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Hot Rods 4-bolt main conversion for 283

Discussion in 'The Hokey Ass Message Board' started by Dave B., Feb 19, 2021.

  1. Dave B.
    Joined: Oct 1, 2009
    Posts: 225

    Dave B.
    Member

    One of my friends is building a gasser-look hot rod, to be used mostly for nostalgia drags. He has a 283 block that he wants to put together for the motor. He'd like to convert it to a 4-bolt configuration and has found the 'center' main caps. He recently ran across someone who claims to have a small-journal 4-bolt rear main cap. He received this photo of it, but the guy who has it doesn't have a Chevrolet part number. He can only tell Bob that it has the number '368' stamped on it. Have any of you engine builders run across this unicorn?

    Thanks in advance for any help!

    upload_2021-2-19_7-6-3.png
     
  2. I read an article once about using a small journal crank in a large journal block. I think Jenkins did it in his race engines. So it can be done, but is it worth the time and cost?
     
  3. COCONUTS
    Joined: May 5, 2015
    Posts: 968

    COCONUTS

    If you did all of this would you have the "likes" of 302 Z28 motor? I guess that you could take this effort a step farther and "pin" the main bearings. If you start screwing around with the mains you are going to have it "line bored". I would just set the clearances middle of the road and run 2 bolt mains.
     
    thintin likes this.
  4. 19Eddy30
    Joined: Mar 27, 2011
    Posts: 1,277

    19Eddy30
    Member
    from VA

    I have not seen one (GM ) But might been a custom Rear cap made.
    Tell your friend to use ARP main studs ,
    It Will be stronger then stock GM production 4 "bolt"
     
    tractorguy, Atwater Mike and thintin like this.

  5. CNC-Dude
    Joined: Nov 23, 2007
    Posts: 943

    CNC-Dude
    Member

    The cap shown above is for a Big Block, so no unicorn. Small blocks only had 4 bolt caps on the center 3 positions. I did see only one factory small journal small block in 15 years I worked in a high end racing machine shop. It was 4 inch bore, and it had cast iron caps with GM numbers on it so it wasn't homemade, so either 67 or 68 Z28 block or 327. It had been decked before, so no code at the front was detectable to confirm and the casting number on the bell housing wasn't in any books at that time to determine what it came in unfortunately.
     
    Last edited: Feb 19, 2021
  6. squirrel
    Joined: Sep 23, 2004
    Posts: 49,265

    squirrel
    Member

    yeah, it's definitely for a big block. gonna be difficult to make it fit.

    And besides, why? folks are running 2 bolt end caps on engines making way more power than your friend will ever make...

    https://www.ebay.com/itm/163628352190
     
    ottoman, tractorguy, Mark Yac and 4 others like this.
  7. F-ONE
    Joined: Mar 27, 2008
    Posts: 2,828

    F-ONE
    Member
    from Alabama

    BOOM!
    [​IMG]
    true.
     
    warhorseracing likes this.
  8. bowie
    Joined: Jul 27, 2011
    Posts: 2,701

    bowie
    ALLIANCE MEMBER

    There are commercially available 4 bolt main conversion kits . They are splayed style, and are made for small journal cranks.
     
    Speed Gems likes this.
  9. Dave B.
    Joined: Oct 1, 2009
    Posts: 225

    Dave B.
    Member

    Thanks to everyone who replied. I'll have to admit that I played around with the description of the sale. Bob doesn't do much with forums, so I track things for him and he made me promise not to mention ANYTHING about ebay; so I couldn't say anything about why he had a photo of a part for sale without having had direct contact with the seller. He's a really good wrench, but one of those guys who decides on a course and will chase it to the ends of the earth...
     
  10. "I'll have to admit that I played around with the description of the sale".

    Confused here ... was this cap being mistakenly/fraudulently advertised as being for a small journal small block or is that the part you played around with?

    I've heard of using a BB oil pump in a SB but I've never heard of anyone using BB mains in a SB (for pretty obvious reasons I believe).

    I am now thoroughly confused and feel the need to rinse my brain out with ... beer :)
     
    Last edited: Feb 19, 2021
    kidcampbell71 likes this.
  11. squirrel
    Joined: Sep 23, 2004
    Posts: 49,265

    squirrel
    Member

    fortunately we're pretty good at finding where photos came from, especially photos of stuff on ebay...google isn't that difficult to use.
     
