We keep getting questions about a cold start rattling noise on the Earth Dreams engine in the GK5.

This has been traced to a weak return spring in the (OEM) VTC actuator. This causes direct contact with the timing chain before oil has a chance to penetrate the area.

Left unchecked, this leads to timing chain wear. If the timing chain stretches and slips, goodbye engine.

This is the $24 part you need. The issue is the labor to get there.

https://spring-start.com/shop/ols/pr...pre-order-sale

Mods, please consider making this a sticky so it's visible on the 3rd gen home page.

 

Is this possibly a mis-translation from a Honda Japan document? The VTC actuator is part of the intake cam gear - it's always in direct contact with the chain.


(Courtesy Honda USA)

My interpretation has been that the oil drains out of the VTC actuator while the engine is off. The actuator has two major parts: A hub attached to the cam shaft, with arms extending out towards the perimeter of the actuator housing, and a outer ring with the cam chain teeth on it, and arms that extend in towards the hub.
Here's a pic of an '09 TSX actuator with its front and back plates off, pilfered from a reddit thread:

The Fit actuator should be similar.

The arms have seals on the end which create pockets (spaces between the arms) that act like little hydraulic cylinders. There's 10 pockets in the pic - the big ones are obvious, but there's a tiny sliver of a pocket on the opposite sides of the arms from the big ones. When oil is pumped into those tiny pockets, it forces the pocket to expand which rotates the hub (camshaft) with respect to the housing (cam chain). The oil gets into those pockets via the camshaft. Look closely at the walls of the center bore of the hub - there's a hole to feed each pocket from a camshaft passage. The small pockets are all fed oil together so they act as one big hydraulic piston. Oil gets into the camshaft from a journal (oil-fed plain bearing) on the cylinder head, which is in turn fed by the VTC solenoid valve. The ECM uses a (multiple? I'm too lazy to look it up) cam shaft sensor to measure how far the actuator has twisted (called cam phasing), then opens or closes the VTC solenoid valve to increase or decrease oil pressure to the actuator to zero-in on the desired cam phase value.

The problem: When full of oil, the actuator mechanically acts more or less as one solid piece, as oil doesn't compress. This is normal - gasoline engines have gotten by just fine for a century using solid cam gears. When the oil drains out, it's replaced with air, which does compress. That's like putting a weak spring between the hub and body of the actuator. During cold start-up, the forces of the rockers climbing their cam lobes (compressing their respective valve spring) and then sliding down the back side of the lobe (spring releasing its stored energy) compresses and expands the air pockets in the actuator. This makes the arms in the actuator slam into each other a few times until the air is flushed out of the actuator by fresh oil flow. The forces of that slamming action get transferred into the links of the cam chain, causing stretch. Stretch accumulates, so unaddressed VTC actuator slap will become timing chain and sprocket problems.

 

The dealer could present you with a bill for $2,600. That's what happened to my son. Look on YouTube for DIY solutions. A good local mechanic said he would not do that job - not sure why. Maybe the lengthy repair involved.