Getting ready to cut the holes thru the hull for the exhaust tips. They are 4". How much bigger do I need to make the hole? The outside dia of the tips are 4 1/8". Don't know if I need to go any bigger since it is exhaust. Thanks

You will want to give yourself a little room just so you can fit it together with no problems and you also need a bit of room for a good sealer so NO water can make it's way to the wood in your transom.

If your OD is definitely 4 1/8" I would go 4 1/4". I am not sure there is a hoel saw you can get between them.

+1 on 4 1/4, i had 4" tips on my baja and there was alittle room for wiggle but not much, also don't forget to seal the tips to the transom, 100% clear silicone works fine for above the water line exit

i would buy a 4 1/8'' hole saw,,they are not a exact fit when you bore the hole and they usually end up 4 1/4''

For a little more assurance of getting water intrusion in your cut out openings, I would wet them out with epoxy first and let it dry than a sealant/silcone after that.

Definitely treat the exposed wood with resin and I would use 3M 4200 to seal the tips.

All the above and some seal on all the srewthreads .

What is a good epoxy? And where to get it?

go yo your local west marine,,all you will need is a&b 1 qt each..