Gentleman, I am looking at a Black Thunder with 230 hrs with 500 hps. Should there be anything I should be concerned about with these motors. . The owner seems like he did all the maint.and doesn't seemed like he would abuse the boat.

Anyone know the longivity on these motors if they are not beaten and slammed. Thank for any info.

I can't speak to the 500 specifically but I would spend the $$ on a survey which includes compressionand leakdown testing. At 230 hours you could be less than halfway to your first rebuild, or it could be around just the corner if it was abused or service was neglected.

Salt water, freshwater? Have you run in the boat yet, how does oil pressure look at idle, mid-range, WOT?

Newer engnes can also be hooked to OB diagnostic systems and give you data on average RPM, how much time at WOT, etc.

The only real problem with those motors was valve springs , if they have not been changed I would change them and go boating . Good luck with the new purchase.

Freind of mine has a 43 BT with twin 1200HP blown motors and runs low-mid 90's, 500's will work very hard to push that big boat.

As said, valve springs should be changed out, if they have not been already. Carbed 500HP's have more issues with the springs than 500efi's.

Thanks for the good advice. It is efi, salt water, cheasp bay boat. I am taking it out this weekend. I have a Marine mech with the down loading machine to survey each engine and see how it has be operated, meaning what RPM's and how long. This should telling me a little about the driveing habits od the owner. It's new valve springs on both engine a costly job?

Thanks, you all have been there/here before, I am a car racing guy and never had a high end performance boat other than twin 454's. Thanks so much for the info

The early carb 500hp's were the ones with valvespring problems. However, all HP500's run camshafts with high lift and steep opening and closing rates. They are tough on valvetrain components. I'd do a valve job no later than 400 hrs. and replace valvesprings and lifters at that time. Do a search here on roller lifters and you will see how many failures there have been and how expensive a failure can be.

Thanks so much for the info. I guess I am just having a hard time understanding the need for replacement at 250 hrs. I would have thought that merc would have looked for more longivity. But understanding valve train, cam lift and all the geometry that goes into it, plus high spring pressure, I can see it is what it is. I a little nevous about spending this kind of money and they having to put out more for springs replacement. I can always do it myselft. I have built hundreds of motors in my lifetime.
I just got nevous when this one boat mech really start shooting his mouth about how merc recommended tearing the heads off and doing a complete valve job and lifter and spring replacement at 250 hrs.
I nevr read anything that stated that. Anyway, I will seach valve springs for more info.
its the springs that is the concern here and not the lifters? is that correct.? Thanks so much.

I forgot to mention this is a 2002 BT

I am sorry, I am new at this posting stuff....
they are 500 efi's 2002 boat, so they may be 2001 model engines??