PeachParts Mercedes-Benz Forum - Help: Valve adjusting locking nut won't come loose

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Help: Valve adjusting locking nut won't come loose

Hi. I just picked up an 83 300CD w/ 263k on it and catching up on all the routine maintenance, starting with the valve adjustment. I'm stuck on the intake valve of cylinder 1.

The valve is tight but I can't adjust it because I can't loosen the locking nut. I'm using bent wrenches, confirmed that it doesn't interfere with the adjustment nut, and turning ccw. I applied a lot of force, enough to be concerned about stripping the nut. Any advice?

Can the bottom nut be broken loose first by turning CW? May be able to apply torque to the nut whilst a helper strikes the nut with a punch and hammer. May have to apply heat to the nut. You could try penetrating oil but that nut is usually bathed in oil so that probably isn't the issue.

Good luck!!!

Quote:

Originally Posted by Sugar Bear (Post 4272977)

I'm an idiot and was turning it in the wrong direction...CW did the trick. I was afraid of using heat or a hammer (my IQ drops by at least 20 points when I pick up a hammer). Thanks!

Good...been there... don't fret over it!!!

This isn't critical but when adjusting valves on these motors there is occasionally a "tighter" spot than others which can be detected by using the large bottom nut to rotate the valve with a feeler gauge in place. If one spot is tighter than another adjust the valve clearance on the tightest spot. Slightly loose is better than too tight

Good luck!!!

When you say you have the bent wrenches, are they he hazel wrenches, or regular open ends that are bent?

I like to setup the wrenches so I can squeeze the handles together to loosen or tighten.

Quote:

Originally Posted by Sugar Bear (Post 4272983)

Quote:

Originally Posted by vstech (Post 4273001)

When you say you have the bent wrenches, are they he hazel wrenches, or regular open ends that are bent?

I like to setup the wrenches so I can squeeze the handles together to loosen or tighten.

Regular open ends bent with a torch. Squeezing is what I was doing, but in the wrong direction. Even pulled out a plumbing wrench (shame!) to get more squeezing leverage.

Either way, job's almost done. Waiting for a new valve cover to come in before calling it done (old one had a surface crack).

Thanks for help. Hopefully I can get through the other maintenance tasks (oil change, coolant, diesel purge/fuel lines/filters, diff fluid, motor mounts/shocks/shock mounts, belts, and a few worn parts along the way) without much drama. Although taking that fan off is proving to be a real pain.

Here's a picture of the top end. Doesn't look too bad for the mileage IMO. The timing belt is real tight.

If the valve was rotated 360 degrees some positions in that rotation would have a SLIGHTLY difference clearance than others. The "tighter" spot is where there is the least clearance and the optimal place to make the adjustment. This is because the valve train doesn't wear perfectly concentric. Again, this isn't critical and if you erred toward the looser clearance you are good to go.

Good luck!!!

Quote:

Originally Posted by rosta (Post 4273006)

Not sure what you mean by the "tighter" spot, but having the feeler gauge in place while tightening was key. Got them all dialed in and erred on the looser side. Had 2 valves that were super tight and all exhaust valves were dialed to non-turbo spec so all had to be adjusted.

Thanks for the CW tip. Hard to get my brain around what loosens and what tightens on my first go at it.

Regular open ends bent with a torch. Squeezing is what I was doing, but in the wrong direction. Even pulled out a plumbing wrench (shame!) to get more squeezing leverage.

Either way, job's almost done. Waiting for a new valve cover to come in before calling it done (old one had a surface crack).

Thanks for help. Hopefully I can get through the other maintenance tasks (oil change, coolant, diesel purge/fuel lines/filters, diff fluid, motor mounts/shocks/shock mounts, belts, and a few worn parts along the way) without much drama. Although taking that fan off is proving to be a real pain.

Here's a picture of the top end. Doesn't look too bad for the mileage IMO. The timing belt is real tight.

That’s not a crack, it is a casting line.
Having only the two locknut wrenches doesn’t complete the job. The third wrench can turn the actual valve and find the sweet spot to adjust the valve gap. But if it has been a long time since the valves were adjusted, you will need to do it again in 500miles…
Also, you have a timing chain, not a belt.:D

It may be just my eyes ...or a camera effect...
It's as if the edges of the rocker arms' "pads" are taking away material from the flat cam lobes' surfaces.
Is it an aftermarket camshaft...or the rocker arms?

ps old bottom nuts seem to have been of a softer alloy compared to the ones MB sells now (they're still available. Good to have a couple spares just in case). Just my observation that may be wrong.