Port motor down...choices choices choices! What did you choose?

So about 6 weeks ago we bought our 1994 400EC with Bluewater 7.4 Gen V carbureted motors and Hurth straight drives, right at 975 hours each motor with no major work. Both engines ran good on our sea trial with good oil pressures and temps, and in the weeks since haven't burned any oil or lost coolant. At the sale, we negotiated an agreed-to price that was reduced with the expectation that with 975 hours, engine work would be in our near future...we just didn't know how soon LOL This past weekend we had her out for a Labor Day excursion 60 miles downriver. On the ride back home the port engine lost almost all thrust power (but still good temp and oil pressure and still showing 3k on the tach)...got a little bit of valve clatter and "chugging" for about 15 seconds....then died. No puffs of smoke, no loud bangs, no messes in the bilge, nothing obvious but wouldn't restart. I left the port engine off and came on home under starboard power, all good. I went to the marina and checked on it yesterday--oil and anti-freeze are both still full and clear, good signs. It will start up and idle at about 1100 while rhythmically chugging, anything less and it dies. I pulled both valve covers thinking I maybe had a loose rocker, bent rod, etc...everything on the top end of the heads appears intact, so I'm pretty sure I've spun a rod bearing. This weekend I plan on pulling the plug wires one at a time listening for the chug to go away to confirm.

If so, now there's choices on what to do...I'm a heavy equipment mechanic by trade, used to laying on the ground in the rain or snow to fix heavy, dirty things While I'm comfortable doing a motor rebuild, after 20+ years of "heavy and dirty" I would rather pay somebody to do it if it's not terribly more expensive. That said, I am tentative about uncoupling the Hurth tranny or messing with a propshaft because I'm not sure what to expect. And even though a short or long block might be an obvious choice for some, for me I'm old school--there's just something nostalgic about a vehicle or vessel having the original motors. The owner for the first 20 years was meticulous, I still have all of the original manuals including both engines, all service and sales records, even a copy of the original build sheet and pricing sticker.

Do-it-yourselfers, has anyone done a bottom end rebuild in the bilge of a 400EC? I've got the seats moved and all the hatches off, looks like there's quite a bit of room.

As I'm looking at it, my choices are:
1.) Rebuild just the bottom end of the motor in the bilge--the least expensive route, fixing only what broke. Disconnect things as necessary, leave the heads on, lift it off the mounts and roll it on it's side to do just the crank, pistons, piston rods and bearings, oil pump, etc. But again, this requires me to unhook the engine from the drive/propshaft and I'm not sure if I might tear up something drive related because of my lack of knowledge on a marine drive setup. And with this option, the top end is still 26 years old and original.
2.) Rebuild the whole motor, have the block and heads reconditioned--have a yard disconnect and pull the motor and load it into my pickup, then have them re-install it after I do the rebuild in my garage.
3.) Skip the rebuild and install a short block with my heads and other parts.
4.) Install a long block--the more new parts, the better.
5.) Go with new crate motors, either OEM 7.4's or maybe 8.1 Horizons.

Am I causing more headaches down the road by doing a rebuild--parts hard to find, reliability not as good as a short/long block with marine technology changes? Share your thoughts as well as "do's and dont's" with me, please!

From your post and unless you have a highly recommended rebuilder in your area, I am going to recommend you do the work yourself. That's the only way you're going to know it's done better than right. Now if you have the coin to drop new engines in, that would be sweet, but probably overkill for that boat. Good luck.

Welcome to CSR!


Plenty of room in a 1994 400 EC to work on the engines. That said.....let's find out what is wrong first before you get to the part about taking the engine apart. Pop the plugs and do a compression test. That will tell you pretty quick if you have a burnt valve or a bad plug/wire. If the fluids are okay and the oil pressure was good.....a bad plug or wire could result in the same symptoms.

I had a plug go bad on one of my 7.4s and it lost power and would die at idle. The only way to keep it running was more throttle.

It may turn out to be worse....but I wouldn't start there. If it is a rod knock.....pull the engine. It is easy to get to by moving the seats and lifting the deck panels. It is far easier to pull the engine and trans together. Just disconnect the shaft coupling, cooling and fuel hoses, engine harness and you are good to go.

just bought 2 7.4 454 MPI new block from eagle marine to replace my 1996 ones after my port engine passed qway
my starboard work very good still but liked to start fresh with new ones
i am using all old parts with it about 14000 for both and 12000 labor

Good advice already given .... you really need to find out what failed before jumping the gun and thinking of a major rebuild .

I went through this years ago with my boat and can tell you the engines come out quite easily transmissions and all ..
After mulling over the options...I ended up with new GM Marine 7.4L Gen 6 long blocks. I did not want rebuilds.
Kept the simple (old) proven technology and carb. but, everything was sourced new and bolted on.
Really couldn’t be happier

PlayDate said:

Welcome to CSR!


