Intermittent Engine knock

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soulezoo

diesel uber alles
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Jan 24, 2008
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Before anyone else starts the chorus, I have spent most of last night using search and didn't really come up with much that pertains to me.

I have a bad knock in the engine, rod knock sounding, but not a rod... I have had that before and know that one. This is intermittent in both intensity and duration. Rpms doesn't make much a difference and neither does load vs no load. Sometimes at idle it knocks steady and goes away with rpms. Other times it will idle smooth and normal for a fair amount of time then knock with rpms. No fuel in oil. No water in oil. No oil in water. oil level normal.

There is some blowby... whitish-grey. It also comes and goes with the knock.

What I have done so far:

I replaced injectors about 400 miles ago with brand new bosch. Ran fine until about a mile from home last week. I have been really easy on the engine for a while now.

triple checked valve train... no evidence of dropped valve seat-- all valve adjustments normal.

It sounded like cyl 1. Thinking leaky injector, I disconnected each injector one at a time (do not have a rail cap) and saw no difference. I swapped injector 1 with 4. No difference.

No blue smoke and oil pressure is good. Rail pressure is normal. I have a PPE dual cp3 set up to a TC rail with dual prv's. PRV's are not leaking. Rail pressure sensor seems to work normally.

Now the scary part... today while trying to nail this down, it started knocking bad and stalled. A tried restart showed the engine seized... going into "oh sh--" mode, I tried to hand crank backward and forward... no dice. Check valves again, nothing obvious. After waiting awhile, it restarted (thinking hydrolock and back to injector theory) and idled normally for a good 3-5 min with very little blowby and no knock at all. So I got brave and increased rpm and knock returned...

Again, this knock gets as loud and sounds like rod knock and then can quiet down... but am pretty sure it is not a rod.

What say you guys?
 
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soulezoo said:
This is intermittent in both intensity and duration.
There is some blowby... whitish-grey. It also comes and goes with the knock.

I disconnected each injector one at a time (do not have a rail cap) and saw no difference. I swapped injector 1 with 4. No difference.

A tried restart showed the engine seized... going into "oh sh--" mode, I tried to hand crank backward and forward... no dice.
Click to expand...

"No difference" meaning it remained intermittent?

"Engine seized" meaning no movement by either starter or barring?
 
Yes to both of the above.

But after it sat for awhile, it was able to turn over and while hard, it did start and then ran normally until rpms went up.
 
sounds like a rod or main brg gone south. was the smoke from the blowby intermitent or the actual volume of blowby?
 
Blowby varied with the knock. When running smooth, little blowby; when knocking quite a bit.
 
had a rod cap snap in half and flex causing the piston to slap the head intermitently.it later spun the rod bearing and scrapped the rod, crank and the top of the piston was matted from hitting the head. The guy drove it for about a week like this. How it didn't throw the rod completly out is a mistery to me.
 
Just a guess....

I think you've got a melted piston that momentarily heat seized, not a hydraulic lock, but an aluminum stuck to steel lock! (A hydraulic lock should be able to be barred in reverse a little, you said it was stuck forward or reverse, correct?) I think the intermittent knock is a combination of melted piston slap and injector knock from the deformed melted piston top.
 
I agree - and with marginal ring land deformation causing intermittent excessive blowby (almost certainly a result of degraded ring seal).
 
Terry, do you have access to a bore scope? I can ship mine up to you if you'd like to try checking the pistons/cylinder walls.
 
Obviously a couple things possible

My take would be hydrolocked and at least one bad injector. I have had two incidents in this during the past year & half where that happened to me due to an injector and it sounded terrible,... like a midget with a ball peen hammer inside your engine trying to beat his way out. Mine never hydrolocked but I think it was close to doing so.

A dealer mechanic told me that this was common and that for some unknown reason to him that it was usually #6. In my case #6 went bad twice in the time frame I cited above!!

No issues since.
 
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BrettWINspeed said:
Terry, do you have access to a bore scope? I can ship mine up to you if you'd like to try checking the pistons/cylinder walls.
Click to expand...

Hi Brett,

I have a Ryobi scope, but it is too big to get into the cylinder so I didn't try. Let me get it back apart and I'll get back to you.
 
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Noise

I just had a 06 in the shop with the same thing. It ended up being #5 injector. I just run the motor until it made the noise and shut down cyl. on at a time until I found which one. Put a new one in and it's running fine. Jeff
 
Run a cylinder contribution test. That should show a cylinder issue.
 
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