I had merc 525 SC with the orginal merc seal on the crank.. to 510 hours.... they were still running when they came out... when we tore them down the pistons actually fell out of the block....... after seeing this I assumed that the 525EFI would run for 500 hours easy.....

My 2007 vintage 525 has about 250 hours and has never missed a beat. I run it hard and have it propped to bump the limiter (5,400) in ideal conditions. I change the oil 2 or 3 times per season. Great engine IMO.

So what stud mount rockers is everyone using now?

Just one other thing to be sure we are on the same page. Have some of these motors that have had issues been altered? Change the RPM, timing, ECM parameters and all engineering bets are off. I have seen first hand in the racing world when people play with the ECM, bump a little compression and call them stock that the failure rate is high. They were engineered to run exactly how they came out of the factory with the seal on them. ITS NOT WORTH THE EXTRA HP TO MESS WITH RELIABILITY on this motor.
Randy

Lets not ignore the obvious, and look at the basics.

The headers, well, they suck. Everyone knows that.

The engines themselves, as far as hard parts, have nothing special in them. Lets not get carried away with all this ''Genuine Mercury Racing" Kool aid. They are GM production blocks, H beam rods, 4'' steel cranks, with some edelbrock heads, crane rocker arms, etc. There is nothing really proprietary about them below the intake manifolds.

The camshaft in them, is not what I would consider a mild stick. Granted it's not wild, but its quite a step up from what was used in the GM based 502 mag engines. When you get into camshafts that have 630+ lift, +240 degrees of duration, and plan to run it like a high performance engine, you need good springs and proper pressures to control the valve train. Even with that being said, your lifespan of the valvetrain isn't gonna be what you might expect from say a 502 Magnum cam with low lift and duration specs.

If you took the mercury racing tag off of them, and they were built by any other quality builder, I would be looking at top end freshen ups around 300 hours. Its a pretty well known fact, the big block chevy marine weak link is the valve train. If you have 300+ hours on these engines, you really need to consider doing some maintainance. When springs get weak, and the valvetrain can no longer be controlled like it is supposed to, $hit is gonna break. Judging by some of the results posted on this thread, besides the headers, I think a lot of it boils down to the spring setup used in these engines.

I don't think Eddie Young posted up his experiances with the 525's coming into his shop, to tell fairytales. He posted pictures of the issues, and the hours they were run, and at what rpm they were run. I have almost identical camshafts in my engines, as the 525's use. My isky springs are set with 165psi on the seat, morel 4603 lifters with Crane Rockers. 120psi on the seat seems awfully weak in my opinion.

I don't know what Crane may have changed as far as their rocker design, but I just replaced two sets of them that came off my engines, which were date stamped 1985. They had a TON of time on them. 2 out of 32 rockers had cracked trunnions. While holding them next to the newer style crane rockers, the newer ones seemed much beefier and better designed.

A lot of the 525 equipped boats demand a higher price tag. And for the boat shopper/consumer, I think its fair that threads like this exist. Because there's nothing worse than dropping a ton of dough on a boat purchase, and finding out you need to spend another 25 grand, replacing leaking headers, and going thru the entire valvetrain/rebuild after a couple hours, because you thought "they are factory sealed merc turn key engines, lets party on!!!"

It's my understanding that Mercury uses raw blocks for their racing engines and machines them in house to exact tolerances. Forged crank and pistons and steel H beam rods are used. Engine is balanced and blueprinted. Heads are made to Mercury specs by Edelbrock. Intake and throttle body are designed and made in house and flow very well. Header problems seem to be more common on multi-engine boats with long, unsupported, tails. The package includes billet pulleys, combination electric and mechanical fuel pump to eliminate vapor lock, large capacity heat exchangers for engine coolant, steering fluid, oil and fuel. Service is available just about anywhere because all high performance shops know these engines well. Am I wrong?

From what I understand, Crane had a bad batch of trunnion bearings get out. Not sure what year or how many got out. As far as I know, it was all the newer style rockers.
Eddie

Have the gm rods (7/16" forged) ever been an issue in a sub 600hp app.? I never seem to read where the dimple rods have ever had a reliability issue in the 5-600hp range. Merc has the fancy looking H-beams, I think I'd trade them for even better springs, tool steel retainers, and something like the Crower Enduro rockers. I'm not an expert, but the HP blocks have always had close to twice the longevity of the valvetrain, why not put the $$$ there?

Mine are bone stock hardware and software. Idle like kittens. I also have them propped to bump the rev limiters which I do at least once on each outing. I make sure to get min 8-10 mins of WOT per outing. I have 330 hrs with no issues and use Merc semisyn 25W-40 every 25 hrs.

Eddie I'm not sure the yr that Crane was having issue either, from what I have heard the steel they are using is the issue. I have heard and seen the rockers from many different builders and the story is the same. This isnt really a big deal there are plenty of other rockers out there that will do a great job.