Plenty of room in a 1994 400 EC to work on the engines. That said.....let's find out what is wrong first before you get to the part about taking the engine apart. Pop the plugs and do a compression test. That will tell you pretty quick if you have a burnt valve or a bad plug/wire. If the fluids are okay and the oil pressure was good.....a bad plug or wire could result in the same symptoms.

I had a plug go bad on one of my 7.4s and it lost power and would die at idle. The only way to keep it running was more throttle.

It may turn out to be worse....but I wouldn't start there. If it is a rod knock.....pull the engine. It is easy to get to by moving the seats and lifting the deck panels. It is far easier to pull the engine and trans together. Just disconnect the shaft coupling, cooling and fuel hoses, engine harness and you are good to go.

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So I went down yesterday to do a little more troubleshooting and I'm thinking its just jumped timing--jumped teeth, stretched chain--or a camshaft issue?

Checked my fluids again--oil and coolant both still full and clear. I started the motor a few times for about 10 seconds each time and it will start and idle at 1100 with good oil pressure but a slight rhythmic hiss as it runs...and as it starts, it "strains then spins, strains then spins, strains then spins" rather than a constant spin. Next I removed the fuel line between the filter and pump and capped th it at the filter to check spark and compression without letting the fuel pump suck air too long. I grounded my spark plug wire tester to the lifting eye and checked the coil wire and each individual plug wire--great spark, all wires good. Finally, onto the compression check. With the fuel still capped I hooked the coil wire back to the wire tester so my spark would flow, disconnected all the plug wires and pulled the plugs (all plugs looked the same--slightly damp with fuel as if running rich, but none looked like they weren't firing or were worse off than any other). I opened the throttle plate and tested each cylinder for four strokes. Three tests in random cylinders order just to make sure I had a good seal because the numbers were so whaky but consistently, cylinders 1 and 2 (the two forward-most cylinders) hold 120psi....all 6 other cylinders are 60psi or less, presumably meaning I've got leaking valves on 6 cylinders? Thoughts? And thanks again for any insight or "here's what I had"....in 20 years of heavy equipment maintenance and repair I've not run across symptoms like these

Couldn't it also be in need of a ring job? That would cause compression issues as well.

Shaps said:

Couldn't it also be in need of a ring job? That would cause compression issues as well.

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The reason I'm not thinking rings or head gasket or anything along those lines is because it's affecting 6 of 8 cylinders, and it was idling and running great prior to a restart, wasn't burning/losing any oil--so either both heads and multiple cylinders suffered a major malfunction at the same time, or it's something that affects/controls those multiple cylinders. The only things I can think of that affect that many cylinders in both banks but still allow the engine to run would be timing or cam, but I might be missing something?

If it jumped timing it should lower compression evenly on all 8, right? Why 6 of 8? Get a cylinder at TDC and see where your rotor is pointing

A leak down test would tell you if it's rings or valves.

At this stage of troubleshooting my bet is on timing chain or possibly distributor

I agree on the leak down test. But squirting some oil into one of the low cylinders will tell you if it is rings or valves at a macro level. The hissing sound you may be hearing may be the leaking intake valves.

Regardless....the low cylinders are the problem. Whether redoing the heads will fix it remains to be seen. Certainly, R&R on the heads is easy to do with the engine in place on your boat. Practically speaking, rebuilding the heads is also a reasonable investment since you would do it independently or with a complete engine overhaul.

I don't think it is a jumped timing chain because all the cylinders would be low but that is also easy to check.

As to why 6 out of 8 cylinders are low..... Did you use a Surveyor when you bought the boat? I'm curious if you did.....what were his compression numbers?

Mikentucky said:

So I went down yesterday to do a little more troubleshooting and I'm thinking its just jumped timing--jumped teeth, stretched chain--or a camshaft issue?

Checked my fluids again--oil and coolant both still full and clear. I started the motor a few times for about 10 seconds each time and it will start and idle at 1100 with good oil pressure but a slight rhythmic hiss as it runs...and as it starts, it "strains then spins, strains then spins, strains then spins" rather than a constant spin. Next I removed the fuel line between the filter and pump and capped th it at the filter to check spark and compression without letting the fuel pump suck air too long. I grounded my spark plug wire tester to the lifting eye and checked the coil wire and each individual plug wire--great spark, all wires good. Finally, onto the compression check. With the fuel still capped I hooked the coil wire back to the wire tester so my spark would flow, disconnected all the plug wires and pulled the plugs (all plugs looked the same--slightly damp with fuel as if running rich, but none looked like they weren't firing or were worse off than any other). I opened the throttle plate and tested each cylinder for four strokes. Three tests in random cylinders order just to make sure I had a good seal because the numbers were so whaky but consistently, cylinders 1 and 2 (the two forward-most cylinders) hold 120psi....all 6 other cylinders are 60psi or less, presumably meaning I've got leaking valves on 6 cylinders? Thoughts? And thanks again for any insight or "here's what I had"....in 20 years of heavy equipment maintenance and repair I've not run across symptoms like these

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With Vdrives, the 2 forward most cylinders are actually #7 & 8.

