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Technical 301 sbc pistons?

Discussion in 'Traditional Hot Rods' started by 1960c10, Aug 13, 2019.

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  1. 1960c10
    Joined: Aug 3, 2018
    Posts: 23

    1960c10
    Member
    from So cal

    Hey everyone, Picked these pistons up the other day ,cheap. Supposed to be 301 sbc domed pistons for use in 283 bored 1/8" . Only casting numbers are je 257 , I need to verify before sending block to be bored out , anyone ever seen these before ? 1565673312787-178141316.jpg 1565673359363-716527583.jpg
     
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  2. Fordors
    Joined: Sep 22, 2016
    Posts: 5,372

    Fordors
    Member

    Because the pistons may vary in diameter due to manufacturing tolerances many guys will send them with the block so it can be bored and honed accordingly.
    If you do not expect to do that then you need to measure a piston skirt perpendicular and level to the pin bore to determine the size. Your pistons are sand cast, heavy by today’s standards and will need .007-.008 clearance.
    Do you know that with those domes you will have a very high compression ratio not compatible with today’s gasoline?
     
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  3. 1960c10
    Joined: Aug 3, 2018
    Posts: 23

    1960c10
    Member
    from So cal

    Yes , I do understand the domes will increase compression, but with a 64cc head , I should be ok . I measured diameter, 3.960 . I will take them with me to machine shop to verify diameter and pin height, thanks
     
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  4. B.A.KING
    Joined: Apr 6, 2005
    Posts: 4,039

    B.A.KING
    Member

    uhhh not to sure about that.maybe with 76 cc heads
     
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  5. 56sedandelivery
    Joined: Nov 21, 2006
    Posts: 6,695

    56sedandelivery
    Member Emeritus

    Measure from the center of the wrist pin hole, to the top of the piston (the FLAT part of the piston); it should be somewhere around 1.80 inches if they are correct for a 3 inch stroke crankshaft; 3 inch stroke and 4 inch bore makes your 301/302 CID. As far as the C.R. goes, you may be able to have the domes machined down to lower the C.R. Have you tried calling JE pistons? Main line is (714)898-9763. I am Butch/56sedandelivery.
     
  6. Deuces
    Joined: Nov 3, 2009
    Posts: 23,751

    Deuces

    Pistons measure what???? 3.960" in diameter????... Not enough for a 301/302.. unless you checked the diameter at the top....o_O
     
  7. Deuces
    Joined: Nov 3, 2009
    Posts: 23,751

    Deuces

    Piston dome look like 12:1s... :confused::eek:
     
  8. that would make the pistons 40 thousands loose in a 4 inch bore or eighty and 1/2 thousands for a 283. They are likely .080 over for a 283.
     
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  9. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,213

    sunbeam
    Member

    The compression height looks to big take a dial caliper and measure from the top of the pin hole to the top of the piston flat. It should be 1.3365" for a 301-302
     
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  10. 1960c10
    Joined: Aug 3, 2018
    Posts: 23

    1960c10
    Member
    from So cal

    Thanks for replies, the pin center to top of piston flat is 1.80, and diameter measured at bottom of piston opposite of pin is 3.9960, so these are 301 4" pistons?
     
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  11. jimmy six
    Joined: Mar 21, 2006
    Posts: 14,795

    jimmy six
    ALLIANCE MEMBER

    Wrap some tape around the piston to take a mold of the top. wax it first. Use plaster of paris. After dry. Borrow a burette and cc the dome. Then use the calculator on Keith Black Pistons/United Machine and figure out which head to use. 58, 64, 76. Head gaskets are usually .042" Cometic sell MSL gaskets different thicknesses so you can get the comp ratio you want.
    Your dome looks to be 25 cc's as I use that style in a 13-1 dirt track engine.
     
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  12. Fordors
    Joined: Sep 22, 2016
    Posts: 5,372

    Fordors
    Member

    Yes, they do measure correctly for a 4” bore 283. I imagine JE hasn’t made a cast piston in at least 40-50 years and won’t have any knowledge of them.
    If you look inside the crown you will be able to see if it is flat or hollowed out into the dome to lighten the pistons a bit. If they are flat inside then yes, as suggested you could mill the domes and not sacrifice any strength. I agree with the others that have said those are at least 12 to 1 compression with a 64cc chamber. Back in the early ‘60’s when those pistons were probably made popular heads were the ‘461 or ‘462’s with 64cc’s.
     
