Oh snap. I missed something

Ian,

I'm not an engine guy, but, as a toolmaker, I am a part-time, would-be metallurgist. Strictly metallurgically speaking.... Spring life is all about cycles. Aside from that, spring steel has to be stressed beyond its yield point in order for it to lose memory before its cycle-life has been reached. Resting within its range of motion does nothing.

Thanks. Brad.

Brad,

That makes sense, and appreciate your explanation/knowledge share. Sounds like Merc didn't choose the strongest or most durable of springs for these motors. Not sure if that was in miscellaneous batches or across the board, (all s/n ranges) but does sound like the springs are a weak spot, at least for some.
Ian

Ian,

My only direct experience is with the 496HO, in which Merc didn't do anything with the valve train itself. It's kinda crazy that they spec'd a specific cam, but stuck with the truck duty valve springs, which were 90lb on-seat. You can compress them some with your fingers. That's probably fine for an engine that's gonna spend nearly its entire life at 1700RPM, but woefully inadequate for one that is going to spend the bulk of its life at 3500, and regularly at 5K for semi-extended periods of time.

Thanks. Brad.

Sorry, another question. I have the Merc service manual, but can't seem to find where (or if) it addresses the use of anti sieze on new plug installation. Aluminum head, 20 lb.ft torque, I know lots of controversy on the use of anti seize for its many useful properties, but some also highlight the introduced chance to over tighten and strip soft Aluminum.....

Anyone actually done the job and care to share their expertise/experience/thoughts?

TIA,
Ian

I always use anti seize.....Im running the same heads.............I never use a torque wrench, for me its all feel

I wouldn't use anti seize on plugs. I believe mercury had a bulletin on not using it.

Yes the 496 springs are very soft. But you don't hear of any issues with them though. A ton of these engines in boats run for 1-2000hrs with no spring issues. And they aren't running 1700rpms in a marine application. Most will turn 3500rpm and above when under way.

Ya, post up that bulletin from Mercury id like to read it

I would personally have Eddie Young do the top ends just for my own peace of mind if they were mine, but I'm very OCD though. One tip I can give you is remove the hatch ram and get you a yoga mat to lay across the engines when changing the plugs on that boat. That hatch should stand straight up and you can secrure it not to fall forward or have someone you trust very well hold it for you while the ram is not connected. Also removing one of the headers between the 2 engines will make things a breeze there.