MerCruiser 496 Mag Issue Help

[backarff]

Yesterday, our boat partners started hearing a knock from the engine at low RPM. We boat in Parker so he took it over to Eddie's and after looking at it, Eddie found the #5 spark plug damaged. After doing a compression leak down check, all held at 10% except #5 which went down 25%. Eddie believes it to be a wrist pin knock at idle that goes away when RPMs are increased. Thought it sounded like rebuild time, but Eddie mentioned due to some inherent 496 mag issues, many repair shops (including his) do not want to do a rebuild on them anymore.

My question, if you were in this fun predicament, would you try and find someone to do a rebuild, buy a low hours used engine, or buy a new engine? Sounds like a rebuild is roughly $10-14k if you can find someone to do it, $1-2k to install a used one if you can find one with low hours, and $25k for a new engine. We have roughly 660 hours on our current engine and it has been well maintained.

Any recommendations on what you would do and who to do it with? We've also been talking with Savage Marine just to get a 2nd opinion before making a decision.

Not the end to boating season we were looking to have, especially since we had a trip planned for this weekend.Thanks in advance for any suggestions or input.

 

[Bpracing1127]

What does your wallet want to do?

 

[JFMFG]

Had to do a motor in mine last season. Went with a new block because I blew a rod through it

 

[MK1MOD0]

I personally would rebuild if....

1) you have a reputable shop
2) they can get proper parts
3) they can give you a timeframe.

 

[Blackmagic94]

Yesterday, our boat partners started hearing a knock from the engine at low RPM. We boat in Parker so he took it over to Eddie's and after looking at it, Eddie found the #5 spark plug damaged. After doing a compression leak down check, all held at 10% except #5 which went down 25%. Eddie believes it to be a wrist pin knock at idle that goes away when RPMs are increased. Thought it sounded like rebuild time, but Eddie mentioned due to some inherent 496 mag issues, many repair shops (including his) do not want to do a rebuild on them anymore.

My question, if you were in this fun predicament, would you try and find someone to do a rebuild, buy a low hours used engine, or buy a new engine? Sounds like a rebuild is roughly $10-14k if you can find someone to do it, $1-2k to install a used one if you can find one with low hours, and $25k for a new engine. We have roughly 660 hours on our current engine and it has been well maintained.

Any recommendations on what you would do and who to do it with? We've also been talking with Savage Marine just to get a 2nd opinion before making a decision.

Not the end to boating season we were looking to have, especially since we had a trip planned for this weekend.Thanks in advance for any suggestions or input.

Anything can be rebuilt if parts are for sale. Shop is a moron.


Tank is selling a pair of HO engines that make 50 hp more. Buy both and sell the the extra I would

 

[Fun Times]

Maybe check out Raylar engineering’s website to see if there’s any interest of help there., https://www.raylarengineering.com/496mag-marine-performance-parts.html

 

[Yoshiro]

I've done a few 496/8.1s . Yes they are worth rebuilding. And when you do it, you can "build back better" and put off the shelf forged Wiseco pistons and 6.7" forged rods in it. These parts are much better than original and the price for each are very fair. Then you will have taken care of the weakest link in the rotating assembly of the 496.
Like was mentioned earlier, just find a good shop you can trust to do it. The Gen 7 big block is a mystery to many therefore not too many shops will rebuild them. That is really too bad, as they are considered the longest running big block built by Mercury.

 

[farmo83]

I will add if you want to upgrade in the future, get a 502 based setup. If not amd you can find a reputable shop then go with it.

 

[Mcob25rg]

As said above, build back better. That’s what I did with whipped add, but I think a used 525 is a MUCH better option.

 

[Havasu blue label]

There’s a boat shop in Pasadena would do it 8 gs with my name

 

[Havasu blue label]

496 is a dependable motor

 

[spectra3279]

@obnoxious001

 

[Singleton]

496 is a dependable motor

in stock form yes. Trying to get more HP out of a 496, is asking for trouble.

 

[SBMech]

25% leakage going where exactly? You paid for a diagnosis, that's it? Wrist pins that knock don't cause a loss of compression or damage spark plugs.

Take it somewhere who actually knows how to properly diagnose an engine before you spend money IMO.

 

[backarff]

I've done a few 496/8.1s . Yes they are worth rebuilding. And when you do it, you can "build back better" and put off the shelf forged Wiseco pistons and 6.7" forged rods in it. These parts are much better than original and the price for each are very fair. Then you will have taken care of the weakest link in the rotating assembly of the 496.
Like was mentioned earlier, just find a good shop you can trust to do it. The Gen 7 big block is a mystery to many therefore not too many shops will rebuild them. That is really too bad, as they are considered the longest running big block built by Mercury.

I think that was one of the most surprising parts to me was thinking about how long the 496 mag has been around and that shops were apprehensive to rebuilt them, especially with under 700 hours on it.

 

[backarff]

There’s a boat shop in Pasadena would do it 8 gs with my name

What is the name of the shop? Our boat is in Parker, but would obviously bring it to Pasadena for a reputable rebuild.

 

[backarff]

in stock form yes. Trying to get more HP out of a 496, is asking for trouble.

That's all we are looking to do - back to what we had. Improvement in performance is always nice, but realistically, this boat is more of a utility boat that pulls kids on inner tubes, wakeboards, skis, and occasionally goes into the high end rpms.

 

[Jay Dub]

rebuild it at a reputable shop

 

[Yoshiro]

With how many 496s are out there, we're coming to a point where the demand for rebuilding or reman exchange is going to be high. Somebody will figure out this opportunity and fill this niche.

Not many know, but the 8.1/496 was developed with LS heads in addition to the old school style heads. At the last minute GM chose the old school style heads I hear due to production schedules or other constraints. Imagine what our world would be like today if they had created the LS 8.1! As many know, the small block LS engines have changed the small block world forever.