LP 1275 Oil Pressure Issues

C

craig bryant

Well-known member
Is there a limit on what would be considered too much oil pressure for an LP 1275 motor? On the first time out with my recently built motor, I had a problem not only with an oil leak, but pressure dropping which I assumed was because of the leak. I am hoping that the leak has been solved. I also installed a new pressure relief spring and valve. When the motor was back in the car, I turned it over with no plugs to build up the pressure before starting it. It got up to 60 lbs. I put the plugs back in and fired it up, and the pressure jumped up to between 80 and 85. I ran it long enough to build up some temperature, and it never dropped below 80. I always thought that under normal conditions in just warming up a motor, that was too high. Is it, and if so, what range should it be at, and what steps should I take to get it there? Any and all advice is greatly appreciated. Thanks in advance.

Craig
 
That doesn't sound too high, in fact that's about what I have now. At idle, you're not going to get much oil temperature, but it's very likely that your pressure will drop significantly with some time on track. Mine drops from 80 at idle to 60 with hot oil (well over 200), and I consider that fine for these engines. If yours does not drop to something like that, you will have to adjust the relief spring pressure to get what you want. I haven't ever used one, but adjustable relief pressure mods do exist, with a screw through the outside nut. Otherwise, you can adjust pressure by changing springs, and/or shimming inside the nut. Kind of a pain, but once set right you shouldn't have to touch it.
 
I agree with Randy on your pressures. The neat thing about making an adjustable oil pressure regulator like Randy mentioned is where it is located on the A series engine, you can even access and adjust as the engine is running. Avoid the the adjustable regulators Mini Mania sells with the big knobs on them, they interfere with our starters on the RWD cars. You can make one easy enough, with 1/4" hex bolt, a o-ring/copper washer, and a jam nut, even the center is easy to drill on the cap nut, is it has a drill center point the inside of cap nut to follow, you can make one in 15 minutes for $2.
 
I'd be very careful using Hap's method UNLESS the big nut has a thread wall thickness that is at least 3/8" thick.........which none are. Remember that to develop full strength in a threaded fastener the conservative rule of thumb is a minimum of 1.5 thread diameters of thread engagement. Given a 1/4" bolt that's 3/8" of threads which simply isn't present.

Sure, that's for high tension applications which this is not......... so good enough is to weld a standard 1/4" thick hex nut on the outside of the big nut (first take a light surface cut on your lathe to make sure it is welded perfectly perpindicular to avoid side loading the oil pressure relief spring) and then use another nut as a jam nut. When I built mine I actually welded on a 7/8" long "coupler nut" to be uber conservative.

When you think about how important oil pressure is and the bad stuff that will happen if the big nut 1/4" threads fail (0 oil pressure, spun bearing, gooberd crankshaft, end of fun for the weekend).......you'll take a little extra time to be conservative here.

BTW- A good rule of thumb for hot oil pressure is 10 psi/1000 rpm shift point. On the other hand the more oil pressure you employ the harder the oil pump has to work and the less torque to the rear wheels. Back in the day some very clever German engineers developed the flat 12 Porsche 917 engine to run like a top at << 40psi hot for this very reason. Maybe someone knows how low the top end NASCAR teams run oil pressure these days...but these guys have the budget to find the very, very ragged edge.
 
Almost forgot.

Using the screw method you also need to make a spring pilot on your lathe....the end of the bolt has to contact something flat rather than the spring. This part looks like a top hat with the top of the hat maybe .010" smaller in diameter than the ID of the spring.

All of this monkey business is why Randy's AN960-4 washer method trumps all ......although inial setup is a little messy. None of this is an issue for me as I have proven over the years to be the master of the 2 hour solution to the 5 minute problem. ;^0
 
Craig - My motors typically get 80 lbs pressure cold and drop to 60 to 65 hot just like Randy's. With 85 cold, that is more than needed so it is robbing power but it may drop to 60 when you get it out on the track so no need to do anything now. With my external pump I can easily adjust the pressure relief to whatever I want and set it at 80 cold.

I also used an adjustable pressure relief on the internal pump engines. Just tap the big bolt as Hap suggested. It will take ten minutes. I'll send you one if you want as I don't need it anymore. Wow Jay - talk about overthinking something. It adjusts oil pressure through the end of a spring for Pete's sake. It doesn't need full threads or to be square.
 
I have been using a similar method as Haps for oil pressure adjustment since around 1987 and have not had a problem with it. I also get around 80 psi with a cold engine. On a very hot day, on the track for a while and pushing hard, I can see as low as 60 psi at around 7,000. rpm. I don't know what it is at 8,000 rpm, I am too busy to take a look at the oil pressure.
 
We have 5 engines with adjustable oil pressure units made out of the stock cap nuts. We use both 1/4 and 5/16 allen head full thread bolts machined down to a flat surface for mating with the spring. The bottom of the bolt head is tapered to fit snug inside the cap nut. End of the threaded bolt is slotted for a screwdriver. For the 5/16 thread nuts we try to find nuts that use a 7/16 wrench. Those usually come out of that big coffee can full of misc bolts and nuts we all have. Gives just a little more room to work in the tight space. As for pressure, we run 50 hot in both the 1275s and the 948s. Also, we use the 9/16 steel ball bearings in place of the stock valve.

Bob
 
Ron Bartell":1opg7nsd said:
Craig - My motors typically get 80 lbs pressure cold and drop to 60 to 65 hot just like Randy's. With 85 cold, that is more than needed so it is robbing power but it may drop to 60 when you get it out on the track so no need to do anything now. With my external pump I can easily adjust the pressure relief to whatever I want and set it at 80 cold.
Click to expand...

Ron, do you use a stand alone pressure regulator on your external oil pump, I did, as David Headley warned me that the TDC external pump's built in regulator could troublesome, so he suggested I opt for the stand alone Peterson regulator, it seems to be a well made piece and work flawlessly so far.

Of course on the MGB, we have the added challenge of needing to run the external oil pump via the water pulley, because of the location of the steering rack to the harmonic balancer, but we have all that figured out now, of course with Headley in the project there had to be a GM part involved :), my system use a V belt set up and the pulley on the oil pump is GM smog pump pulley :)
 
Acme Speed Shop":15nrws60 said:
Ron, do you use a stand alone pressure regulator on your external oil pump,......
Click to expand...
No I don't use an external regulator, but I do use a Peterson in-line filter screen to keep any possible debris from getting to the pressure relief because we have had them jam. When I was having un-related oiling issues some bearing material got past the screen and locked up the shuttle valve on the pressure relief. I bought a Peterson remote but never used it because we found the cause of the oiling issue and haven't had trouble with it since.
 
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