: Engine knock after rebuild 2005 northstar

10-04-12, 03:59 PM
I bought a 2005 devillethat had engine problems. The timing chain jumped the intake cam on one bank and bent all intake valves. So, I was going to do upper end rebuild, because pistons looked fine besides a small dent. I tore it down and then decided to just finish it with rings and bearing. I put it all back together and it fired right up but after it warms up it has a knock not sure were it's coming from. Any ideas?

10-04-12, 04:19 PM
Did you replace the pistons, rods, and crank ? 8 bent valves, even if on one bank only, usually destroy the engine guts, and you can't regrind/true these cranks. Did someone magnaflux the pistons for cracking ? (Wrist pin bosses and top ring groove)

10-04-12, 10:23 PM
I did replace all those parts. I just did a basic inspection, no magnafluxing. So, you think the engine is junk? I figured I wasn't going to take it all apart again. So I've been driving it like it is. The weird thing is you don't hear the knock/tap when engine is cool, but when it warms up it obvious. I put 500 miles on it since rebuild.

10-05-12, 08:11 AM
No idea if the engine is "junk" - just fishing for the depth of damage diagnosis done at overhaul - even a connecting rod can be bent/twisted out of spec and get noisy very quickly.

The fact that the knock gets louder as the engine warms is not good, though.

The knock could also be torque converter related - can you determine if the noise occurs at engine crank speed or half that - cam/valve system speed ?

Manic Mechanic
10-06-12, 07:46 AM
When it's warm and noisy unplug one fuel injector at a time. If it goes away with the right one unplugged it almost certain to be a bottom end problem on that cylinder. If it never changes perhaps it's upper. Usually it's bearing clearance issues that get worse as the oil heats up. All it takes is one under-torqued bolt or one incorrect bearing shell. You can't be to careful.


10-06-12, 05:40 PM
I will give that a shot. If it's a bearing or a piston it will stop making the noise if you unplug the injector?

10-06-12, 06:07 PM
That will either stop or significantly alter the knock sound if it's a rod, bearing, or piston. There should be NO sound change if it's valve train noise........... of course, the idle will get a bit shaky.

10-10-12, 11:36 AM
Found a mint 99 concours that has rod knock after head gasket repair. Too bad motor needs to come out. Car has a ton of new parts. And NEW Caddy rims. Ironic, or sad, they had motor out and now it needs to come out again.

10-19-12, 02:57 PM
So I'm thinking I will just replace the motor with a used one. Do I have to do any thing special if it's the same 2004-2005 "Y" vin motor like crankshaft position sensor relearn or any thing else?

10-19-12, 03:51 PM
Stud the used one..

10-27-12, 11:50 AM
Stud the block? It needs a new rotating assy. I am sure any used 05 motor will be pricey? Poster is new. Probably will never hear from him again.