HP 500's
 

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

Re: HP 500's
 

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!!!!!!!!!!!!!

Re: HP 500's
 

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

Re: HP 500's
 

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

Re: HP 500's
 

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)

Re: HP 500's
 

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.

Re: HP 500's
 

Cool!! What was your retrofit recipe?

Re: HP 500's
 

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..........

Re: HP 500's
 

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.!

Re: HP 500's
 

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

Re: HP 500's
 

you cant unless you reduce the combustion chamber to 100cc. I wrote that incorectly (sorry) I was thinking of some 604's that i am Dyno ing now . MY MISTAKE!!!! the 502's bored .030" had small dome JE's similar to the stock 502 pistons..

Re: HP 500's
 

I also took my 99 HP 500 Carb motors in for vale spring replacement at 270 hrs. After a leak down test we decided to refresh both motors. When we got it apart 8 of the valves on one motor were cracked and near ready to break apart. The springs on both were weak but none of them were broken. The cylinders, piston's and all the bearings looked great. Based on what I have read all the HP500 valve trains are on borrowed time after 300 hrs. Replace the springs at a min.
By the way mine ran fine before I took it in, no sign of a problem.

Re: HP 500's
 

PM any performance gains noticed after refresh?