496/8.1L short/long block replacement

cbruck

Member
Jul 5, 2016
40
Ocean Springs MS
Boat Info
2010 SR Sundancer 390 I/O's with 496 MAGs and Axius Drive
Engines
496 MAG's
I've got a sundancer with mercruiser 496's, 2009 model year. Which by the way, I heard was the last year they were made. Something in the lower unit let go this weekend with 550 hrs on one engine. I'm trying to figure out the easiest and best way to get it repaired. Mercury only sells long blocks at $12-13k. I have one bid at $20k to replace the engine with a new long block engine. I believe a short block is all I need as everything around the engine, ie the manifolds, water pumps, starter, alternator etc are all new in last year or two. But it seems like I can also get a rebuilt long block from various vendors in the $5-6k range which includes the cylinder head. In a short block rebuild I would need to send the heads off to get rebuilt. Some vendors have new engines at $5-7k but not in the 496, probably because they can't get new blocks anymore. As I have not done this before, it seems like the hardest part is getting the boat out of the water and have someone come and lift the engine deck off and get the engines out. Swapping the parts on a long block seems relatively easy by swapping manifolds and accessories.

I am looking for any input along these lines. Especially where to buy the short/long blocks. Also concerned about fit, I don't want any modifications, ie plug and play.

Just on a related note. Should I rebuild both engines? If I resell with one engine that has 550 hrs more than the other, set red flags? Or just rebuild and leave it go from the 550 hrs.
 
Wait. Why does a 10 year old engine need replacing?

Mine is 50 years old and still reaches full rpm at WOT.
 
I've got a sundancer with mercruiser 496's, 2009 model year. Which by the way, I heard was the last year they were made. Something in the lower unit let go this weekend with 550 hrs on one engine. I'm trying to figure out the easiest and best way to get it repaired. Mercury only sells long blocks at $12-13k. I have one bid at $20k to replace the engine with a new long block engine. I believe a short block is all I need as everything around the engine, ie the manifolds, water pumps, starter, alternator etc are all new in last year or two. But it seems like I can also get a rebuilt long block from various vendors in the $5-6k range which includes the cylinder head. In a short block rebuild I would need to send the heads off to get rebuilt. Some vendors have new engines at $5-7k but not in the 496, probably because they can't get new blocks anymore. As I have not done this before, it seems like the hardest part is getting the boat out of the water and have someone come and lift the engine deck off and get the engines out. Swapping the parts on a long block seems relatively easy by swapping manifolds and accessories.

I am looking for any input along these lines. Especially where to buy the short/long blocks. Also concerned about fit, I don't want any modifications, ie plug and play.

Just on a related note. Should I rebuild both engines? If I resell with one engine that has 550 hrs more than the other, set red flags? Or just rebuild and leave it go from the 550 hrs.

I’d take a step back. What really happened? You might not actually need a rebuild. You said something in the lower unit let go, are you saying the bottom end or something in the drive?

I thought I spun a coupler a couple years ago, turns out I blew the lower on one of the drives instead. Still sucked, but an easier fix than pulling the motor. I’d say do some diagnostics first, it might not be so bad
 
I’d take a step back. What really happened? You might not actually need a rebuild. You said something in the lower unit let go, are you saying the bottom end or something in the drive?

I thought I spun a coupler a couple years ago, turns out I blew the lower on one of the drives instead. Still sucked, but an easier fix than pulling the motor. I’d say do some diagnostics first, it might not be so bad


First, the engines have been very well maintained. Fluids have always been kept up and oil changes every year etc. A mechanic already took a look at it and we can hear something metal in the oil pan as we turn over the crank by hand. It's either a rod or a bearing that let go and as you turn the crank over by hand you can hear it bounce in the oil pan.

I'm looking for quality remanufactured/rebuilt engine suppliers. Recommendations?
 
I'm also looking for advice on replacing the long block by myself and a mechanic. My mechanic is a friend that has rebuilt engines from the ground up but out of trailered boats. It looks relatively straight forward but are there any gotcha's or tricks in pulling the 496's that require special tools etc?
 
