I had installed 2 454HO in my old Formula it had over 300hrs when I sold it and it must have at least 500 now and runs perfect still. It had 750 Holleys jetted fat and Stock mercruiser center rise exhaust, but is still running today. Mercruiser and all the other manufactures use them. Keep looking for the problem.

What was your engine running at for temps before they let go? As everyone has said, marine engines are clearanced a little more than regular automotive. If you are running to cold, the aluminum pistons expand at a faster rate than the block and the clearance on the pistons become zero. this will score the pistons and everything then heats up and chews up and you get the idea. leaving the bottom end unhurt. This can also happen if you don't let them warm up enough before you hammer on them. These failure seemed to happen awfully early in the life of the engine. How hard were you running them? How did you or the mechanic break them in? The bigger carbs don't necessarily richen up the mixture either. They should've put bigger Jet's in the carbs and possibly different power valve depending on what was in the carbs to start with. If they put the bigger carbs on an ran the same jets, it would actually make it run leaner. As Mr. Cig said, he's running 750's jetted fat. This cools the combustion chamber temp and in turn cools the actual piston temp, this keeps the pistons from expanding as much and you maintain your piston to wall clearance. The other end of this is also the possibility that you had an air pocket in the cooling system and they overheated without seeing it on the guages. I'd really look at the possibility of the engines running to cold. Just another idea for you to think about.

there is one thing I have noticed from this board that really still leads me to the mechanic.after all this time and all the people on this board not even one has mentioned they have had a problem with these 454's. Another thing I found out was when looking for the serial #'S on the motors, they where all manufactured months apart from one another. If no one here has heard of a problem and mine are 3 to 4 months apart being manufactured how can it be the manufacturer defect, i'd understand it more if they where consecutive numbers of the line. some asked about temp. if i recall right the temp would go up to about 190 then drop down to 180 after thermostats opened. From what I gather from everyone, is the main 4 things to do is make sure the mechanics 1. primes the water system and gets all air out. 2. primes the oil system. 3. sets the advance timing no more than 30 to 32 degrees advanced. 4. make sure I either buy new oil coolers (which i did) or clean the old ones. 5.(get a new mechanic, which i would if he already didn't have all my money). but 1-4 looks like what I have to make sure he does. please let me know if there is anything else I should check for before I let him fire up a new set.

Was hoping to get an update.

CS

Well I've been on land all summer. The mechanic has turned it into his insurance company to see if they will make good. As usual have not heard anything back yet. Nobody else wants to here it. No one has even bothered to look at it to see what the problem was. Its funny it hard for me to believe that anyone could afford boating, problems can arise so fast with out warning and everything cost a arm and a leg and your first born and no one stands behind there work or product. If I ran my business like this I'd be out of business. If the insurance company comes through, I going to look for someone who can build me some nice motors. Hopefully there is someone locally on this site that everyone will recommend that will build me some nice strong blower motors reasonable and install them. I'll keep everyone informed thanks for all your help ose

BLOWER motors? You think you got problems now? I'd do it too if i were you though,just had to rib you a little,good luck,Smitty

Vinny, Speak to Audiofn and he'll steer you in the right direction with a reputable engine builder in your area. I would stay away from the blowers,the TRS' will be expensive.

Wow sounds like mechanic is a real winner. Going the let's see what the insurance company says route. Insurance is there to cover his loss in the event of product failure, my take that means he should be taking care of problem with you either way. I certainly would be making sure he knows that the insurance is his problem seeing as you paid him for the job, but that's JMO...
Good Luck to you!