If water entering through the exhaust is the cause of your valve issues, it would make sense that to 2 forward most cylinders are relatively unaffected. The motor sits on a tilt with those two cylinders higher than the others. Throw in a little gravity and that pretty much explains it.

Espos4 said:

With Vdrives, the 2 forward most cylinders are actually #7 & 8.

If water entering through the exhaust is the cause of your valve issues, it would make sense that to 2 forward most cylinders are relatively unaffected. The motor sits on a tilt with those two cylinders higher than the others. Throw in a little gravity and that pretty much explains it.

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Mine is a straight drive, not V--the forward most cylinders are 1 and 2.

Mikentucky said:

Mine is a straight drive, not V--the forward most cylinders are 1 and 2.

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I stand corrected on the cylinder numbering.
The tilt of the motor is still relevant as relates to the reason why #1 & 2 could be less affected if water is the reason for the valves not sealing.

Espos4 said:

I stand corrected on the cylinder numbering.
The tilt of the motor is still relevant as relates to the reason why #1 & 2 could be less affected if water is the reason for the valves not sealing.

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Thanks for the thoughts! I think you might be onto something...I've always had outdrives prior to this boat, so exhaust backpressure has been a consideration but never really a concern, even while backing up. But I can see on an inboard setup where it might be easy to introduce water through the exhaust and back through the valves into the cylinders...does this sound plausible, or far-fetched--marine engines are plumbed so that an owner doesn't have to be too concerned about excessive packpressure?

Thinking back on the situation immediately before the engine condition changed--in a nutshell, we pulled up to the dock to refuel with everything fine, once we left the dock was when things were different. For specifics...we had been travelling upriver for about an hour running about 3000rpm. We were pulling up to a "layalong" boat dock that was in the river flow to be refueled so we could continue upriver. Due to the layout and positioning of the dock, the refueler signaled to us to spin around 180 degrees and point downriver so he could access the fuel fill openings. The current was pretty strong...I used the transmissions to spin around but had to use relatively substantial throttle while both were in reverse to back us about 10 yards upriver into position and then just to hold position while we tied off.

PlayDate said:

I agree on the leak down test. But squirting some oil into one of the low cylinders will tell you if it is rings or valves at a macro level. The hissing sound you may be hearing may be the leaking intake valves.

Regardless....the low cylinders are the problem. Whether redoing the heads will fix it remains to be seen. Certainly, R&R on the heads is easy to do with the engine in place on your boat. Practically speaking, rebuilding the heads is also a reasonable investment since you would do it independently or with a complete engine overhaul.

I don't think it is a jumped timing chain because all the cylinders would be low but that is also easy to check.

As to why 6 out of 8 cylinders are low..... Did you use a Surveyor when you bought the boat? I'm curious if you did.....what were his compression numbers?

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PlayDate, I did shoot a couple squirts of oil into each of the low cylinders just to see if that would "prime" some compression with no luck on any cylinder. And we did not have a survey or even an oil analysis done--there was a survey from the last sale in 2016 on board that I used to judge the general vessel condition, and as we discussed engines the PO discounted the price to compensate for potential "future engine work". Not enough to replace both motors, but an amount we were both comfortable with.

Mikentucky said:

PlayDate, I did shoot a couple squirts of oil into each of the low cylinders just to see if that would "prime" some compression with no luck on any cylinder. And we did not have a survey or even an oil analysis done--there was a survey from the last sale in 2016 on board that I used to judge the general vessel condition, and as we discussed engines the PO discounted the price to compensate for potential "future engine work". Not enough to replace both motors, but an amount we were both comfortable with.

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I would yank the heads to see what is really going on. Easy to do on your boat. The hardest part will be getting the old intake off. Make sure to spin the motor around to TDC before you pull the distributor. Also, mark the base of the distributor so you have an installation reference.

It is a good time to replace the manifolds and the risers if they haven't been done for a while. With your skills....I would guess you can have the heads off in four or so hours.

My only reservation is the knocking noise you heard. It could have been a number of things but we really won't know until you put the heads back on.

Well now there's something you don't see every day....both banks apparently simultaneously blew the head gasket between the rearmost three cylinders LOL It doesn't look like there's anything wrong with the heads/valves but I'm taking them to get magnafluxed just to be safe, then a 3 angle valve job. I'm also putting on new exhaust risers, manifolds and cooling hoses while it's torn down this far, and tearing the heat exchanger down to make sure it's clear.

Seeing as how I was running great prior to the refueling and backing upriver against a strong current, I'm still thinking at that point I sucked some water into 5 and 6 via the exhaust valve and then on the compression stroke the hydraulic pressure deformed the two equally weakest points--the spot between the adjoining cylinders. From there it was just a short matter of time before the now deformed spots blew out.

Fascinating pics, thanks for sharing! Are your exhaust flappers/shutter valves still intact and or in good shape? Maybe you had a small leak around the exterior of the flappers so water backed up with the continuous river pressure.