Ok guys, I need an honest opinion about service & maintainence for these engines. I have a single HP500 Carb in my 1998 Baja 25' Outlaw. I run the boat on a fresh water lake in Upstate NY. I do run the boat hard sometimes, but hardly abuse it. Just stretch it out from time to time. Anyway, I am by no means an "internal engine" mechanic. I understand the basics, but anything internal I would have to leave to the pro's. My question is how many hours (average) should I be able to run this engine with simple maintainence (25 hr oil changes, etc). A lot of people on this board talk about replacing valve springs at 200 hrs, tear downs, and other stuff. I find it hard to believe that I will have to do this so soon considering how and where I use the boat.
There is 180hrs on it now, and it runs like a top. I just want to do what I can to make this puppy run the long hull. I had great luck with my last boat (7.4 330hp). That motor still runs geat with over 800 hrs. Any past experiences or suggestions concerning an HP would greatly be appreciated.

I have no idea what the Merc Manual says. But I would stick with a 50hr. oil change. The reason I say to do the upper end work at 250hrs. is because you have a lot more lift and duration in the cam in the HP500 as compared to the 330's. The 330 could run for a long time and never have a problem.

The problems you will run across is that if you don't replace the springs they will fatigue and become weak, or even break. When this happens, you may get some back-firing thru the carb when you pump up the gas at idle, or a loss of power. And the biggest problem is the valves will float from less spring pressure, or better yet you risk dropping a valve. If that happens you will be spending a lot more money!!! Nothing like a little preventative maintenance!

Although, I do have a friend who has HP500 EFI's with over 400hrs on them with no service.

I change oil every 25 hours (cheap insurance). I have 165 hours on mine ('99s) and plan on doing the springs around 250 hours more as preventative maintenance than anything else.

Honest opinion

Stop using the boat right now! Change the valve springs, Use the comp cams springs to replace them.
Sorry but myself and others have had costly repairs because of the bad design or matching of the springs that came with your motors. A few articles have been written on this subject including one by Teague in Powerboat. Crane has changed the part number for the old springs but they still seem to have excessive seat pressures. The comp cam springs seem to be the answer!

If you want to take it further send the heads out for some porting and exhaust relief. I changed cams over to the crane 168731 this combo seems to work well and I have seen mph gains across the whole rpm range! I'm guessing that I have increased HP by about 60 or so per motor. Remember that is a guess not fact. You will have guy's suggest the 168741 but after a lot of research it seemed a bit much for the work that I had done and might of hurt performance instead of helping it.

This is just my opinion and the results of many hours researching but there may be better choices maybe Dennis will jump in with some better ideas

BTW I had a lifter fall apart at 160 hours and bad inner springs causing the cam to wipe out and the motor to fill up with metal and a lot of roller bearings!

Good luck, Scott

"Although, I do have a friend who has HP500 EFI's with over 400hrs on them with no service."

They use the Comp Cam springs

Thanks Guys, that does make sense due to the cam. There is a high peformance marine engine builder in town that does wonders with marine engines. I think I will see if he can give me a figure. I assume that 5,200 r's is ok to run WOT at. That's where I am now after a good lab finishing job on a Bravo 1 24p. I guess there is a price to pay for owning a high performance engine, but I love that blue

I agree with the previous response, stop and have it fixed.
Advantage or dealer never sent warranty card so I wasnt
notified of problems with this motor, found out too late.JC

Do the newer 500efi have this spring problem????

"Do the newer 500efi have this spring problem????"

No they use the Comp Cam springs!

Thanks