Valve Spring Squareness and Height Comparison

The short version — a valve spring has to be square and the right free height, or it loads the valve stem off-center, chews up the guide, and can let the valve float or drag at high RPM. You check squareness with a square and a flat surface, and you check height by comparing springs side by side; anything out of spec gets replaced.

Why the spring matters in the first place

The valve spring's whole job is to provide the closing force that returns the valve to its seat and keeps every valve train component — lifter, pushrod, rocker — in constant contact with the camshaft lobe through the entire cycle. Think about the sequence: the cam lobe lifts the valve off its seat, working against spring force, and once the lobe rotates past peak lift, the spring's stored energy snaps the valve closed and holds it seated until the next lobe comes around. If the spring can't do that job correctly — because it's out of square, sagged, or the wrong height — the valve train loses control of the valve, and that shows up as real, testable symptoms.

Checking squareness

Spring squareness is checked by standing the spring up on a flat surface next to a square (or a dedicated squareness fixture) and rotating the spring while watching for a gap between the coil and the square at the top. If the spring is square, it stays tight against the square all the way around. If it's out of square, you'll see daylight open up between the top coil and the square as you rotate it.

Why this matters: an out-of-square spring loads the valve off-center, which means:

• side loading on the valve stem and guide
• accelerated guide wear
• uneven valve seating

None of that is subtle over time — it's a slow-motion failure that starts with a spring that never sat square in the first place.

Checking height and comparing springs

Spring height comparison is exactly what it sounds like — you line springs up and compare them to each other (or to spec) to catch spring fatigue/sag, which shows up as loss of free height and pressure. A sagged spring isn't providing the closing force it was designed to provide, even if it looks fine sitting on the bench.

Other failure modes to watch for while you're at it:

• spring breakage — fractured coils, often the result of fatigue or overheating
• coil bind — caused by incorrect height, which can damage the spring itself or take out other valve train components

Because coil bind and sag both trace back to height being wrong, height comparison and squareness checking go hand-in-hand — you're really doing one inspection with two measurements.

What weak or failed springs look like in a running engine

You won't always catch a bad spring on the bench first — sometimes the engine tells you first. Symptoms of failed or weak springs include valve float, reduced power at high RPM, valve-to-piston contact, rough idle, or a ticking/tapping noise from the valve not closing properly. Valve float happens because the spring can no longer keep the valve train following the cam lobe at higher engine speeds — the valve literally can't close fast enough, which is the direct real-world consequence of the "spring keeps everything in contact with the lobe" function described above.

Don't skip the seats and retainers

Before any spring goes back in, inspect the spring seats and retainers for cracks, wear, or damage — a damaged seat or retainer can throw off spring seating and squareness even if the spring itself tested fine. A perfect spring on a cracked seat is still a problem.

A safety note that matters on the test

Whenever you're using a valve spring compressor during inspection or removal, handle it carefully to avoid a sudden release of stored spring energy — that release can cause the tool to slip or send a component flying. This isn't just shop-safety filler; it's tied directly to the fact that the spring is storing real force the whole time it's compressed.

Easy to mix up

• Squareness problem vs. height problem — squareness is about the spring sitting crooked (checked by rotating against a square, looking for a gap); height/sag is about the spring being shorter than it should be (checked by comparison). A spring can fail either test independently, but both point to the same root symptom category: poor valve seating and valve train control.
• Sag vs. breakage vs. coil bind — sag is a gradual loss of free height and pressure; breakage is a fractured coil; coil bind is a mechanical stacking problem from incorrect height. All three are "failure modes" but they are not the same defect.

Check yourself

Question: How do you check a valve spring for squareness, and what are you actually looking for?

Stand the spring upright on a flat surface next to a square (or squareness fixture) and rotate it. You're watching for a gap opening up between the spring coil and the square at the top — that gap means the spring is out of square.

Question: Technician A says an out-of-square valve spring can cause accelerated valve guide wear. Technician B says an out-of-square spring only affects spring pressure, not valve seating. Who is right?

Technician A is right. An out-of-square spring loads the valve off-center, causing side loading on the stem and guide, accelerated guide wear, and uneven valve seating. Technician B is wrong — squareness problems directly affect how the valve seats, not just spring pressure.

Question: An engine shows valve float and reduced power at high RPM, with no other complaints. What valve spring condition would explain this, and why?

Weak or fatigued springs (sag/loss of free height and pressure) fit this symptom. The spring's job is to keep the valve train in constant contact with the cam lobe and snap the valve closed after the lobe passes peak lift. If the spring is too weak, it can't keep up at higher RPM, so the valve doesn't close in time — that's valve float, and it costs power.