Abarth top-hat oil pressure relief valve

Discussion in 'Rear-Engine Fiats' started by Frknfiat, Aug 24, 2019.

  1. Frknfiat

    Frknfiat bad day on black top

    Location:
    earth
    upload_2019-8-23_20-4-31.jpeg

    This is a stock Fiat 600/850 pressure relief valve.

    We know this type of relief valve are mounted in the blocks of Fiat 600/850.

    Abarth modified this valve to incorporate a longer spring to increase the oil pressure relief opening point, as the stock relief opening pressure was in the 50 psi range, Abarth was higher.

    The Abarth Top Hat valve had an extension hood brazed on to the head of the modified hex headed bolt that retained both the plunger and spring - the hex head has a hole drilled in it to allow the taller relief spring to pass through into the new brazed on TOP HAT extension cover - hence the name of the Abarth style relief valve “Top Hat”.
    abarth top hat oil pressure relief valve modified.jpeg


    Now this little bugger has been known to move from its original block location and find itself adapted on to the oil pump itself, allowing the now vacated oil relief fitting port in the block, where the oil relief valve once was, to become a free port for hooking on an oil line to redirect oil to a full flow filter and/or cooler.
    fiat 850 full flow oil mods to block clark edwards.jpeg


    This is the basic concept and use of the oil pressure relief valve, modifications done to it, and why it was relocated to allow for oil filtering and cooling purposes.

    As Abarth, PBS and many others have modified these relief valves into Top Hat versions - what are the specifications for the spring and for the extended top hat length, a combination that seems to be constant between most versions in use?

    The "Top Hat" shown was made by PBS
    It has a 20mm extension "hat" braised on to the oil pressure relief valve's top most bolt hex face.
    Spring has a 9.37mm OD and a 6.73mm ID, spring is 50mm long, 1.32mm spring coil diameter, 18 spring twists, I have not measured or compared the spring to a stock oil pressure relief valve's spring. - the spring looks used, probably taken from another vehicle's relief valve and repurposed ? Anyone know more?

    I bet many are interested to know the exact design details of a modified oil pressure relief valve called a Top Hat - please discuss.
     
    Last edited: Sep 9, 2019
    khnitz likes this.
  2. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    I'm curious why not just use either a stiffer spring of original length in the stock relief body, or a longer spring of original tension compressed into the stock body, or add shims to compress the stock spring to increase the pressure?

    If the modified "top hat" relief will fit on the oil pump (relocation aspect), then I assume a unmodified one will as well? In which case, combined with what I said above, why is a modified 'top hat' relief needed?

    Honestly these are only questions, I have absolutely no knowledge about these engines and never heard of a 'top hat' relief before this. So I am merely curious and my intent is sincere. I'm sure there must be something I'm missing. Please enlighten me, I'd love to learn more about it. It might offer me ideas I can use on other engines. ;)
     
    khnitz likes this.
  3. myredracer

    myredracer True Classic

    An oil pump from an A112 is a good option which has an integral relieve valve in it. That's what I've got in my 903 block that has been bored/stroked to 1050cc. The hole in my block is going to used to run a line to an Abarth remote oil filter. The remote oil filter also has a relief valve in it but don't know which one will open first.

    I think it was Greg Schmidt who used to sell the extended springs??
     
    khnitz and Austin74 like this.
  4. Jeff Stich

    Jeff Stich True Classic

    Location:
    Norco, CA
    For illustration, here's a 600D-based Abarth 850TC engine with the reverse-flow oiling setup, which relocates the stock Fiat oil pressure relief valve from the engine block to the oil pump as noted above. The original oil pump-to-front main cap oil feed pipe is cut halfway across its "arch", & the relief valve is brazed/welded onto the end of the pipe still connected to the oil pump. The other "arch" half of the feed pipe is discarded & a blanking plate is bolted onto the top of the main cap. Note that the former oil return port on the block (seen just to the right of the oil pump base) gets tapped & plugged with a hex screw as part of this conversion.

