2000 FV270 350 mag mpi engine issue

gherkin

All.
Took the boat out yesterday and when getting up on plane I heard a bad knocking.  I quickly idled down.  Engine seems fine at idle. Hear a bit of a knock when revving in neutral. But when under load around 1800 rpm the knock starts. It is quite bad. I am guessing that something happened to a rod, or rod bearing.   Before i start tearing into it. What do these symptoms sound like to others. Just looking for some other thoughts.  

PickleRick

How is your oil pressure? 

Some also describe a failing gimball bearing as a thud thud thud.  

The gimball bearing is still spinning in neutral.  

Have you drained the oil from the bottom of the engine and looked for metal in the oil?

Willhound

Best case scenario is a bad spark plug, next is gimbal bearing and then engine. Having someone operate the throttle in neutral while you carefully listen might help locate the issue. 

PickleRick

Speaking of plugs, corrosion or damage to a plug wire will also cause a miss.  A plug wire that's allowed to rub against the block or touch a y pipe/manifold can eventually wear through and ark. Sparks can be seen at night jumping.

gherkin

I’ve had 3 people plus myself listen and we all seem to agree that the noise is coming from the bottom end of the engine.   But my oil pressure is good. I have another guy coming to take a look with me and get his thoughts.  Plugs and wires are brand new a couple weeks ago but I will check them.  This is definitely not just a normal miss or spark tapping.  

PickleRick

Have you done a compression test?  Look at plug tips?

Im not that good at it but i bet Alswag can tell you if each one has ring wear, leaky valve stem seals etc.

I can only read lean or rich.

PickleRick

I've tried using those and i dont have the ear for it. Granted the engines i specialize in are single or twin cylinders and the 4 strokes have no rod bearings, the bearing is the rod/end cap and when they spin they break as they are aluminum with 6 or 8mm bolts.

I also cant tune a guitar or ukulele by ear

But i have tuned 2 strokes by ear for 20 years. I dont tach out my 2 or 4 strokes.

My issue with using a stethoscope is i can still hear the knocking traveling through the block so i cannot pinpoint where in the block its coming from nor would i be able to distinguish rod knock vs spun main bearing without dropping the pain.

I suppose it would distinguish rod knock from gimball bearing clunk

gherkin

Well i have had multiple people listen to it and all of our consensus is that it is a rod bearing.   I’m working to pull it out now.  Anybody have recommendations for where to get long blocks or short blocks. i have done all sorts of google searches but so far my best bet seems to be taking it to a local engine shop and having them rebuild it to the tune of 2500$. Thought I could find a long block or short block cheaper but the couple places I have seen cheaper ones have terrible reviews.  Any recommendations?  

Aqua_Aura

For $2500 I would have it rebuilt. Can't imagine getting a short block for cheaper and if it's a local shop you can oversee the process and maybe do some upgrades. Make sure they build it for Marine and not automotive. 

PickleRick

Automotive vs marine makes zero difference in clearances, balancing, block, bearings etc.  If we are building high perfomance go fast boats vs a track car yes, a stock low 9s compression ratio vortec 5.7 truck engine to a marine, they are the same other than a few easily swap able parts.  The clearances, tolerances are the same.

Marine engines dont use special forged internal parts.  They do use special freeze plugs and head gaskets.  They also use a marine distributor, alternator, starter and other electric components.  A raw water cooled motor will use a different water pump.  Many marine vortec long blocks come with a bi directional water pump as v belt drive spins opposite than serpentine.    Keep this in mind when buying water pumps

The marine cam on the vortec motors seem to be slightly more aggressive than what comes in a 1 ton truck.  In a 20 ft boat you'd probably never tell the difference.  In a 10k lbs boat its worth the extra 200 bucks for a better than what came in your boat vortec marine cam


Michigan motorz has good prices in 5.7 long blocks but so would your local speed shop/GM dealer speed shop.  These are new not rebuilt blocks, no core change.  These new blocks are 2700 to 3200, msrp in your area may be different.

You would need to swap your cam and head gaskets on the on direct from GM motor, I've heard most of the newer crate engines already have brass plugs. You'd have to verify.  If closed loop the freeze plugs wont matter although salt air will eat them from the outside if not painted.

The stainless head gaskets are not necessary with closed loop cooling.

Many times the engine failure is due to an external failure and the person swapping motors takes all external parts off old motor and puts them on the new one.  This kills the new motor.

So water pump, thermostat, oil cooler, exhaust manifold, risers, intake manifold should all be inspected and most likely replaced.  Oil coolers are a great place for shrapnel to gather from the old engine, waiting to jump into your new motor.

Ive seen marine 4 bolt mains, marine 2 bolt mains 350.  The 327 motors used back in the 70s, many w were taken right off the corvette assembly line. Under powered but had vette numbers so salesman pushed them.

The 5.0 and 4.3 engines had no choice on mains and we still saw them in marine applications.  Some gaskets and freeze plugs as well as cam are swapped out on the assembly line, then given black paint for mercruiser or red for volvo.  Then marine bolts are added.  

