SP 135 Knocking Sound

Hoping for some thoughts here. Our starboard 1987 SP 135 has started making a very unpleasant loud knocking sound. Im no a mechanic (at all) but here is what the "mechanics" have done.

Had normal servicing done on Heat Exchangers and coolers. Bad fitting and hoses replaced, coolant replaced.

At sea trial, starboard engine shuts down. Mechanic blends some air, but engine won't stay running.

Next day mechanic starts engine at dock...runs fine. Run the engine in gear at dock...runs fine.

2nd sea trial after 40 min engine starts making loud knocking sound.

Mechanic suspects fuel prob.

Today mechanic tests fuel system. Checks out.

Mechanic fears water has entered 4,5 & 6 via exhaust elbow causing cylinder damage.

Here is what I know.

Engine has never: hydro locked, overheated, burned exclusive oil or had any issues starting. There is heavy corrosion on the 4, 5, 6 side of the exhaust manifold interior.

Really appreciate any thoughts.

You don't need to hydrolock or overheat to experience sea water backing up into your exhaust, although this is the first I have heard it happening to a NA Lehman. Do an oil sample. High sodium is a good indication of sea water intrusion in addition to the corrosion you are seeing inside the exhaust manifold. Also look inside oil filler port for corrosion on valve train.


David

As far as corrosion, if you mean rust, on the exhaust manifold where it enters before water cooling....pretty sure that is normal. Mine is rusty on all 6 though.

If the mech is at a loss and the knockING is that obvious...I would suggest a boroscope exam by someone who is very experienced at it.

With no known issue, and a ominous knocking, testing by patch repairs and using the wait and see approach sounds inefficient and possibly more damaging to the engine.

If you have the time, the oil sample idea by David is a cheap way of seeing if a significant event has happened inside the engine.

Oil sampling is on the list for today, and I have a new riser elbow arriving. Brian Smith at AD (and a few others) have suggested that the knocking may be originating at the valve train. Plan on having the mech pull the cover and inspect. Would compression tests on the cylinders tell me much at this point?

How did the mechanic test the fuel system?

Did he try and isolate each cylinder by cracking each injector in turn?

He did. We've now removed the valve cover. Valve train appears ok. Pulled injectors. 4, 5 and 6 have light rust in the tips. Scoping the cylinders now.

So it appears we spun a bearing in 1, 2 or 3. 2 is the greatest suspect. Hours of conversations with Brian at AD.

None the less the plan is to leave tomorrow for Punta Gorda from Stuart on the port engine only.

At least I'll save money on fuel.

Thanks for all the input.

Ouch. Could have been the stalling was from the bearing seizing, then releasing when it cooled.

Not easy to diagnose a spun bearing until oil pan is dropped. How was that determination made?

RonM55, I like the way AD is supporting the product for you. Hope it works out with a good not too pricey repair.