W116 450 SEL 6.9 piston set MAHLE 003 17 01 – oversize guide
Anyone restoring a 450 SEL 6.9 quickly runs into a sourcing problem during the engine overhaul: pistons for the M100.985 have not been produced in series for decades, and a complete, matched set in the right repair size is hard to find. This guide explains how to recognize worn pistons, what to look for when buying a piston set for the 6.9 and which part number belongs to which bore.
How do you recognize wear or damage?
Pistons and piston rings seal the combustion chamber and transmit the combustion pressure via the connecting rod to the crankshaft. If this seal deteriorates, pressure escapes past the piston instead of doing work.
| Finding | Meaning |
|---|---|
| Falling compression on several cylinders | Piston/piston ring sealing is deteriorating – indication of wear in the crank drive |
| Rising oil consumption, heavy blow-by | Combustion gases get past the piston into the crankcase |
| Declining power with measured low compression | Pressure loss at the piston; an engine overhaul with boring to oversize is due |
| Loss of power or starting problems with normal compression | Another cause, mostly in the fuel supply – see Defective fuel pressure damper on the W116/W126 or Fuel accumulator and starting problems |
Important: A compression or leak-down test is the basis of every decision. Only once the engine has been disassembled anyway and the cylinder dimensions measured is it clear whether standard pistons suffice or whether the cylinders must be bored to the 1st oversize.
Causes
After decades of operation, piston rings and cylinder walls wear. The cylinder wall loses its honing pattern and goes out of round, and the rings lose tension and sealing effect. Long periods of standing, as is common with collector cars, add to this. If the cylinder wall is worn beyond the permissible dimension, it can only be restored to the next repair size by boring and honing – and then matching oversize pistons are needed for all eight cylinders in a uniform size group.
What to look for when buying
- Identify the engine: The set is intended for the 450 SEL 6.9 (W116.036) with engine M100.985 (6,834 cm³, V8). The 450 SE/SEL 4.5 has the M117, the 300 SEL 6.3 and the 600 (W100) the M100.980/981 with 103 mm bore – it does not fit there.
- Check the bore dimension: MAHLE 003 17 01 has a diameter of 107.51 mm for the 1st repair size (bore 107.5 mm, +0.5 mm). For the standard bore of 107.0 mm, MAHLE 003 17 00 (107.01 mm) is provided.
- Uniform size group: All eight pistons should carry the same size group. In the set offered, all eight are marked 107.51 mm.
- Compare dimensions: Compression height 45.6 mm, overall length 85.6 mm, piston pin Ø 26 mm, tin-plated skirt, weight approx. 1,086 g per piston.
- Condition and completeness: Look for unused stock with piston rings, pins and retaining rings. With NOS parts, age- and storage-related marks on the boxes are normal; new retaining rings may be necessary.
Solution
Once the overhaul with boring to the 1st oversize has been decided, a complete set of original pistons in a uniform size group is the proper way. We offer a MAHLE piston set 003 17 01 with 8 pistons (Ø 107.51 mm) from old stock: original MAHLE series production from the model's production period (Made in Germany), unused, in the original packaging (4 boxes of 2 pcs each), with fitted piston rings (chrome-ring configuration), piston pins and retaining rings. Price: 7.980,00 €. The set is a one-off item – you will find more parts for the W116 in our section Mercedes W116.
MAHLE piston set 003 17 01 – 8 pistons, 1st oversize
Mercedes 450 SEL 6.9 (W116) · Engine M100.985 · Ø 107.51 mm · NOS
7.980,00 €
View offer →Compatible vehicles
| Model series | Model / engine | Note |
|---|---|---|
| W116 (1975–1980) | 450 SEL 6.9 (W116.036), M100.985, 6,834 cm³ V8 | only with 1st oversize bore of 107.5 mm |
Does not fit for 600 (W100) and 300 SEL 6.3 (M100.980/981, bore 103 mm), 450 SE/SEL 4.5 (M117) as well as engines with standard bore 107.0 mm.
FAQ
Does the piston set 003 17 01 fit every Mercedes W116?
No. The set is intended exclusively for the 450 SEL 6.9 (W116.036) with the V8 engine M100.985. It does not fit the 450 SE/SEL 4.5 with M117, the 300 SEL 6.3 or the 600 (W100) with 103 mm bore.
What does 107.51 mm 1st oversize mean?
The standard bore of the M100.985 is 107.0 mm. At the first repair size, the cylinder is bored and honed to 107.5 mm; this requires pistons with a diameter of 107.51 mm, i.e. MAHLE number 003 17 01. For the standard bore, 003 17 00 with 107.01 mm is provided.
Can I install the pistons without machining the cylinders?
No. For this set, the cylinder diameter must be bored and honed to the 1st oversize of 107.5 mm. The pistons do not fit into a standard bore of 107.0 mm.
What's included in the scope of delivery?
Eight original MAHLE pistons with fitted piston rings (chrome-ring configuration), piston pins and retaining rings, packed in four original boxes of two pcs each. Due to their age, new retaining rings may be necessary.
How do I make sure the set fits my engine?
Send us your VIN (chassis number) and model year before buying. We will check both against the parts catalog and verify free of charge whether the set fits. Please also compare the actual bore dimension of your engine.
KFZTeile-Thot is a specialist company for tested and refurbished Mercedes parts with its own test benches and has over 1,000 positive eBay reviews. Do you want to know whether the piston set fits your engine? Call us: +49 179 8991069 (Mon–Fri 8 am–6 pm) – or use our contact form. You will find another guide on the W116 at W116 engine control unit faulty.