My 525 is in the shop getting new stock springs, retainers & keepers installed. Leakdown test was good. Not going to second guess Mercury on their choice of springs. How many years has the 525 been in production now?

im not arguing with you but quite a few members tried to steer you in the right direction.mercury marine buys parts to get the engine past the warranty.they will use the cheepest parts that will accomplish this.the bean counters dictate what parts merc selects,not the engineers.if you talk to bob madera he will confirm this.yes the merc replacement parts will work but they are not the best choice. imo you could have got better parts for less money just by picking up the phone and calling bob.

Mercury uses Crane valvetrain parts on the 500's/525's, and etc,etc.. Crane is an aftermarket company. Therefore, you know aftermarket companies offer many different variations of the same part. Many valvespring choices, etc,etc.

With cars, boats, sleds, bikes, etc,etc somethings, yes, the factory parts are better. With somethings, the aftermarket parts are better.

90% of the time if a person or mechanic is not sure if factory or aftermarket is better, than going with factory is a good decision to make.

I couldn't agree more with you Mike. I've spoken at length with Bob and other very well respected performance engine guys and they all agree about the parts used in the stock setup and if one takes the time to really listen to what they are saying.. it's very scientific and makes complete sense. And the truth is that there are enough failures out there to back up their claims. In all three of my engines, the valve spring installed heights are not even up to the spec that is in the Mercury manual and they are bone stock. What does that tell you? It means, they were assembled to "good enough" tolerances..

I still think the 525 is a great engine, but it has weaknesses and it's a choice to make on how much risk to assume. I'm going to do anything I can to prevent another catastrophic failure and that means upgrading the valve train. Not trying to start a debate, just saying what my choices are. For the record, I've gone with Isky Tool Room springs and Crower stainless rockers.. overkill?? maybe... but what do you tell yourself if you cheap out and then the motor grenades on you....

toolroom springs and crower ss rockers is what merc should have went with but then they would sell a lot less parts down the road.i have never seen an engine fail because someone used better than stock parts.

Used this same combo a few years back on my 500's when I had them done. Overkill, maybe but you do get what you pay for with these manufacturers. Part number of the spring you used?

valve train issue are the #1 failure in these engines, almost always starts with the springs, rockers right behind, anybody that has run these 500/525hp's should be very aware of the ticking bomb over 250hrs, also merc does not make valve springs, as a matter of fact there are only 2-3 manufactures of spring period, many companys sell them, few make them, PAC, PSI are 2 that do and have very good product, when doing the replacement new retainers/keepers should be part of the job as well, also set the installed height correctly...not hard but may just throw them on...kinda that pull and pray deal...the last thing if you are redoing the whole engine DO NOT restrict the oil to the top of the engine(this was a oil drag race trick even I used to do to keep more oil down low) but the oil spray is the only COOLER for the spring that get unreal heat build-up..remember breaking a spring or rocker can cause the retainer to come off dropping the valve and it's not pretty nor cheap after that..

I should have said stock spec parts (Isky). My engine showed no problems after about 350 hours and I run it at 5,400 on top. I do not see how adding more pressure and stress to the valve train will help things. I'll stay with Mercury's choice of spring pressure.

Which part # spring did you go with? What is your install height ?

I'm at work now and don't have the part numbers here. Maybe Brian Orlandi will see this and answer or I will find out later. Normally I would do this myself but Brian did a leak-down test and a visual of the combustion chambers with a scope and there was no sign of reversion. He will check installed height. Also, I have silent choice and it is fine if you only use it at idle. I pulled the headers and will pressure test them before re-installing.