Mercedes timing chain rattle on cold start

Which Mercedes engines are affected?

This page covers two engine families. For other Mercedes work, see our Mercedes-Benz specialist page.

OM651 diesel. Mercedes workshop information on timing chain rattle covers the OM651 in:

• V-Class and Vito (447)
• Vito and Viano (639)
• Sprinter (906)

The OM651 is also fitted to Mercedes cars. If yours is one of them, we check the timing chain at inspection.

M270 and M274 petrol. Owners of cars with these engines, including the B 250 and E 200, report timing chain and camshaft faults.

If you are not sure which engine you have, put the registration in the enquiry form and we will check.

What are the symptoms?

OM651: a rattle or knock for two to five seconds after the engine starts.

M270 and M274: owners describe a rattle only on a cold start, followed later by the engine warning light and a stored camshaft timing fault.

When you book, tell us:

• when the noise happens, for example only from cold
• how long it lasts
• whether any warning lights are on

What causes it?

OM651: Mercedes links the rattle to elongation of the timing chain, which it ties to the chain tensioner. On early engines, camshaft sprockets made before March 2012 also wear.

M270 and M274: owners report a slack chain, tensioner faults and camshaft adjuster faults. We confirm at inspection which parts have worn before we quote.

How do you confirm it is the timing chain before fitting parts?

A fault code is not a repair, and a rattle is not a diagnosis. Before we quote for any parts, we confirm the cause.

OM651. We follow Mercedes’ procedure:

• listen to the engine from a cold start
• measure at the tensioner how far the chain has stretched
• inspect the camshaft sprockets

On the vans the procedure was written for, a reading below 82 mm, or below 84 mm on engines that have covered more than 250,000 km, means the tensioner alone needs replacing. A reading above that limit means the chain needs replacing too.

M270 and M274. We read the camshaft timing fault data stored in the engine control unit and check the basic timing of the camshafts.

We then show you what we found and send a written price. No part is fitted until you give us your written approval.

What does the repair involve?

OM651: what the measurement shows. That is the tensioner alone, or the chain and tensioner together, plus the camshaft sprockets if they are the early version or worn.

M270 and M274: we replace the parts the inspection shows are worn.

Once the work is done, we check that the noise has gone and verify the repair, including a road test where appropriate.

How long does a timing chain replacement take?

It depends on the engine and on what the measurement or inspection finds.

Before any work starts, you get a written price and a promised time for your next update. If the car needs to stay with us, ask about a courtesy car when you book.

Is there a recall for the Mercedes timing chain?

DVSA’s recall records include:

• R/2022/116: timing chain replacement, for some C-Class and E-Class built from February 2016 to February 2019.
• R/2014/182 and R/2014/184: an oil leak from the chain tensioner seal, for some cars and some Vito, V-Class and Viano built from February to November 2014.

Whether a recall applies depends on the individual vehicle, so check your registration on gov.uk. Recall work is done by the manufacturer’s network, not by us.