A buyer measured the pistons I sold him, I made the mistake of not measuring them first. According to the service manual they should be between 95.469mm to 95.481mm. Can a piston diameter wear almost 1mm? Could they have been measured wrong? I thought maybe these were 8V 2.3 but those would be around 89mm. These pistons were removed from my 16V parts engine and has the Mahle 95P54 stamped inside so most likely they are original.

__________________
'88 300TE, 175k, black RENNTech 3.6L Recaro C's AMG 1 SOLD
'92 500E, 110k, Spruce green, stock SOLD
'94 E320 Cabriolet, 130k, E500 wheels, Emerald green SOLD
'94 E320 Cabriolet, 110k, black, stock, SOLD
'88 300TE, 229k, dark grey, SOLD
'90 300CE, 212k, white, new paint, SOLD
'91 300E, 209k, white, rebuilt head SOLD
'74 914-6, grey, 2.7L 325hp twin turbo Audi conversion

Where the piston is measured is of great importance. Pistons are always measured near the bottom of the skirt, 90 degrees to the wrist pin. Anywhere eles will give erroneous numbers, the crown especially. When cold, the crown diameter will always measure much smaller than any other part of the piston , because that will become the hottest part of the piston during operation, and will expand out to nominal size at operating temperature.

The 8v pistons are the same (it still needs to make 2.3l).

__________________
Prost!

.

The BORE is 95.5mm & the piston needs about 0.1mm of clearence....therefore a piston of 95.4mm diameter. OOPs

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Sounds like a measuring error.

Re: piston clearance
1mm=.03937 inches
normal piston clearance=.0015-.002 inches, or ~.051mm
At 1mm piston skirt clearance the pistons would make so much noise that anyone in their right mind (who was not deaf) would immediately shut the engine off.

I'm trying to imagine how a piston can wear 1mm undersize if that's what truly happened. Wouldn't overly worn rings lose too much compression and leak too much oil thus preventing driveablilty and further wear?

Thanks for you input!

__________________
'88 300TE, 175k, black RENNTech 3.6L Recaro C's AMG 1 SOLD
'92 500E, 110k, Spruce green, stock SOLD
'94 E320 Cabriolet, 130k, E500 wheels, Emerald green SOLD
'94 E320 Cabriolet, 110k, black, stock, SOLD
'88 300TE, 229k, dark grey, SOLD
'90 300CE, 212k, white, new paint, SOLD
'91 300E, 209k, white, rebuilt head SOLD
'74 914-6, grey, 2.7L 325hp twin turbo Audi conversion

good link:
Automotive Mechanics: Piston measurement and clearance
The originally cited specs are the correct ones, per the manual.

__________________
Prost!

1. Pistons, MB included, are supplied in oversizes, not undersizes.
2. Long before the clearance due to combined bore and piston wear reached 1mm (.040") the rings would have ceased to seal, and the skirt of the piston would have broken.

Suggest that the purchaser send you a picture of the measurement process, so that you may see where the micrometer or caliper is being applied to the piston. As noted in a post above, the correct point of measurement is just above the bottom of the skirt, 90 deg. to the pin axis.

The buyer sent a picture of the rings in the cylinder (without pistons) and the original rings had a closer gap than the rings on my pistons. I'm having him return them and will recheck the measurements.

__________________
'88 300TE, 175k, black RENNTech 3.6L Recaro C's AMG 1 SOLD
'92 500E, 110k, Spruce green, stock SOLD
'94 E320 Cabriolet, 130k, E500 wheels, Emerald green SOLD
'94 E320 Cabriolet, 110k, black, stock, SOLD
'88 300TE, 229k, dark grey, SOLD
'90 300CE, 212k, white, new paint, SOLD
'91 300E, 209k, white, rebuilt head SOLD
'74 914-6, grey, 2.7L 325hp twin turbo Audi conversion