With a lot of hours of use on unleaded gas the exhaust seat will recede and the valves will sink deeper into the head.
If you have the head off anytime, I would put hardened exhaust valve seats in the head.
How many hours will it take?
My previous boat, a 1966 Mark Twain/150 Mercruiser that Dad bought new, didn't get leaded gas for about 25 years!! I sold it in 2005.
Engines that run on propane or natural gas seem to run for EVER!
I think there may be "much ado" about unleaded gas...... It's right up there with E10 and the Oil-Snakes.......
Um.....how many pleasure boats out there have 12:1 compression?That's why the old muscle cars could run a 12:1 compression without detonation.
I'm not saying one shouldn't install hard seats in an engine when it's apart...... (I had hard seats put in my Ford Y-block when I rebuilt it)I've taken old heads (60's automobile) apart that the seats we 1/8" deeper than stock. How many miles (hours), I didn't ask. I tell my customers if they're going to drive it more than 10000 miles a year and the heads are already off; I would put new exhaust seats in them.
Um.....how many pleasure boats out there have 12:1 compression?
In fact, how many over the road cars have 12:1 compression? Or better yet, how many cars (other than on a drag-strip) have 12:1 compression?
I'm not saying one shouldn't install hard seats in an engine when it's apart...... (I had hard seats put in my Ford Y-block when I rebuilt it)
I'm just saying it's not worth doing it to boat engine (unless you're going to do a complete rebuild)
It's not worth tearing the engine down or even removing the head if it's running fine.
It's also not worth worrying about it. When it comes time to rebuild the engine or repair a head that DOES have a valve problem......it's absolutely worth it to put hard seats in it. (I don't think ANYONE does soft seats any more........)
Leaded gas is pretty much gone and when they finally get a replacement for 100LL Avgas, the ONE company that still makes tetraethyl lead will vanish.
this thread probably needs to be moved to Engine Frequently Asked Questions (FAQ)