Briggs & Stratton 850EX Series
The premium-tier walk-behind Briggs — fitted to AL-KO and pro-spec Cobra
The story of this engine
The 850EX is the bigger sibling of the 750EX, fitted to premium walk-behind petrols including the AL-KO Highline 5.2, Cobra MX534SPC top spec, and some Murray and Lawnflite mid-models. Pressure lubrication (with a proper oil sump cover) rather than splash makes it a noticeably longer-life engine than the 675EX class, especially when the mower spends time on slopes.
Why owners like it
- Pressure-lubricated bottom-end is rare at this price — typically only found on Honda GCV equivalents
- ReadyStart auto-choke gives one-pull starting reliably to year 10
- Briggs dealer network supports parts and service everywhere in the UK
- Quieter than the 675EX equivalent due to the OHV refinement
Where it falls short
- About £100 premium over the 675EX equivalent in host mower
- Limited number of host mowers — finding one outside AL-KO or top Cobra is harder
- Slightly heavier than the 675EX block
- Service kit pricier than the 500E/675EX category
Service intervals & costs
What this engine actually needs every year, and what it costs to keep alive.
| Interval | Task | Cost |
|---|---|---|
| Every season (or 50 hours) | Oil change — SAE 30 or 10W-30 | £10 DIY / £40 dealer |
| Every 2 seasons | Air filter (paper element) | £15 OEM |
| Every 3 seasons | Spark plug | £5 DIY |
| Each season start | Drain stale fuel or use stabiliser | £6 stabiliser |
What goes wrong, and when
Every engine family has predictable failures by age. Knowing what's coming saves money on used buys and makes negotiation easier.
Parts cost reference
UK 2026 prices — OEM (genuine) vs aftermarket. Generic parts work fine on consumables; stick to OEM on anything that affects timing or tolerance.
| Part | OEM | Aftermarket |
|---|---|---|
| Air filter | £15 | £8 |
| Spark plug (NGK BPR4ES) | £8 | £3 |
| Carburettor service kit | £35 | £18 |
| Replacement engine (used) | £200–£280 | — |
The right engine for a premium walk-behind mower where you want better-than-675EX longevity without paying for a Honda. Fits the AL-KO Highline 5.2 and top-spec Cobra perfectly. The natural step up from a 675EX for buyers who want one more rung of build quality.
Related reading →Mowers in our catalogue with this engine (1)
See every engine family
Side-by-side hub of all the engines we cover — Briggs, Honda, Kawasaki, Stiga, Loncin and more.