BMW 3 Series cambelt: it doesn’t have one
every 3 Series uses a timing chain — but on this model, two of those chains have earned their own maintenance advice.
- Timing chain no schedule
- N20 & N47 known issues
- Preventive chain job £900 – £1,900
The BMW 3 Series has no cambelt to change — every engine, petrol and diesel, uses a timing chain that BMW treats as a lifetime part. For the six-cylinders that’s the whole story. The asterisks sit on the four-cylinders: the N20 petrol (most 320i/328i, roughly 2011–2015) has brittle chain guides that specialists now replace preventively, and the N47 diesel (2007–2014) carries the rear-chain problem covered on our 1 Series page. Engine-by-engine below.
3 Series timing by engine
No 3 Series needs routine belt money — the table shows what, if anything, to watch instead. The pattern worth noticing: both problem engines are four-cylinders of the same era, one petrol and one diesel, and both were fixed by their successors.
| Engine | Timing | What to know |
|---|---|---|
| N20 petrol (320i/328i, ~2011–2015) | Chain — front of engine | Brittle plastic guides; specialists advise preventive replacement around 70,000–100,000 miles |
| N47 diesel (316d–320d, 2007–2014) | Chain — rear of engine | Documented stretch/failure risk; cold-start rattle — full story on the 1 Series page |
| Older 4-cyl petrol (318i/320i, N42/N46 era) | Chain | Tensioner and chain wear known; a lasting rattle warrants inspection, jobs from ~£750 at specialists |
| Six-cylinder petrol & diesel (325i–330d) | Chain | Robust with on-time oil changes — the safe harbour of the range |
| B48 petrol / B47 diesel (2015 on) | Chain | Successor engines with updated parts; the reputations don’t carry over |
Chain work is a repair, not a service item — priced when needed. Typical UK specialist prices: N20 chain and guides £900 – £1,900; N47 £1,200 – £2,500 (engine-out labour); older four-cylinder petrols from around £750. Main dealers quote higher throughout.
The N20: the one chain with a schedule — unofficial, but real
The failure is the guides, not the chain — and it can be silent. The N20’s plastic chain guides turn brittle with age and heat, crack, and shed fragments into the sump. The textbook warning is a high-pitched whine or whirr between about 1,500 and 2,500 rpm — the same engine’s oil-pump sprocket wears too, whirring louder with revs — but specialists regularly open engines with snapped guides and no symptoms at all. When enough debris reaches the oil pickup, the engine starves and the failure is sudden. That combination — catastrophic outcome, unreliable warning — is why independent BMW specialists have quietly written the schedule BMW never did: replace the chain and guides preventively around 70,000–100,000 miles, sooner for hard-worked city cars.
The money, honestly. Done preventively, the job runs £900 – £1,900 at a UK BMW specialist depending on parts grade, often including the revised oil-pump sprocket. If broken guide pieces are found, dropping the sump to clear the pickup adds roughly £700 – £800 — which is still cheap next to the rebuilt engine that oil starvation writes. Two practical checks cost nothing: a specialist can test chain slack through the oil filler with a pick in minutes, and early-2015-onward builds (and every B48) carry updated parts. The question to ask the garage: “has the chain slack been checked through the oil filler — and does the quote include the guides and oil-pump sprocket, or the chain alone?”
The 320d and the chain at the wrong end
The other asterisk is the one that made the 3 Series famous in timing circles: the N47 diesel in the era’s 316d, 318d and 320d — the default UK company car of its day, which is why so many are now on their third owners. Its chain sits at the gearbox end of the engine, so the £1,200 – £2,500 repair bill is mostly the labour of reaching it, and the warning to respect is a metallic cold-start rattle from the rear. We’ve told that story in full — symptoms, buying checks, which years improved — on the 1 Series page, and every word applies here: it’s the same engine in a bigger car. The one 3-Series-specific note: the sheer volume of used 320ds means the bargain-priced example with no history is common — and on this engine, “no history” is a number, not a mystery.
Buying a used 3 Series: triage by engine code
Let the code sort the risk before the test drive does. Six-cylinder petrol or diesel: relax and check the oil-service history. B48/B47 (2015 on): clean sheet. N20 petrol: ask for a chain-and-guides invoice — one exists on the good examples now, and its absence past 70,000 miles is a £900 – £1,900 line in your negotiation. N47 diesel: cold-start it yourself and listen at the rear, exactly as the 1 Series checklist says. On this model the invoices for chain work aren’t service history — they’re equity, and sellers who have them advertise them.
And the oil rule carries the whole page. Every timing system here lives on oil pressure and oil quality — the guides, the tensioners, the sprockets. On-time changes with the correct spec are the only maintenance a 3 Series chain asks for, and skipped ones are the common thread in the failure stories. It’s the least glamorous £100 a BMW owner spends, and the highest-leverage.
FAQ
Does a BMW 3 Series have a cambelt or a timing chain?
A timing chain on every engine and every year — there is no cambelt and no scheduled replacement interval. The exceptions to “fit and forget” are the N20 petrol and N47 diesel four-cylinders, whose chains have documented weaknesses worth knowing about.
What is the BMW N20 timing chain problem?
The N20’s plastic chain guides (most 320i/328i, roughly 2011–2015) turn brittle and break apart, and the debris can block the oil pickup and starve the engine. Warning signs are a whine or whirr around 1,500–2,500 rpm — but failures with no warning at all are documented, which is why specialists advise preventive replacement.
When should an N20 timing chain be replaced?
UK BMW specialists advise doing the chain, guides and oil-pump sprocket preventively at around 70,000–100,000 miles — sooner with symptoms or hard city use. It’s the one BMW chain with a de facto schedule: the £900 – £1,900 job is insurance against sudden oil-starvation failure that writes off the engine.
What does a 3 Series timing chain replacement cost?
Depends on the engine: £900 – £1,900 for an N20 petrol at a specialist (add £700 – £800 for a sump-off clean if guide debris is found), £1,200 – £2,500 for the N47 diesel’s rear-mounted chain, and from around £750 on the older four-cylinder petrols. Dealers quote higher throughout.
Is the 320d timing chain problem the same as the 1 Series?
Yes — it’s the same N47 engine (2007–2014) with the same rear-mounted chain, same cold-start rattle warning and same £1,200 – £2,500 repair. Our 1 Series page covers the symptoms, the improved post-2009 builds and the used-buyer checklist in full; all of it applies to the 316d–320d of the era.
Which BMW 3 Series engines are safe from chain problems?
The six-cylinder petrols and diesels have robust chains with no equivalent reputation, and the B48 petrol and B47 diesel fitted from 2015 onwards carry updated components — neither inherits the earlier problems. On all of them, the chain’s maintenance is simply on-time oil changes with the correct spec.
How do I check a used 3 Series for chain trouble?
Identify the engine first. On an N20: listen for whining at 1,500–2,500 rpm and ask a specialist to check chain slack through the oil filler — a minutes-long, usually free test. On an N47: cold-start the car and listen for a rattle from the rear of the engine. On either, a chain-work invoice is worth real money.
Do BMW timing chains need oil changes more often?
They need them on time, every time — chains, guides and hydraulic tensioners all live on oil pressure and quality, and neglected servicing is the common thread in chain failures. Sticking to the schedule with the correct specification oil is the only chain maintenance any 3 Series asks for.