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  13. 1960c10
    Joined: Aug 3, 2018
    Posts: 23

    1960c10
    Member
    from So cal

     
  14. 1960c10
    Joined: Aug 3, 2018
    Posts: 23

    1960c10
    Member
    from So cal

    Thanks , that was what I was thinking, i am planning on running 64 cc heads and milling the dome a bit or run 70cc heads as is . Just a fun little screamer that if it blows then , build another one.
     
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  15. We will just have to wait until squirrel gets back home from his Lemons trip in his Hudson. He will know exactly what they are.
     
  16. Fordors
    Joined: Sep 22, 2016
    Posts: 5,372

    Fordors
    Member

    Hey @Old wolf, you ever hear this?
    Don’t put all your eggs in one basket.
     
  17. In one post he stated the diameter was 3.960 and later 3.9960? If you did not already know Squirrel is the go to guy on here. he likely has a old catalog telling the part numbers ect.
     
  18. I can't claim an extensive knowledge of these things, and maybe it's just me. But if these are in fact cast pistons this is a lot more clearance than I would have expected. It actually sounds more like what I would have expected to see for forged pistons.

    As I recall, cast pistons were used in most modern production engines because they were more thermally stable and ran quieter when cold. And they could be fitted tighter in the bore and still didn't expand so much at operating temperatures that they'd scuff the bores. They just didn't have the same "brute strength" as a forged piston for heavy-duty or racing purposes.

    Or am I remembering this backwards?
    :rolleyes:
     
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  19. Beanscoot
    Joined: May 14, 2008
    Posts: 3,053

    Beanscoot
    Member

    Not backwards. Cast pistons (oem and oem style replacements, anyway) use much less clearance than forged.

    Obviously they should be brought in to the machine shop with the cylinder block for the machinist to measure them up and use his knowledge and experience to guide him.
     
  20. Fordors
    Joined: Sep 22, 2016
    Posts: 5,372

    Fordors
    Member


    The old JE and Jahns cast pistons are solid skirt unlike pistons that had expansion slots or steel struts cast in them to aid in controlling dimensional change. Most OEM pistons, if not all today, are hypereutectic and are using slipper skirts with no slots or struts. Improved designs and a high silicon alloy to cast with allowed the change.
     
    Last edited: Aug 13, 2019
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  21. Fordors
    Joined: Sep 22, 2016
    Posts: 5,372

    Fordors
    Member

    F1AA4DF1-6A4E-42FD-A22C-464E061E3619.jpeg 635E1F8D-0CDE-40A2-987A-491A6A668982.jpeg 9E516AC3-C2ED-42AA-9B28-6488270AD379.jpeg
    Here is a look at two pistons showing their different skirts. The first photo shows a magnet stuck to the con rod of a really dirty SBC 400 piston and rod, and the second shows the same magnet on the steel strut in the 400 piston.
    Photo 3 shows a Jahns cast, barrel skirt with no expansion slot or struts. The skirt is cam ground, as are most pistons and that is why they are usually measured at 90° to the pin and on the pin center line, typically the largest diameter is found there.
     
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  22. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,213

    sunbeam
    Member

    Be sure to have it balanced those old Jahns pistons weigh a bunch.
     
  23. Thanks for that explanation. I went back for a closer look at those pictures and those aren't even close to being a slipper type piston. They have a lot more meat on them than I was expecting to see. :rolleyes:
     
  24. JeffB2
    Joined: Dec 18, 2006
    Posts: 9,484

    JeffB2
    Member
    from Phoenix,AZ

    Your J&E's are probably 12.5 to one's the 283 F.I. pistons is shown here,notice it's lower dome. You could probably run your pistons "as is" with 76cc castings "what to look for" https://www.enginelabs.com/engine-tech/cylinder-heads/small-block-cylinder-head-id/
     

    Attached Files:

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  25. To be realistic those pistons are not even a viable choice. Too many issued to overcome. It would cost more to use them than they are worth.
     
    ottoman likes this.

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