I need some help on this.My cowl fits fine but on one side it is nearly touching the top of the muffler bolt(four stroke) and it is burning a hole where that is..i would prefer not to make a bigger hole any suggestions on something i could put on the inside of the cowl to stop this?I was thinking maybe that silver tape but if ya have any better suggestions i am open to them thanks Kieth

If it's actually touching the muffler enough to burn it, it's gonna crack it from vibration anyway, so I would go ahead & cut the hole out so that you have some clearance between the cowl & the muffler. JMO

these work pretty darn good. ya didn't say which engine but they make one for just a bout every saito there is

[link=http://www.horizonhobby.com/Products/Default.aspx?ProdID=SAI65111]flex exaust[/link]

its an os 91 surpass II its hitting where the muffler threads into the engine and then there is a nut that tightens against the engine...that nut is touching and there is not a way to get it to not short of a hole there is actually about 1/16 of an inch between the cowl and the nut but it gets hot enough so that it is causing a hole.

you need a minimum of 3/16 an inch. your going to have to cut the cowl. The motor will virbrate and tear it up as well and the high temps coming off the motor is going to make it worse. towerhobbies have flex exsions. Is it hitting on the bolt nex to the head or the one right on the muffler, if it right one the muffler the extension would alow you to rount the exuast to the bottom of the cowl and stick the tip of the muffler out the botom. I couldn't find any flex pipes though.

4 strokes exhausts run substantially hotter than 2 stroke exhausts. You need a MINIMUM of 3/16" clearance (1/4" is better ) from ANY part of the exhaust to the cowl. Less than that and heat and vibration will melt and/or crack the cowl.

If the cylinder head sticks out through the cowl you need a MINIMUM of 1/4" for engine cooling. If the engine cylinder/head is over 50% covered by the cowl you need additional cooling to let the hot air out. Use a 1:3 ratio for this. For every 1" of air INLET (air coming in ) you need 3" of opening for the hot air to get out. Without this there is an extremely high probability of the engine overheating. I realize that in a lot of cases this does ruin the appearance of the plane, but that is the price we pay to fly certain types of planes.

To minimize any cracking and reenforce the opening, after you enlarge the opening, take some 2 oz fiberglass cloth, and using THIN CA, glue it to the inside of the cowl. Trim any excess after the CA dries. I also suggest doing this around the outer edge where it attaches to the fuselage (minimizes/prevents the attaching screws from cracking the cowl.

Hope this helps.

Thanks for the replies i ended up opening up the hole and after doing so it didnt look at bad as i thought it would ..Thanks for the tips on the cowl work that sounds like some good techniques on makeing it tougher so it doesnt crack Kieth

Fashion a piece of 1/16 ply for your application, and thin by sanding to meet your clearance. The ply will deflect and absorb most of the heat.