Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

[tpenfield]

Well, my boat ran into some engine issues a couple of weeks ago. So, I thought that I would start a thread to get some input and ideas as to what to do about it.

A little background . . . The engine was only about 5 hours into the season this year, and last season, I did a valve job and replaced the exhaust manifolds and elbows avec OEM gaskets, etc.

July 7th we were out in the boat . . . cruised for a short while and then anchored for a few hours. I went to start the engine when we were ready to go back home and the engine would not turn over. I spent some time diagnosing it as battery and/or starter problems, then finally pulled the plugs a couple of days later. the entire port side of the engine had water in the cylinders. :facepalm: Salt water no less. The starboard side was fine.

Then I checked the oil and it was clear golden, but up about 1 quart. . . I dumped about 1 quart of oil down the carburator and spun it through the engine to get some oil into the cylinders, etc. Since then I have been dis-assembling the engine in my spare time to see the extent of the damage and determine the course of action. I was able to run a compression test, but I was not able to run a cylinder leak test as I cannot turn the engine with a breaker bar . . it comes to a hard stop just after # 1 TDC. When I ran the compression test, I was feeling a 'thumping' as the engine turned . . . so maybe a bent connecting rod or something. #1 is 100 psi, #4 is 115 psi, #7 is 130 psi some were 140 psi and a few were indeterminant as they still had a bunch of oil in the cylinders.

So, the port side cylinder head had a rusty valves all the way down. The starboard side cylinder head had rust on #4 valves only.

I believe the port side has bent connecting rods as those 4 cylinders do not seem to come up to the top of the block as the starboard side cylinders do. They all come up about 1/2" lower than normal. (so, now I am thinking 4 bent connecting rods)

All the gaskets looked fine as I took things apart, they are all new OEM/Marine from the valve job over the winter. So, I was thinking that maybe the intake manifold rusted out and sprung a leak and water got sucked into the engine, etc. I tested the water duct in the intake manifold and that seems to hold water fine and does not leak into the intake ports.

So, now I am thinking that maybe a cylinder wall ruptured, causing a plethera of water on the port side of the engine. the exhaust manifold on that side had a water mark at each cylinder port, so lots of water.

What is surprising is that the engine did not seem abnormal or anything like that while it was running

I plan on taking the engine out of the boat tonight, so I'll be able to examine the crankshaft, connecting rods, etc.

My thinking is a this point that the engine is a gonner and a new long block would be needed.

In weighing my options:

1) Remanufactured Long Block = $2,500 - $3,500 (7.4's have become rare as they are no longer in mass production)

2) New GM Marine Long Block = $5,000 - $6,000 (they still make 7.4's for marine replacement blocks, I guess)

I read too many horror stories about remanufactured engines being hit or miss as to their quality and longeveity. I am also thinking that amount of investment in the boat (1991 Formula) is not worth it.
.
3) I could just offer the boat as a salvage boat and take about 1/2 the $$$$ of an operational boat.

Thoughts, ideas?

Thanks in advance for any thoughts you may have . . I am trying to look at all the possible angles.

Meanwhile, I have a boat search trip planned to NY, NJ in search of the next boat

 

[MarkSee]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

Seems to me that if there is no kind of rotting going on with the stringers/hull, the drive was operating fine and the fact that you are capable of doing the R&R of a new engine yourself, stick with what you got and just replace the engine.

Mark

 

[RogersJetboat454]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

Tough break guy

Just looked over at Summit, and even a GMPP short block is over 4 grand. Suppose you could call around to different bone yards to see if they had an unmolested truck engine. But even carefully used BBC are few and far between, and big money when their available.

Is yours a Mark IV or a gen 5?

Nothing beats the torque and sound of a BBC, OTH few things top the high price of building one.

 

[HT32BSX115]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

July 7th we were out in the boat . . . cruised for a short while and then anchored for a few hours. I went to start the engine when we were ready to go back home and the engine would not turn over. I spent some time diagnosing it as battery and/or starter problems, then finally pulled the plugs a couple of days later. the entire port side of the engine had water in the cylinders. :facepalm: Salt water no less. The starboard side was fine.

Hi Ted,

It really sounds like it might have been a riser gasket failure allowing a small amount of water to run back into open exhaust valves. If it sat in there over a winter, it could explain the rust etc. (I had the same thing happen in a 460 OMC but never had it in salt)

I would say that you have a decision to make. You have to decide whether the boat with a new engine is worth (to you) what it will cost to replace that engine regardless what you replace it with.

