Low Oil Pressure on 4106

[OneLapper]

Hey People,

I have driven the bus about 4000 miles but never had a working oil pressure gauge up until recently.  When I got both the electrical and mechanical guages working, the engine showed only 10 psi going down the road.  This got me worried.

Here is some info on the 4106 8V71 low oil pressure.  After work today I rigged up an adaptor using the mechanical oil pressure gauge on the oil manifold and attached it to the hose coming from the block to the tee fitting on the engine generator.  This test took the generator out of the oil pressure loop and let me check the oil pressure coming directly from the engine block.  The results: Oil pressure used to show 10 psi cold idle when connected to the generator.  When bypassed, cold idle is 55 psi! Ah ha!

The previous owner told me he install a used generator when the original one went bad.  The orginal came with the bus along with an extra starter, wiper motors, new lenses, windows, etc.  I pulled out the generator and promptly called Luke at US coach.  He confirmed that the original generator's back plate has a small hole cast into it to act as an oil flow restrictor.  I removed the back plate and he was spot on, a small orfice, maybe .050" cast into the back plate where the oil supply tee/hoses attach.  In short, the gernerator currently on the engine is not specifically for this application, although it does fit on a 8V71.  Luke mentioned to swap back plate and that will correct the low oil pressure reading. That's tomorrow's task.

Sorry for the long post, but I figured that this info might be of some interest to you all.

Mark
'64 4106

[Barn Owl]

Sharing information like you have is what makes these boards so valuable to us all. Thank you for taking the time to do so. I would have never thought that there would be different setups. Is there any way you could post some photos of the orifice and where it is located on your alternator? That way others would know exactly what to look for.

[TomC]

I had a similar story.  When I first bought the bus ('77 AMGeneral transit with a 8V-71 V-drive) it had a belt driven radiator fan.  I had a gear driven adapter installed that also allowed running a right hand fan, since the gear drive reversed the engine rotation.  I never had very good oil pressure, but then, it was a 2 stroker.  When I had it turboed, the extra oil line to the turbo took it over the top where only about 20psi was being pumped.  Don Fairchild discovered that the original mechanic that installed the fan gear drive did open up the oil passage to the gear, but no restrictor on the hole-just an open 3/8" hole (which would flow a tremendous amount of oil).  Don put in a bolt with a 1/8" hole and wala-45psi again at hot.  He also disconnected the Luberfiner 750 that also was using oil pressure.  I'll just change the oil more than the 2 1/2 years I did before-course with oil analysis first. Good Luck, TomC