Chapter 23 - Section 7

Engine Cooling Baffling


When the Plan said it's a biggie, I know its going to take time. This is the Chapter we get to learn about working with sheet metal. More head scratching and more tools.  First of all, there are many different baffles and it was not clear to me where they all go. The worst part is that I do not know how the baffles should be positioned to 'optimize' the air flow for cooling the engine. Clark Canady loaned me a set of his used paper templates since we have the same engine (IO-320). I tried them on and found we have differences between our engines. Some modifications have to be made...unfortunately.


While talking to other Cozy builders, it was brought to my attention that Van's sells a baffle kit for the Lycoming engines. It was pointed out that its a time saver at reasonable cost. I checked out the Van's site and found a baffling kit for an IO-320 at about $270, so I decided to give it a try. The kit arrived within a week. It is a well made kit with match drilled baffles, small connecting parts, all the necessary nuts, bolts and rivets. Accompanying the parts are detailed assembly and installation instructions - written in English...


The 'usable' parts fit very well onto my IO-320. The 'usable' parts include both sides and the forward baffles. The aft section differs greatly from our Plan's version. The reason being that Van's baffle was designed for air entering from the propeller direction and it's for down draft cooling. Therefore, most of our aft and middle baffles still have to be made per Plan.


Trimming Van's Baffles

I did not give it any thought regarding the differences between Van's cowling vs. the Cozy cowling until the Van's baffles arrived. Substantial trimming will be required. I taped the Cozy templates on my engine and mounted the top cowling back on. Using small strips of paper and masking tape, I formed a rough profile of the cowling along the Cozy paper templates.








Then, I mounted the 'usable' Van's baffles (forward and sides) temporarily and taped the Plan's paper templates (w/paper strips) against them. I traced out the Plan's outline onto Van's template for trimming.  As shown in the picture (left), there was quite a bit of trimming. The Van's baffles saved some time, but not a whole lot, in my opinion. However, it showed me how it should be fitted with the remaining baffles - a great learning process that earns good value points. Actually, I extended more height to the traced outlines such that the top of the baffles are about 1/4" from 'touching' the cowling - as suggested by the Plan.


[Hindsight] I revisited these baffles for final touch up and assembly, I realized that there were some nice stiffening attachments with the Van's kit. They made the side walls a lot more rigid than the Plan's baffles. 



Aft Baffles

Once the forward and side baffles (from Van's) were installed, I proceeded to the Plan's aft baffles. I made a set of paper templates by making copies of the Plans' baffle drawings onto thick 11"x17" papers (from Staples). Then I cut them out and started my trial fit process. Once all paper templates were fitted (with additional overlays and/or extra trimmings), I started with metal sheets per Plan.



Here's my left and right aft baffle with additional baffle enclosing the exhaust pipes.










Here's a picture of my aft left baffle. I deviated from Plan by dividing this baffle into two pieces because my left baffle will not line up with the right (due to the cylinder offset). In addition, the left baffle has to slide in ~1/2" such that I can bolt it flush against the alternator mount. Please do not hesitate to contact me if my description is not clear.








A closer look at a couple of seams (starter and exhaust pipes). It took a lot of trial and error to get there. I hope its worthwhile!










Alternator Skirt

Due to the swing of the alternator when tightening and loosening the belt, we have to leave a big hole in the aft baffles to accommodate its movement. In order to keep the hole covered up at all times, I had to make a 'skirt' that fits around the alternator. My problem is that the face of the alternator is not parallel to the aft baffle. therefore, the skirt has to cut across the body of the alternator, somewhat diagonally. It was a real pain to get the skirt to fit nicely around the alternator. I have made and discarded 4 different sets of skirts for one reason or the other. The 4th set actually fits quite well, until I decided to buff it up, so it will look nice and shinny. Of course, the buffer wheel caught the inner edge of the skirt and sent it flying like a boomerang before I could say @#$%. After it bounced off the 4 walls and made its rough landing, it looked like a bicycle wheel that got ran over by a truck. It took me 30 minutes to pound it flat again while chewing myself out the whole time, though I knew from the start that I would not be happy with a pre-twisted skirt. The 5th set finally made it to its rightful position - but no buffing for this one!  To add to the stiffness of the skirt, I used 0.32" aluminum sheet.   


Top Inner Baffles

The inner top baffles are the most challenging ones. The template that comes with the Plans, in my view, does not fit well between the cylinder heads because the seam between them is not a straight line, its in steps. You just cannot sit a V-shape sheet metal baffle and expect a good seal (picture left). There is a big gap under the inboard end and the middle of the baffle - may as well not use one... I just did not like it.