For future consideration, you might think about closed cooling. If you decide to get another engine you also might think about dry-joint manifolds and risers which would reduce the riser gasket problems in the future. I think they're available for the SBC and 496 BB engines........ (not available for the 454's though I think)

For what it's worth, The 383 is supposed to perform the "same" as a 454. I would want closed cooling and Dry-joints......


When I replaced my OMC 460 in 2005, I found the entire replacement engine and drive on Craigslist in a wind damaged boat. since then in the Pacific NW, I frequently see engines (and drives etc) for sale in various states of repair/disrepair 454/496 etc......

You'll have to decide if it's worth it to do the job. If you can do it all yourself, (and not count your labor......It's a 'hobby, right?) Then you can probably make it "worth it"


If you can't, and you have to pay someone to do it all, you might start getting ready to either part it out or sell as-is and call it good (or BAD!)


Sorry about that.



Rick

 

[tpenfield]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

Tough break guy

Is yours a Mark IV or a gen 5?

Nothing beats the torque and sound of a BBC, OTH few things top the high price of building one.

It is a Mark IV . . has the 4 bolt main, mechanical fuel pump, self adjusting valves, oval ports. A year or 2 afterwards, the Gen 5 engines came along.

I was originally thinking about a rebuild, because I can get some rebuilt heads fairly cheap. BUT . . . if there are bent connecting rods, then there is potential for crankshaft damage or stress, piston damage, etc., so a long block would be the safer route. I'm still trying to put my finger on the cause. Maybe I'll know tonight when I open up the lower end of the engine.

I have been planning on selling the boat for a while, but I guess the boat has other ideas
.

That is why I am considering going the salvage price route and not put additional money into it . . . use that money towards a new(er) boat.

 

[kd7isf]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

Sounds to me like your exhaust manifolds rusted out.
Then you turned it over with water in the cylinders and caused hydrolock damage.

Mainfolds are only really designed to last 5-7 years or so at the most...

 

[Eric 3.7LX Alpha 1]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

If it were the cylinder wall, you could/may be able to have a sleeve pressed in, and bored out to whatever you needed.

 

[undrh2o]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

there is a running 7.4 w/outdrive for $2000 listed on CL under North Carolina boats...I think in Fayetteville

 

[tpenfield]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

Sounds to me like your exhaust manifolds rusted out.
Then you turned it over with water in the cylinders and caused hydrolock damage.

Mainfolds are only really designed to last 5-7 years or so at the most...

Manifolds and elbows are brandy new. . . 5 hours on them . . . gaskets looked good when I pulled it apart, etc. The engine would not turn at all when I went to start it, so I think it hydro-locked as I shut it off before anchoring. At this point, it is really hard to tell. I did a leak test on the manifold and it was fine.

I did not quite get the engine out this evening. So, I'll have to wait until tomorrow to see what the lower end looks like.

Interestingly enough, I have a couple of offers on the boat from my ad on CL. This is all through email, so I'm not quite a sure about the offers. I probably won't let go of the boat until I really know what is wrong with it and determine that it is not worth my while.

I may Check out that 7.4L & outdrive in NC though. I wish I saw something like that here in MA. . . it would be worth fixing myself.

In better news, I got a call from a buddy that had his boat in the shop for about 3 weeks now. Initially, they told him that a valve had tuliped . . . but now they tell him that it was just sticking. So, the $2,000 estimate came down to about $700.

 

[Bondo]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

Ayuh,.... Tough break Ted,... Sorry it hear it....

Any chance of wave backwash,..?? donno why, only 1 side...

As for fix, or replace,... Soundin' like that 1 is gettin' closer to a moorin' block,...

 

[tpenfield]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

Ayuh,.... Tough break Ted,... Sorry it hear it....

Any chance of wave backwash,..?? donno why, only 1 side...

As for fix, or replace,... Soundin' like that 1 is gettin' closer to a moorin' block,...

Yes, a mooring block would be good, as I am looking at getting a 28 footer with twin engines. Just booked the hotel for the road trip to go see some boats.

As for the engine and the hydro-lock circumstances . . it is very odd, because it is a good 10 minutes of idling at no-wake speed in the harbor until we got to the anchoring area. One of my first thoughts were that there may have been an obstruction in the exhaust tube that goes thru the transom. But both tubes were clear.

Maybe I'll know more tomorrow, if I can get the engine out and have a look inside the block.

 

[tpenfield]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

there is a running 7.4 w/outdrive for $2000 listed on CL under North Carolina boats...I think in Fayetteville

Just saw a 454 Magnum w/Bravo 1 - complete engine package with transom assembly and trim pump on CL in my area. So, maybe, just maybe. . . .

