collective list of lower end knock sounds in mc165 inline 6

[rpeter46]

I think I'm gonna change my handle to inline_6_knocker. I have 3 inline 6s - all have or do knock at one time or another. Taking advantage of the fantastic collective experience on this forum, I'd like to make a short list of possibilities, and their troubleshooting steps.

1-fuel pump- it rides on the camshaft and after many hours or years, the spring on the fuel pump can break or weaken. This can cause a sinister lower-
end knocking sound - troubleshooting steps- replace pump(any more?)

2- broken piston skirt - poor material found in early inline 6s pistons and wide tolerances causing the piston skirt to break off and subsequently "knock"

3- buildup of carbon - Caused by excessive idling (or other causes?) can be removed physically, or with chemical additives. nasty knocking sound.

4- exhaust gaskets - loose exhaust manifolds or bad gaskets can allow a motor to have a loud knocking sound that is remedied by a new set of gaskets or
a simple turn of the wrench.

What are the others and diagnostic processes? I'm a little self-serving here. I have my third that runs smooth and sounds great-at idle. At 1500 RPM, I start getting a lower-end knock. That's why I got it as a parts boat! However, I wonder if it's really a fatal flaw, so I'm trying to go through all the diagnostics. cylinders 5 & 6 are a little low on compression(and come right up with a little oil) and are probably rings. At 1500RPM when the knock is present, I tried pulling wires one at a time to listen for the faulty cylinder to identify itself, but I can't get the knock to stop or quiet down by pulling wires. I have an automotive stethoscope, but can't seem to put my finger on one location-but it "seems" to be closer to cylinders 5 & 6. What else could it be?

Knocking in St. Clair
Paul

 

[Volphin]

Re: collective list of lower end knock sounds in mc165 inline 6

Worst case scenario for engine knocking is a thrown rod.

V

 

[RogersJetboat454]

Re: collective list of lower end knock sounds in mc165 inline 6

Loose/spun bearing. How does your oil pressure look?

Have you pulled the oil filter off and cut it open to check for bearing material?

 

[rpeter46]

Re: collective list of lower end knock sounds in mc165 inline 6

Volphin- thanks. I'm looking for a process of elimination. What are ways to tell one failure from the other before a complete teardown?

Roger - oil pressure was good. I can't remember the exact number, but I remember looking and it was probably at least 60 PSI, or I'd be more concerned. No, didn't tear apart the filter. How should I do that without adding debris? Should I pierce it, and use sheetmetal shears?

 

[rpeter46]

Re: collective list of lower end knock sounds in mc165 inline 6

Roger- is low oil pressure a pretty sure sypmtom a spun bearing? Or is that just a cause of spinning bearings? As I've said, I would like to eliminate all causes that don't require pulling the motor. I'm not lazy, just don't want to pull the engine needlessly!

Paul

 

[RogersJetboat454]

Re: collective list of lower end knock sounds in mc165 inline 6

If you see low oil pressure, 9 times out of 10 it's because the bearings are worn out. The extra clearance between the bearing and crank is allowing the oil to leak past alot quicker then intended. Of course ultra low oil pressure caused by a bad pump or restriction is detrimental to the bearings too. 60 Lbs sounds pretty healthy though, maybe a tad high.

You could try cutting the filter open with sheers. An old school can opener (the type with a blade) may work too. I would usually just conservatively buzz them open with a die grinder (with cut off wheel) near the rim, and keep in mind that the pleats near that area may have some of the steel from the case of the filter. They do make a specific tool used to cut open oil filters, probably wouldn't be worth the investment though.