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Joined: Oct 2009
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Joined: Oct 2009
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Going through my part boxes and I came across a box of six nice rod bearings in Mopar part boxes, 3967 B 001. So I am guessing .001 under. I am not sure how I came to acquire them but any chance someone knows what these bearings are for? Would like to find a home for them as all I have are inline Chevy motors.
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Joined: Oct 2007
Posts: 5,017 Likes: 47
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I don't know about the ones you have but if I remember correctly the Hudson rod swap into a GMC requires the narrowing of the rods and the use of Mopar rod bearings.
"I wonder if God created man because he was disappointed in the monkey?" Mark Twain
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Joined: Jan 2005
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For those not familiar with a prior thread: a 292 (Gen-3) L6 connecting rod can be used to offset grind a 235/261 crank throw by reducing the journal diameter eccentrically from 2.311" (stock) to 2.100" (292), giving approximately 3/16" more stroke. The same technique can be used on the G.M.C. 2.311" crank throw, reduced to the Hudson & Chrysler 25" L6 2.125" pin size. In both cases the new rod length greatly affect the piston's compression distance and final deck height, the 6.76" 292 rod is shorter than the 6.8125" original (total change with 3/16" stroke added: -.04125"), the Hudson at 8.125" is far is longer than the original 7.000" (total change with 3/16" stroke added: +1.219"). The Chrysler rod was made in 3 lengths: 7.750", 7.875", & 8.000". Also possible: Pontiac 239" L6 at 7.5625".
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Joined: Dec 2018
Posts: 6
Active BB Member
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Active BB Member
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So on the GMC with a Hudson rod you need to grind down to the Hudson 2.125 pin size. We can assume your GMC crank isnt perfect, so say you have a 2.300 dia to work with. To get to a 2.125 you can offset grind to (2.300-2.125)/2 = 0.0875 extra stroke. SO you go from a 7" to 8.125" rod gaining 1.125 plus the 0.0875" stroke gives 1.2125" higher pin height. Original Comperession height of 2.359 gets reduced to 1.1465...starting to look like a modern piston.
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Joined: Jan 2005
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offset grind to (2.300-2.125) = 0.175 extra stroke
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Joined: Oct 2007
Posts: 5,017 Likes: 47
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Great information , thanks. What is the wrist pin size on the Hudson rod? With a 4" bore (302) would any off the shelf pistons come close even with not doing the off set grind? Bore the piston to fit the rod or bush the rod?
"I wonder if God created man because he was disappointed in the monkey?" Mark Twain
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Joined: Oct 2007
Posts: 5,017 Likes: 47
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That is really good information. Great pictures. Thanks for keeping this going!
"I wonder if God created man because he was disappointed in the monkey?" Mark Twain
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