My next boat will likely be a 42 Lightning with 525's and I've heard they need a top end rebuild around 250 hrs, anyone know why? I typically run at 3000 rpm 99% of time so i don't run it hard.

For a stock merc engine, the 525 runs a relatively aggressive cam profile. It requires somewhat stiff valvesprings. This tends to be harder on parts such as lifters. I believe they recommend just the top end at 250 hours. Lifters, springs, etc. Good engines, and the cams make them sound aggressive with the cmi headers.

Well that doesn't sound too bad, I've replaced valve springs without pulling heads before.

Usually its recommended to pull the heads and replace the head gaskets, make sure the heads are flat, possibly redo the valve seats, etc. A "top end" job usually means the whole head, check the lifters, etc.

Hey Speedfreak,

I'm going to be putting my 06 42X up for sale in about a week. Over the winter I rebuilt both 525's completely. As of right now they have about 25 hours on rebuild. If interested drop me line.

I should note that the 525's only had about 225 hours on them before the rebuild. Motors did not need a rebuild I'm just that way with engines. Dyno'd motors before rebuild and after rebuild.

can you tell me the hp on the dyno before and after. i am going to rebuild mine this winter it has 330 hours on it. thanks

From what I have gathered it would seem that the jury is still out on the valve spring deal on the 525's. Unlike the HP 500 spring issue there does not seem to be that many out there with the hours on them yet to begin to show the failures. Would be interesting to see what others believe or may have experienced. I'm close to 200 hours now and do not see anything in terms of performance drop off that, in my mind, would warrant a look see at the valve train.

Question here would be ........... anyone know exactly what Merc Racing used as the OEM valve springs in the 525's?