OM617 - How to test for worn cam lobe vs. wrist pin bushing or other lower issue
 

Hi,

Have a loud metal knock......definitely doesn't go away with cracking injector lines. Saw @Jarods video and discussion on his nailing/knocking ending up being worn cam lobes and followers: http://www.peachparts.com/shopforum/diesel-discussion/383541-some-ideas-om617-knocking-tapping-nailing-2.html

Here's his video (almost positive I have the same noise): https://youtu.be/zzLLIDDYk4o

After spending quite a bit on other repairs lately, I was hoping to avoid another 500-1k repair like replacing the cam, etc, unless I"m positive that is what it is, rather than something lower on the engine like wrist pin, etc.

Does anyone have a suggestion how to confirm it would be cam related vs lower end related?

Here's some more info along with video I took of the car cold starting today: https://youtu.be/uLplmSMMaHE

So, here's the background: own a 82 300TDT with 270k miles on it. Purchased it two years ago. Ran decent with no really nailing or loud engine knocking to speak of. I had to run to Riverside, CA to pick up some cycling parts for a repair and thought I'd take Bru (Brunhilde, to be exact) for a nice cruise from Long Beach, CA. It was a low-90's day but the water temps never went above the usual, and I kept the engine speed below 70mph. By the time I arrived I very loud nailing noise was occurring. At idle it sounds like a carpenter's steel hammer hitting the inside of the engine head once every 1/2 second.

After the noise started (and prior to finding Jarod's post) I took did a valve adjustment (all were decently within spec) and overhauled the injectors with new nozzles. This didn't fix the issue so took to my local diesel Merc mechanic and he did a leak down test. He said it was Cyl 2's exhaust valve burnt and it would need valve job, recommend new valves across the board if one is getting replaced. So we did that and I had him do the timing chain and parts since he was in there. After all that, sound was still there. His explanation was piston rings had worn the cylinder walls . . . which sounded suspicious to me. We've since moved so I've done some more home-investigation myself....so I decided to do a compression test. Prior to installing the tester i checked all the prechambers for missing prechamber balls but they're all there...phew.

Here's the results of a cold compression test (will do warm test tomorrow):

Cyl 1 = 295 // Cyl 2 = 265 // Cyl 3 = 305 // Cyl 4 = 295 // Cyl 5 = 305

Here's my questions:

1. Do those numbers look (especially Cyl 2) or seem to indicate a worn cylinder that could be slapping against the walls?

2. The noise came about suddenly after the drive on the freeway and so if it is a similar issues to Jaron's with a worn cam lobe, does it make sense for the lobe to wear and cause that noise so quickly? I would expect it to slowly get louder and louder unless there was a severe lack of oil dispersion, which leads me to ask, should I be looking for oil dispersion issue up near the valve cover (no the valve cover was not leaking oil nor was any other area leaking oil).

3. Based on Jarod's post, I'm assuming the cause of the noise is the cam lobe slapping the follower and making that noise. It it possible to adjust the interface so that noise is less?

4. If no adjustment can be made, what sort of damage can occur if we continuue to drive the car as is? Would it only damage parts that would initially be replaced when replacing the cam, or could I also cause damage to other parts that would then require additional costs? I'm only thinking of driving it for another 3-6 months to save some extra cash after spending a healthy amount on the valve job and timing chain.

Thanks for the feedback.

Use a stethoscope to listen.

Have you tried loosening injector lines?

I reckon that's more likely to be the vacuum pump

Step #1: Remove cam cover.
Step #2: Look at cam lobes.
Step #3: If lobes are OK, adjust clearances.

Thanks for the suggestion. I haven't tried a stethoscrope and don't have one but will certainly try that route after inspecting the vaccuum pump and pulling the valve cover to inspect the cam lobes along with shooting some pics of the lobes for review. Thanks for the suggestion . . . do you suggest a certain stethoscope? I've read on other posts of pulling the injector and running the scope that way?

Had that on the "next up" list, since it seemed like the easiest to inspect and rule out. Glad to hear another feelsl like the VP could be the culprit.

Will try that after the VP if the VP internals seems to be working decently. Will report back tomorrow on the VP on here with some pics/video since I've never pulled one before. I've read a few threads to have a decent idea of what to look for in terms of problems.


One thing I noticed which is hard to discern from the video is the idling tends to rev up and now about 200-300 rpm (guessing since the tach isn't working). Would that be due to a bad vaccuum pump or should I assume I need to work on the IP?

Thanks for the suggestions.

