GS Oil Pressure Gauge thread size

[Dphillips030]

Looking at running a oil pressure gauge on my gs. It's a 77. I was going to mount it in the oil plug right above the points. Does anyone know the thread size of that hole?

[Nessism]

I don't know the thread size off the top of my head, but it's been discussed in threads now in the archives so the info is available for you to mine.

I installed a VDO pressure gauge on my old 850 by drilling and tapping into the existing plug. While running the needle vibrated like crazy and in short order wouldn't go back to zero when the engine was turned off. The GS oil pump system is almost 100% reliable and I think it's more risky to run the gauge than not. If the bike fell over and broke the gauge you would be stranded. The gauge developing an internal leak is a possibility too. Just about the only way the oil pump could stop working is if the clutch hub nut came off and the drive gear came away from the driven gear. I think your clutch would be all but inop at that point though. Bottom line is I believe adding a gauge increases your risk of getting stuck somewhere, not lessen it.

[Dphillips030]

I believe it's a 14x1.25. Same thread as the spark plugs. I've never had an issue with the oil pumps in any of my gs's but just wanted to have a way to double check and be certain

[bwringer]

That's the correct thread for this plug. You can go ahead and take the plug out and measure it if you like -- nothing will squirt out at you (unless the engine is running).

All we know is that you've got a '77 GS of some sort (don't be coy -- what is it?) but assuming you've got a GS750, one thing you have to understand is that these roller bearing crank engines run very, very low oil pressures. All they have to do is pump oil up to the cylinder head so it can splash around where it's needed and then fall back into the sump. Nothing is pressure lubed as with a plain bearing engine -- there are no real restrictions anywhere to build up pressure.

So if you were to install a gauge, you'd routinely see less than 5psi (this has caused many panics in the past...). And that's perfectly OK. Gauges that read this low are somewhat delicate and so the needle will be flapping around all over the place from vibration. As Nessism mentioned, the gauges don't last long, the information isn't all that useful, and they create a failure point in what is widely known to be a stone ax simple, dead-reliable oiling system.

The 1980 and later 16 valve GS750 and GS1100 engines could indeed develop problems with top-end oiling and roast their cams, but those are completely different engines.