Rod knock sound

Randy N Connie

Registered User
I had a head gasket leak under boost only.No anti freeze
in the oil.

I have a sound that sounds exactly like a rod knock.But
after the motor warms up the knock gos away.

I have been trying to convince myself its not a rod.Because
the bad rods that I have heard ,do not stop knocking after
warmup,they just keep knocking.

Has anyone had this happin,could it be somthing else.

Randy
 
What Type /wieght oil are you using? I have been using 10w30 and when my car is cold i get the same sound. When I was using 5w30 never had this sound. so that may be one thing to check.
 
Ouch! I had a 351 CJ that did that for a couple of months. Eventually the knock became a continuos(spelling) thing and once it did that it went downhill FAST. Rod bearing #3 was shot.
On the other hand I have a 5.0 that has done that for over 5 years and has never turned into a constant Knock, not yet at least. As long as the engine is cold it knocks, once warmed up it stops.
My theory and its only a theory is that there is a rod bearing that is right on the ragged edge of allowable tolerance and one day it WILL become an issue.
The really strange thing about it is there is no drop in oil pressure, not until the knock becomes constant.
I know 3 or 4 other people with 5.0's that do the same thing.
Since this motor is supercharged I dont think I would wait for the knock to become constant before I checked it out and corrected it.
Something's loose down there. Loose parts in the bottom end and supercharging do not go good together.
 
While I would be concerned about the rod bearings as well, I would first consider trying a slightly lighter weight oil (unless you're already running something like 5W30). If the oil is too thick, it will take more time for it to reach and "pump up" or "fill" the lifters, which would explain the noise you're hearing. I would also try to determine if the noise is coming from the valvetrain or the crankcase, either by using an automotive stethescope or the old screwdriver trick. If it's in the valvetrain, it could very well be that the lifters aren't receiving oil right away, if it's in the crankcase, plan on rebuilding soon.

-Rod
 
Forgot to add:

It definitely could be the rod bearings, especially if coolant was going into the cylinders when you had the headgasket leak. As we all know, water doesn't compress like air, which could have placed a much larger load on the rod bearings than usual. Were you getting white smoke out of the exhaust when the headgasket went?

-Rod
 
Rod, Before I tore it down I drove it for about a mile and it made
a jerk twice in about 1 1/2 seconds.It felt more like a hydraulic
than a electrical miss.

When I took the driver side head off .The rear cylinder had about
1/4 cc of green anti freeze tear drop hanging from the side of the combustion
camber lip.So I think the cylinder may have hydraulic.The motor never had
any white smoke.

The head gasket leak was in the rear cylinder,in the rear of the cylinder
head,between the two large water jacket opening in the rear of the block.
The head gasket leak was between the block and head gasket.

It appeared to be just a worn gasket from the anti freeze eating on the
paper part of the gasket.The fire ring looked ok.

I have had a cold idel miss all this year that I could never find.And I would
have a miss during boost on the dyno.The day I first met you at Stiegemeier's
back in March.It was doing it then.

So I have finaly found my cold idel miss.I have the motor torn down now
with the heads off.And rebuilt ready to put back together.Valve job,seals
ect.That took about 3 1/2 weeks for for me to complete.I am slow.
.Put the heads back together stock.but polished.Going for the bling thing,
instead of speed.

I decided to pull the heads when I felt what I thought was a hydraulic.
The last time this happined was on a fuel bike during a race.The head
lifted and bent the frame and fractured 2 of my ribs.About 20 foot
off the line.

I am hoping that I don't have any crank damage.(Wishful thinking)
I put a dial indicator on a couple pistons they looked to be the same
height.So I do not think that I have a bent rod.

I had the rod knock sound before I felt the hydraulic feel.

I bought a tranny from Chris Wise.IT needs that put in also.So
I think it would probley be easer to just yank the block out to
get the tranny out through the engine bay.Than droping every
thing behind the tranny.

I need to know a fast track way to get the bottom end rebuilt
so I can make the shoot out.And have enough time to get the
bug out before the race.

This will make me go through every part of this SC.but the rear
end .I don't want to miss any thing on this SOB of a car.So I
need a complete mark VIII from you.

RANDY
 
It does sound like that cylinder was hydraulicing. I would probably pull the engine and transmission out as a unit, rebuild the bottom end of the engine, bolt on the new transmission, and slide them back in as a unit.

It will still be a little while before I can part ways with that Mark 8 setup. I move pretty slow too, and progress on my current project car will slow down even more in a week or so when I head back to school. I should begin wiring the car this weekend, and I'll at least have the front suspension all set up before I head back to school. Then I'll need to pull the engine/trans/wiring from that Mark 8, which will be when you'll be able to get the rear end. I'll keep you informed.

-Rod
 
Nope, I can't say that I do. I'd try calling a couple machine shops to figure out what they'd charge. There is an excellent shop near me (quite a drive for you) called JCM machine in Otto, MO. I have their number somewhere, I just can't find it right now.

-Rod
 
A drive is not a problem.Just need a place that will
give me a good job fast and and I can afford.May
need the crank polish to.

I can balance the rods and pistons .But I don't have
the machine or the bob weights to balance the crank.

I will see if I can get in on the GP for pistons, rods ,ect
on this sight.

Thanks again Randy
 
My motor used to knock when cold from about 40K miles to 140K. I always assumed it was a collapsed piston because it would go away when warm. Then I blew headgaskets and its never knocked since. It didn't sound like a rod knock to me, but it was a knock nonetheless.

My machinist told me it was likely a carbon knock. I guess carbon is real hard when cold, but when it heats up it softens, hence the quiet when warm and when I had it apart I cleaned the tops of the pistons..

Who knows, the thing still runs. What I did was get a real oil pressure gauge and since I've never lost oil pressure I never worried about it.

I run 15W50 in my car FWIW.
 
I've seen sets of 8 351W I-beam forged rods for $225 a set. Can't do much better than that. Pistons are the bitch on these things.
 
I had that same problem with my engine. Sometimes it was real light. I had two different dealerships look at it and no one could tell what was wrong. I was told that sometimes a rocker arm on our engines stick and make noise. I drove my engine for about 20,000 miles like that before I put in a rebuilt engine.
 
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