Video: Diesel engine knocking noise

[billyonemate]

Hi All,

Am trying to work out the source of the heavy knocking noise on this Jeep Diesel engine (see video link below). The oil cooler failed and it did overheat as there was contamination of the coolant with oil. Oil cooler now replaced and coolant flushed. Now coolant is good with no contamination, but there is this metallic knocking noise, any thoughts what it might be?

http://youtu.be/Ux9mR-hmguU

thanks

 

[ivymike]

I'd guess overfueling of a cylinder (more likely), or incorrectly timed injection (less likely). How do your injector tips look? Tops of your pistons? There isn't by chance one with a big hole in it is there?

 

[DanEE]

from the sound as the starter is turning over the engine, one cylinder has lower compression than the others... no guess on the knocking sound, other than wondering if a valve is badly sticking in the guide..

Do a compression test on all cylinders and see if one is suspect.. If so, a boroscope is a handy tool and easy way to look inside the cylinders and see what might be amiss..

 

[ivymike]

I have seen a much larger diesel (300L) make a similar noise when it was getting a bad speed signal from the mag pickup @ the ring gear. The ring gear had some missing teeth, and the governor was seeing an oscillating speed signal, which it tried to overcome by jiggling the fueling up and down dramatically. The knocks were "large" combustion events when the gov was trying to abruptly increase speed.

 

[MikeHalloran]

You've definitely got a 'soft' cylinder on cranking.

I'm guessing there's a piece of a valve or piston banging around in one cylinder.

A compression check will tell you which cylinder, and a borescope will help figure out what's going on, but further cranking or running will do more damage, and you'll have to pull the cylinder head anyway, so I'd just go ahead and open it up.



Mike Halloran
Pembroke Pines, FL, USA

 

[LadaTrouble]

If it wasn't common rail I'd say a sticky injector....and there would be white smoke as well. I haven't heard common rail diesels make that noise....but as it's a single cyl I'd be isolating an injector first, and swap to another cyl to confirm. A check of valve train before going further would be in order too.

 

[NickJ67]

Does it have hydraulic cam followers? I used to have an old 5 cyl (petrol) Audi that made a noise just like that and when cold and shut up after about 5 miles. That was a tired hydraulic tappet. However, that did not cause a soft cylinder.

I also think you need to have the head off it - reckon you'll find a valve problem.....

Nick

 

[BrianPetersen]

Make sure the injectors are properly clamped down.

I've heard diesel engines do that because an injector is not properly seated, and I've heard gasoline engines do that because a spark plug was coming unthreaded and was only held in by the ignition coil above it (coil-on-plug engine - a regular engine would have simply sent the spark plug flying).

 

[BigClive]

The clanking seems to me to be a half-engine-speed sound.
Meaning that it is possibly in the valve gear somewhere.
The clanking is so sharp and unmuffled I would guess that it's in the top of the engine somewhere.

Probably just a very wide rocker clearance (like 1/8 of an inch) caused by a dead hydraulic lifter or bent pushrod.

 

[ivymike]

Half engine speed is also the firing frequency of any given cylinder, so that lines up with several of the other suggestions too

 

[moon161]

Pull the valve cover, you'll be able to see pretty quickly. If you have a compression tester, you'll be able to see pretty quickly.

An intake valve that doesn't open will make for a soft cylinder since it will pull a vacuum on the intake stroke.

 

[BigClive]

Ivymike - it could be a fuel problem etc. - but it just sounds too mechanical/metallic to me.

 

[LadaTrouble]

Uncontrolled combustion in a diesel will sound metalic - a sticky injector sounds like a rod or piston has gone.

 

[rmw]

That doesn't sound like diesel rap to me. Rather, it sounds like a blown head gasket or exhaust manifold gasket leak right at the head. Head gasket would explain the soft cylinder at starting.

rmw

 

[potteryshard]

Broken valve spring? No seal during cranking, but valve would slam shut during compression stroke.

 

[ivymike]

if it was a broken valve spring, it seems unlikely to me that the valve would remain in its installed location... they seem to prefer lodging in the top of the piston.

 

[patprimmer]

Isaac, maybe not on a side valve with 5:1 compression, but certainly for a diesel with 16:1 plus.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[ivymike]

I always figured they should make valve seats out of the same material as the piston, so the valve wouldn't find the piston any more comfortable and might stay where you put it.

 

[BigClive]

I hope this is not going to be another of those situations where we never hear from the person who posed the original question.
They must know what is (or was) wrong by now. We all learn something when we all told what was wrong -otherwise -nothing.

 

[ivymike]

I was a bit curious about the intitial statements in the video - "got it put back together... had the sump off, had the head off, well as much of it as I could get off" (isn't it a slab head on this thing? either all-on or all-off? figured perhaps he'd removed some over-head pieces for a while)