Viewing 11 reply threads
  • Author
    • #58046

      I have an Alpine Series V. The oil pressure is low, only around 20 lbs at 3,000 rpms. The car has less than 28k miles, so the internal components should not be worn. The car has been run just a handful of times the last 8 years. I am going to change the oil and oil filter to rule out any issues with those.

      I’ve seen the article on modifying the pressure relief valve to increase the oil pressure. However, before making any modifications, I’d like to check whether the oil pressure relief valve is working properly. I read the Rootes maintenance manual and have searched the web site and forums, but I have not been able to find any description for how you check if the relief valve is working properly. Does anyone know the procedure for checking if the relief valve is working properly?

      I see from bulletin 66-6 that there was a change in oil pressure relief valves during the Series V production run. I checked my relief valve and it has the small plug in the center of the hex head. Therefore, it is the original relief valve for the series V (part number 5043949).


    • #65263

      If the relief valve is stuck, or severely worn, it should be apparent upon dis-assembly. Take it out and press on the plunger gently. The plunger should travel back into the relief housing body, so that it clears the relief holes on the sides. If it sticks or binds up, then its likely sticking during operation, and causing low oil pressure. If it operates smoothly, then I’m sorry to say that its unlikely that its the main cause of the low oil pressure condition.

      A simple modification can be done to increase oil pressure, but this will only be successful if there’s a healthy pump and healthy engine clearances.

      You’ll need to ask yourself what oil you have been running, and exactly what was done 28 thousand miles ago. If the cam bearings were not done at that time, its a likely culprit. The Alpine engine is designed to all wear out evenly through its life. Pump, Crank Shells, and Cam bearings. (Refreshing bearing shells on the crank does not an overhaul make.)

    • #65270


      Thanks for the info on the pressure relief valve.

      The car has 28k original miles. Hence, I would not expect internal component wear to be a problem with the low mileage. My father purchased the car from the original owner in 1979. I’m not aware of any engine rebuilds having occurred and I don’t see any invoices in the car’s folder for the parts to do a re-build.

      I have no idea how the original owner maintained the car. The original owner tallied up around 27k miles. It appears my father was using Castrol RX 15W-40 motor oil. I found a partial bottle of the Castrol oil along with Castrol LMA brake fluid, Sta-Bil fuel stabilizer, and lead alternative fuel additives. My father had multiple classic cars, but it would seem all those liquids were being used for the Alpine.

      Do you have any recommendations for motor oil? I’m in the mid-Atlantic region and I doubt I will drive the car when it is below freezing or above 90 degrees. I was thinking 10W-40, 15W-40, or 20W-50 would be appropriate viscosities.


    • #65271

      20w-50 or straight 30 would be my first choices as the shop manual recommends these for summer driving…. especially if low oil pressure is a issue. Its not uncommon for an Alpine to have low oil pressure. As a first measure, change oil and, try the pressure relief mod and see if you can dial up the pressure.

    • #65272
      Bob and Jean Webb

        the pressure relief valve may not be the problem. these engines do not behave like todays cars. you could have enough wear on the bearings to cause the oil pressure to start falling. you also could have wear in the oil pump which would lower pressure. you need to have close clearances on the bearings and the internal parts of the pump. this was covered in the repair manuals. I have known engines that needed bearings at 30K to 40K miles. these alpines ran at a lot higher RPM’s than todays engines. series 5 alpines had a 4.22 gear in the rear compared to the 3.89 in other series. at 60 mph engines were turning rpm’s in the high 3’s. that’s twice what my chevy and GMC are running at the same speed. check the relief valve first but if it’s ok, check the bearings.

      • #65298

        The oil pressure relief valve was stuck open causing the low oil pressure. I removed the solder joint on the valve and extracted the spring and piston. The piston was stuck and the spring was compressed in its center. Photo of the parts after extraction is here:

        I am going to do the modification laid out by Tiger Tom to make the spring tension variable.

        A few questions:
        Does anyone know the specs for the spring – what length it should be and how much force it should normally provide?

        I’d like to test the modified PRV to get it within a reasonable spec prior to installing it on the car and testing it out. At what oil pressure psi should the relief valve open up to allow the oil to flow through the by-pass vent holes? Is it around 40 psi?


      • #65299

        Yup, it looks like that spring is cooked. Is it rusted? or is it overheated to a point of weakness?

        The spring should keep the relief valve shut until the pressure exerted on the plunger is about 50 psi or so, per this service bulletin.

