- Safety first
- Work on a cold engine (valve clearances set on a cold engine unless a specific manual says otherwise).
- Park on level ground, set parking brake, chock wheels, remove ignition key and disconnect the battery negative terminal to avoid accidental starting.
- Wear safety glasses, gloves, and keep rags/cleaning solvent to stop dirt falling into the head.
- Keep fire extinguisher and good lighting nearby.

- Basic procedure summary (what you will do)
- Remove rocker/valve cover, clean area, rotate engine to bring each cylinder to top dead center (TDC) in firing order, measure valve clearance with feeler gauge, loosen locknut, adjust screw to correct clearance, tighten locknut while holding screw, recheck clearance, reinstall cover and gasket, run engine and check for leaks/noise.

- Tools you likely already have and how to use them
- Socket set with ratchet and extensions
- Use to remove the bolts that hold the rocker/valve cover and any air/intake piping in the way. Choose the correct socket size, pull straight to avoid rounding heads, use extension to reach recessed bolts.
- Combination wrench set (open and boxed ends)
- Use boxed end to loosen/tighten locknuts on adjusters; open end to hold adjuster screw head if needed. Use correct size for a snug fit to avoid rounding nuts.
- Screwdriver (flat and/or Phillips depending on adjuster)
- Some adjuster screws have slotted heads. Use a screwdriver that fits the slot to turn the screw while holding the locknut with a wrench.
- Feeler gauge set (metric and imperial blades)
- The essential measurement tool. Insert the correct-thickness blade between rocker pad and valve stem tip while the valve is closed; the blade should slide with light resistance. Use the specified thickness for intake and exhaust.
- Torque wrench (recommended)
- Use to torque rocker cover bolts and any nuts/bolts with a specified torque (if manual lists torque). For locknuts on adjusters, specified torque is often not given — tighten firmly while holding adjuster.
- Adjustable pliers/vice grips (with care)
- Useful to hold things but avoid using on adjuster locknuts if possible — use because they can round nuts; only use as last resort.
- Clean rags and parts cleaner (degreaser/brake cleaner)
- Clean surfaces before reassembly to prevent dirt entering the head and to get a good seal for the valve cover gasket.
- Flashlight or work light
- Illuminate the rocker area so you can clearly see adjuster screws and measure with feeler gauge.

- Extra tools you may need (why they’re needed)
- New valve cover gasket
- Valve covers often need a new gasket when removed. A new gasket prevents oil leaks; reuse increases leak risk.
- Replacement rocker arms/rocker shaft assembly
- If rockers are worn, bent or have pitted surfaces, replace them. Worn rockers give noisy valves, poor adjustment hold, and can damage valves.
- Small magnet or pickup tool
- Helps retrieve dropped nuts/bolts from tight spots.
- Feeler gauge blocks or thickness set (if precise calibration desired)
- Provide more accurate measurement than cheap multi-blade sets for critical adjustments.
- Soft-faced mallet
- Gently tap components like the rocker shaft if it’s tight; prevents damage compared with a steel hammer.
- Puller or press (only if replacing pressed-in bushings)
- If rocker arms have pressed-in bushings that must be removed/installed, a press or puller is required. Most owners replace whole rockers or shaft assembly instead of pressing bushings.
- Service manual or model-specific data sheet (strongly recommended)
- Gives exact clearance specs, torque settings, and cylinder firing order. Use to confirm values for your specific MF model.

- Typical valve clearance values (common for Perkins-based MF tractors; verify in a service manual)
- Intake: about 0.20–0.25 mm (0.008–0.010 in)
- Exhaust: about 0.25–0.30 mm (0.010–0.012 in)
- Use these as a guide only; if you can, confirm with the model service manual before final adjustment.

