Buda HS-6 oil pressure

[tvscum]

I have a 1927 farm truck with a Buda HS-6 engine. Oil pressure is low after it heats up. Cold, it's around 25 lbs at 1000 RPM. Warmed up, it drops to 10 lbs at 1000 RPM. From Buda literature:

6 cylinder engines, page twenty nine:
http://gotfredson.org/models/6_cylinder_engines.pdf

[i:1c6294bfee]"Run the engine at about 1000 revolutions per minute. On all 6 cylinder engines the oil pressure should read about 30 lbs. On HS-6 the oil pressure is regulated at the oil pump."[/i:1c6294bfee]

Engine specs, page two:
http://www.gotfredson.org/models/BUDA_HS-6.pdf

[i:1c6294bfee]"LUBRICATION: (Patented) Force feed pressure to all crankshaft, camshaft, and connecting rod bearings through a seamless steel distributing pipe cast in the crankcase. Oil pump is gear driven from the camshaft. Regulation is by an adjustable spring relief valve in pump."[/i:1c6294bfee]

So, I assume this means I have to drop the oil pan and somehow adjust the "spring relief valve" inside the oil pump? Can someone describe the operation of this valve and how it might be adjusted? Or, is the low oil pressure most likely just related to the very old, 1927 engine?

Cheers!

 

[jm.]

Most of the time what you describe is a result of worn bearing clearance and not adjustment of the
relief valve setting. That relief valve is probably doing its job , you just have some much leakage
around the bearings when the oil heats up the pump just cannot hold the pressure up there. Overhaul
is the solution more than likely.

 

[teddy52food]

The relief valve is there to relieve excess pressure to protect the oil pump. Your
pressure is below that so it won't help to adjust it.

 

[Steve@Advance]

It is very rare that the relief valve is out of adjustment, or that tightening it up will raise idle oil pressure.

Unless the spring is broken, the plunger is stuck, or something is holding the relief valve open, the problem is not in the relief valve.

Is this something new? As in a sudden loss of oil pressure? Is there any thing else unusual, like temperature increase, loss of power, unusual noises, extra blow-by?

If any of these are present, there is a problem that needs addressing.

But if it's been running near that pressure, or has very slowly dropped over the years, and everything else is still sounding and running the same, I would not be too concerned.

General rule of thumb, minimum allowable safe pressure is 10 PSI per 1000 RPM. That means if it has as low as 5 PSI at warm idle, it is moving oil through the system. I've seen old engines that would barely move the needle at idle, and they ran that way for ever.

Also consider it's use. This is not likely a working truck, and I hope it's not getting out on the freeway! So it probably has a fairly easy life.

Other things to consider, any chance the oil is contaminated with gas?

Has anything else been changed, like a hotter thermostat (if equipped)?

Does it have a canister type oil filter, and was it recently changed or added, or modified? The filter is likely a by-pass type that meters a small amount of oil through the filter and dumps back to the crankcase. If the orifice was enlarged or removed the oil pressure will drop.

The old engines were designed for straight weight, usually 30 weight oil. I personally prefer 15w40 diesel oil in the older engines, or stay with straight 30 or what ever the mfg recommended. It's rare low oil pressure can be corrected with heavier weight oil, but very light oil can lower it.

Hope there is nothing serious and it will be around for many more years!

 

[Steve@Advance]

After reviewing the manual link, I see it has shimmed bearings.

It may be possible to carefully adjust the bearing clearance.

That will raise oil pressure. Also look at the condition of the oil pump.

That's a neat manual! They sure don't like aftermarket parts! Would have never imagined that was going on back then!

 

[tvscum]

Thanks for the advice guys. I just recently started the engine after the truck was sitting in a junkyard for 40 years! I adjusted and lapped the vales, scraped off the carbon, and rebuilt the water pump. Fixed a crack in the manifold. I dropped the pan and cleaned three inches of gunk out, then refilled with 30w oil and started her up. No oil filter or thermostat on the engine. No gas in the oil. Sounds like she's just a bit worn. I think I will just let her be as she only does laps around the museum in Campo, CA.

 

[tvscum]

Thanks, good idea! I may try removing some shims next time the pan is off. Maybe get some Plastigauge.

 

[Janicholson]

Good advice below. I will add that the engine bearings in old tractors do not depend at all on pressure, they depend on oil being in the journal. Oil
pressure loss as a cumulative issue is wear on bearing inserts or babbit poured bearings and journals that reduce the pressure because it can leak out
sideways easier. Another reason is wear on the oil pump end plates or bushings that pump less pressure due to bypassing. Failure of the engine can
come from excessive clearance allowing hammering of components, or a plugged passage starving a journal of any oil. if the truck is a parade/show unit,
use 20/50 oil in it and grin all the way home. If it is loaded and used, and you are flush enough to make it happen pulling it down and going through
the lower end is the way to go. Jim

 

[Traditional Farmer]

I don't know anything about your motor,but on the Buda motors like were used in the Cockshutt tractors the oil pressure could be adjusted by a bolt that screwed in from the outside of the block and held in place with a lock nut.

 

[tvscum]

That is correct on some Buda motors. Not on the HS-6 though. Thx.