    XXL__ likes this.
  12. dreracecar
    Joined: Aug 27, 2009
    Posts: 3,174

    dreracecar
    Member
    from so-cal

    first, you cant use a wet sump 4-bolt rear main cap on a SBC without a custom pan or modifying a stock pan. Ive run blown SBC Donovans for years. Later years Donovans that are dry sumped, eliminated the pump shaft hole in the block and cap the reconfigured the stud layout so that a stock pan could be used without pan mods
     
  13. Dave B.
    Joined: Oct 1, 2009
    Posts: 225

    Dave B.
    Member

    OK... Bob can have his paranoid moments. The description on this part

    https://www.ebay.com/itm/163628352190
    leaves a lot of questions unanswered. Plus, the seller isn't responding to Bob's questions sent thru ebay. Bob wanted me to find out as much as I could without mentioning that the part was listed on ebay, in case that it was really a rare find. This meant that I had to get creative, which I don't like to do. So, no, the seller didn't misrepresent the part - he just didn't provide nearly enough information. Bob's been a good friend for many years, so I try to help whenever I can - it's just that sometimes I get myself into minor predicaments doing that.
     
  14. 1971BB427
    Joined: Mar 6, 2010
    Posts: 6,899

    1971BB427
    Member
    from Oregon

    Anyone building a engine who doesn't get it line bored is not building it correctly. No engine shop would ever build an engine without line boring, unless they checked everything and it was already perfect.
     
    COCONUTS likes this.
  15. anthony myrick
    Joined: Sep 4, 2009
    Posts: 8,107

    anthony myrick
    Member

    cranks usually broke before any main issues
     
    COCONUTS likes this.
  16. 55blacktie
    Joined: Aug 21, 2020
    Posts: 372

    55blacktie

    There is align boring and align honing. It shouldn't be necessary to align bore when using the original caps. Align boring likely necessary when the caps aren't original to the block. I can't help but wonder why, when I couldn't even give away two 283 blocks, one of which was a recently rebuilt short block. I ended up get $40 for scrap.

    If you insist on using the 283 block, I would use studs and girdle. Whenever you drill holes, you weaken it. You're better off getting a 4-bolt 350 block and using spacers that will allow you to use the 283 crank. you will then have a 302. Some of the 283 cranks were forged steel. The 283 block will have to be bored 0.125 to give you the 4-inch bore of a 302, 327, or 350. I would not suggest doing that unless you have it sonic checked first.

    Sounds like a costly undertaking/w little to gain.
     
    tractorguy likes this.
  17. anthony myrick
    Joined: Sep 4, 2009
    Posts: 8,107

    anthony myrick
    Member

    MILIDON Still lists the center caps for a 283/327 sj
     
    bowie likes this.
  18. anthony myrick
    Joined: Sep 4, 2009
    Posts: 8,107

    anthony myrick
    Member

    just loaded up a 283 in the truck at lunch, locked up but has power pack heads
    I have another one that was a freebie when a friend cleaned out his shop
    both are standard bore blocks
    may use one in the 56, who knows
    but if I was wanting HP the 350 is a much cheaper way to go
     
  19. squirrel
    Joined: Sep 23, 2004
    Posts: 49,265

    squirrel
    Member

    yes, it does. Most likely, the seller doesn't know anything about it....that's pretty common on ebay.

    The "368" thing is the number that is cast into the part, which is probably the last three digits of the casting number. I don't have any 4 bolt big blocks apart right now to look at, but I do have a 2 bolt sitting in my shop, and it has the number 367 cast into the rear main cap.
     
  20. I was going to suggest splayed 4 bolt caps. They are not expensive in the whole scheme of things and if you are building a monster they are the only way to go.

    I have built a ton of high revving 2 bolts motors over the years. Way more zot than anyone but Smokey Yunick will ever pull from a 283 and had them hold together just fine. Before I would bother sourcing 4 bolt caps and converting I would spend the bucks on a stud girdle if I wanted to stabilize the lower end.
     
    bowie likes this.
  21. DDDenny
    Joined: Feb 6, 2015
    Posts: 15,052

    DDDenny
    Member
    from oregon

    You may want to check this HAMB thread out and PM HAMB'r Nick Smithberg about this, although not on here often lately I'm sure you could call his shop.

    upload_2021-2-19_14-11-51.png

    https://www.jalopyjournal.com/forum/threads/breathing-life-into-a-283-jr-fuel-destined.1085889/

    https://www.smithbergracing.com/

     
    winduptoy and 402BOSSMAN like this.
  22. 402BOSSMAN
    Joined: Jul 26, 2015
    Posts: 343

    402BOSSMAN
    Member

    Guilty, been buried with work but I lurk once and awhile. Wish I had some time to get back to work on it. Heads work next!
     
    ottoman and winduptoy like this.

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