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Projects Old school cool 248 Gmc

Discussion in 'The Hokey Ass Message Board' started by Neb Hillbilly, Dec 26, 2019.

  1. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

    Has anyone added trays/baffles to their stock pan? It has a front and back baffle but I was thinking of adding horizontal plates to keep it from splashing up the back/front under acceleration/braking.
     
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  2. jimmy six
    Joined: Mar 21, 2006
    Posts: 6,671

    jimmy six
    Member

    Take the backs off and look at the casting. Chev does have 2 holes (except for 1939) and the GMC has 1. Our 40 ran yesterday for 30 minutes with the new 15" mechanical fan and shroud from Summit. Extremely effective. Temp stayed at 160-170.
     
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  3. jimmy six
    Joined: Mar 21, 2006
    Posts: 6,671

    jimmy six
    Member

    I've never had a problem with normal driving. When drag racing at the end all the oil is trying to get into the timing cover and the oil pressure guage would spike down. I riveted in a piano hinge on the front baffle over the holes on the back side and never saw the problem again.
     
  4. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

    Went down early this morning and did a few things. Put in my plug for full filtered oiling. Spent the money and bought a 9/16 Allen for ease of removal later. Pro tip, install the breather baffle before the cam to reduce the anger/frustration and speaking in sailor speak. Chevy water pump will NOT fit, I am going to see how good the 302 one is. Finding a rebuilt pump is difficult and NOS will likely have a seal leak. IMG_20200430_055328.jpeg IMG_20200430_054316.jpeg IMG_20200430_054744.jpeg IMG_20200430_054818.jpeg

    Sent from my S48c using The H.A.M.B. mobile app
     
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  5. Six Ball
    Joined: Oct 8, 2007
    Posts: 3,386

    Six Ball
    Member
    from Nevada

    Contact this guy. Sammy was my main source 20 years ago when I worked at CarQuest. He does a lot of older stuff. Surprised to fine him in a Google search this morning. He got tired of working for the big outfit.(Cardone)
    S&N Auto Electric, Sacramento CA
    Phone: (916) 920-2233

    https://www.snautoelectric.com
     
    Last edited: Apr 30, 2020
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  6. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

    Thanks! I have 2 248 pumps and a 302 pump. One 248 has been without water for a long time the other was on the original 248 is likely bad as well and one on my 302. I will see if one of the pumps is good enough for break in etc and send the other off to get rebuilt. I do have one of the 302 but I want to leave that mostly together right now.
     
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  7. Six Ball
    Joined: Oct 8, 2007
    Posts: 3,386

    Six Ball
    Member
    from Nevada

    They are not hard to rebuild if you can find the seal and bearing. Just a press and elbow grease.
     
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  8. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

    Do you think your friend can supply that? Not sure where to get one locally. I might do a bit of searching here.
     
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  9. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

  10. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

    apparently 37-40 Chevy cars share the 598309 water pump with GMCs according to the internet

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  11. Six Ball
    Joined: Oct 8, 2007
    Posts: 3,386

    Six Ball
    Member
    from Nevada

    I used to know that stuff. :( I think the seal and bearing are standard listings. We used to look them up by measurements. The bearing should have a number on it.
     
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  12. 302GMC
    Joined: Dec 15, 2005
    Posts: 6,185

    302GMC
    Member
    from Idaho

    Several of the '' Put a GMC in your Chevy'' magazine articles from the '50s used the '37 - '40 Chev pump.
     
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  13. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

    Well the 248 I originally bought came out of a shop.that had a 37 sedan in it and the 248 came with a 37 Chevy 3 speed on the bell so I ass-u-m-ed the water pump was a car pump not knowing that most Chevy and GMC pumps were different. The casting number comes up as both so who knows. It spins nice but a 70 year old pump is likely to leak right away.

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  14. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

    So, new problem. This whole time I was excited that I could use a factory GMC PVC system. I had 2 crank case vent valves, problem is one has been soldered shut and the other is missing the pintle and spring. Anyone know of a place to get a NOS one? I liked that it was hard piped to the intake instead of using hose. I am sure I could use a modern one but like the GMC one.
     
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  15. saltracer219
    Joined: Sep 23, 2006
    Posts: 760

    saltracer219
    Member

    All American Classics in Vancouver Wa. or Old Car Parts in Portland Or.
     
