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How to fit a scarifier blade

Updated: October 2026

The part is on the bench and the machine still has a blade or a drum underneath it. How to fit a scarifier blade depends on which part you bought. A bar under a rotary mower and a roller on a scarifier are isolated in different ways, and both will tear a lawn if the first pass is on the lowest setting. Make the host unable to start, fit only what the listing describes, then run high. Which part to buy is already settled on the [scarifier blade comparison](/hub/lawn-and-garden-equipment/scarifier-blade). Peter F. followed the fitting lines on those listings. We did not fit every bar. A qualifying purchase can earn a commission at no extra cost to you.

The part is on the bench and the machine still has a blade or a drum underneath it. How to fit a scarifier blade depends on which part you bought.

Our top picks

Einhell Einhell 3420021

Best overall

Einhell Einhell 3420021
9.0/10about £37.95
View offer
OTOTEC OTOTEC HO195W

Best value

OTOTEC OTOTEC HO195W
8.6/10about £15.99
View offer
Oregon Oregon 690-521-0

Alternative

Oregon Oregon 690-521-0
8.4/10about £37.02
View offer
On this page
  1. 1.Make the machine unable to start
  2. 2.Fitting a bar under a rotary mower
  3. 3.Fitting a roller or a spring set
  4. 4.The first pass, and when you stop

Make the machine unable to start

On a petrol mower, Honda UK’s pattern is: stop the engine, take the spark-plug cap off, and block the blade with wood before you put a spanner on the bolt. Wear gloves. A hot engine can still fire with the cap on. On a corded host, unplug it from the 230 V socket. UK plugs are BS 1363. On a cordless host, take the battery off. A petrol scarifier follows the same idea: engine off and cool, spark-plug lead removed, and do not tip it so far that fuel runs out. Do not roll a petrol mower onto its carburettor unless the manual allows that tilt. If you scarify as paid work, PUWER 1998 sits on top of these steps. A householder is outside that regulation.

Fitting a bar under a rotary mower

With the cap off and the blade blocked, slacken the mowing blade and keep the bolts, washers, and any adaptor the deck already used. Photograph which face was down. The Oregon kits include fittings, washers, and push-on tines. The perfektGarten bars include springs and bore adaptors. The Redpart listing does not state what fixings are in the box. If a piece the title promised is missing, stop before you drill or grind. Offer the bar up and turn it by hand. One review of the about £26.30 perfektGarten bar describes tines hitting on the highest setting. A review of the 51 cm Oregon reports damage to a Hayter Harrier 41. No listing here states a torque. Grinding locking slots is a modification. If the bar only goes on after you remove metal, it is the wrong bar. Why the grass box often stays empty is on scarifier blade for a lawn mower.
Einhell Einhell 3420021

Testsieger

Einhell Einhell 3420021
9.0/10about £37.95
View offer

Fitting a roller or a spring set

On the Einhell 3420021, for the petrol GC-SC 2240 P, the listing says a hexagonal socket wrench and gloves. Reviews that matched the shaft cite about 15 minutes. If the pulley bore is about 1 mm small, or the drum sits about 1.5 cm short, stop. A corded Einhell PDF is a different scarifier. The Bluemars roller for the BM-GP1003 fits at the end of the bearing. If the bearings are seized, stop. On a named Parkside, loosen the nut, leave the bearings on the drum, and replace the coils. Free length is not printed, and reviews say springs were too long for a PLV 1500 B1. The title says 45 pieces, and a fan drum usually uses 44.

The first pass, and when you stop

Mow to about 2–3 cm first, on a lawn at least a year old, then use the highest setting for one strip. STIHL UK puts a domestic depth at about 2–3 mm, and at 4 mm only on a neglected lawn. Rake if there is no box. Whether the debris is moss or thatch is on scarifier springs or blades. Stop if the turf comes up in sheets or a tine has marked the deck. STIHL UK points to April and May once the soil is about 10°C. The RHS points to October or early November when the job is moss. Bare soil across the lawn means you went too far.

Common questions

Do I disconnect the spark plug to change a scarifier blade?
On a petrol mower, yes. Honda UK says stop the engine, disconnect the spark-plug cap, and block the blade with wood. A corded scarifier is made safe by unplugging it. A cordless one is made safe by removing the battery. A throttle set to stop, with the cap still on, leaves a way for the machine to turn.
How do I change an Einhell roller?
For the GC-SC 2240 P roller, the listing says a hexagonal socket wrench and gloves. People whose shaft matched describe about 15 minutes. If the pulley is about 1 mm out or the new roller is short, the part is wrong. A corded Einhell PDF with two screws and a square drive is a different model.
How do I fit springs on a Parkside drum?
On the models named for the OTOTEC pack, loosen the nut, leave the bearings where they are, and swap the springs. Match wire and coil to 1.6 mm and 12 mm, and compare free length with a spring you took off. Springs that only fit after you bend them are the wrong length. Count 45 pieces against a drum that usually holds 44.
What height do I use on the first pass?
The highest setting, after you have mown to about 2–3 cm. STIHL UK’s depth is about 2–3 mm, or 4 mm on a neglected lawn. A conversion bar that touches the deck on the highest setting is finished as a fitting attempt. Do not start at the bottom because the lawn looks bad.
The old roller will not come out. What now?
If the drum slides off once the fixings are undone, continue. If the bearings are seized in the chassis, stop. That is no longer a spare-part swap you finish with the hex key in the box. Heating and hammering a seized seat is how the housing cracks.

Related pages

Scarifier blade buying guide

Scarifier blade

Best scarifier blade: name the host before the stars

Scarifier springs or blades: moss comb or thatch slit

Scarifier blade for a lawn mower with a matching hub

Sources

Buying notes from the sources below, checked for this page on 22 October 2026. Prices, stars and review counts are from the amazon.co.uk captures of that date.

  1. RHS: autumn lawn care (retrieved 22 October 2026)
  2. RHS: moss in lawns (retrieved 22 October 2026)
  3. STIHL UK: lawn scarification (retrieved 22 October 2026)
  4. Lawnsmith: types of scarifier and raker (retrieved 22 October 2026)
  5. Gardeners' World: scarifying a lawn (retrieved 22 October 2026)
  6. BS EN 13684:2018+A1:2024 (retrieved 22 October 2026)
  7. HSE: PUWER overview (retrieved 22 October 2026)
  8. Honda UK: lawn and garden maintenance (retrieved 22 October 2026)