×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Video: Diesel engine knocking noise

Video: Diesel engine knocking noise

Video: Diesel engine knocking noise

(OP)
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

RE: Video: Diesel engine knocking noise

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?

RE: Video: Diesel engine knocking noise

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..

RE: Video: Diesel engine knocking noise

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.


 

RE: Video: Diesel engine knocking noise

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

RE: Video: Diesel engine knocking noise

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.  

RE: Video: Diesel engine knocking noise

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

RE: Video: Diesel engine knocking noise

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).

RE: Video: Diesel engine knocking noise


  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.   

RE: Video: Diesel engine knocking noise

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

RE: Video: Diesel engine knocking noise

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.

RE: Video: Diesel engine knocking noise


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

RE: Video: Diesel engine knocking noise

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

RE: Video: Diesel engine knocking noise

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

RE: Video: Diesel engine knocking noise

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

RE: Video: Diesel engine knocking noise

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.
 

RE: Video: Diesel engine knocking noise

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.  ;)

 

RE: Video: Diesel engine knocking noise


  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.   

RE: Video: Diesel engine knocking noise

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)

 

RE: Video: Diesel engine knocking noise

(OP)
Thanks for your helpful suggestions, really appreciated and has kept me really well informed.
I am still waiting for a full diagnosis. But I had a guy come round this morning and have a quick look, its common rail and he loosened off the fuel intake on the middle cylindar and reckoned it wasn't that, loosened the second one and it looked like the noise died a little. It started fine cranking over and ticking over ok so he thought the compression was fine. The follower seems to be fav at he mo. He gave me the number of an engine guy who said he would take a look when he is next down my way which should hopefully be this week.

i will keep you posted, the cranking issue is not a problem now at all (that was because i had to disconnect the fuel lines to get the oil cooler off when i was replacing that)

thanks again   

RE: Video: Diesel engine knocking noise

Isaac

If you fail to undo  a bolt or two at one end of the head and use a really long breaker bar lifting at the other end, you might remove most of the head.  winky smile

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules
 

RE: Video: Diesel engine knocking noise

Thank you Billy - let us know what happens - it is an interesting problem.  

RE: Video: Diesel engine knocking noise

(OP)
UPDATE: the jeep has been off the road for 2 months now as getting parts at a resonable price here is not easy. But have eventually got some new injectors (at suggestion of local diesel engine specialist) imported, they have been put in, but the knocking noise is stil there - dissapointed - where next?

BigClive seems the most likely "Probably just a very wide rocker clearance (like 1/8 of an inch) caused by a dead hydraulic lifter or bent pushrod"

RE: Video: Diesel engine knocking noise

Not much knocking when its cranked?  An exhaust leak can sometimes sound like a knock. Why haven't you removed the valve cover and examined it? Run it with the valve cover off.
It does act like a low cylinder when cranking.

  

RE: Video: Diesel engine knocking noise

I will bet my left foot that you have at least spun a big end bearing.......That sounds just like my toyota diesel when I spun a bearing....There is definitely low compression in at least one cylinder as mentioned earlier....you need to take it apart, trying to fix it with bolt-ons is going to get too costly!

RE: Video: Diesel engine knocking noise

(OP)
finally got the valve cover of ... not so simple as required either dropping the engine or drilling some holes in the bulkhead to get the injectors out ... went for drilling the holes in the end.

anyway here's a video of it cranking with the valve cover off, notice it cuts near the end after we take one of the cams off, i'm still confused as to what is causing the noise though - any thoughts ?

http://youtu.be/zF14UVlkJsw

RE: Video: Diesel engine knocking noise

How do you make that video work?

RE: Video: Diesel engine knocking noise

No - neither of the two new links work for me.

RE: Video: Diesel engine knocking noise

Billy - thanks for the video.
A twin-cam, four-valve diesel? So much for theories about bent pushrods and damaged lifters etc.

RE: Video: Diesel engine knocking noise

Any news on this one? Did you find the problem?

RE: Video: Diesel engine knocking noise

(OP)
well, four months on and we have finally got the head off and got to the bottom of it - did anyone go for piston ring?

youtu.be/4m0dLbrenws

RE: Video: Diesel engine knocking noise

Mike Halloran did.

Several others suggested compression checks which at least hinted toward piston.

That twin rail thingy all jammed up with scuffed off piston bits is an oil control ring.

You still need to ensure you rectify the cause for the piston to scuff up like that. It very nearly seized. It is probably a result of overheating, but also possibly poor timing. Basically the piston got to hot and grew to much for the bore.

The bore might also now be out of shape.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules

RE: Video: Diesel engine knocking noise

That first piston looks to have a discolored upper big end bearing,take a closer look at it, my left foot is at stake here!

RE: Video: Diesel engine knocking noise

(OP)
yes, well done mike, and thanks everyone for the help over the last four painful months, hopefully it's a rebore, new rings, skim and put back together job now - hopefully...

RE: Video: Diesel engine knocking noise

If the bore is still relatively straight and round and within spec on dia, a simple hone and one new (or even second hand) piston and new rings might suffice if on a tight budget.

I would at least check all the bearings as the load from that damage being caused may have harmed them. Also the metal contamination may have found its way to the galleries and bearings and oil pomp.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules

RE: Video: Diesel engine knocking noise

Billy, what market offers Jeeps with that engine? Who makes the engine?

RE: Video: Diesel engine knocking noise

One hint from bitter experience:

If you can't account for every last gram of piston ring material, you need to expose and brush clean every bit of the engine interior including the oil galleries.

That includes specifically pieces smaller than a grain of sand that can go through the oil pump screen. On the first cold start, they will flow through the oil filter bypass valve, and take out a rod journal.

Mike Halloran
Pembroke Pines, FL, USA

RE: Video: Diesel engine knocking noise

Well, this happened a while ago, but it is quite interesting.

When analyzing power cylinder failures it is always best to analyze the cylinder with the least amount of damage, for it will tell you how the scuff started. It can start on the ring, or on the skirt or on the pin, all different kinds of issues.

The image from the piston is quite consistent with overheating, because we can see that the scuff occured almost all the way to the face tranversal to the pin, and since we all know pistons are oval, it makes sense that the scuff on a overheated piston will start there and progress from there.

It is difficult to analyze now with just one screwed up cylinder because the scuff progressed pretty badly on that one, and it takes away evidence of the cause.

But it makes sense that this piston (It must be the one farthest from the coolant inlet) will scuff first. And then you corrected the issue with the coolant and it was ok. Also, all the post failure cranking to hear the noise, will do more damage to a scuffed piston, thus making it harder to evaluate.

Power cylinder failures are always very good exercises for the mind.. I've worked through several of those, and I can say, the engine always surprises us with new screwed up ways to scuff and break down.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources