Hard knock

[jgreg53]

My p15 has a hard knock. I don't think it's a valve. It hasn't hurt anything. Always been there. Any ideas?

[keithb7]

Miles on engine since last rebuild? Oi pressure? Main and rod plasti-gauge clearances?  Cut open filter to inspect for possible material? Take an oil sample, send it in for analysis? Pull 1 spark plug at a time to determine if rod or piston pin knock at which cylinder. Current measured compression of all cylinders? 

[jgreg53]

I've never had this motor opened up. Compression is good all cylinders. 

[Kilgore47]

When I was a teenager I had an old car with a loud knock.  Dropped the oil pan and replaced all the bearings.  In the drive way.  When I got it back together the knock was still there.  Turned out it was the exhaust pipe hitting the cross member.  The engine mounts compress over time and the exhaust got closer to the cross member.  After a couple of weeks there was a real engine knock.  My 16 year old mechanical abilities were not as good as they are now.  Probably put something in backwards.  Had to find another 100 dollar car after that.  And I still break things sometimes but that doesn't stop me from trying.

 

I can fix that - I think

[Sniper]

A couple of years ago my SIL called me to come look at his truck, he had a noise he thought was a rod knock.  I got there, heard the noise and told him it was his catalytic converter,  Had him shut off the truck, got underneath it and thumped the cat with my fist, sure enough that was it. 

 

So maybe put the car up on jack stands and use a rubber mallet to thump things and see if you can find the noise maker.

[D35 Torpedo]

It's a hard knock life. Get a stethoscope and have a listen. It might point you in the right direction.

[MarcDeSoto]

Sniper, I think you nailed it.  He's got a bad catalytic converter!

[Sniper]

20 hours ago, MarcDeSoto said:

Sniper, I think you nailed it.  He's got a bad catalytic converter!

Yes, that's his problem ?

 

Point was to use percussive maintenance to locate the offending poster, err I mean part. ?

[JerseyHarold]

The flywheel bolts may need tightening.  It could also be a crankshaft throw hitting the oil crossover tube in the crankcase because it was installed backwards.

[OldPly]

Just a thought

[Young Ed]

I've read somewhere the fuel pump can make a noise like this

[Dan Hiebert]

"Percussive maintenance"...I like that.  Reminds me of that old muffler shop (?) commercial with the mechanics holding an obviously too big muffler and a big hammer, telling the customer..."We'll make it fit."

 

Finding just where the knock is will alleviate the guesswork, as some of the responses noted, there are a few potential culprits.  If you don't have a stethoscope or don't want to get one, a length of garden hose will work pretty darn good.

Edited March 22, 2023 by Dan Hiebert

[Bryce Mcclintock]

16 hours ago, Young Ed said:

I've read somewhere the fuel pump can make a noise like this

I've had that and still do! caused alot of sweating when I started up the rebuilt engine . The fuel pump was rebuilt as well must be the lever arm itself that's worn .