I have a 1997 Fountain 35 Lightning with completely stock Merc 525 SC motors. 235 total hours. They seen to run just fine. Boat is never beat on and motors have had an easy life with appropriate maintenance.

At what point should the vavle springs be replaced?

Pull some off and check them.

Based on your findings you could replace them now or go a few seasons more.

You should be fine for another 100hrs or so. The 525SC has a relatively low lift cam and isn't hard on the valve springs like the 500hp's and 525EFI's.

Thank you for the replies Powerplay J and Griff.

I'm hoping to be lazy and not check the springs...with the blowers and factory CMI headers removing the valve covers may be a hassle.

I was hoping the HP525SC motors are easier on valve springs than the HP500 motors. Another 100 hours on my motors would be at least a couple more years of use for me. That would be GREAT!

Other than basic maintenance, a couple raw water pump rebuilds, and carb rebuilds these motor have been bullet proof! The older I get the more appealing that becomes!

You should be able to remove the valve covers without removing the exhaust or blower, if you wanted to have the psi checked on the springs. Just use a 1/4 inch drive socket with a wobble.
I do think you will be fine though and the valve springs are nothing to be concerned about for a while.
The 525SC has flat tappet cam with about .550 lift and much slower ramp speeds than HP500 roller cams with .600 lifts.

I had one of the left bank valve covers off some time ago...I remember it was a PIA. I foget exactly what I did, but I know I did not touch the exhuast. I recall getting to the bolts with 1/4" drive socket was not difficult. I think I lifted the cover and slide it forward after moving some water hoses.

Thank you so much for the reply!