Mercruiser 496 MAG Refresh Thread

[AShipShow]

Hi to all the Merc experts out there... I'm in the process of giving my new-to-me 496 MAG (0W358880) a good once over since I have it out of my boat. I figured instead of creating a bunch of new posts whenever I come across something, I'd just start a general thread that I can ask the questions in.

So far I've checked compression and leakdown and everything seems peachy there. I've also dealt with some corrosion on the oil pan by sodablasting and repainting. Next was the seawater pump which had some serious internal grooving so i replaced it with the Hardin Marine stainless pump. Also threw a new starter on as the old one was very corroded and initially needed some percussive maintenance to get it to turn over. I've also inspected the exhaust manifolds with a boroscope and did an acetone test and all looks well there. At this point I'm reassembling everything I removed to do the work above.

My initial question at this point seems like a basic one but want the experts opinion.
I went to put the flywheel back on yesterday and noticed the dowel pin was missing.
I'm 99.9% sure it wasn't there when I removed the flywheel so I looked at the merc parts diagram and sure enough there is one listed. So my initial gut instinct was just get the replacement and put it in, but then I was second guessing myself on if the motor was possibly rebuilt at some point and balanced with the flywheel in a different orientation... Not sure what the likelihood of that is and honestly would like to meet the guy that would have balanced it with the flywheel in a different orientation. I assume I'm overthinking it and should just buy the dowel and reinstall it, but wouldn't mind a second or third opinion.
Side note: if I reinstall, do I need the merc one or will any GM 8.1L dowel work? Anything special about it?

Thanks

 

[Scott Danforth]

the 8.1 is internally balanced. just align the non-tapped hole with the locating hole in the flywheel.

 

[AShipShow]

the 8.1 is internally balanced. just align the non-tapped hole with the locating hole in the flywheel.

OK, so no worries over like shear forces on the bolts or anything? I'm assuming not simply because from what I can tell, the dowel pin is a spring pin anyways, not solid, so it couldn't really provide much rotational resistance anyways.

 

[AShipShow]

Back again with more confusion... I'm an idiot and removed my power steering pulley with a 3 jaw puller before finding out that thats a terrible idea and you need to use the PS puller that you can rent from autozone/etc.. So after reinstalling the pulley and checking my alignment, I realized the pulley was now bent and has a decent wobble to it..
I went to search the part and I'm getting conflicting info... it seems like its either no longer available or a special order item...
This is one of the Saginaw Type 2 pumps and the older ones had 19mm shafts and the new ones are 17mm shafts.. The confusing thing is, my serial number should be the "newer" style, but my bore size is 19mm (the older style)... I'm having a hell of a time finding the right pulley... The only thing I've found that looks like an option is the hardin marine billet pulley kit, but thats $190 dollars.. lol

Just curious if anyone else has run into this issue with this PS pump. I was hoping the pulley would be an easy to find $30 part but of course its not.

 

[Scott Danforth]

go to NAPA, talk to the pot-bellied grey haired guy behind the counter. should be about $20 for a stamped steel PS pully.

you can also straighten yours out with three blocks of wood and an arbor press

 

[AShipShow]

go to NAPA, talk to the pot-bellied grey haired guy behind the counter. should be about $20 for a stamped steel PS pully.

you can also straighten yours out with three blocks of wood and an arbor press

I'll have to give the pot-belly route a shot...

I don't think the arbor press route will work because its not warped like a potato chip, its more that the angle of the bore of the pulley no longer perpendicular to the plane of the pulley. If it put i on a flat table, there aren't any raised areas... I almost thought about putting a 3/4" steel shaft in the bore and clamping the pulley to my workbench and trying to bend the bore back into alignment..

If none of that works, I already threw my wallet at the computer monitor and ordered the hardin marine billet pulley out of frustration.

 

[Scott Danforth]

put in a 3/4" bolt and straighten the bore.

 

[AShipShow]

I'm back again, got the pulley thing straightened out (no pun intended).. I wasn't able to fix the old pulley as much as I tried, and even the hardin marine pulley kit didn't fit right so I must have won the lottery of in-between weird years from Mercruiser.. I ended up having to turn down the new hub on my lathe so I could press the pulley on further to align with the crank..

Anyways.. I've been doing some pondering over the holiday and trying to decide how deep I want to dive into the Bravo transom assembly. I already have the bellows kit and shift cable and plan to do all that, but I'm wondering if while I have the engine out and the drive off if I should consider replacing the steering pin and seal... I have no reason to believe its worn or bad but just thinking its never going to be easier... just obviously would translate into then needing to buy more tools, parts, etc.. Again the boat is a 2006 in basically fresh to minimal brackish, so I don't know what the life expectancy of these things are.

 

[Lou C]

I would say that anything that might possibly fail and result in the need to pull the engine again, I'd for sure do it now. That includes all possible leak areas on the transom mount/exhaust Y pipe, etc.

