OM605/6 piston advice - PeachParts Mercedes-Benz Forum

spock505 · #1 03-29-2009, 02:47 PM

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 · #2 03-29-2009, 03:46 PM

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 · #3 03-29-2009, 04:07 PM

Hey bud,

Quote:

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 · #4 03-29-2009, 05:19 PM

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!

atypicalguy · #5 10-08-2015, 05:05 AM

Quote:

Originally Posted by spock505

Hey bud,

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,

That is potentially a big no no. They are often aluminum oxide and shed particles of that incredibly hard abrasive down Into the motor as you scrub. Many rebuilders were using these pads to remove traces of head gasket leading to early engine failure until the problem was discovered.

Sent from my SAMSUNG-SM-N910A using Tapatalk

spock505 · #6 10-10-2015, 10:06 AM

Yup, that was way back - car now on third owner I believe.

If anyone else has stuck rings with pistons removed, opt for bucket of hot water, works a treat.

JonL · #7 03-29-2009, 06:20 PM

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.

spock505 · #8 03-30-2009, 07:08 AM

Thanks for all the replies, will answer in order.

Please see comments posted with photo, the marking is very light but looks worse against the black carbon background.

This will polish out now the piston is out.

Quote:

Originally Posted by 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 · #9 03-29-2009, 06:26 PM

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

spock505 · #10 03-29-2009, 06:30 PM

Quote:

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 · #11 03-29-2009, 06:56 PM

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

compress ignite · #12 03-29-2009, 07:15 PM

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 · #13 03-29-2009, 07:33 PM

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.

spock505 · #14 03-30-2009, 07:18 AM

Quote:

Originally Posted by 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).

The piston wasn't forced out as most of the carbon removed with kitchen scourer, I think oil scraper may have already been broken.

On the next four pots I will use one of the following recommendations below to remove all of the build up to allow them to slide out freely.

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!

I am a bit confused here when you say 'ring lands' are ok, are you referring to the slots which the rings sit inside on the piston itself?

If so there is no damage at all as the rings are fully compressed and stuck completely inside the grove protecting it so to speak, this is why there was little or no resistance getting them out.

There was nothing protruding to catch onto the remaining carbon.

babymog · #15 03-29-2009, 07:34 PM

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)?