Topic: 78 CB750A Oil Pressure Relief Stuck

[LiveeviL81]

Hello, I noticed this year that on cold start my bike will show 120psi at idle with 3 different oil pressure gauges Tee-d off of the main gallery. Using Honda GN4 10W-40, after warming up, its usually around 15-20psi at idle. (800 RPM). I assumed it was a stuck oil pressure relief valve and drove on it for 1000 miles. In the process of rebuilding the engine, I checked what is called the "oil pressure relief valve" in the manual, and I noticed when I took the cotter pin out, the spring and backing plate came out, but the steel "piston" was stuck until I was able to pop it loose with a stiff piece of plastic pushing on the face. I'd estimate 7-8 lbs of force to release it, and assuming it was stuck, could that be related to my oil pressure issues, and what would be the next step? trying to sand the casting slightly larger?

Kaleb

[BenelliSEI]

Good catch. That piston needs to move freely in that bore so it can in fact open up under excess pressure and bleed off volume and pressure. If that engine sat for a long time it might just have been stuck in gook?

If not that, find /whittle up a dowel of wood you can gently stick in the back end of the piston. Cover it in a bit of valve lapping paste and spin it in and out of the bore until it moves freely and easily.

[LiveeviL81]

If not that, find /whittle up a dowel of wood you can gently stick in the back end of the piston. Cover it in a bit of valve lapping paste and spin it in and out of the bore until it moves freely and easily.

Great idea! That is exactly what I will do. Do you know of a spring pressure for the relief or something to check before I reassemble and find out it's still an issue?

Thanks,
Kaleb

[BenelliSEI]

No…. But check some manuals. Honda often gives a service range for the free length of a spring (the measured length just sitting on your bench). As long as it’s within the  spec it is fine. I bet that valve was just glued shut with gunk….