Technical One cylinder dull knock under load

352FE, cylinder #6 has a dull knock under load, idles quiet as a kitten. Hydraulic lifters, does it hot or cold. Only thing that makes it louder is load. Oil pressure at least 40psi cold.

Engine rebuilt by PO with about 10,000 miles on rebuild. Pulled oil pan and am going to pull rod and main caps etc. This engine is spanking clean. I know the crank was replaced during the rebuild as this was originally a 3.3 stroke 332, and now is a 3.5 stroke.

What else can I look for without pulling the heads off? I'm hoping it isnt a wrist pin....

 

I've had a couple engines come into my shop over the years with a solid rod knock that turned out to be carbon build up on a piston hitting the head. If your engine is fairly fresh I doubt it would be that simple.

 

How's it looking?

 

I had a dull knock on a T/A I bought off a guy that swore the motor was bad. It was a broken two piece damper/balancer. $50 bucks, ran great till I sold it.

 

Easy stuff is the front harmonic balancer sepperating

torque convert bolts coming loose.

Other then those two I would be looking at the bottom end , rod or main bearing would be my guess.

 

Manual transmission, have the flywheel out. No signs of anything amiss anywhere.

This is the bottom of #6. I'm pulling caps off this evening if I have time.

 

First thing I thought was wrist pin. HRP

 

Be sure all the bearings are the same under size. A set could have an odd or miss-boxed pair.

 

How did you figure it was number 6 knocking under load? Will it do it by just reving the engine in neutral?

 

Yes, it is not hugely pronounced, but it will do it when revving in neutral. I pulled one plug wire at a time until I no longer heard it.

 

Plastiguage is your friend.

 

JMO, but I would just pull #6 cap and check with Plastigauge first, as Pat mentioned. Hope it's not wrist pin. Pulling the intake is bad enough news

Joe

 

That is one clean engine inside. I'd agree with plastigauge it and look at both halves of the bearing real close.
I'd think that any engine that idled long enough to build up carbon on top of a piston would be a bit dirtier on the inside.
When my grandfather got older and was in the early stages of Alzheimer's he would sit out here in the yard with his car idling for hours on end to either run the heat or AC and carbon it up to the point it would knock and rattle like crazy. I'd take it down the road and dribble a quart of trans fluid though it and take off down the road until it cleared out and ran. I think that the guy down the road who has all the old tin in his yard is still mad at me over that. Lots of smoke drifting across the road.

 

Piston on the rod wrong way round??

 

Water works just as well as tranny oil or Seafoam. Just cheaper. Water turns to steam and cleans the top of the pistons very fast. Saved a tourist when I worked at the Grand Canyon. His first day of a 2 week vacation . He stopped at the Fred Harvey garage where I worked with his O/T Fairmont 6 cylinder just knocking like crazy. The shop leader walked out and told him it needed a new motor. I overheard the conversation and went and got a paper cup full of tap water and asked could I try something and they said sure so I brought the motor up to about 2500 prm's and slowly metered the water down the carb .
By the time the cup was empty the folks were smiling and my boss was pissed because I made him look like an idiot and a thief. Which he was a little of both.
The car owner handed me a $ 50 and told me he had saved both his vacation and his marriage.
Just because it is low mileage doesn't mean it hasn't had a lot of low speed or idling time . Wouldn't hurt to drop a bore camera in the spark plug hole.

 

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I agree.

 

I would pull the lifters if hyd. and open them up and clean them out. The plunger might be too small and when the lifter heats up, it expands while the oil is getting thin, then the lifters inner piston starts to bang around inside the lifter shell..
Years ago one cam company sold lifters with slightly smaller plungers that would would leak when the oil got hot and thin. They would also tick, what this did was lower the duration of the cam at low rpm to give more bottom end power. Something like Rhoads lifters do but without the relief of the slot on the inner cyl.

I used Rhoads lifters in a couple cars when the cam had too much duration and no bottom end. These things do work and are really made well.. But they tick like crazy, much louder then having solids..

Articles (rhoadslifters.com)

 

I had the same issue with an OT truck I purchased. It was a super clean truck and bought it cheap because of the knock. The plan was to buy a remanufactured engine. While trying to sort out which builder I was going to buy from, I drove the truck around and found that it ran really well and only knocked under load. The knock went away at idle. So I decided to fix the problem. I pulled the pan, check all clearances and bearings. Then I rotated the engine by hand, then would try to move things around. Long story short, it was a piston slapping the cylinder. I pulled the piston/rod out, put new rings and honed the cylinder with a drill driven honing stone. Put it back together and ran perfectly fine with no knock.

 

I don't understand ... you removed the piston, put new rings on it, honed the cylinder and put it back together. I thought piston slap was a piston loose in its bore ... how would honing help that? I would expect honing would make it worse if anything.

 

I had a 300 Ford straight six that had a rod/wrist pin type knock that turned out to be a scuffed piston, driver said the oil pressure was dropping then picking up again for a few weeks ( waits until it's knocking to say something) ...sound went away when spark plug wire pulled. Turned out to be a scuffed piston that transferred some aluminum onto the cylinder wall due to what looked like milling flash from the machining process stuck in the oil pump pressure relief....research said to clean the aluminum off of the cylinder wall with muriatic acid , honed the one cylinder, one new piston and back together.

 

Sounds stupid....but....bad plug, bad wire? I just did this on my 36, wires it was.....

 

I probably did not explain it very well. The rings on the one piston were collapsed so when the piston was at the bottom of the cylinder, it hit the cylinder which made the knocking noise. I honed the cylinder to clean up the surface of the cylinder wall.

 

Might be a cracked piston.

 

Mine had a knock when I first got it. 361 V8. Turned out to be the torque converter was not aligned with the mark on the flywheel.

 

Took some rod caps off. Some say Michigan 010 and some say Fm 010. Found one to be way too tight.

No obvious signs of contamination above the copper part, which was on the rod side. All other rod bearings look very good.

Crank looks good on the tight rod.



Going to borrow a micrometer and see what the diameter of the crank is. My caliper says the rid journal is 2.429" I really cant measure the ID of the rods with them still installed I dont think.....

 

I’m no machinest but there is something funky going on with the parts or the machining, either that or you have no oil supply to that journal. I’d be pulling the engine for a complete tear down before something really goes bang.

 

I have never seen a rod bearing wear in a pattern like that .
Being it has 10000 miles on it,,,,I would check all the bearings,,,,mains as well .
It could be just a defective bearing,,,,and after 10000 the wear finally came to light .
It is worth being checked closer to find out the problem though .

Tommy

 

yes , engine out, measure all crank journals and the ID of all the rod big ends. something is way wonky.

 

Mine too !

 

The way that bearing is worn makes me wonder if big end of rod is round.

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