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  16. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

    Did a few things today. Had to clearance the Clifford headers to fit the Nicson intake. Drilled and tapped the 1/8th npt for the oil pressure gauge. I should have done it earlier but I got it done and cleaned out the hole with a magnet and caught all the iron. Also blasted and painted the headers in VHT silver because we had it. Would have preferred white but this will work. Now on the hunt for a a couple of cans of GM 514 crimson red to paint this jewel. IMG_20200502_095203.jpeg IMG_20200502_095649.jpeg IMG_20200502_111739.jpeg

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  17. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

    Oh also cleaned up my oil pump, shimmed the spring and assembled it all.

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  18. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

    Didn't get a lot done today but I did have some GM-514 paint mixed and put into cans to paint the block and finally found a copy of this book so I can be an expert like all of you guys. IMG_20200504_191908.jpeg IMG_20200504_191927.jpeg IMG_20200504_205244.jpeg

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  19. Six Ball
    Joined: Oct 8, 2007
    Posts: 3,386

    Six Ball
    Member
    from Nevada

    That book is great But.........Some of the people who have posted here and others have important information about these engines that has been developed since Bill Fisher put this book together. If this is the GMC Bible we need a New Testament. There was no SBC V8 when that was written.
     
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  20. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

    I understand, my statement was a bit tongue in cheek. I like that it has a bit more information but the fact that it is 21 years older than me, leads me to believe there may be a lot left out or developed later. I did see that it says the top of the heads crack, which is exactly where the head on the truck's current 248 is cracked.
     
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  21. jimmy six
    Joined: Mar 21, 2006
    Posts: 6,671

    jimmy six
    Member

    Many heads were cracked. Funny thing is I have never had one. From what I’ve read it was always from overheating and I wonder how many had the water line running from the 1/2” pipe hole owner #6 to the left side of the thermostat housing. When I was to young to know it’s where I put the temp gauge when it really belonged over #5 and not #6. Took me some time to learn also.
     
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  22. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

    I planned on running the bypass through the bottom of my nicson intake to warm it.

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  23. jimmy six
    Joined: Mar 21, 2006
    Posts: 6,671

    jimmy six
    Member

    A good bet where you live; we didn’t on my sons here in So Cal and so far so good. Temp on the aluminum risers to the Howard intake are pretty warm. Might be because of the Nicson cast iron exhaust.
     
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  24. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

    I keep thinking the Nicson will be too small and I should find a Howard or 3x1 Nicson but I just need to finish it first. Not sure what the BVOX-2s flow or what more cfm will gain.

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  25. Gofannon
    Joined: Feb 8, 2007
    Posts: 563

    Gofannon
    Member

    How about finding a stock 302 intake for a 2bbl and adding flanges for 2 more? That's the plan I have, although my intake is for big port and 1bbl, so I'll have to make 3 flanges. Use 5 1/2" spacing like the common SBC 3x2bbl intakes and you can make use of readily available linkage kits etc. The intake would work for 1, 2, or 3 carbs.

    Or add 2bbl adaptors to your Nicson.
     
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  26. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

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  27. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

    Though if I am going to build an intake I will be starting from scratch and calculating the intake running length and plenium volume. Adapters really don't work. It causes fuel drop out and other flow problems. I will just try running the intake and carbs I have. Really I should keep remembering this is a truck for the cruising and the drive in ice cream shop not a drag racer. I will chassis dyno it to dial in the carbs and timing so I will know what it makes. Plus intakes are easy to swap.
     
    Last edited: May 6, 2020
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  28. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

    Well I wasted $75 dollars this morning breaking one of the water pumps I had. The second one has a weird number on it so not sure if it isn't a GM pump or what. It has a B124 on it and it is copper colored. Hoping I can rebuild it.
     
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  29. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

    Took apart my other 248 pump today. Got it apart without breaking. Not sure if it is a GM pump or not because of no casting numbers. Ordered a kit for it from commercial water pump rebuilders in Houston TX. Comparing this pump to my broken Chevy pump, they have the same impeller but the Chevy pump has every other fun ground off the back of the impeller. Anyone know why? less cavitation at high rpm? IMG_20200508_070909.jpeg IMG_20200508_070914.jpeg IMG_20200508_070919.jpeg

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  30. Gofannon
    Joined: Feb 8, 2007
    Posts: 563

    Gofannon
    Member

    That was something that was done back in the day. An old timer that raced in the 50's told me that. Slowing the flow somehow aided in cooling, probably for higher RPMs. You need to ask someone knowledgeable in thermodynamics how this might work.
     
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