        I don’t know the spring k-value off the top of my head. If you don’t have another relief valve to use for parts…. You could arrive at the new spring by a little math and experimentation.

        You can calculate the area of the relief valve plunger in square inches.

        A = Area (in square inches)
        d = diameter (in inches)

        A = 3.14 * (d/2)^2

        Then convert pressure required to open the valve in pounds per square inch to a force in pounds. Select a spring and try it on your bathroom scale. Assemble the pressure relief valve then press on the plunger. When the valve reaches the open position read the scale. Try different springs to get the expected force you calculate below.

        T = target pressure opening (in pounds per square inch)
        A = area of the relief valve plunger (in square inches)
        F = force on the spring required to open the valve (in pounds force)

        F = T * A

        Then use the modded adjustment on the outside to tweak it in once installed in the car. This will adjust for leakage and tolerance in the mechanism.
        Don’t set it too high, which will result in an explosion of your oil pressure gauge… or too low which will result in poor oil pressure to the engine bearings (which is what you are trying to avoid in the first place).

      • #65300


        Thanks for the info. Oddly, I don’t have permission to view the forum link you sent. The 50 psi target number for dumping oil is the number I sought.

        The spring was not really rusted when I pulled it out. It was somewhat dirty, but not too bad. I manually pulled the compressed section apart to stretch it back out. It generally seems in ok shape. It doesn’t seem to have any weaknesses. However, given I have the valve apart, I’m going to try to find a replacement spring.

        I will definitely be doing some math and experimentation to figure out the right configuration, erring on the side of having slightly lower than desired pressure initially and working my way up to the desired pressure.

        A friend is fabricating a new tube from steel. The tube should be ready this weekend. I drilled and tapped the nut already for the tension adjustment. Just seeking a replacement spring at this point.


      • #65301

        I corrected the link.

      • #65310

        I wanted to provide an update for this thread. My friend completed the fabrication of the replacement steel tube. I found a replacement spring online made from 302 stainless steel. I matched the diameter and wire size. I figured the length was within a 1/4 inch. I had no idea about the spring rate or max load. In the end, I wasn’t too worried about the spring specs, given the tension can be adjusted.

        We tried some test solders, using paste flux and stay-brite silver solder (probably 8% silver), on some scrap parts and failed initially. I did some research and paste flux is not the way to go for soldering steel. I purchased the Harris solder kit with the Stay-Clean liquid flux and Stay-Brite silver solder. I did a couple more test solders on scrap parts using the kit flux and solder, and everything worked ok. I soldered the steel tube to the valve nut and thankfully it went great. I cleaned the flux off and installed the pressure relief valve back into the engine. The initial oil pressures were promising even after the engine warmed up – around 20 psi at idle and 40 psi at higher rpms. I adjusted the bolt on the pressure relief valve to increase spring tension and ended up with high 30s psi at idle and low to mid 40s psi at higher rpms. Given I have no idea how accurate my oil gauge is, I took those specs as a victory! I knew I needed to seal the adjustment bolt to prevent oil leaks. I tried counter sinking the locking but and using rubber washers with no luck. The washers kept getting squeezed out when the locking nut was tightened. I ended up using a sealing washer and it seems to be leak free. I changed the oil and filter to get rid of any crap that might have been freed up. Post oil change, the pressures are still looking great.

        I think I am missing the washer that sits under the pressure relief valve head. Hopefully, that should be simple to address. It is unclear if the lack of a washer is causing an oil leak or not.

        I took the car out for a short drive in my neighborhood tonight. It was the first time the car had moved in over 8 years. I’m stoked. 😀

        Thanks for all the advice.

      • #65311

        Victory for certain!
        Drive it to the United.

      • #65404

        I drove my 1959 Singer Gazelle with a 1966 1725cc Sunbeam Alpine engine installed, 1200 miles to the United this year. First day of driving the oil pressure was a hair below 50psi, part way through day two and all day the third day it dropped to about 35psi at cruising speed. Don’t ask what it was at idle. Friday at St. Michael’s in the hotel parking lot I switched out the oil pressure relief valve with a spare I carry. Oil pressure went back up to 50psi and held the 1200 miles home.
        The oil relief valve removed from the car had a definite ‘stick’ when the plunger was depressed, a bit of brake cleaner sprayed on the valve removed any dirt from the valve and it seems to work fine. Always have a spare!
        What a great show you guys put on, so happy we went. Both Bob (’53 SunbeamAlpine) and myself made it home safe and sound and we both would go to a United again, a bit closer next time though.

    Viewing 11 reply threads
    • You must be logged in to reply to this topic.