Check Valves

Small spring end against ball!


H2Rtuner wrote:

Stock relief pressures should be between 4.5 and 4.6 psi, most relieve down at 2.2 to 2.4 psi, and need to be adjusted.

I made a fitting to check the pressure relief, took an oil pump end hose banjo bolt, two aluminum washers and a nut, installed same in each line, one at a time, and connected my pressure tester.

I evacuate the line of oil, then hold the valve end near my ear, so I can hear the air pressure relieve when the valve opens. reading the pressure when the "air" changes gives the relief rate.

To adjust, unscrew the valve parts, remove the spring and GENTLY pull it apart, A VERY LITTLE AT A TIME, put the valve back together and retest, stretch, test until the correct relief pressure is attained, tighten the valve, go to the next one.

Edit: I cannot stress enough to go very slow and gentle in stretching the spring, it is very touchy and small, and can be super easy to damage/destroy.

Edit: I set the blowoff pressure to 4.6 psi, that way, I figure the spring will sack back to 4.3/4.2 psi when it gets happy once again. When rechecked after being run a few thousand miles, the spec of 4.3/4.2 comes in steady.

Using a hose and oil can filled with two stroke oil, connect the oil pump end of the line with the pressure check bolt in place, and GENTLY fill the line, return it to the bike, bleed and go. Stops down the time to fill the whole line from the oil pump, and you won't need to use premix to bleed the pump/lines.

My Bridgestones all have valves that have hose bibs and use rubber hose between the pump and valve. I will look, as I think there may be more bikes that use that type of valve setup, like a few Suzukis and Yamahas of the past. Most Suzukis used a hard line plastic line like our stuff has.

There may be fittings available in generic form for the oil pump end from companies like McMaster-Carr, which has a web site, don't remember the address right off. 6mm bolt hole will relate to 1/4th inch (.250) in non-metric sizing. I'll have to go with the rubber hose when I case reed my next engine, as the oil injection inlet will be in the front of the cases, with the reeds.

I just looked in the McMaster-Carr book, no banjo fittings for the oil pump ends. No check valves either.

May have to look into the hydraulics industry for these parts. I'm working on it.

On check valves rated at 7.0 psi, not easy to change the spring rates downward in them, as the first thought would be to simply cut coils off to get the right rate. Not easy because when a spring is shortened by cutting, its rate goes UP, not down, as it has less spring materials (coils) to compress.

On other boards I visit, lots of people cut their coil springs for their cars, half coil, full coil, then are just amazed the suspension gets stiffer from the cut.

OK, speculate all you want, Kawasaki specifies 4.6 psi blowoff pressure.

Since there is a metering orifice in BOTH the bottom of the banjo bolt, for the crank, and in the oil passage in the inlet port, the reversion pressure is dampened, so the differential backwards doesn't adversely affect the check valve. Lower end vacuum/pressures are at the 1.50 to 1.75 psi range, lower than the check valve blowoff pressures.

I have checked new valves out of stock at KMC, Santa Ana, when it was still there, and got between 2.0 and 2.9 psi.

We got in trouble one time for blowing the check ball all the way through the spring to the other end of the valve on F series valves from the 125 psi pressures from the air hoses we used to break 'em, Japan didn't think it was funny, and that is where the Kawasaki failure code "OU812" came from.

Late ('74 on) Check Valve Removal

H2Dude wrote:

We know the early check valves can be cleaned when faulty BUT later ones can't or can they. I had a look to see how kawi put these together and viola they do come apart. you have to be very gentle on the little brass plug. BE careful as to not loose the ball when removing brass insert!!

I put the check valve in a vice and with pliers I remove the metal guard then using a hot air gun I gently start to heat the line while gently pulling ..Not the small line.
Be ready it will pop off. When putting back on , gently heat the line and push it back on.
I only broke one trying to pull the line off without heating it first on my test line that was screwed.


Here is an alternative check valve used on many Yamahas...
Yamaha pn# 8CH-1316A-00-00. Crack pressure has been measured at 2-5 psi.


Also see: Check Valve Test