Mercruiser 7.4 bravo sprinkler

[sirhc76]

I?ll try and keep this short and provide enough info, Ive read more threads than I remember and its time to just ask for help. You can skip to the bottom if you just want the question

We bought our first boat in April 2015, Wellcraft Eclipse 240, 7.4 Bravo, serial OK193466 with 450 hours on it. It never really had the power I thought it should when loaded with more than 3 people. With a load of 4-5 adults it would plane fine but top out at 25-30 MPH with a 19p 3 blade stainless.

After doing some reading, well lots of reading, I learned that the nice new Edelbrock carb the previous owner had installed to replace the Weber was a 1406. It was neither a 750 nor marine carb as it should have been. We dealt with it for the few runs mainly because I didn?t want to tell the wife I made a bad decision. I made it a winter project.

I winterized the boat last fall and during the process noticed the fresh water pump was cracked. Those winter projects turned into spring projects and I finally ordered the pump along with new wires, plugs, rotor, coil, fuel filter and belts from iboats. I flushed the shredded impeller out of all hoses up to the oil cooler and found nothing at the Tstat.

When I replaced the carb with the new Edlebrock 1410 I realized the pre vious owner had installed the Mercathode mounting bracket between the carb base and intake. Obviously there was a small gap and most likely a huge factor in performance. I addressed all these issues.

First run of the season was a little better but still not where I thought it should be. We don?t really run the boat for long periods of time, 10 min max then shut down and float in the coves for hours. Second run we shut down for the evening to let other boats clear the ramp. Tried to start and it wouldn?t crank, pulled the cowl and the motor seemed a little warm, temp gauge never went about 170?. Checked the oil and there didn?t appear to be any water in it.

I realized something wasn?t right and didn?t continue to crank it, got a tow in and pulled it home. Pulled the plugs and all of the cylinders had water in them. Turned it over with no plugs and it cranked fine, just looked like a sprinkler. I dried out the cylinders and ran a compression test followed by a leak down. Cylinders 2-8 were all between 150 and 154, same on 1-7 although 3&5 were 90. Leak down test was low on 3&5 as well. Sprayed some oil in 3&5 and the results were the same. Assumption was head gasket or manifolds.

I?ve already ordered all the gaskets from iboats less the intake set which wasn?t stocked. Exhaust and intake are off, two head bolts are iffy and almost rusted all the way off so they will be fun. After removing the heads which direction should I go?

I obviously have the peanut heads, should I just have these heads rebuilt, buy a rebuilt set, or go back with different heads and intake or just replace the gaskets and clean the heads up. I don?t have the funds this year to replace/rebuild the motor so I just need to get through this season.

Thanks,

 

[bruceb58]

I have a 24' Wellcraft Eclipse in my sig and can get over 45MPH at sea level in salt water if I open it up. I have a Volvo DuoProp

EDIT: I was suggesting Vortec heads and now I am not too certain what the difference is on the 7.4L.

 

[HT32BSX115]

Howdy,

Welcome Aboard!

It never really had the power I thought it should when loaded with more than 3 people. With a load of 4-5 adults it would plane fine but top out at 25-30 MPH with a 19p 3 blade stainless.

More info is needed. How are you measuring speed? did you use (phone)GPS or the boat speedo?

What was your RPM at WOT.......... If that's a Bravo I, I'll assume you have a 1.50:1 drive ratio? Did you adjust drive trim for max speed while underway (on plane)


I have a 21ft Four Winns (with a 454/Bravo) that probably could be called a 23 if you include the swim step (like they do nowadays) and it'll do 57 flat out with the same engine. I also have dual contra-rotating props (Mercury Calls it a Bravo III)

The guy I got my engine from (previously installed in a 24ft Bayliner) told me he could get it to go around 50 or so.

It really looks like you had riser gasket (or riser/ex-manifold) leaks on both sides.

How about some pictures of the heads and cyls ( if you have the heads off?)

Also, look in BOTH y-pipe exhaust tubes. do you have BOTH exhaust shutters intact? Do you have 3", 4" or NO riser extension? (I have 3" riser extensions in mine)

When you shut the engine the last time, did you turn off the key or did the engine quit before you came off plane? Was the boat sitting low in the water and another come by the back with a BIG wave?

With no (or stuck open) exhaust shutters and no riser extension, it's possible for a big wave to push water into and up over the "hump" in the riser if the boat sits "LOW" in the water (there's a Mercury recommended "Minimum" distance between the top of the riser and the observed waterline. (hence the existence of 3", 4" or even 6" riser extensions)

It is not all that likely to have a "blown" head gasket. I don't mean it's impossible, it's not all that likely the way you describe your problem.

