OM605/6 piston advice

[spock505]

I have posted on a several threads during the past few months as I went through the various steps of diagnosing the problem (engine failed to start after reconditioned head fitted)

The title includes the OM606 as the 605 is the same less one pot.

I am glad to say that it appears I have finally found the cause of the issue after exploring many options and now need advice on how to proceed.

There's quite a bit missed out as its on assorted threads but in essence stuck rings were suspected so head pulled followed by sump to gain access big end journals.

Ok, first piston is out - needed a small tap from underneath to get past carbon residue - as I did this and the piston released I felt something drop on my head, it looks like a piece of the oil scraper?

It was quite a gentle tap and unless these rings are very fragile its been like it for some time, I suspect this is what has caused the scoring on number two cylinder (this is number four).




Ignore the scoring on the middle of the crown, this is very light and my last attempt at jiggling the piston back and forth to free the rings.





Bore looks good;



Here's the main problem (apart from the above) the top two rings are completely flush with the side of the piston, no wonder she wouldn't start!




This looks to be where the ring joins, as can be seen it's fully compressed;



My plans were to hone the bores and replace the piston rings with a standard set but I would be interested to hear any other suggestions before going ahead.

If anyone has a OM605/6 and needs a bit of help I have taken a few photos along the way.

[sixto]

Before FI says it, I'll suggest the sticking rings resulted from VO at an inappropriate temperature. Do you have another conclusion?

Why did you replace the head in the first place? Was the engine running to the point you removed the head?

The 602/603 manual has specs for transverse and longitudinal diametric measurements taken along the height of the cylinders to determine how true the cylinders are. The 602/603 manual has no advice for correcting cylinder problems other than liner replacement so it would surprise me if oversize rings are available for your engine.

Are you sure the there's moisture corrosion in the ridge?

Sixto
87 300D

[spock505]

Hey bud,

Originally Posted by sixto

Before FI says it, I'll suggest the sticking rings resulted from VO at an inappropriate temperature. Do you have another conclusion?

When I purchased the car it had a long history of not being used sometimes only 800 miles in a year, the inactively continued in my ownership due to two problems below;

Why did you replace the head in the first place? Was the engine running to the point you removed the head?

I had a stuck glow plug which I tried to unsuccessfully drill out, ended up sending the head in to be reconditioned resulting in more non use.

The head came back and was duly fitted but had an bad tappet problem despite all of the hydraulic lifters being replaced so it went back again.

The 602/603 manual has specs for transverse and longitudinal diametric measurements taken along the height of the cylinders to determine how true the cylinders are. The 602/603 manual has no advice for correcting cylinder problems other than liner replacement so it would surprise me if oversize rings are available for your engine.

I don't propose to fit oversize rings unless necessary, i hope to get away with a de-glaze and new standard rings.

Are you sure the there's moisture corrosion in the ridge?

I didn't mention moisture corrosion, not seen anything to that effect?

Sixto
87 300D

Overall the engine looks in good shape, any recommendations for removing the carbon lip at the top of the bore - used a kitchen scourer today which took ages hence me only getting one piston out.

Cheers,

[mash]

Spock my man, The Service DVD says use a Ridge Reamer to remove built-up carbon or the piston ring lands may be damaged. Cast Piston alloy is relatively soft and damages easily. Those pistons are about 250US a pop. I would highly recommend buying the original repair dvd as it is an indispensable tool and filled with trouble-shooting guides, torque values, special tool part#'s, ect. I shutter at the thought of doing major engine overhaul without it. Good luck!

[JonL]

I don't like the looks of the center of the piston crown where the prechamber gets close... it looks like it is eroded or even worse that the piston has hit the prechamber. Maybe it's just the picture.

[lietuviai]

What's with all the pitting in the upper part of the cylinder bores?

[spock505]

Originally Posted by lietuviai

What's with all the pitting in the upper part of the cylinder bores?

In the carbon (black band) area? they are all like that -

Bores are smooth, I covered them with engine oil for protection, some lint maybe caught in the photos.

[lietuviai]

Yes, the black band area. I've never seen any diesel's bore with carbon like that.

[compress ignite]

Please be Very,Very Careful not to remove Too Much Material...
Only the Carbon!
OP is correct,You can "Bust" the ring "Lands" if the carbon ridge is left in place
when removing pistons upwards...(Then you are Screwed).

Your "Crosshatching" on the Cylinder Walls is still evident visually.'Can you "Feel"
it with a fingernail?If so, I'd be tempted to do nothing else than remove the
carbon ridge at the top of the Cylinders (and IF the ring Lands are O.K.),and
install new rings and fire her back up!

[spock505]

I have to apologise, it looks as though I have just gone straight through to this part without any preparation but there has been a slow lead up to where I am now.

The carbon on the lip was removed using oil and a kitchen scourer which took forever, is there a problem with using a dremel on this? I wondered as a lot of replies said the same about removing only the carbon but does it matter as the piston/rings dont go up that far?

At the moment only one piston has been removed until I get confirmation of the next best step.

CI, thanks for your input, one of the questions I had was how to free the rings, they are stuck fast and need soaking in something just to get them off, perhaps oven cleaner?

Open to suggestions -

Burning the mid night oil this end, catch you tomorrow all.

[babymog]

I would be concerned about the ring lands / spacing if the piston was forced out across a ridge. Measure them before installing new rings.

I am also very curious why the ring grooves are so impacted with carbon/crap. Will you be so kind as to enlightnen me/us on what besides burning SVO might have led to this problem (possibilities such as extended idling, oil additives with Teflon/PTFE, past engine problems et al)?

[babymog]

If you don't have a ridge-reamer, I would try using a die-grinder or Roloc with a fiber disk, the disk harness > cast iron. I have such a tool, can't remember the name.

Dremmel would probably work with the same fiber/abrasive disk but with anything harder than the cylinder liner it would be extremely difficult to control it and avoid damaging the liner.

It's all about the hardness of the abrasive, they make them for so many types of materials, and the right one is magic.

[compress ignite]

Oh, a question for KESTAS (ABOUT the Soaking Solution for the Pistons)...

The Pistons are an Aluminum Alloy ('Maybe proprietary?) and Oven Cleaner is
mighty "Basic"...
(I'm just "Freaked" at the cost of NEW Pistons and would
treat the old ones like they were cast out of Platinum and Jewels)

[babymog]

Yes, oven cleaner is a bad idea IMO, most say on the can to avoid ALUMINUM as it is extremely corrosive to alkali metals.

They can be boiled in a solvent tank, your friendly neighborhood machine shop should be able to provide this service at a reasonable price and leave them looking like new. Same deal with the cylinder head.

Great pictures. Can you take some of the cylinder head and camshafts?