W124 FSM section 03-7021aw provides a piston protrusion spec for the 601/2/3 series. 0.74-0.96 front and rear for a "new" block, 0.96-1.16 for a machined block. It doesn't provide a fore-aft variance spec which would be nice to confirm bent rods before refitting the head.

If you go deeper into the engine, it's pretty obvious to see from piston skirt wear if any rods are bent -



Note the bright patches on #1 and #6. Main and rod bearings on this block were withing installation spec, not just service spec. I'm tearing into another block with similar bright patches on #1 and #2.

Sixto
87 300D

Even the main tensioner looks good. Are you sure it hasn't been apart before? Does it have an old or new style vacuum pump?

Sixto
87 300D

You know I thought the same thing in regards to the oil pump chain tensioner. I'll look at the vacuum pump to see if it has been updated.

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Jim

Have you checked piston protrusion?

Sixto
87 300D

Not yet. I was going to spend some time on the block tomorrow.

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Jim

There is ~.300mm difference in the gap between the front and the back of the piston. I called and discussed it with the owner and he said he was using a qt every 400 miles so we're going with the 3.0 liter.

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Jim

The FSM says to measure the vertical protrusion of the piston.

Sixto
87 300D

I did. I just shot these pics like I did to show the difference. One rear protrudes ~.605 and the front is ~.300.

I think I'm going to tear it on down.

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Jim

Jim, the differences in piston gap and piston protrusion indicate bent connecting rods and oval cylinders. I would consider that block toast. From what I have read there is insufficient cylinder wall thickness to increase the bore size. No sense in tearing that engine down unless you want to confirm the bent connecting rods.

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Fred Hoelzle

Curious, I like to know if there is any discernible wear on the cylinders? Pronounced ridge left at the piston crown portion? It would seem with those numbers you would be seeing wear on all the cylinders.



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1983 123.133 California
- GreaseCar Veg System

Doesn't matter since MB doesn't sell oversize pistons and rings for the 603.97

Sixto
87 300D

wowzer - pistons are pricey. I think we've about decided to find another long block.

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Jim

This is a 3.0 liter out of an 87. Plans are to put it on the stand, replace the head gasket and all seals and bolt it in with it's original IP. Any thoughts in regards to the oil pan with the extended section on the side on the '87 engine. It looks like it will fit without any issues.

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Jim

A quick peak at the SDL K-member should tell you whether or not the side sump will fit. Any reason to think a 126.134/5 has a different K-member from a 126.125?

If you're not pulling the oil pan, at least pull the side sump to see if any bits of an old vacuum pump remain. Maybe you can peak into the pick-up screen with a dental mirror.



Have you replaced a 60x rear crank seal? It's a bit tricky on an engine stand but I'm sure you have a hoist handy.

Sixto
87 300D

now that you mentioned it I remembered.

It looks like there is plenty of clearance in the '91 for this oil pan. I will pull the side piece and inspect it.

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Jim