Take the car to an automotive machine shop / engine builder and offer to pay them to take a listen.

Solid lifter / non hydraulic camshafts can wear the clearance take up ramps and develop a valve tap even with proper valve clearances.

The OM617 has no valve lifters.

One would have thought that the Mechanic would have checked the Camshaft and the rocker arms. No one has ever reported a broken valve spring but you can look for that.

Since 2007 when I joined I think one person had the valve adjusting nuts come loose.

As others said if when you do the injector cut out test there is no change in the sound then it is not likely rod or bearing. Because with no injection and the resulting pressure of combustion it would make it hard to make a knocking noise.

Of course a valve could be hitting a piston and that would continue to knock.

Specifically locating where the sound is coming from is a great idea and especially around the Vacuum Pump. Except for testing you should not be driving the Car till you find out what is causing the noise.

Note inspect the Air Filter Bracket to see if it is broken or the rubber attachments are not stripped out or broken. When mine was loose I thought that the engine was going to come apart.

Check the torque on the bolts holding down the rocker arm assemblies.

I'm using that in a generic sense, manual lash adjusters would be more accurate.


One would have thought that the Mechanic would have checked the Camshaft and the rocker arms. No one has ever reported a broken valve spring but you can look for that.[/QUOTE]


There would have been a generic visual but no one is going to put a dial indicator on every lobe and make a lift map every few degrees as this would be $$$.

Is there a diagram somewhere of the OM617 camshaft and it's parts? Curious to see if I can detect this on my own after pulling the cover.

Also, it's hard to tell from the my YT video I posted above, but I don't see very much oil sloshing around or dripping on to the front cam lobes. Should that be cause for concern (thought I saw another post of a video of opened oil filler cap and it looked like oil was dripping on to the lobe. It wasn't completely full, but you could at least see a puddle of oil in which the cam lobes would run through. I don't see that on mine.

Some results after pulling the VP (pics attached, here's the video link: https://youtu.be/TvsD1p1DOV0

1. The ball bearings on the VP spin well and have zero drag/pitting.

--Is there another part of the VP that should be inspected/considered as the cause for the loud knock?

2. Looks like there is no trace of the VP gasket remaining on the mounting surface of either the VP or black, which I think would at least partially explain the heavy amount of buildup around the VP (I took about a 1" thick glob of buildup off the A/C Compressor.

--To that end, has anyone put a VP into a Ultrasonic Cleaner or is that advised against? I'm not familiar with the internals of the rest of the VP

If I were you I'd carefully clean as much of the inside of the vacuum pump as you can. Use something like brake cleaner - try not to get too much going down the bore of the piston pump. The seal / piston ring around the piston itself is a PTFE-like seal that might not enjoy serious heavy duty cleaners.


It is very good news that the bearings are intact.


Now that you have the pump removed try to push / pull the timing device to see if there is any detectable longitudinal play in the intermediate shaft bearing (that sits behind the timing device). If you can feel anything "by hand" then it is really buggered and needs attention immediately. The specifications for the allowable play are in the FSM - I can't remember the value - but it is a tiny fraction of a mm (that you can't feel by hand)


When refitting the vacuum pump the gasket is a very important part to replace. Whilst it is partly there to stop leaks it is mostly there as a spacer - if you install with liquid gasket the chances of vacuum pump damage is high cos it sits too close to the block

One dull cold winter a few years back I did this thread about piston vacuum pumps =>

http://www.peachparts.com/shopforum/diesel-discussion/339870-more-than-you-likely-ever-want-know-about-om61x-piston-vacuum-pumps.html

There's a little bit more information there if you have the life span to look through it all (!)

Thanks for the tip. I use a two different sized ultrasonic cleaners for bicycle service and the shallow version will work well for this job. I think if I lay the VP spring side down in the Ultrasonic cleaner and at half full it will just barely touch the top of the inside portion of the VP. The nice thing about the machine is it uses heat, sonic waves, and whichever cleaning solution you choose. In this case I've a 1/2 diluted version of Simple Green's Pro HD cleaner to work very well without being as caustic to a part's finish or rubber pieces. Will give that a go and report back on results.

I've never used an ultrasonic cleaner on something so dirty - I'd expect it'll make a mess of your nice cleaner.


You'll be surprised how quickly these things wipe clean with a little / careful amount of solvent


You'll also be surprised just how fast it'll get dirty again and look just as bad as it does now! I'd give it ten operational minutes...


...the point of cleaning is to help look for damage - I should have made that clearer