I decided to make a two-halves baffle, rivet them together and tuck it in the slot (space) between the two cylinder heads (picture left).


Then came the afterthought... What happens after engine shut down and the temperature rises? How much spacing do I need to accommodate the expansion? I decided to scrap the idea and post a question to the group...







A couple of solutions were suggested by wetting out a couple layer of glass with RTV and attach it directly onto the fins...


I bought some High Temp RTV (Copper +750F) from our local auto store, taped down the fin areas, wet out 2 layers of glass and laid it over the cylinder heads. I used duct tape because I wanted the baffles to be removable instead of a permanent install at this time.








The RTV took a couple of days to cure. To my disappointment, the RTV turned out to be a soft rubbery cover instead of a rigid one - making it difficult to tie down or secure.










I decided to combine the two approaches. I divided the baffles into 3 separate parts and made them out of thinner material (.020" thickness). I also made a hold down arm out of a 1/4" aluminum tubing. Then I re-taped the cylinder heads with packing tape and repeated the RTV method. This time I pressed metal soft baffles over the RTV while it cures, making them as an integral part.


After it cured, I popped the entire assembly off and trimmed off the excess RTV/glass around the edges. I think it will work out OK.








Here's a picture of the my inner baffles...










Making it Shine!

My baffle set consists of a combination of Van's, Plans, my own design and the inner bottom baffle that came with the engine. The fore and sides are Van's baffles. The cylinder and aft baffles are per Plan. The inner baffles are homemade. Once completed, I decided to buff them up and make them shine!


Here's a couple pictures of my shinny baffles...the right aft view...and...   




the left aft view...

Eventually, I will either have it painted or anodized. However, I will wait after all the electrical hook ups are completed at a later date.




Plugging the Hole

I have an undesirable opening at the right rear baffle to give room to a protruding fuel line. I tried using Play-Doh to form a mold for a glass cover - without much success. Making it worse, the Play-Doh actually caused rusting around the opening. I eventually had to remove the baffle and re-buff it to get the rust marks off. I decided to make an additional cover for the entire mess. The cover was somewhat difficult to make given the odd shape surroundings.













I eventually made a three piece cover as shown - one for the front and two side panels. They are held together with rivets.










Here's a look when all the sheet metal baffles are in place. Done...or so I thought. How about the clearance between the baffles and the cowling, the cowling fences and the rubbery baffles?










I bolted the upper cowling back on to check the clearance between the inner surface of the cowling and the edge of the baffles. It is important to maintain certain clearance because the engine shakes a lot during start and shut down. I trimmed a stir stick to 1/2" width and slid it against the gap between the cowling and baffles. At the same time, I used a fine marker and traced out both sides of the stir stick - one on the cowling and one on the baffle. The line on the baffle is for trimming while the line on the cowling is the future cowling fence line.


If you look close, you can see both lines.


[Hindsight] I decided to make the cowling fence and trim to width before I started trimming the baffles (explained below).




Building the Fences

I soon realized it is easier to build the fence by laying 2 BID on the cowling and resting the angled surface against the baffles (cover with packing tape first). Once cured, I popped the cowling off and laid 2 more layers against the back side of the BID per Plan. After that, I marked and trimmed the fence to ~1/2" height. Since the cowling was off the fuselage, trimming to consistent height was easy.


After trim, I re-bolted the cowling back on. With a marker, I re-marked the match line on the baffle surfaces. Adding 1/4" clearance from the fence trim line, I will have 3/4" clearance between the baffle to the inner cowling surface. It is important to note that the fences are slightly offset from the baffles as intended.




I ended up adding a fence along both sides of the upper cowling (per Plan), the forward side of the upper cowling (not to Plan), and the aft side of the lower cowling (shown left, not per Plan).










Adding Neoprene Asbestos Strips

A roll of black Neoprene Asbestos material was included in my Van's Baffle Kit, I may as well use it. Surprisingly, I can cut it quite easily with a regular pair of scissors.


Instead of riveting the strips onto the baffles, somewhat permanently, I decided to make them removable. I made a matching strip (1/2" wide .032: thick aluminum) along the edges of the baffles. The strips are used to 'sandwich' the Neoprene strips in place. I drilled a set of 3/16" holes, 2" apart, 1/4" in from the baffle edges. I plan on using AN3 bolts and nuts through the baffles and the matching strips.