Knock, Knock
 

Hi to all!

Though I am not new to diesels or their characteristics, I am somewhat concerned w/ my 24V CTD. This is my first CTD as I am a former Powerchoke owner & have since seen the light and made the purchase of my very own REAL truck!

On to my question...Have any of you ever encountered what sounds like a bottom end knock? My truck is what I call relatively low miles @ 231K. It is a 98.5 and until I purchased (@187K) was completely stock. I have since installed a set of 275's, a TST PM3, BHAF, removed muffler and silencer ring, and of course gauges and a SBC. I keep a very close eye on my Pyro and other gauges as well as routine maitenance. I am concerned with this noise because it sounds deep in the rotating assembly! It does change with RPM and temp does have an effect on it (cold and it is worse). However, I have had many other enthusiasts listen to it and they tell me it is normal engine noise. I have been driving it like this for nearly a year with no real change, but the other day I had it on a hoist at work (I am a service manager @ a Ford dealership) and started poking around. I had a tech in the cab with it running, with a technicians stethoscope listened to the bottom end from front to rear. I noticed that with it idling cylinders 1-3 were relatively quiet (no knock), but the further back I went the worse it got! Settling under cylinder 6 at the back of the block, the noise was unbearable through the tech scope! As we increased RPM the noise sped up, however not as loud.
So what do I do now? Is this the making of a catastrophic failure?
Piston slap? Wrist pin? Rod bearing? Help!

I don't want to pull the pan prematurely as this does not look like fun!

Again any help here would be greatly appreciated! Thanks in advance!

Perhaps an oil analysis could tell you something.

your eng. has thrown the piston oil cooling sqirters out- a real common problem in the early 24 valve till they moved the crank counter to the front................but thats only my opinion, to verify this just pull your pan...and if you find little green tube (s) you have found the culprit.
typically they make a vibration/noise @ 1700 and most noticable in 3rd gear.
pm me if you want to know.............b.t.d.t.g.t.t.s.

I did not see what trans was in it, but wonder if it could be a loose flywheel. Guess SBC means south bend clutch. If it is an automatic could it be the flex plate broken? You said you are diesel experienced is the knock light and metallic or the impression I got was a deeper knock like a main or flywheel.

Have you tried loosening the injector nuts one by one to try to isolate it. That would be the next step to me. Also see if pushing the clutch changes it.

If it were a bearing I would expect it to get louder as the oil heats up and thins. I believe that what I have read about the cooler jets coming out, if they do the involved bearing starves for oil and goes bad. So if that was the case it would be a rear main bearing knock. How is the oil pressure?

Thanks for the quick response!
The truck is in fact a 5 spd manual. The "knock" is heavy in nature. Much like that of a ball peen hammer on the side of the block. It's definitely not as "light" as I would prefer. The noise is most apparent at a cold idle. Though as I drove it in to the shop after letting it warm up, you could feel it in the floor pan as well. I do
not understand why it seems to get better when it is warmed up or the ambient
temperature is 70's or warmer. The next step is to do what "Haulin" suggested, w/ cracking the injector lines one at a time and see what that does. Almost forgot, pushing the clutch in has no effect on the noise or it's frequency. Wish me luck!
Thanks again everyone!

don't have much experience with diesels but it deffinitly sounds like a lower end knock. They can be werid sometimes. I would check your oil pressure. Only way to really tell is to pull the pan. Have fun!

Stew

Sinwagon I have the same knock in my engine and have had for about 30,000km. Knock is right under number 6 cylinder as you describe and gets slightly quieter as engine worms up. My truck is a 2000 and has 180,000km on it now and is an automatic. I have not tried loosining enjector lines to track the cylinder yet. Shure is a scary sound to be normal.

Cutlass-

I agree with your last statement of it being scary! My next move is to do the injector cut out test and see what happens. By the way my oil pressure is around 80 psi while driving and 60 psi at idle how about yours?

Thanks everybody!

I'd pull the oil filter and cut it apart. If anything really bad is starting to happen you will often find debris inside.

sinwagon My oil pressure is about the same. I havent cut an oil filter appart as I am leaning towards a bad injector. By the way my cummins dealer told me the only way to chech if it is a bad injector is to do the injector cutout test to identify the bad cylinder and swap out that injector with one of the others to see if the noise follows. I will get to it eventually.

i guess you guys do not want to belive me...........you will not get a bad oil sample....your main bng. on the rear of the crank is no longer doing anything hence the wobble and vibration.
In other words it is not being a bng. anymore.
t.m.o.

Hello Again,

Just got off the phone with Cummins Mid-States Power in Indianapolis! Found out
some interesting information about my truck and it's past. Originally I called to get
some info about my noise but here is what I found instead!

First at 112000 miles, the vehicle was in for a complaint of excessive engine noise.
Come to find out cylinder #6 was scored and the piston was scuffed. Their repair was to overbore cylinder #6 and hone the remaining cylinders. Then they replaced the #6 piston and rod assembly.
Then at 166000 miles, it was in again for excessive engine noise. This time it was a broken exhaust valve in hole #1 causing progressive cylinder, piston, and head damage. So they replaced the head, honed cylinder #1 and replaced the piston and rod assembly.

So with that being known, I don't know if it is a possibility that I have a scuffed cylinder or something else. The thing I can't help but think is that it is worst case scenario and I am going to have to pull it down.

Any other input is appreciated! Thanks again, Chris.

Thumper this is not a flame just a question, if the rear main bearing was gone why do I have good oil pressure? My engine has been nocking for 30,000km, would the crank hold together under the flexing required to make this sound? I will try loosining #6 injector line this weekend to see if the noise stops. At least I will know for sure what cylinder is the problem. I have no experience with diesel engines only gas so any help would be appreciated. Sinwagon sorry for stealing your thread like this.

No hard feelings Cutlass,

I just don't want to prematurely tear this thing down and not find the root cause.

Just here to help if I can....the oil pump is huge !!!! and hense the oil P. will read pretty good off idle.......The ez thing to do is drop the pan for a look and I hope I am wrong.........drop the rear main then grasp all the rods and give them a brutal shove in all directions...if in doubt drop a couple of rear ones for a peak.