Corey W. 1275 Race Motor Build

Discussion in 'Classic Mini' started by Minidave, May 24, 2022.

  1. Minidave

    Minidave Well-Known Member
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    Dec 22, 2009
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    Just getting started on this build.

    I have a 12 page "guide" I'm following from Kent Prather at Prather Racing Engines, lots and lots of little steps to do and document.

    First thing we did after ordering in a bunch of expensive race parts (rods were $1200 the set - spared no expense!) was to get it over to the machine shop to have it rough bored, so I can dry build the engine with the new pistons and take a bunch of measurements - such as how much to take off the deck so we can get the 14:1 compression ratio he wants (!) and whether we'll need to flycut the pistons to make clearance for the valves.

    IMG_20220524_152205R.jpg

    IMG_20220524_152213R.jpg


    Also, #1 cylinder was scored on one side from the pin getting loose and rubbing on the cylinder walls, to get past that issue we had to offset the bore by 4 thou, but it cleaned up nicely so we'll be good there.

    I now have the block mounted up in the engine stand so I can do that and a thousand other little tasks. Once we're happy with all that I'll take it back to the machine shop so they can bore and tap for the extra end studs and finish hone the cylinders among other things. We had thought we were going to do a 4 bolt center main cap, which would have required a line bore, but Kent thinks for the racing Corey does the stock mains will be fine. Plus too and also, I couldn't find anyone who had a small enough boring bar to do it! Or anyone who could even look at it in less than 6 months. I don't have access to mills and lathes and such, and we're trying to make a race mid July (very unlikely, but we'll see!)

    IMG_20220524_145949R.jpg

    IMG_20220524_150038R.jpg

    I have over 90% of the parts we'll need and an owner who's willing to spend whatever it needs to make it fast - we're shooting for 150 hp at the crank!

    The head is all done, ports matched, combustion chambers reshaped and some trick 1.5 roller rockers fitted. It's also will be drilled for the end studs, I could probably do that myself, but Ima let the machine shop have at it and tap the block too.

    IMG_20220524_152217R.jpg

    IMG_20220524_152310R.jpg
     
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  2. 00Mini

    00Mini Well-Known Member

    Feb 24, 2013
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    This is going to be one impressive build.
     
  3. Minidave

    Minidave Well-Known Member
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    Dec 22, 2009
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    Nah, they're all alike.....:p

    Yes, should go really fast and make great noises!

    If I can get it built in time - gonna be tough - we'll get it on the dyno for a proper break in and I'll get some video.
     
  4. 00Mini

    00Mini Well-Known Member

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    What’s this engine going to call home ??
     
  5. old81

    old81 Club Coordinator
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    Used to work making computers run fast!
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    Nice shiney bits should make some good power with the proper hand putting it all together, wow love when someone get to play with nice bits. :)
     
  6. Minidave

    Minidave Well-Known Member
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    #6 Minidave, May 25, 2022
    Last edited: May 25, 2022
    It will live in a Bugeye racecar.....#89 in the pic below.


    imagejpeg_0.jpg
     
  7. Minidave

    Minidave Well-Known Member
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    Dec 22, 2009
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    Measuring for thrust clearance.....right now I have zero, tho the crank turns freely (so there must be some) I've noticed I have to machine a few thou off the thrust washers on every build these days - doesn't matter who supplies them. It's a PITA but you need 3-4 thou clearance.....

    IMG_20220526_111325R.jpg
     
  8. Minidave

    Minidave Well-Known Member
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    Oil gallery tapped for threaded plugs, also tapped a hole for a breather vent where the fuel pump would go on earlier versions of this engine. Later ones like this used an electric fuel pump so the boss is a perfect place to put a breather.

    IMG_20220528_125041R.jpg
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    I also marked the block so we can drill and tap for two more cylinder head studs - I'll let the machine shop do this on their mill so they'll be both accurate and square to the deck. IMG_20220528_125633R.jpg


    Speaking of the deck, I measured 37 thou from the piston to the deck, so we'll be taking 32 thou off to help with compression ratio.

    I didn't do the cylinder head, so I don't know yet what the chamber cc is, till I get that I won't cut it down any. I also need to figure out how much clearance there is for the valves, and whether we'll need to flycut the top of the piston. We don't have a ton of extra metal on top, so this could get interesting.

    The pistons and rods are marked and assembled, although I still have one or two more small mods to do to them before they go to be balanced.

    IMG_20220528_125056R.jpg

    The rotating assembly will go to Kent's shop so he can balance everything, once it's all back from the various machine shops it will be time to put it together and make some noise!
     
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  9. Minidave

    Minidave Well-Known Member
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    Dec 22, 2009
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    I've decided to turn this one back over to Kent Prather Racing, it required work that I don't have the proper tooling or instrumentation to do.....
     
  10. 00Mini

    00Mini Well-Known Member

    Feb 24, 2013
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    I was looking forward to hearing this engine on your stand but understand you have to what’s best for the owner.
     

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