    tce02.JPG


    An "aerial" view showing (part of) the new main cap blanking plate, the modified oil feed pipe/pressure relief valve setup, the plugged block oil return port, & the former pressure relief valve location now fitted with a blue anodized AN-type metal hose connector for an external/remote oil filter.

    tce13.JPG


    Side view showing the same blue AN-type metal hose connector, & the former oil pressure "idiot light" sender port now enlarged to accept another AN-type metal hose connector (for oil returning from the new external/remote oil filter).

    tceleft.JPG


    A Fiat 850 engine with the same modifications:

    PBSengine03.JPG PBSengine06.JPG PBSengine09.JPG


    A good detail view of the former oil return port now plugged with a hex screw as part of this conversion:

    PBSengine10.JPG
     
    Last edited: Aug 25, 2019
    Dr.Jeff and Frank L. Di Gioia like this.
  5. myredracer

    myredracer True Classic

    I have an Abarth cam gear oiler as in the photo. It's missing the banjo bolt and I can't remember exactly where these got mounted inside the block. Also have the braided line that mounts to the bypass tube on one end. Not sure where the other end went or if this was for the gear oiler mod. Or did the end with the threaded fitting attach to a relief valve? It looks well made and could be an Abarth part?? I have no need for these and if anyone is interested, let me know. This came with a bunch of parts I bought from the estate of an Abarth enthusiast and vintage racer. DSCF0980.JPG
     
  6. Jeff Stich

    Jeff Stich True Classic

    Location:
    Norco, CA
    On the 600D (850TC) block, it goes here: tce06.JPG

    On the 850 (OT1000) block, it goes here: ot07 copy.JPG

    The threaded mounting hole & the flat/surfaced area around it are not there on stock Fiat blocks, these need to be machined into the block.

    I've never seen this braided hose used for the oiling conversion mod, nor is it an Abarth part.

    I'll take the gear oiler banjo fitting. Hopefully it's (near) the same size as one I already have, & I can just make a copy of my center bolt to use with this one. ;)
     
  7. myredracer

    myredracer True Classic

    Okay!:)
     
  8. myredracer

    myredracer True Classic

    I found this on the weekend while rummaging through some boxes. Someone (not me) had done the reverse flow/remote filter mod and this is what he did with the relief valve. I don't need it if anyone is interested. DSCF1066.JPG
     
  9. Jeff Stich

    Jeff Stich True Classic

    Location:
    Norco, CA
    I'll take it, just toss it in my pile o' stuff. ;)
     
  10. Frknfiat

    Frknfiat bad day on black top

    Location:
    earth
    FYI for newbie's there is newer distributor drive shaft oiling method that requires a 0.010" squirter hole be drilled into your camshaft big bearing bush, an internal oil groove will be required to channel oil to the new 0.010" squirter hole - every 600/850/a112 engine has this bearing, simply modify the bearing. SANY0693_ml.jpg
     
  11. Jeff Stich

    Jeff Stich True Classic

    Location:
    Norco, CA
    "Newer" would be a relative term. ;)

    PBS devised the drilled cam bushing method 30+ years ago, & I can vouch 100% for its effectiveness (I've done this mod on a few of my 600 & 850 engines in the past - works great!).

    My desire to have the old banjo-style oil squirter is simply to replace a missing original one on a spare engine block I have (as part of a "period-correct" rebuild of that engine).
     
  12. Frknfiat

    Frknfiat bad day on black top

    Location:
    earth
    all good, no toes stepped on here, comment meant for "newbie's"and yes a PBS innovation for sure.
     
    Last edited: Sep 9, 2019
  13. myredracer

    myredracer True Classic

    Duly noted and done...
     
  14. myredracer

    myredracer True Classic

    Paul vander Heyden was using this method when he was building engines in the US and was drilling the holes at 0.03".
     

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