Fitting a T-REV Crankcase Pressure Reducing Valve to a BMW G650GS (Without Cutting the Original Hose)

Hello everyone, Boo here.

This post is about fitting a crankcase pressure reducing valve to my G650GS.

Single-cylinder bikes are known for strong vibration and strong engine braking.
I like singles because they run cooler, the engine can be light, and the bike can be compact.

But the strong vibration of a single has its downsides too, such as numb hands and a numb backside.
One way to reduce vibration is to fit a crankcase pressure reducing valve.

Here I show how I fitted one to my G650GS.

There are various reducing valves on the market, but I chose the T-REV from TERAMOTO (a Japanese maker).

To decide where to fit the T-REV on the G650GS, I used its sister model, the F650GS, as a reference. TERAMOTO's website (https://www.teramoto.biz/trev_fit.html, in Japanese) does not show a fitting location for the G650GS, but it does show one for the F650GS.
The two bikes have almost the same engine, so I followed that.

What I used

[Tools]

Hose clamp pliers for Clic R clips
Hacksaw (not needed if you use the bike's original breather hose)
Metal file (not needed if you use the bike's original breather hose)

[Parts]

T-REV (for a 9 mm breather hose, 0.07 mm shim)
Cable ties
*If you cut the bike's original breather hose and fit the T-REV into it, you don't need the parts below.
I wanted to be able to return the bike to standard later, so I bought a separate breather hose.
KIJIMA breather hose, 9 mm (part number: 105-0879)
POSH spare indicator (turn signal) stay bolt, M8 × 30 mm (part number: 010201-30)

Steps

Check where the hose runs

First, find the breather hose.
The breather hose is marked with yellow arrows in the photo. It comes out of the right-hand side of the crankcase, runs near the frame and the radiator hose, and connects to the airbox.

Routing of the original breather hose on a BMW G650GS, from the right-hand side of the crankcase to the airbox (yellow arrows)

Decide where to fit the T-REV

I decided to fit the T-REV close to the crankcase, around the spot where I could fix it to the frame with cable ties (the yellow area below).

The place on the breather hose near the frame where the T-REV will go (yellow mark)

Remove the breather hose

Disconnect the crankcase end first. (There is a reason for this, explained below.)
At the crankcase end, the breather hose is held by a clip called a Clic R. Remove the clip and pull the hose off.
I'm a bit of a worrier, so after pulling the hose off I covered the opening with a plastic bag to stop dirt getting into the crankcase.

The Clic R clip (a special type of hose clamp) on the breather hose at the crankcase

At the crankcase end, the breather hose is held with a Clic R clip

These clips, fitted at both ends of the hose, are called Clic R clips.
You can just about remove them with a flat-blade screwdriver and pliers, but there is a special tool for them, and it is easier and quicker to use that.

Next, disconnect the airbox end.
The airbox end is screwed in, so you have to turn the breather hose to remove it.
That is why I disconnected the crankcase end first: so that the hose was free to turn.

The threaded joint where the breather hose screws into the airbox on the G650GS

At the airbox end, the breather hose is screwed in

Prepare the new breather hose
(Not needed if you reuse the bike's original breather hose)

Fit a hollow bolt to the airbox end of the breather hose.
For the hollow bolt, I used a POSH spare indicator stay bolt, M8 × 30 mm.
Cut the head off the indicator stay bolt with a hacksaw, and file off the burrs.

Cutting the hexagon head off a POSH indicator stay bolt (hollow bolt) with a hacksaw

Cut off the hexagon head of the hollow bolt

The cut hollow bolt next to the end of the original breather hose, to compare the thread length and size

Check that the hollow bolt matches the end of the original breather hose.

Measuring how far the cut hollow bolt sticks out, with a vernier caliper

Check how far the bolt sticks out (I matched it to the end of the original hose)

I pushed the cut hollow bolt into the new breather hose and secured it with a clip.
With the bolt secured, screw the breather hose into the airbox.

The KIJIMA breather hose with the modified hollow bolt, screwed firmly into the airbox

The cut hollow bolt pushed into the breather hose, secured with a metal clip, and screwed into the airbox.

Cut the breather hose and fit the T-REV

Once the airbox end of the breather hose is secured, cut the hose where you want to fit the T-REV.
Fit the T-REV into the cut.

The right-hand side of the G650GS engine after fitting the T-REV

Finished!
I fixed it with cable ties in several places so that the weight of the T-REV does not make it swing about.

After fitting the T-REV, fix the breather hose and the T-REV to the frame and so on with cable ties.
I also used cable ties to join the breather hose to the T-REV.
The T-REV body is aluminium, so I thought a metal clip might clamp it too tightly.

The T-REV fixed to the breather hose and the frame with cable ties instead of metal clips, to protect its aluminium body

The T-REV is aluminium, so I used cable ties instead of metal clips

And that's the job done!

The fitting itself was not particularly difficult.
After fitting it, all I can say is: I'm glad I did.

I used this T-REV for about three years. Before I sold the G650GS, I removed it to return the bike to standard. It gave me no trouble in that time, but it did need regular maintenance.

For my impressions, see the article below.