First, the engines have been very well maintained. Fluids have always been kept up and oil changes every year etc. A mechanic already took a look at it and we can hear something metal in the oil pan as we turn over the crank by hand. It's either a rod or a bearing that let go and as you turn the crank over by hand you can hear it bounce in the oil pan.

I'm looking for quality remanufactured/rebuilt engine suppliers. Recommendations?

Fair enough, definetly need to pull it then. I just wasn't sure based on your first question what you meant by lower unit, that's usually referring to the drives.

I repowered one side this year. Had my marine mechanic pull the boat and motor, we took it to a very good local engine builder who rebuilt and dyno'd it, then the mechanic dropped it back in. I'll let more experienced folks chime in on the specifics to your 496's
 
Yes, the outdrives were new 2 yrs ago and we had them off last year just to inspect but when we pull the boat and drop the outdrives we will check again before we pull the engine. I am considering doing this ourselves as "good" mechanics are 100 miles away.
 
I'd pull it out and tear it down to see exactly how much damage you have first.
 
To answer your question as asked, I recently went through a similar issue. I had a piston melt and take out much of my lower end on the starboard side. I had just done a complete valve job on the other engine two weeks before, which had depleted the disposable income a bit. I decided to take a plunge, and got a long block from enginesdirect.net. The cost was about $3,800 shipped to me. They were easy to deal with, and the engine appeared to be very solidly put together. It is in the boat currently with 20 or so hours and no issues. Time will tell if it was a good decision in the long run. I also replaced the gen 3 fuel module, external cooler, manifolds, etc. All in all, I had about $7,500 in parts into it. On mine, I used the fork lift to stand the hatch straight up with rams detached and get the engine out easily. My engine was heavier, as it was engine and tranny due to v drives. Good luck!
 
Thanks for the direct input. Just to clarify, you used a forklift to open and hold the engine hatch straight up without detaching it and then something else (lift truck?) to lift the engine out? Also curious why you replaced the fuel pump? The only thing not new on my engines are the fuel pumps and power steering pumps.
 
Not quite. I used the fork to lift it up to 90 degrees. Then we tied it off to the mid cleats going forward and the stern cleats going back. We removed the table base to allow looping the line around the top of the hatch, and used ratchet straps to get things taught. Then we used the fork to lift out the engine and trans.

As to the fuel pump, prior to my piston meltdown, I was experienced an issue where the engine would not run at lower rpms after it warmed up.(would run all day long at plane, etc) That is indicative of a bad fuel pump. As the melted piston could also be caused by no fuel to the cylinder, I not only put a new pump in, I serviced all the injectors.
 
Very good, thanks for the information. I didn't think about the fuel injectors. Also curious how many hours you had on the engine?
 
I'm getting ready to pull the boat and the engine. I am looking at Michigan Motorz, Jasper and PPT for the long block replacement. Does anyone have any comments on these or someone else not mentioned? Most of the negative comments are in regards to warranty. Obviously I don't want to be replacing the new engine either under or not under warranty.
 
I bought a pair of 5.7’s and a bunch of other stuff from Michigan Motorz to repower my old 300 Sundancer about 8 years ago.
The owner was great and gave me a lot of guidance and valuable information. Their prices were very competitive too.
After speaking to the owner and making up my shopping list he handed me off to a salesman to place the order.
The salesman was a nice enough guy, but shipping took longer than he told me it would and there were some missing and incorrect items that came with the order.
It was difficult to get the salesman on the phone to deal with the problems with the order which added to delays.
In the end, I got everything I was supposed to get but not without a little bit of aggravation.
I think the problem was with the particular salesman who had little motivation to deal with me after the order was initially placed. Stupid way for a salesman to be and insured that I wouldn’t refer anybody to him.
But I think the company itself, and certainly the owner (who ultimately resolved the problems), is pretty good.
 
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Could be wrong about this but my understanding is 8.1 blocks can not be rebuilt due to the relatively small amount of thickness in the cooling passages. If you bore them they overheat. As you know, they are no longer available which is a shame because they are great engines. Hope I'm wrong but I have heard this a number of times and when you look around for 8.1 blocks it is slim pickin's.
 

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