2004 6CTA 480CE M-4 valve seat failure avoidance

WMK,

Welcome to the forum.  My wife and I bought a 2005 460 Sundancer in April of 2021.  I will insert the thread so that you can read and get the full details.  For me, what it came down to was #1 could we buy the boat for a price that allowed us to pay for the upgrades #2 would we be happy with it once we were done.  We wanted a 2006-2008 48 Sundancer with QSC540’s but those were flying off the market here in the Great Lakes faster than we could make offers…….

So we bought our 460(fresh water boat and very clean) and just got done with the multi-year upgrades and splashed last week.  Read this thread and understand the journey that you might be starting and understand that this is an expensive proposition but LESS EXPENSIVE than a melt down.

We are about 10 feet longer than your 390 and weigh close to the same.  We prop’d down, then replaced the heads.  You could do the same or do it all at once.  I have posted other threads and this is the info you are probably most interested in……..  The invoice for the head work was 90hrs @$150/hr plus parts.  So the head work cost $27K.  Here is the thing.  We bought the heads over a year ago so our cost on those very expensive parts was about $1500/head less than I see they cost now.  So figure on close to $30K, or more depending on rates and parts availability in your area.

The alternative is even more expensive of having the engine(s) drop a valve seat and cause internal damage.  The other aspect of this you will want to get your head around is the salt water corrosion that has been at work for the last 19years.  If you choose to have the head work done then the aftercoolers and heat exchangers are coming off anyway so the labor is baked in, just have them fully serviced and hope that father time and mother ocean have been kind to those parts and the gear and fuel coolers as well.

If you are going to run at or just below 2300 for long runs then I would want to know that everything that is going to be working hard is in working order.  The other option is to slow down and take your time.  Hull Speed is a nice way to go if you have the time.  You pay the piper one way or the other.  In time, or Money.

We have 2 of those 390’s in our area and we are acquaintances with one of the couples.  They are retired and decided NOT to replace the heads and they are cruising at hull speed.  They do not cruise far distances like we tend to do.  So we made the choice to spend the money and make sure we have a solid cruising platform that we can depend on.  Yes we are still a little over the curve but I know it, and I will live with it and keep an eye on fuel burn and EGT on our long runs when fully loaded.

We cruise @2220 – 2250rpm burning in the 29-30gph range and we make 22.5mph on average.  We tend to carry 300gallons of fuel max even though we have a 400gallon capacity.  Our dog has a tolerance limit of about 5 hours.  So we stop at fueling marinas to take on fuel and let him off to stretch his legs and take a “break”.  We have found what works for us.  We are happy for the most part.  I would like a different hull shape for our final purchase.  A Grand Banks 46, a Sabre 47 or maybe even a Fleming55 if we can make the stretch. 

In the end I figure making an educated choice that is right for you is the best way to go.  Know your limits and Towboat towing insurance is very cheap for what you get.  Unlimited Gold is a very low cost peace of mind that I do not Cruise without.

Enjoy!