You also might have cracked exhaust manifolds. If they're not drained properly, they can retain enough water to crack when it freezes. The engine starts up and runs great the first time. Shut it down and all that water runs back into open exhaust valves. If you have a cracked intake manifold, you have water on the intake side of the engine

You can check your head gasket integrity by pressure-checking your entire cooling system BEFORE removing the intake manifold and heads. (excluding the exhaust manifolds which are isolated from the cooling system prior to pressuring it up)

If there's no cracks in the intake manifold and the head gaskets are holding, you can pressure the cooling system to about 15psi and it'll hold it indefinitely.

Not being able to get to WOT RPM, have a look HERE Lot's of good stuff .........look particularly at #15


Regards,


Rick

 

[NHGuy]

The short answer is, you have a "definite maybe" on getting back in the water quickly. Rick has the right approach. Do the steps he listed & keep us looped in. This will save you from redundancy.
If any of the common GM parts are unavailable from iboats get them from your auto parts supplier.

 

[tpenfield]

Sirhc76 -

I've been there, done that on the Mercruiser 7.4L. Same thing happened and I trashed the engine. . . ended up selling the boat with the engine in pieces.

First thing would be to figure out the cause. It could be either bad gasket seal between the exhaust manifold and the exhaust elbow. . . . or . . . it could be the heads or intake manifold are leaking. The valve guides on the 7.4L peanut heads tend to rust through, so you should have a pressure test done on the heads. If the engine is still together, it is easier to do a pressure test of the whole cooling system, as mentioned.

The signs of water in the intake ports can be from reversion, which will happen at idle speeds.

Second thing would be to determine the amount of damage already done to the engine. It is possible that the connecting rods on those middle cylinders (3 & 5) are bent and that is why you are only getting 90 psi. So, you will want to check the rotating assembly of the engine. How were cylinders 4 & 6 ?

Anyway, plan on some big money to fix the engine . . . probably $2K with parts and machining, if you have the heads done and can re-do the rest yourself. You might be able to find some re-built heads on CL that could save some $$$.

Check the head bolts to see if some are loose, as that would be signs of hydrolock stretching the bolts. You should get a new set of head bolts regardless.

You will need the top-end gasket sets, which it sounds like you may already have. (make sure they are for marine use and have the cutouts for parallel flow. Based on your serial number, it looks like you have the "Gen 6" (Gen VI) version of the 454 engine block, so you will need to make sure to get parts for that version. Double check my lookup though, as some of the 454 Mag (Gen 5) engines have the same serial number range. There are some other identifying numbers on the engine block to confirm the version.

The best that I could tell on my engine was that the valve guides in the cylinder head(s) started leaking and let a bunch of water into the engine which caused the problems.

 

[tpenfield]

FWIW - here is my thread from 4 years ago when the poop hit the fan on my boat, in case you have not already seen it. Sad part was that I had just re-done the heads and exhaust, but neglected to do a pressure test on the heads.

http://forums.iboats.com/forum/engi...r-7-4l-hydro-locked-and-pretty-much-destroyed

 

[Scott Danforth]

those do not look like peanut heads. what year is the block. they look more like the 96 and later L29 heads

I agree, leaking risers / manifolds.

I have a Gen 6 BBC apart in my garage currently

 

[sirhc76]

Thanks everyone. Manifolds and intake were off before I posted. I read the pressure testing thread and figured my results would be the same is the leak down so I opted to dive in.

I should have the head off today with more pictures. Ill answer a few questions,

I measured speed with a GPS to check the speedo. WOT was always under 4k, it would never get above 3500. Bravo 1 and I played with the trim to get as much speed as possible. First boat owned although I've driven many throughout the years. I have 4 inch risers on the exhaust, Ill check the shutters.

The motor was shut down after we were idling for a few minutes while waiting for the other boats to clear the ramp. No waves that day, I thought the same thing on the swamping but it couldn't have happened that day. Texas summer with no wind and it was calm in a no wake zone.

There is obvious rust on the valley pan and the rust in the intake couldn't have happened in the 3 days it took me to get it the parts off? Something has been leaking for awhile?

tpenfield, I have read almost all your posts and your site and some of your posts on other sites Thanks for the info. Notice the two rusted head bolts, they almost have no heads on them and are both between 3&5, I'm assuming the aren't holding much torque in their current state? Well I cant upload the rusted head bolt picture for some reason.

Heads are casting number 10114156

 

[tpenfield]

Oval port heads . . . I think my current Gen 6 MPI engines have those same heads. There are a few on eBay

I think you want to pull the oil pan and get a look at the crankshaft and connecting rods. Have you pulled the engine from the boat, or just taken the top-end off of the engine?

BTW - my 242SS would do 48 - 50 mph at 4400 RPM's Dry weight of the boat was 4750 lbs, 24 degree hull.

