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View Full Version : Hole size for Transom Exhaust?



jbowen60
06-27-2007, 09:00 PM
Adding thru transom exhaust on my z22. I'm using 4 inch OD exhaust tips/mufflers. What should be the hole I need to cut? 4 inch ID for a snug fit or do I need a air/caulking gap for expansion/contraction, like 4 1/8 hole?

Help or opinions here are appreciated.

john b

oldandtired
06-28-2007, 08:44 AM
I was super careful to get the right size hole saw in order to have a perfect fit only to wind up using a drum sander for clearance. I would give myself at least 1/4" clearance if I were to do it again (that would be a 4 1/4" for your app). Make sure to seal the exposed wood in the transom with epoxy prior to installing the tips.

Rene

mrfixxall
06-28-2007, 09:49 AM
Use a 4'' it will end up being 4 1/8'' when your done,no hole saw is ever true to what it reads on the side of it...try making a hole in a piece of plywood and do a test fit on exhaust tip first to make sure theirs room for the screws.

When your ready to make the big hole mask off the area with tape first this will help keep the gel from chipping..when the hole is marked start by drilling a 1/4'' hole first, then put the drill in reverse and start cutting through the gel first (with the drill going backwards the gel wont chip that easy) now put the drill iin forward motion and start cutting,,let the drill do the work..when the holesaw gets to the end of the hole your cutting becareful because the holesaw may bind and jerk the drill out of your hand so hold on the it and go slow..it also helps to have a spray bottle with water in it in hand to help cool the hole saw and it also keeks the fiberglass from making a big bust storm..

when the holes are drilled wipe out the holes and dry them out,i use a heat gun...now you need to seal the exposed wood and fiberglass,i usually use a skim coat of the sealer i use to seal the tips (life seal get it at west marine)
ill also seal the tips from the inside..

good luck