- Step-by-step actions (bullet sequence, one action per bullet)
- Park tractor, shut engine off, let it cool, chock wheels, disconnect battery negative.
- Remove any obstructing ducting, air cleaner parts or pipes that block access to the rocker cover.
- Clean top of valve cover area with brush and rags so dirt does not fall into the head when cover is removed.
- Remove valve/rocker cover bolts with a socket and carefully lift off the cover; if stubborn, gently pry under the lip with a flat screwdriver protected by a rag.
- Inspect inside for sludge, metal flakes, or obvious broken parts; wipe lightly with clean rags.
- Rotate engine to TDC for the first cylinder to be adjusted:
- Use a breaker bar or socket on the crank pulley bolt and turn in engine’s normal rotation direction until the timing marks or TDC marks align, or watch rocker movement until both valves for the cylinder are closed and the pushrod/rocker has maximum play (valve on base circle).
- If no marks, turn engine by hand slowly and watch the valve lash for when it’s correct for the cylinder you’re setting.
- Measure the clearance using feeler gauge:
- Slide the correct gauge blade between valve stem tip and rocker pad; the correct blade should slide with light drag. If too loose or too tight, adjustment is needed.
- Adjust clearance:
- Loosen the adjuster locknut slightly with a wrench while holding the adjuster screw head with screwdriver or second wrench.
- Turn the adjuster screw until the feeler gauge reads the correct resistance.
- Hold the adjuster screw to keep it from moving and tighten the locknut securely. Recheck the clearance after tightening because locknut movement can change the setting; repeat until stable.
- Repeat for each valve following the firing order / cylinder sequence for your engine (adjust at TDC when the valve is on the base circle).
- After all valves are adjusted, clean mating surfaces and fit a new valve cover gasket if the old one is cracked or compressed; a new gasket is inexpensive insurance against oil leaks.
- Reinstall valve cover, torque bolts evenly to specified torque (or snug in a criss-cross pattern if no torque value available), reconnect any removed pipes, reconnect battery.
- Start engine, listen for valve noise and check for oil leaks; recheck clearance after a short run if noisy.

- How to tell if parts must be replaced (what to look for)
- Rocker arm wear
- Scored or shiny worn contact surfaces where rocker meets valve stem or pushrod; if visible wear or a groove exists, replace rocker arm.
- Bent or broken pushrods
- If pushrods are bent or have lost straightness, engine will run poorly; replace pushrod(s).
- Loose or stripped adjuster threads / broken locknuts
- If adjuster screw cannot be held or locknut strips, replace the adjuster/locknut or rocker assembly.
- Excessive oil leaks from valve cover
- Replace valve cover gasket and check cover and bolt threads.
- Metal flakes or heavy sludge
- Could indicate deeper wear (camshaft lobes, rockers) — further inspection required and likely part replacement.

- Replacement parts commonly needed
- Valve cover gasket
- Cheap, easy to fit, prevents leaks after cover removal.
- Rocker arms or complete rocker shaft assembly
- Replace if wear, pitting, excessive play, or seized rockers. Buying the complete shaft assembly is often easier than replacing individual rockers or bushings.
- Adjuster screws and locknuts
- Replace if threads are damaged or locknuts do not hold.
- Pushrods (if bent or damaged)
- Replace matched sets if affected.
- Valve stem seals (if oil consumption or leak down)
- Only if you see oil on stems or excessive consumption; this requires more disassembly.

- How to source correct parts
- Use dealer part numbers for MF255/MF265/MF270/MF275/MF290 or trusted aftermarket suppliers; match part numbers or compare old parts.
- Prefer full rocker-shaft assemblies if bushings are pressed and you don’t have a press.

- When a professional shop is recommended
- If you find cam lobe damage, broken parts, heavily worn rockers, or if removal of the rocker shaft requires pressing bushings.
- If you lack tools to press/replace bushings or to properly torque and set timing marks.
- If you’re uncomfortable rotating the engine to find TDC or interpreting symptoms.

- Quick troubleshooting after adjustment
- Persistent valve noise after correct clearance: inspect rockers, pushrods, cam lobes for wear; consider replacing affected parts.
- Oil leak from cover: if leaking at gasket, tighten cover evenly or replace gasket; if cover cracked, replace cover.
- Engine runs poorly after adjustment: confirm you set clearances on the correct cylinder positions (valves must be on base circle/TDC for that cylinder).

- Final checklist before finishing
- All locknuts tight and adjusters stable.
- Valve cover gasket fitted correctly and cover bolts snug.
- Tools and rags removed from engine area.
- Battery reconnected and engine started to verify quiet operation and no leaks.

- Short safety reminder
- Never work with engine running except for final listening checks; moving parts can cause serious injury. If unsure at any point, stop and get professional help.


rteeqp73

Massey Ferguson 255 - Overview This is my Massey 255, I have decided to part with it even though I love this machine. I grew up with Massey Ferguson tractors and ...

Massey Ferguson 255 PTO engage issue solved PTO would grind when attempting to engage on the engine side, easy fix this time.

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