Re: [AMC-list] 258/242 questions

[Frank Swygert <farna@xxxxxxx>]

As far as bearings and caps the bottom ends of the older six is identical to the 4.0L, thrust ("stress") bearings are in the same position. Wrist pins are the same -- use the ones with the pistons. 

I'm assuming you have the proper oversize pistons? Even with zero wear at the top you MUST check wear at the bottom of the cylinder. These relatively long stroke sixes wear more at the bottom than top. I've seen absolutely NO wear in the top and 0.010-0.015 wear in the bottom. Usually there is a barely visible/"feelable" (barely catch with fingernail) ridge at the top (0.002-0.008" wear) at the top and 0.015-0.020" at the bottom. That needs to be bored before putting pistons in. 

The raised "dot" is the front side indicator. The caps may be marked on one side for position. If not DO SO!! Use a punch and make 1-5 dots on the center mains -- maybe first too, but the thrust cap and rear main cap should be obvious. The thrust cap needs marking to keep it turned correctly though. Put matching dots along the same side on the flat near the cap so the sides match as well. 

You can't mix the caps in position (lengthwise or side to side)!! The block was finish bored (line bored) with the caps in position so they match ONLY in that same position. If you've removed them and they weren't marked you have to visually put them in then plastigauge the bearings and move them until clearances are all the same (or VERY close). You may not be able to turn the crank by hand even just in the mains if the caps are mixed up, especially turned side to side. If it doesn't spin by hand (will be hard to turn by hand with no pulley or flywheel, but should turn) then one or more caps may be mixed up (without plastigauge installed -- that tightens it considerably!). Caps used to be stamped from the factory with numbers, then you used the raised dots to get them turned right. Newer engines still have the dots but may not have a stamped (or on real old ones cast in) number. Punch and dots is easy!

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Date: Mon, 1 Mar 2010 18:41:55 -0800 (PST)
From: russ hathaway <russh97309@xxxxxxxxx>

I have a couple of questions on putting a 258 bottom into a 4.0 Jeep.
I have a 75 '258 and pulled the bottom. I will yank the slugs off the rods and I already have the 4.o pistons. What wrist pin do I use, or does it matter?
The crank nestled right down on the bearings nicely and I plastigauged everything, looks good. The Jeep main caps don't have an arrow on them to point north, but they do have a little bump on one side of the cap, is this the foreward locating indicator instead of arrows, like AMC has done forever.
Lastly, is the number three cap the "stress" cap like the 238 (sorry, I can't remember the proper term for it right now, I just got off work and it was one of those days when everything went wrong in the shop). The one main has an imprint of a "stress" bearing but I stripped this engine about 2 years ago and never got around to it.

--
Frank Swygert
Publisher, "American Motors Cars" 
Magazine (AMC)
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