from where. If not just be sure to label every wire indicating what terminal it goes to. A good digital camera helps here too showing routing locations etc.
Day 2: Firewall prep & engine mount repair. I ran into a snag with the lower right engine mount extrusion. Fortunately I was not in excess of the allowable limit on this and after a day or research and sweating was able to save a ton of $$$ and at least 3 days of work. A separate article should be written on this repair and a good procedure for inspection for this. I stripped the firewall down of dirt and paint. Since I've never been real great with a spray can I elected to have Jeff paint my firewall. Before and after photos of this will appear here shortly.
Day 3: Hanging the engine (AKA how many washers & where do those spacers go?). Not having a manual that have a visual for the dynafocal mount I was unsure of the placement of the spacers used with this type mount. Numerous phone calls later I did acquire the info I needed. The spacers are placed the same as for the AA5 and AA5A. Finding the drawing for an AA5 at the shop proved beneficial. Basically all four spacers go behind the mount. There are also washers that are used to shim the engine up/down or left/right. Every application is going to be different. If using new Lord mounts (which I'd highly recommend) make the spinner slightly (I used 1/4") high in relation to the nose bowl. The mounts will settle in and at that time the alignment will be correct.
Day 4: Baffling. Using the STC from AirModsNW proved the most beneficial here. When Cliff Hansen said he spent 40 hours I thought, no way (he wasn't kidding). Having engineering drawings as well as full scale templates for the baffles proved invaluable. I photo-copied the drawings to keep the originals in good condition. Using the photo-copies of the templates I was able to create baffling using the aluminum from the RV6-O320 kit that fit my engine perfectly (well almost, I had to modify the forward baffles some after I thought I was done; see below). Fitting to the cowling took some hours. The rear and sides went together well. Keep in mind do not apply the flex baffle to the top until you have verified the height of the upper cowl. One of the guys helping me got the cart before the horse on this and we had to cut the baffles down after he spent quite a few hours applying the flex baffles. The two front baffles took more time than all of the other baffles combined. I'm still not pleased with how they turned out and plan on modifying or changing them out at some time in the future. My temps on 1&3 cylinders are great but I'd like to get #2&4 down about 50 degrees. It was suggested to check to make sure I don't have any flashing issues before tearing my baffles apart *again*.
Several months later: Replaced the oil cooler with a seven vane.