If your machine shop has a great reputation, go with them.  I would

gherkin

I’m just gonna take it to the local shop.  Reviews are good and word of mouth is good.  I got the drive off and most everything disconnected yesterday.  Couple more things today and then hopefully the guys at the marina will help me lift it out next week with the fork lift 

gherkin

So just one more thought.  Got the engine all ready to pull.  It was quite easy.  I have not rebuilt an engine myself in many years but I have done both gas and Diesel engines in the past.  But never an electronically controlled fuel injection engine.  I’m thinking that once I get this thing on the stand I will likely just continue to tear it down to the block myself and take it in just for the machine work.  I’m sure I’ll save a lot this way. But if I send it in and they bore it 30 over which I think they usually do. Do I need to mess with the ECM at all.  Or can it handle that change without issue. Just a thought. Let me know if anyone has any ideas on this.  Thanks. 

212rowboat

Just 030 ought not be a big deal, but..... if you can fatten the pulse width (trim) on the fuel just a little you'll be safer... that 030 will most likely remove the safety barrier the ecms are programmed for (and run a little rich)...  There is a place in Vegas I think (of all places) that tunes mercruiser ecms, and that is a good place to ask for certain... you can also play with trickery and find some injectors a little heavier... i THINK yours are 35# at 43.5psi... you'd be looking for perhaps 37# at same pressure.  

If you choose the injector route, call Bruce at fiveomotorsports.com and tell him Drew from bionic mopar sent you.  He knows injectors though he doesn't know boats... you'll need to know the fuel pressure and the current injectors... displacement too... he has a table (that he guards last I heard) he can cross reference for not only boring but stroking, boosting, and different pressures and different cam profiles...  The pressures and selection matters as some lose their spray characteristics when pressures are changed.... you want sprayers not spitters.  He'll likely know off top of his head precisely what you'd need... it'll likely be the difference between 250cc/hr and 260cc/hr as an example... 

Its the only time I miss carbs... mpi is superior in every other regard.  

rasbury

Dumb question...if you have a rod bearing, why are you boring out the cylinders? How many hours on this motor, why did it fail?

PickleRick

Any good machine shop will check cylinders for wear, line bore and crank journals.  The block and heads will be checked for cracks.  The valve guides, valve seats and valves will also be checked.

I wouldn't think bore would affect tune so long as direct replacement pistons are used, same spec cam and compression is kept equal to original. I don't know 100%  so hopefully an expert can chime in.


Don't forget a new oil cooler.

212rowboat

Without doing the math 030 over on a 350cid is worth about two inches displacement over 8 cylinders.... thats worth asking the question about fuel trim, especially because these engines aren't monitored with o2 sensors to make short term or long term trim adjustments... you get what you get based on temperature and air flow or pressure... 

If the tube are just honed/polished, that's another story altogether... same pistons go back in... no additional displacement... but he said 30 over... gonna need new pistons for that. Gonna need to investigate fuel trim and adjust the tables on the ecm to do it right.  

Its a popular procedure. I imagine the information is a Google search away. 

212rowboat

A matter of fact, isn't the mercury reman called the 357mag a 350 at 030 over?  Its most often carbed, but can be had with MPI .... and something mercruiser does.  The carb version is 275ponies while the mpi is 325 iirc.... A quick call to them solves this.  And, they could tell you which injectors if you took that route, precisely... they'd likely steer you toward ecm, though. 

PickleRick

.030, the thickness of about 3 business cards

212rowboat

Alswagg said:

Oh my.  Too much.   Just rebuild it, bore it if needed. You don’t need to change a thing.   The load sensing fuel mapping will compensate.  It’s not like you are increasing hp over the stock bore.  .030 is hardly anything 

Map or maf,  temperature and rpm... i thought these things ran strictly off tables... i didn't know they have ability to adjust... i guess MAP or MAF allows load to be sensed precisely as a vacuum gauge does, though, so I should have known... i guess they simply can't reconcile and make tiny adjustments (like crossing zero) without an o2 sensor? 

And thirty ain't much... agreed... but why risk it if its just a phone call?  Thats all I was saying. 

69fastback

Alswagg said:

Oh my.  Too much.   Just rebuild it, bore it if needed. You don’t need to change a thing.   The load sensing fuel mapping will compensate.  It’s not like you are increasing hp over the stock bore.  .030 is hardly anything 

Lol I’ve been reading this thinking the same thing. Why over complicate it. Tear it down, mic it out, Replace bearings and rings for sure, and do anything else as needed. It’s a SBC, not rocket science. Refresh and run it. 

gherkin

Thank you all I didn’t think I had to worry about it.  Not sure it will need to be bored. Believe it has about 900 hours on it. It fires up instantly so I assume compression is good. So I will leave it to the machine shop to see if it has to be honed or bored. 

Michael T

.....maybe replace the oil pan too. The friggin' things tend to rust-out and are a pain to replace later. While the engine is out I'd have a go at the bilge area - get a quart of white expoxy paint to apply after a good de-greasing and some sanding, clean-up some wiring, check grounds....a great opportunity to do some preventative that could be a lot harder later?

gherkin

All,  So I pulled the engine and took it home to tear apart.  Turns out there was also a crack in the block, wasn't causing any leaks or oil/water issues, but luckily I was able to find a machine shop that had the same block.  So they are doing all the work and then I will begin re assembly.  Here is my list of new stuff aside from the normal engine related stuff that I plan to do.  Any other recommendations. 

full closed loop cooling system, engine connector, water circulation pump, exhaust flappers, idler pulleys, oil pump, timing chain,

I was on the fence about the closed loop cooling, but when I saw how dirty the engine ports, intake, etc... were I decided this was worth the investment. 

Any other recommendations.  I want this thing to be like new when done so not afraid to throw some money at it. 

rasbury

Sounds like you have a handle on it! Closed loop was on my must have list for our 270
...glad I found it.