Dreaded rod knock, how do you test?
Thread Starter
Drifting
Joined: Apr 2002
Posts: 1,720
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From: Manhattan Beach Ca
Dreaded rod knock, how do you test?
Thought knocking sound was coming from tranny or clutch but now seems more engine related. Seems to get louder with RPM mainly above 2000.
Is there a way to confirm a rod is loose or bearing clearance is too loose?
Is there a way to confirm a rod is loose or bearing clearance is too loose?
Race Director
Joined: May 2005
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From: Millington Illinois
St. Jude Donor '08-'09
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From: San Antonio TX
You can pull the plug wire from each cylinder until the knock goes away. Creating a dead cylinder takes much of the load off the bearing.
That it occurs only above 2k rpm is a quirk in calling out a rod bearing, though. Normally, it is a load-dependent noise until it becomes really worn. You'd hear it off-idle.
That it occurs only above 2k rpm is a quirk in calling out a rod bearing, though. Normally, it is a load-dependent noise until it becomes really worn. You'd hear it off-idle.
Thread Starter
Drifting
Joined: Apr 2002
Posts: 1,720
Likes: 19
From: Manhattan Beach Ca
OK, undid water pump to make sure, still had noise.
Unplugged plugs 1,3,2,4 one at a time still had noise.
So using the screwdriver to the ear trick I listened carefully and it sounds like typical rod knock since I have experienced that noise before. But the odd thing is I put the long screwdriver on the back end of the engine and also heard the noise just as loud as the front. Maybe since everything is steel and tight the noise can travel all over.
So anyway I have my original engine in running order I can swap in a couple days hopefully. It's been sitting 3 or 4 years now but should run. At least I should be able to get to the bottom of all this if noise is gone after swap.
Unplugged plugs 1,3,2,4 one at a time still had noise.
So using the screwdriver to the ear trick I listened carefully and it sounds like typical rod knock since I have experienced that noise before. But the odd thing is I put the long screwdriver on the back end of the engine and also heard the noise just as loud as the front. Maybe since everything is steel and tight the noise can travel all over.
So anyway I have my original engine in running order I can swap in a couple days hopefully. It's been sitting 3 or 4 years now but should run. At least I should be able to get to the bottom of all this if noise is gone after swap.
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Brett Foote
Safety Car
Joined: Mar 2007
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From: Bridgewater nj
Usually cold running knock won't be heard until the engine warms up but if you alway had low oil pressure when hot you were already having problems.
By low I mean 10-15 psi at idle when hot. If you were reading this or lower than the bearing were worn out. Time for a stroker
By low I mean 10-15 psi at idle when hot. If you were reading this or lower than the bearing were worn out. Time for a stroker
Drifting
Joined: Aug 2004
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From: Lubbock TX
I'd double check the flywheel/clutch/tranny before you tear the engine down. I know that a cracked or loose flexplate sounds like a rod knock, there's enough parts to a clutch/flywheel setup that it's possible that something is making the sound.
Pull your oil filter and cut it open. If you have a bearing gone to the point it's knocking, there should be some bearing material in the filter.
Good luck, hope it's something cheap!
Pull your oil filter and cut it open. If you have a bearing gone to the point it's knocking, there should be some bearing material in the filter.
Good luck, hope it's something cheap!
Pro
Joined: Jan 2009
Posts: 525
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From: Kings Park NY
Don't forget the fuel pump rod. If you have a lazy fuel pump the rod will bounce around and sound like a engine knock. That's how I got my 2nd 78 Pace Car so cheep the PO thought it was a rod knock and I changed the fuel pump in his driveway and drove away with no knock.
Thread Starter
Drifting
Joined: Apr 2002
Posts: 1,720
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From: Manhattan Beach Ca
Yeah I read about the fuel pump rod and want to rule that out somehow before I pull engine. I replaced fuel pump just 6 months ago but I am finding out these replacement pumps are all junk lately. Maybe I should try another since they are only $30.
Drifting
Joined: Jun 2010
Posts: 1,781
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From: Oxford Ohio
I'd just drop the pan and check the bearings. It costs you a gasket. You can spend a lot of time avoiding the direct route to the most likely cause. It would also give you a good idea what condition your bearings are in.
Le Mans Master
Joined: Oct 2002
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From: Las Vegas - Just stop perpetuating myths please.
Check the inspection cover on the bell housing.
Had me fooled. Found the crank flange was hitting a bent corner tip in the sheet metal bell-housing inspection cover. Its definitely worth a look.
cardo0
cardo0
Drifting
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From: Syracuse NY
Drifting
Joined: Aug 2004
Posts: 1,883
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From: Lubbock TX
Yeah, and if the knock is double the speed of the light strobe, you'll know it's happening every stroke, not just when that cylinder fires.
Thread Starter
Drifting
Joined: Apr 2002
Posts: 1,720
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From: Manhattan Beach Ca
Update: Took two weeks for me to swap engine since I only worked a couple hours here and there. So got old engine running and sure enough no rod knock sound anymore.
So my 383 must have bearing problem. I put new forged pistons in a year and a half ago with new bearings for rods but didnt replace crank bearings. I'll tear it open little by little and report back when I discover what it is.
So my 383 must have bearing problem. I put new forged pistons in a year and a half ago with new bearings for rods but didnt replace crank bearings. I'll tear it open little by little and report back when I discover what it is.