Reringing while replacing the head good or bad?
 

I'm slowly gathering parts to replace my cylinder head on my 85 300d to find the source of a knock coming from the head.

I was wondering if I could slip out the pistons and replace the rings without getting uneven compression.

The bottom end is new but I never touched the pistons before.

I don't have the money or time to replace the sleeves, so it would be half a rebuild.

Compression is fair and the motor is seating at about 160k.

Also, how hard is it to replace the wrist pins.

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Anything in the block below the head will need the engine removed to replace it. The only thing I can think of in the head that would make a knocking sound is the valve guides slipping down in the head (had it happen once), or injector nailing (no need to remove the head to fix).

to answer your question... maybe.
new rings IF THE CYLINDER IS NOT WORN can improve compression... but odds are good if the rings are bad, the pistons are bad... new rings won't fix bad pistons...

I'm thinking its a wrist pin honestly.

The noise is worst at cold start, better when warm and sometimes gone after getting off the freeway.

Changes pitch depending on if I let it warm up or if I just take off.

I'm wanting to get in there and see if the piston is lose.

From the bottom half everything looks great.

I've rebuilt injectors and timed the pump.

Starts when 10 below.

No one can figure it out.

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I was reading this manual a member showed me that showed that the lower pan can be removed in the car if the motor is lifted slightly. Really don't want to try it if I don't have to.

No need to lift anything to remove the lower pan, it's the upper pan that needs the engine removed in order to remove/replace.

Here are some other facts I've put together. The lower oil pan looks to have been replaced. The motor came out of an junk yard car that set for god knows how long, at least 5 years. The crank case breather was capped and driven like that for a few miles before dying, owner thought the rings were shot and sold me the car. The motor is easier to turn by hand until one of the pistons hit the top of its stroke, unknown which, and then requires more effort and I hear a very small clack.

I'll post a video and a picture of my new head later for kicks and giggles.

I have done a "ring job" w/ engine in car in several gas motors (Chrysler 2.4L & 383), but wouldn't try it on my 300D. I disassembled one of my 300D engines on a stand, and thought it would be almost impossible to re-ring it in the car. I think a few people have removed the upper oil pan in the car, but it was probably harder than removing the engine. You might be able to replace only the #1 connecting rod bearing thru the lower oil pan opening. Look at photos here.

I suspect that better than a simple hone & re-ring, you would do better to replace the cylinder liners first. I have done that (see my post). However, that requires then taking it to a machine shop to deck the block and bore/hone (haven't done yet).

Did you take a compression test? Did it indicate low compression? if the engine truly has a hundred sixty thou miles it is very unlikely to be a problem in the bottom end....the top end either for that matter. have you checked the vacuum pump?

Does it do this every crankshaft revolution or every other one?

If every rev you probably have something in a cylinder. As the piston rises the object hits the head.

If every other, you have a valve sticking or something on a piston just below a valve.

Pull the valve cover and see if you can coordinate valve action to the sticking. ( Turn the engine just until it gets tight, see if any rocker arms have lots of lash. )

Answer
 

I strongly suspect you have a combination of:
* Cold injector nailing.
* Fuel delivery (to the injection pump body) pressure LOW.
* Seriously bad fuel quality.

Injector + Heat shield + Nozzle, Prechamber + Collar, and Nailing. LINK THREAD
http://www.peachparts.com/shopforum/diesel-discussion/211750-injector-heat-shield-nozzle-prechamber-collar-nailing-link-thread.html

Diesel Fuel Delivery:
http://www.peachparts.com/shopforum/diy-links-parts-category/142399-fuel-delivery.html

Fuel pressure problem solved '80 300SD
http://www.peachparts.com/shopforum/diesel-discussion/333779-fuel-pressure-problem-solved-80-300sd.html

Strong nailing
Strong nailing - PeachParts Mercedes ShopForum

Fuel injection pump starvation with a good lift pump
Fuel injection pump starvation with a good lift pump - PeachParts Mercedes ShopForum

Fuel pressure relief valve adjustment
Fuel pressure relief valve adjustment - PeachParts Mercedes ShopForum

lift pump test
1979 300td -- Can anybody walk me through a lift pump test? - PeachParts Mercedes ShopForum

fuel pressure
fuel pressure - PeachParts Mercedes ShopForum

great internal injection pump pictures
http://www.peachparts.com/shopforum/diesel-discussion/300531-injection-pump-sluggish.html#post2738138

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