This is the VTEC spool valve and solenoid unit that sits on the left hand side of the cylinder head.
Basically its operation is to enable high pressure oil into the shafts that the valve assembly rockers sit on; passing this oil into each of the 8 rocker assemblies forces a pin to lock them together and in turn enable the VTEC cam lobe to take over.
Here looking where the valve sits on the side of the head, looking down one of the rocker shafts.
The solenoid sits on the top, mated to the (main body) spool valve by 3 number 10mm (m6 standard x 17mm) bolts. Once taken off it looks like this.
The solenoid is basically an electronically operated switch, altering the flow of oil when it reads 12v positive, a quick test for operation is to give the wire a 12v feed whilst earthing the body, if it clicks then it's probably working fine (notwithstanding any blockages).
Onto the main body which is called a spool valve. Inside is found 3 moving parts, a spring, a plunger and a cap for the plunger.
Some spool valves have an oil pressure sensor attached (JDM thing?) and some do not, but the ones without can have the sensor retrofitted as they just have a bolt in this place blocking up the hole.
There is not too much to do to the spool valve to service it, basically take the 3 moving parts out of the top of the body and submerge the valve body, spring, plunger and cap in thinners / degreaser until clean, after that you can re-oil the moving parts and refit; or do further paint/descale for OCD points.
Gaskets:
The larger of the two gaskets is the spool valve gasket, often commonly mis-described as a solenoid gasket. Over time these become brittle and start to leak, additionally if the filter screen becomes clogged with crap, VTEC stops working. Both issues are easily fixed with a new gasket (or the latter by just cleaning the mesh filter). Gasket part number 15825-P08-005.
The smaller gasket is the solenoid gasket, which rarely ever fails. But if you want to service the spool valve, you’ll need a new one of these. The original part number for this gasket is 36172-P08-005. Unfortunately, Honda has superseded this part with 36172-P08-015, and will sell you that even if you go in and specifically request 005 (which I did). The problem here is that the newer gasket does not sit very well on some solenoids, it is too thin.
Here is an old shot showing the thicker gasket that has the screen integrated (36172-P08-005):
Here is why there is a problem, difficult to see in the pics, but the gasket recess on one solenoid is slightly deeper than the other, additionally there is also the obvious difference of the protruding collar:
And how the newer design sits in each of them, not well enough to give a good seal in the deeper one.
Less deep solenoid where the gasket should be ok:
Unfortunately there is no difference at all between the two solenoids externally, so until you get inside you’re not sure which gasket you’ll need. I suspect early 4ths (91-93) need the older part, and everything after needs the newer one, but that is just a guess.
The two different gaskets, side by side, they are not interchangeable between the different solenoids.
