What do you think about those engines having 290 hours on them, they are 99's is it time for problems? they have been maintained by a Merc dealer and the boat is owned by a MATURE person, any help would be helpful,, Thanks

1999 had bad valves springs be careful and check it good i did a complete
rebuild at 290 hrs and all ways changed oil every 20 hrs!!!!!!!!!!!!!

id did mine at 350... 17k ... but now theyre better than new 520 hp

I have a 1999 HP500 carb engine that I bought with 180 hours on it.

Since these are known to have valve spring problems, I redid the top end of it then.

All the springs were very weak, and two valves were spinning. The head gaskets were not leaking. Everything else looked perfect.
I had a valve job done, and went back with Felpro head gaskets (the Merc head gaskets are junk). I also went with new Comp Cam 929-16 springs, and new retainers and keepers from Crane.

Some others (on another forum) had far worse happen to theirs, even close to the 200 hour point. A few had leaking head gaskets, bad valve seats, and broken springs.

If a spring breaks, you can start to tear up lifters, cams, and the metal can do all kinds of damage to things...
=========
I believe you are running on borrowed time! At the very least, change out the valve springs.

Take care,
Kent

Just did rebuild on two, for customer. Changed cam ,springs ,intake , and carb only.Ended up on the DYNO 570hp , 622ft lbs torque at 4,500 RPM's. also made 500ft lbs at 3,000. we did re-balance, blueprint also 9.5:1 on pump gas.
Kevin's Machine & Engineering (Hawk Marine)

I just tore apart my '99 HP 500's (325 Hours) 1 side had 5 or 6 broken springs - (funny thing engine ran fine before pulling apart) doing complete head job on both engines.

Cool!! What was your retrofit recipe?

Just lucky i guess!!! kidding . no really the engines looked real eficient on the dyno. otherwords simply put for all the air & fuel put into the eng. Maximum torque & power came out. No hidden secrects here, just on the shelf parts were used, crane marine hyd roller cam,JE small dome,stock every thing else,not even any port & polish on stock rect. port heads. They were balanced & blueprinted. I try to take sewingmachine technique to building engines..........

Don't mean to hi-jack a thread, but if anybody is interested, I have a brand new set of Crane 929-16 valve springs still in the box that I don't need since I sold the boat. I will sell them for $100 bucks plus shipping. These are the springs Teague reccomends to replace the Hp500 springs with. Anybody interested, write me at [email protected]

thanks.!

I am rebuilding my 500's as well. How do you get 9.5:1 using flat top pistons and stock Merc (GM) heads? Thanks