 

[Scott Danforth]

Gen 5 cylinder head (1991 - 1995 with 118cc chambers). can use the Gen 6 cylinder head on the gen 5 block, however not the other way around without the special gaskets. the Gen 6 heads have the swirl inducers and are 100 cc chambers)

 

[sirhc76]

Just the top end at this point, if the motor has to come out it wont be until next year. I agree with you and normally I'd just drop the pan and check, its not going to be possible with this boat unless the motor comes out. I would go back in with a built motor if I did that which leads to another question. I've read a little about the differences, how much different are these engines than normal vehicle motors.

I know guys who have swapped the mercruiser 4.3s into jeeps and I've swapped LS motors into jeeps. I can find built 454s locally for 2-3k but when I look at some of the marine places a rebuilt stock long block is $3500. I only found one set of rebuilt heads on Ebay and they were $680 for a pair. Looks like I might be able to use different casting numbers, if that is the case do I have to change the intake as well?

I had found the page listing all the casting numbers but they are only showing them as oval, understand Oval, small oval and rectangular. Are these the "peanut" style? The gasket set I bought is 27-8M0050225.

Still couldnt get the pics of the head bolts or underside of the intake to load.

https://drive.google.com/open?id=0B0XJsDgz_E4TQi1CcU9aU1hrSWs

https://drive.google.com/open?id=0B0XJsDgz_E4TMzZJYzl3WDZPR3c

Thanks,

 

[Scott Danforth]

Block, heads, and rotating assembly same. Marine head gaskets, brass core plug and can for marine (or towing).
If you search for a motor, the gen 6 is a better starting point than the gen 5. Look for a 1996-2000 3/4 ton or larger truck. You can swap over your marine accessories and add new exhaust manifolds and risers

 

[tpenfield]

My comment is to make sure with the heads off all of the pistons come up to the top of the deck as you rotate the engine crankshaft, as that would be an indication that the connecting rods are fine. If some of the pistons fall short of the top, then you probably have some problems in the lower end.

 

[sirhc76]

My comment is to make sure with the heads off all of the pistons come up to the top of the deck as you rotate the engine crankshaft, as that would be an indication that the connecting rods are fine. If some of the pistons fall short of the top, then you probably have some problems in the lower end.

Ahh yes, I plan to do that for sure.

 

[sirhc76]

Well yeah, 4 of the exhaust manifold bolts on the even side have heads rusted almost off. Easy off wouldn't grab them, this should be fun.

 

[tpenfield]

Same here when I took my 7.4L apart . . . I bought an 'End Mill' bit and milled the heads of the bolts off with a drill so that I could get the manifold off. then I had about 1/2" of the stud portion of the bolts to grab along with a little liquid wrench and some heat to get the remaining portion of the bolt to come out cleanly.

I might have use the easy-off / easy-out set to grab the stud portions . . . can't quite remember.

Here is a link to my thread, which you may have already seen.

http://forums.iboats.com/forum/engin...-exhaust-ports

 

[Scott Danforth]

your manifolds are junk any way. I would fire up a 2" razor wheel on the die grinder and cut off the heads of the bolts. then pull the manifolds off.

if you nick the manifolds, it wont matter as they will need to be replaced.

once the manifolds are off, a vice grips will remove the bolt with ease.

 

[sirhc76]

your manifolds are junk any way. I would fire up a 2" razor wheel on the die grinder and cut off the heads of the bolts. then pull the manifolds off.

if you nick the manifolds, it wont matter as they will need to be replaced.

once the manifolds are off, a vice grips will remove the bolt with ease.

Die grinder is the route I was going to take but I only have burr bits, hopefully I can make that work. I have to get the two head bolts off on the other side using this method as well.

Now that I have access to the 8 inch inside of the swim deck, Ill be able to install that new longer swim ladder I bought for the mother in law last year. Ill at least get some brownie points for that

 

[Scott Danforth]

pick up an arbor for running the small cut-off wheels (razor wheel) vs the burr bits. I actually prefer the 4.5" cut off wheels in the 4.5" grinder, however in the confines of a bilge, not sure I would want that shower of sparks.

 

[sirhc76]

pick up an arbor for running the small cut-off wheels (razor wheel) vs the burr bits. I actually prefer the 4.5" cut off wheels in the 4.5" grinder, however in the confines of a bilge, not sure I would want that shower of sparks.

Four of the eight wont budge, PB blaster on the two nights in a row before trying them all today. Head bolts are turning out to be a bear as well. I don't have enough work space to maneuver around beside the motor to see what I'm doing. Going blind on a bolt head with a cutoff wheel might night be a good idea. I'm about to just yank this thing out and be done with it.

I found a built 454 locally for $2500 and the wife may just have to pony up the funds if she wants to get out on the lake this summer, after all its "her" boat. Ill give it another shot tomorrow, if I know it wouldnt catch the whole thing on fire, which might not be a bad thing, Id torch those bolt heads off.