Vinny P

This is a simple question but I am sure there will be a wide range of responses. I have a mostly stock 454 Magnum E.F.I. gen VI. Currently I have 265 hours on it with absolutely no problems at all. I suppose that at the seasons end, I will be in the 300 hour range. As of now, the motor leak tests good. But, I am still considering pulling it out and freshening it up. I would love to add more power to it, but I am not willing to go with the re-mapped ECU. I feel that this motors weak spot lies in the valve train. I don't like the idea of not having inconel valves and having 3/8" bolt non-adjustable rockers. I am thinking of a set of inconel valves, a minor port and bowl deburring, a good valve job with matching springs and a set of Jesel shaft mount rockers, and the standard lower end freshen. I know that all of this will most likely yield no gains in performance but I am sure it will strengthen the valve train. The cost is not a factor as I can do almost all the work myself. I would also rather pull the motor out and work in the garage comfortably than pulling the heads in the boat and being uncomfortable.
So here is the question--- Now I know that the answer depends on how much you beat it up, but lets assume that everyone here maintains their equipment but uses it hard. With that in mind, how many hours do these motors normally go before needing to be freshened?

Cord

iTrader: (2)

Around 500 hours. I honestly don't see any benifit to making the specified improvements. The combination that you currently have is just fine for its application.

Vinny P

Thanks guys. Yes I know it would be overkill, but that's just the way I believe motors should be. While I have the motor apart, I would be going for a full roller set-up anyway, so why not get the better parts?

Cord: 500 hours seems like alot!! Do you guys get that many hours out of stock Merc. motors?

paradigm shift

Got a 502 mag mpi with 500hrs and ran hard. No major problems. Could use a valve job to freshen. Leakage at rings is very acceptable. Oil pressure is same as it was new. Yea 500hrs + is very possible if taken care of. Just my .02

All Trimed Up

Hey checkmate454mag
I just went though my 454 this year and I had around 650hr on it. I have a 1991 251GTX and we run it very hard. I say kept running that thing. You have a couple of years before you ever have to change a thing. If you want to do some work sell it and buy a 502.

baja bailey

I have a friend that has a 26' Powerquest with a 502, it has 700 hours on it and has had no major problems yet. He does not baby it either.

Crazyhorse

I'm with the rest of the guys that say the shaft-mounted rockers are overkill. but hey, it's your motor and your money, and I'm sure it's a bulletproof setup.
It wouldn't surprise me if you got the heads off to find that it's top-end time. It's always the guys that try to get that extra year that end up with just a handful of lifters.
By the way, mine are coming out for a freshening this fall at 200 hours, and I tell the people that ask my opinion to do a tear-down of the 365, 370, 400, and 420 motors at 400 hours. It usually saves them a bunch of money.

Griff

I did a valve job, cam,springs and a couple other mods at 400hrs on my 454mag/365hp. The worst things were some cam wear that was allowing it float forward and spring pressures were down. Other than that, everything was fine. I would run it at least one more season.

BTW, If you have a Gen VI, then you have a roller cam already. Not sure if you have roller rockers or not. If not, ARP makes a 3/8 bottom screw in stud with a 7/16 top that you could use to add them.

Pismo10

My 1979 Mercruiser 305 with a 4brl carb is now over 3000 hours without a rebuild. Lots of new accessories, starter, alternator, etc. but it has never been opened. Still spec compression. Fresh water, original manifolds, everything. Has sunk twice, runs better than ever. Points, condensor, carb. Something to be said for old technology, very low performance, low technology, much, much less to fail.

I hope my new 502 MPI holds up as well.....I'll let you know in thirty years.

SL

blue thunder

I think all this advice is correct, although I tend to agree with Griff the most. Go one more season on the engine. Unless you are the type that hold the stick to the pin for 15 or 20 minutes at a time, the top end is good. If your normal cruise is between 3000 and 3500rpm with limited wot blasts, 400-500hrs is a good point for top end job on a 454.

BT