617 vibration diagnoses - PeachParts Mercedes-Benz Forum

OM617YOTA · #1 03-04-2016, 09:46 AM

Howdy folks. Got another mess that I'm hoping to pick your brains on.

Engine is out of an 83 300SD. When cold it's mostly fine, as it warms up there's a vibration that is very obviously matched to engine RPM. Rises as I accelerate through a gear and goes back down when I shift, then rises again with the next gear. Idle I notice no difference, revving while sitting I notice no difference. With the clutch engaged and drivetrain loaded, either on the throttle or coasting down using engine braking, there's significant vibration. Put in the clutch and let the engine idle while the vehicle is still moving and in gear, vibration goes away. Power is good, throttle response is good, no unusual noises. None of this for the last 16k miles.

No inspection port to check out the clutch/flywheel, which would be my preference at this point. Considering dropping the transmission this weekend, unless one of you says "nope that's classic rod bearing behavior". Have a lot going on and will probably have to wait on any of this until after the move. At least then I'll have a nice shop to work in.

Thanks everyone.

OM617YOTA · #2 03-07-2016, 03:28 PM

Bump. Any ideas?

Almost feels like a missing cylinder, but only at speed/under load.

Dan Stokes · #3 03-07-2016, 03:52 PM

Hard to diagnose this one without being there. I'd start by looking at all the mounts (engine, trans) as a quick and easy thing to cross off the list. The basic engine is known for being tough so that makes the power plant a less likely suspect - though of course bad things happen to good engines.

Just a thought - did the vibration dampner ring slip on the elastomer? I don't know how common that might be on a 617 but it IS possible. Again, worth a look.

I'd have wondered about the driveline (driveshaft, clutch, etc.) being out of balance but at least the driveshaft is likely ruled out because it doesn't do it with the clutch disengaged. The clutch is a maybe if it tossed a balance weight or something along that line. BTW - Centerforce pressure plates are somewhat known for that.

Sorry I don't have more ideas on this.

Dan

mach4 · #4 03-07-2016, 04:45 PM

Obviously it could be most anything but the fact that it's tied to engine load rather than driveline speed would be a good reason to focus on engine stuff first. I'd probably focus on stuff like pulling the injectors and popping them (and while you're in there inspecting the prechambers), doing a compression test and for good measure check the valve clearance (needed for a compression test anyway).

The other thing that could be load related is something to do with the trans adapter kit....loose bolts maybe??? something that would only show up under load.

Without being there, that's the best I've got...and no current plans to pass through on the way to Canada.

OM617YOTA · #5 03-08-2016, 09:43 AM

Thank you, gents!

Motor and trans mounts were the first thing I checked. It's eaten the passenger side motor mount before, came out in pieces.

It's definitely part of the drivetrain on the engine/clutch side of things. I'll do a valve adjustment and compression test, the basics. Maybe I'll get lucky and it's just a tight valve that stays open enough to vent compression when hot.

If it was a balance issue I would think the vibration would happen all the time, but this only gets bad after the engine has gotten up to temperature. My thought is that my already marginal IP has just plain worn enough that at operating temperature, when clearances have expanded from cold, it's no longer able to generate enough pressure to pop the injector on one of the cylinders. I haven't noticed a decline in power coinciding with the vibration, but I have noticed a decline over the last few months. Not just subjective, hills I used to take at a certain speed in a certain gear are no longer possible. If that cylinder was declining over the last few months and is now not firing, there might not be much power loss to notice. My thought for testing is to pour cool water over the IP(carefully so as not to crack anything) and see if that solves/improves the problem temporarily, until it heats back up.

I hope that's it, I can swap the IP from my spare motor over relatively easily.

Idle thought: Wonder what one of our 617 gurus would charge for a 617 that's been gone through and is in good shape?

OM617YOTA · #6 03-12-2016, 02:22 PM

Update:

Reset valve lash, many valves were significantly tight. Checked compression:

Front
340
350
380
340
340
back

The outlier is weird, but not so much so that I'm concerned. All compression numbers are significantly better than in the past.