 

[Scott Danforth]

FWIW, everything was new with my boat in 2020 when I splashed it..... may have to pull my motor just to get room in the bilge for replacing the LED service lights I added to the bilge , and add the water tank for the transom shower I am adding.

 

[AShipShow]

FWIW, everything was new with my boat in 2020 when I splashed it..... may have to pull my motor just to get room in the bilge for replacing the LED service lights I added to the bilge , and add the water tank for the transom shower I am adding.

Yea I know.. My previous 20' bayliner was a 30 minute job to get the motor out and I've pulled the motor just to give the bilge a good cleaning... but my new situation, my gantry is 14' tall and the motor BARELY clears the cockpit.. its sort of integrated into my temporary boat shed in the driveway, so to rebuild the gantry in the future is a much more intensive task so I'd really like to avoid needing to do it anytime again soon...

Is there anything else transom assembly related I should be considering that would be a good idea while the motor is out? its a bravo 3 FYI.

 

[cyclops222]

Did you ever find how so much water corroded all the lower parts of the engine so badly. That they needed replacement. Bilge pump not working ? Water leaking into hull at openings below the waterline ? Some boats have Fresh Air Inlets accidently installed FACING FORWARD. That rams water into the bilge at high speed crossing of waves and wakes. Leaking water around a Sonar Transducer hole. Stopping too fast causing the Wake Wave to slide way up the transom and enter any loose bolt holes.

 

[AShipShow]

Did you ever find how so much water corroded all the lower parts of the engine so badly. That they needed replacement. Bilge pump not working ? Water leaking into hull at openings below the waterline ? Some boats have Fresh Air Inlets accidently installed FACING FORWARD. That rams water into the bilge at high speed crossing of waves and wakes. Leaking water around a Sonar Transducer hole. Stopping too fast causing the Wake Wave to slide way up the transom and enter any loose bolt holes.

No... Hard to say with the boat sitting 3 years... My assumption is just rain water because I think the boat was out of the water on the trailer for about 3 years so probably no battery and or working bilge pump... You'd think they would pull the transom plug though. Either way, got it all cleaned up and repainted.. Looks like the oil pan never had any zinc primer from factory... The paint flaked off just looking at it.

 

[alldodge]

Anyways.. I've been doing some pondering over the holiday and trying to decide how deep I want to dive into the Bravo transom assembly.

while I have the engine out and the drive off if I should consider replacing the steering pin and seal... I have no reason to believe its worn or bad but just thinking its never going to be easier...

I wouldn't

 

[AShipShow]

Found something weird today... the mercruiserparts dot com diagram doesn't have any of the exhaust y pipe components.... I found out that the coupler from the elbow to the y pipe on the port side is delaminating internally so I'm going to replace both.. However, it uses wet exhaust hose, not a regular rubber coupler. I've seen a few google images that show the same thing as mine so I think it came from Mercruiser that way.
Oh well, not a big deal.. The thing that was extra confusing... The hose I pulled off says "Green Line G388 Softwall blah blah blah"..
I hit up the google machine and wouldn't you know it, you can still buy the stuff.. So I measured the circumference of the y-pipe to get the average diameter since its oval and it works out to about 3.86"... weird.. So I also measure the circumference of the old hose both in the middle and where the hose clamps were, both worked out to be about 4.25"... I check the OD of both 3.5" and 4" hose on the greenline site and they are 4.09" and 4.57" respectively...
So to me, it seems like the hose SHOULD be 3 3/4" which Green Line doesn't make... again... weird..
Anyways, I found that SHIELDS makes 3 3/4" softwall exhaust hose so I ordered that..
No point to this story other than I keep running into odd stuff like this and the mystery power steering pulley. And I can't even blame the previous owner.. This was all factory stuff...

 

[Scott Danforth]

4" marine exhaust hose. (rated at 250F like the expensive marine exhaust couplers). I used 4" 5-ply Nomex turbo hose for al my marine exhausts. rated at 500F and about 500% stronger.

 

[AShipShow]

Well, the pile of problems continues to get larger faster than I can take care of them... Just discovered two of the tubes in my heat exchanger are leaking.. I've seen mixed reviews on repair vs replace.. The mercruiser manual actually states that you can plug up to a certain number of them, but my fear is, if two are leaking, how many more are just around the corner from leaking.. I think brazing two of them shut would be pretty simple, but I don't love the idea of the rest of them potentially leaking soon after... I guess the heat exchanger is easy to get to so maybe its worth trying a repair??
I'm just trying to think about what the failure causes?? Just raw water getting into the cooling system?? Which in and of itself probably isn't that big of a deal in fresh water, but then I'd run the risk of my block freezing if I don't notice that the coolant has been diluted...

Damn boats!!!

 

[Scott Danforth]

Are the tubes bad, or the braze joint to the header sheet

 

[AShipShow]

Are the tubes bad, or the braze joint to the header sheet

From what I can tell it seems like the tubes

 

[Scott Danforth]

Top row?