Oil Pressure Gage

[Vicman]

I have a question about oil pressure gages.
I've seen them on bikes and for sale but not sure where they are picking up pressure from. It looks like they just replace one of the bolts going into the crankcase?

 

[PharmD750]

I know cycle x makes a nice one. Check it out.

 

[Vicman]

I've seen several of them just never understood where they were picking up pressure from.

 

[dirtdigger]

If you are referring to a gauge coming off the right side just above the point cover and just behind the cylinder that is the primary oil gallery for the 750 motor.

 

[Vicman]

Thanks DD,
So is it just a matter of pulling that bolt out and screwing the gage assy in?

 

[dirtdigger]

Its not a bolt it is an o-ringed plug with a hex head. But yes it is that easy if you have the correct adapter.

 

[Vicman]

Cool,
Thanks for the info.

 

[Dave]

This was on my bike when I got it, over 10 years ago, and it has never leaked. I do carry a 1/4" npt plug in my toolkit in case it ever does. The previous owner just drilled and tapped the plug on the right side and used a few simple fittings to mount a plain aftermarket 2 1/16" guage.

 

[dirtdigger]

I was going to mention tapping the oem plug but the plug is thin and the aluminum is not the best quality and I have seen the tapped plug fail. But yes you can tap the oem plug and thread the fitting into it.

 

[Vicman]

DD, you mentioned that location is a main oil gally. Is it advisable to pull the plug and swab it out?
I suspect I've got a sending unit going bad as after a little while the light comes on intermittently. Gotta tell you it kinda freaks me out when it does. Hence I'm thinking about putting a gage down there just as a back up.
Next question. Where the hang is the sending unit at? Is it in the rubber boot above the starter cover? How big a deal it it to replace?

 

[dirtdigger]

I would not swab the gallery for chance of dislodging stuff loose and not getting all of it out. What weight of oil are you using? Is your idle speed low? Should be 900 to 1000 rpm. Does it flicker at idle only after a long ride with the motor hot?

Yes the sending unit is under the rubber boot by the starter cover. Easy to remove...unscrew the wire then unscrew the sender.

 

[Vicman]

I'm running 10-40, rpm is a nice low 1k or less and very smooth. Yes it will flicker occasionally at idle but very low. I remember it doing that 30 years ago when I rode it as a kid.
What is concerning is that everything is normal when I first start the ride. I'm not hammering it when I ride so most of my backroads riding is in the 3-5K rpm range. After the engine has been running for about 15 min the light will start to come on after a low rpm pause, say if I am coasting down a hill in a high gear. The bike is completely warm. The light doesn't come on when it's cold.

 

[dirtdigger]

This is normal for the light to flicker with hot oil and at idle. The oil gets a lot thinner as it gets hot an your oil pressure naturally goes down when it gets warm. When it is cold the oil is much thicker. As long as it stays off when it is brought just above idle then you are fine. It never hurts to have a gauge to monitor oil pressure though.

 

[Vicman]

I'm trying to get at least 500 miles out of this oil change. It sat for 25 years and this is the first bit of running it has done so I am a little concerned about globs floating around and possibly stopping up the sending unit. Most of the rides have been short 10-15 mile jaunts, again not flogging it at all.

 

[Vicman]

Got some bar stock and am getting ready to make an adapter for a gage. Pulled the plug on the 71 and it looks pretty spartan down the hole. I really hope it's just a bad sending unit and not a pump.