Engine runs much more smoothly now, which has made the other vibration much more obvious. I was easily able to verify that the vibration happens when just sitting stationary in the driveway and revving the engine, both with the clutch engaged and disengaged. The vibration does seem to be slightly less with the clutch engaged, spinning the transmission in neutral.

Killed cylinders one at a time, none made a larger difference than any of the others, although I didn't rev the engine to the vibration range with cylinders deactivated because it shook so much.

Cooled the IP with water, no difference.

Engine + transmission mounts are good.

Still need to remove accessory belts and rev it, see if it might be one of the attached accessories. I tried holding the engine at vibrating RPM and feeling the front and back of the engine to see if I could tell a difference in vibration, but nothing.

At this point I'm thinking I have some issues with the conversion flywheel/clutch/spacer bushing. All of which will have to wait until after the move.

Anyone have any ideas?

leathermang · #7 03-12-2016, 02:46 PM

From your first description I would think that it is NOT the engine.

That is sure taking a chance letting valves get tight...
after a certain point ...with the valves not being able to dissipate heat to the head via good solid contact... burning a valve can happen really fast... like within a few miles... and then you have a huge cost to deal with...

Stretch · #8 03-13-2016, 02:08 PM

Clutch pedal down == no vibration is screaming at me!

Tell me about the gearbox (if I remember rightly this isn't Mercedes)

Stretch · #9 03-13-2016, 02:20 PM

Food for thought?

Pilot bearing did not last very long

OM617YOTA · #10 03-14-2016, 01:36 AM

Thanks for the replies, folks.

Yup, definitely not good letting the valves get tight. In my defense, they were adjusted less than 5k miles ago. Obviously I need to be checking them more frequently.

Vibration is now clearly present when revved while sitting still, with the clutch engaged or not.

mach4 · #11 03-14-2016, 02:01 AM

OK, my guess is loose flywheel due to the aluminum spacer in the adapter kit.

OM617YOTA · #12 03-14-2016, 03:03 PM

Mach4-

The aluminum spacer is where I'm heading as well. Have been uncomfortable with it ever since it was installed.

With the past reasons you've had to make a dash to Canada, I'm GLAD you have no reason to do so right now.

I pulled the starter and tried to wiggle the flywheel as best I could, no noticeable movement, wasn't really expecting any. Next step is to stick a dial indicator on it and rotate the engine and see what kind of runout there is.

Thanks again everyone, I appreciate it.

OM617YOTA · #13 04-03-2016, 01:44 PM

Update:

Negligible runout, under 3 thou.

Grabbed harmonic balancer and tried to move it, got nothing.

Sigh, dropped the transmission. Adapter is fine, clutch looks in good shape with very little wear, all bolts were tight and snug, no wiggle anywhere. No wear marks or marring on the aluminum adapter at all. Despite my original misgivings, it appears to be a solid setup.

I'm thinking the vibration is delivery valves or internal engine at this point.

Very strongly considering just dropping in the spare engine w/ 150k less miles on it - I've already done the lion's share of that job w/ dropping the transmission. This is a particularly inconvenient time to roll the dice on another used engine that will have it's own unknowns, but with the troubles my current engine is having and has had, it's probably not that big of a difference.
Any thoughts or ideas?

OM617YOTA · #14 04-03-2016, 01:46 PM

More pics.

mach4 · #15 04-03-2016, 03:20 PM

Good news bad news - good that it wasn't the adapter...bad that you haven't yet found the problem.

I'd be inclined to put the new engine in, reason being that it would definitively show whether the vibration is in the drive train or engine. If it's gone it's the original engine and if it stays it's the driveline. The fewer miles aspect is a bonus...of course, that's just me. Let the record show I was wrong on the adapter hunch.

The only thing I'd suggest is to double check the match balance situation with the new engine.