In-Car Cam and Valve Spring Upgrade on the GR Yaris / GR Corolla

In-Car Cam and Valve Spring Upgrade on the GR Yaris / GR Corolla

In-Car Cam and Valve Spring Upgrade on the GR Yaris / GR Corolla

 

Swapping cams and valve springs on the GR Yaris or GR Corolla can be done with the engine still in the car. and i’s not a shortcut or a hack 

If you’re comfortable working around cam timing and valve train components, this is a very achievable job.

Why Do the Job In-Car?

On the GR engine, valve spring replacement requires cam removal anyway. Once the cams are out, the springs are directly accessible, so doing springs and cams together makes sense.

Leaving the head installed avoids:

  • Disturbing a perfectly good head gasket
  • Extra teardown and resealing
  • Unnecessary downtime

As long as the valves are properly supported, the process is controlled and repeatable.

 

Parts We Typically Use

On our GR builds we run:

  • Kelford camshafts
  • Matching Kelford valve springs

The process below applies regardless of brand, but spring rate and installed height always matter. Make sure your spring choice matches your cam profile and intended RPM.

 

Tools You’ll Need

You don’t need anything exotic, but you do need the right tools.

  • HRB In-car valve spring compressor designed for the GR engine
  • Compressed air and a spark plug adaptor, or clean nylon rope
  • Tweezers or a small magnetic pickup for the valve keepers
  • Torque wrench
  • Cam timing tools and basic hand tools
  • A clean way to organise caps, bolts, and components

Trying to do this with a generic valve spring compressor usually turns into frustration. Access is tight and visibility matters.

HRB toyota GR Yaris In Car valve spring tool - On cylinder head

 

Supporting the Valves

Before removing any springs, the valves must be held up.

Compressed air method:

Screw an adaptor into the spark plug hole and apply shop air. Around 90–120 psi is typical. Some leakage past the rings is normal — just keep pressure applied while the spring is off.


Rope method:

With the piston at bottom dead centre, feed clean nylon rope into the cylinder. Rotate the crank to bring the piston up and trap the valves against the head. Always leave one end of the rope outside the engine.

Both methods work. Use whatever you’re more comfortable with.

 

Camshaft Removal

Remove the camshafts carefully, following the factory sequence. Keep cam caps in order and organised — they are not interchangeable.

This is also the point where you’ll install your upgraded cams later, so take your time and keep everything clean.

 

Removing the Valve Springs

Install the in-car valve spring compressor over the retainer. On the GR engine, clearance and sight lines matter, so make sure the tool is seated squarely.

Compress the spring just enough to expose the keepers. Remove them with tweezers or a magnet. Don’t rush this — dropped keepers waste time.

Slowly release the compressor and remove the retainer and spring.

If you’re replacing valve stem seals, this is when you’d do it.

 

Installing the New Springs

Install the new spring and retainer, making sure orientation and seating are correct. Compress the spring and refit the keepers.

A small dab of grease on the keepers helps them stay in place while releasing the compressor.

Once seated, give the retainer a light tap and visually confirm the keepers are fully locked before moving on.

Repeat the process one valve at a time.

 

Reassembly

Once all springs are done:

  • Reinstall the camshafts
  • Torque caps to spec
  • Set cam timing correctly
  • Rotate the engine by hand and check for any interference

Only once everything checks out should you button it up and start the engine.

 

Why Tool Choice Matters

Doing this job in-car is entirely dependent on control and repeatability. A tool designed for the GR head geometry makes a big difference — especially when you’re doing every valve, not just one or two.

We built our GR valve spring tool because modifying universal tools was slowing the job down and making it inconsistent. Good visibility, proper alignment, and predictable compression make the difference between a clean job and a frustrating one.

 

Final Notes

An in-car cam and valve spring upgrade on the GR Yaris or GR Corolla is a solid, workshop-level job when done properly. It saves time, avoids unnecessary teardown, and keeps the focus exactly where it should be — on the valvetrain.

If you’re methodical, organised, and using the right tooling, it’s a straightforward process and one we’re completely comfortable doing on our own engines.

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