Author Topic: S Crank Interchange  (Read 542 times)

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Offline Boss9kid

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S Crank Interchange
« on: December 04, 2018, 01:54:10 pm »
Can an "S" crank be used in a "T" engine with "T" rods if the crank is balanced properly? Or is the rod journal width different?

Offline RmK57

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Re: S Crank Interchange
« Reply #1 on: December 06, 2018, 04:32:09 pm »
Did a quick search on the 429-460 site and found this......

You are describing "T" Boss 429 parts ( with exception to the DO rods, however they are direct replacements for the c9 parts) The cranks for the "s" and "T" engines are the same forgings except for balancing , the "S" engine used shorter 6.549" center to center distance rods as compared to the 6.605 "T" engines. Nice parts! The Nascar engine has a totally different crank and rod setup. They are a full 1" wide at the big end and use .04 wider rod bearings, have a c-c distance of 6.785" and the crank has threaded cleanout plugs instead of pressed in cups.

Offline ed meyer

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Re: S Crank Interchange
« Reply #2 on: December 06, 2018, 10:13:02 pm »
If anybody needs the spacer that goes on the early s cranks i had some made at machine shop let me know.

Offline Boss9kid

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Re: S Crank Interchange
« Reply #3 on: December 07, 2018, 01:36:06 pm »
Okay and if I balance the assembly, C9AE-B rods and pistons to a C9AE-A crank, the weight of the crank should pretty much match that of a "T" motor crank as long as the balancing was done correctly, right? I just want to be sure I'm not going to end up with a heavier crank than I should have. By the way, my crank has the threaded cleanout plugs and spacer.

Offline pbf777

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Re: S Crank Interchange
« Reply #4 on: December 08, 2018, 09:01:58 am »
       Assuming that the original crankshaft forgings were the same, and that the only machining differences were for the different balance values, then re-balancing for the intended bob-weight would present an acceptable unit.  It's generally easier (cheaper) to start with a crankshaft previously balanced for a heaver value and reduce it than the inverse.  I'm not sure whether the counter weights for the cranks utilizing the shorter rods are reduced in diameter to permit clearance, or some other profile difference, but I would sure check it. And even if the counter weights & webbing were perhaps a little "fatter" to present the necessary values, perhaps leading to a heavier overall weight, this would present no real issue (lets not get to deep here), any more than a flywheel and/or clutch assembly of more or less weight difference of the same value.     ;)

     Scott.

Offline Boss9kid

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Re: S Crank Interchange
« Reply #5 on: December 10, 2018, 08:02:29 am »
Okay, thanks!

Offline KK1826

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Re: S Crank Interchange
« Reply #6 on: December 11, 2018, 08:25:27 pm »
but why do this ????

Offline JohnSlack

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Re: S Crank Interchange
« Reply #7 on: December 12, 2018, 03:40:49 pm »
but why do this ????

Plus one, just get the easier to aquire "T" crankshaft.
John
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Offline Boss9kid

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Re: S Crank Interchange
« Reply #8 on: December 17, 2018, 02:49:13 pm »
I already have a useable "S" crank I don't have a "T" crank.

Offline pbf777

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Re: S Crank Interchange
« Reply #9 on: December 17, 2018, 03:28:58 pm »
     Since you possess the "S" crankshaft, first measure the rod-journal widths, and compare to your rod widths, establishing the difference, which equates to the rod side clearance sums,...........is it reasonable?       :-\

     Scott.

Offline Boss9kid

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Re: S Crank Interchange
« Reply #10 on: Today at 12:44:43 am »
I did check the side clearance and it appears to be okay. I used to think that S motors had different rod bearings, maybe they are indexed differently on the S motors than the T?