I have read that the cowl cracks and breaks at the mounting screw holes. I used servo grommets fitted into enlarged holes in the cowl to isolate it against the vibrations. I used servo mounting screws, the ones with the built in washer, to secure the cowl to the plane. I also secured the plastic tank in place with thin foam strips and an 'L' shaped strap running from the l.g. mount to the firewall so the tank is easily removable. I didn't care to glue it in per the instructions.
Perry Rose

Just as a matter of interest while I realise that an engine cowl improves the looks of the model, does the cowl actually aid in cooling or anything else as I remember that back when I was in my teens (seems like a hundred years ago lol ) but I am actually talking about mid 60's to about 1973 which is when when I took up flying combat most of the time, I don't know if anyone is familiar with me but I originate from England so I mainly used diesels, except on my Mercury Crusader and Sirotkin Spacehound which I used Enya .35's on I tried a used Merco .35 but it had been over used and wasn't much good, I also had a new that I never managed to get properly broke in Glo-Chief .35 and a new cheap McCoy .29 shiny case green head I believe, I put that on a Calamity Jane.
 The main stunt models I flew were KK Spectre AM 2.5cc powered and Mercury Monarch AM 3.5cc diesels in, I had to fly those models without the cowls because the engines would overheat with a cowl, I did try different methods to stop that happening but with my inexperience this was mid 60's  so I was 15 years old and the friend I flew with had less knowledge than I did, so due to the problems with the Spectre and Monarch, I did make cowls for the larger glow powered models but never tried to use them due to being scared I would wreck these models, incidental the only one of those models I wrecked was the Crusader when it fell in doing a wingover in about 30+ mph wind just after it crossed overhead the model always seemed underpowered and floaty no chance of saving it even though I ran like heck to try to get line tension, the other's I either gave away, sold or traded I do remember getting a used MK3 Oliver for the Spacehound & a KK Spectre.
  I got over my fear of wrecking models not long after I started flying combat with Oliver Tiger's in them as you cannot avoid wrecking models in combat as I am sure everyone knows that had anything to do with combat.
  I realise this is kind of drifting off subject but I would like to now if using a cowl nowadays does aid in cooling more than anything else especially as I have a Nobler ARF with an L&J Fox 35 with every modification done to it including the newer type of crank on it I cannot remember what it is called I just don't want to chance damageing this engine from overheating as it is not a cheap Fox 35 anymore and I want it to last.

I used blind nuts and 4-40 x ¼” long button head screws to hold the Nobler cowl on. The maiden flight will be tomorrow. We will see how the cowl holds up.

John Tate
Norfolk Aeromodelers

For those who wish to go electric with the Nobler ARF, the stock cowl is very roomy; allowing for easy "bedding" location of the timer board ,ESC, and wiring. It also allows a great deal of air to pass through.
There is very little reason to take it off 'cause there isn't an accumulation of exhaust or fuel  residue .
Being as we're dealing with an ARF anyway, it made sense to me to keep it.
 
No doubt though- carved wood cowls are a  really nice touch...