 

[tpenfield]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

UPDATE -

I have the engine pretty much torn down and have been able to look at the water and hydro-lock damage, and isolated a cause.

It appears that one or more valve guides on the port side exhaust were leaking and began to leak at a fast rate during the last outing of the boat . . . its final outing. Water from the port side was pushed over to the the starboard side through the exhaust cross-over port, causing water and rust on #4 cylinder and valves.

Reversion ( valve overlap) pulled water from the exhaust ports into the port side cylinders while the engine idled, stressing (bending) the connecting rods on the port side. Water being expelled from the port side exhaust accumulated in the exhaust manifold and then settled back down onto the exhaust ports and valves when the engine was turned off.

. . . and that my friends is how the engine met its fate. :facepalm:

 

[tpenfield]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

BTW - I decided not to go look at the 454 Magnum engine 'package' as it came off an 1989 Baja with "many, many" hours. so, there is something about putting an old engine into an old boat that did not add up (to me).

Anyway, I have listed the boat on CL as a fixer-upper and have some folks coming to look at it this weekend. I decided to put money towards the 'next' boat and not towards 'this' boat. I have 2, possibly 3 boats to look at on the first weekend in August.

So, we shall see.

 

[04fxdwgi]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

BTW - I decided not to go look at the 454 Magnum engine 'package' as it came off an 1989 Baja with "many, many" hours. so, there is something about putting an old engine into an old boat that did not add up (to me).

Anyway, I have listed the boat on CL as a fixer-upper and have some folks coming to look at it this weekend. I decided to put money towards the 'next' boat and not towards 'this' boat. I have 2, possibly 3 boats to look at on the first weekend in August.

So, we shall see.

Ted,

That is a shame. Sorry to see you letting her go, as I have been following your threads for a while and really like your boat (I'm from the South Shore, myself). If I didn't have my 2550 SX Chap, I would jump on it and take her off your hands in a heart beat. My boat has 1300 hours on it and still purs like a kitten.

 

[Lou C]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

Ted I am sorry to hear that, I followed your top end rebuild and stringer/rot repair and was impressed at what you were able to do yourself. I know how it is when you get to that point with a boat, I did the rot repair (stringers n deck) and new interior on my '88 FW but the gel looked so bad, I was embarrassed to keep using it. Finally got it painted in red Imron this year, looks great but still has a 24 yr old engine in it. Running good, uses some oil (no smoke, no leaks, no oil in exhaust water, good compression) so I just keep monitoring it and will run it as long as it will run.
One thing I wonder about, I have the one piece OMC manifolds, two sets actually and have never have had any water in the cylinders because there is no joint to leak. I like this design but it was not popular, probably cost too much to cast.

After what you put into that boat, and it being a Formula which is head and shoulders above the typical I/O style boats in quality, I'd have a hard time getting rid of it. Any used boat can have engine issues too. When the time comes I am repowering my old one with a NEW GM long block 4.3 and closed cooling. If there is any way I could adapt the Merc dry joint manifolds I would, but that might be too difficult. I don't really trust remans unless I know people who had direct experience with the person doing the work. New in the case of a little 4.3 is not all that much.

 

[tpenfield]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

Thanks for the condolences Guys . . .

Since I am looking for a new(er) (and bigger) boat, it does not make sense for me to keep it and the money to fix it up would probably be better spent on the 'next' boat. I was on the fence about this for the past week or so, but I think it is best to go forward. It looks like I might have 3 showings this weekend.

But when you think about it 20 years in salt water - that engine is done.

Of course I have learned a lot of things about boats with this boat, so hopefully that experience will be beneficial for the next boat. I am now becoming a big fan of Fresh Water Cooled engines, so that will be a factor in my search for a Formula 280 SS.



Someone is supposed to be here in 1/2 hour to look at the boat . . . and it is raining, soon to be thundering.

 

[tpenfield]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

SOLD !!!

The guy came in the poring rain. . . looked around at it, had his wife take a peak in the cabin . . . took a look at the engine parts, etc. Offered me near my asking price . . . Done.


I guess I gotta change my signature now . . .

 

[Lou C]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

Wow, that's the good luck you needed to come out of the bad luck!
Fresh water cooled and straight inboard for the next one?
No outdrive in salt water would be nice!

 

[NHGuy]

Re: Mercrcuiser 7.4L Hydro-locked and pretty much destroyed

Good for you. I recently rode with a friend with a 26' SS Formula and it's stupendous, so the 28 can only be better. Glad you escaped the failed motor as well as you did.