Re: [AMC-list] What Did You Do on Your AMC this weekend?

[Frank Swygert <farna@xxxxxxx>]

I've almost got my engine ready to put in. Just have to install the 
thermostat and put the belt and motor mounts back on. Then it's off the 
engine stand for the tranny, and back in the car. Might get that done 
Monday, will by the end of next week.

One thing I haven't mentioned -- the amount of wear in the stroker 
block. My 4.6L stroker had roughly 60K miles on it. It had been bored 
0.030" over. To clean up at 0.030" the machinist may have left a little 
extra clearance near the bottom of the bore. I say that because AMC 
recommended 0.0021" as the maximum piston to sidewall clearance all 
around (0.004" if you push the piston all the way to one side) on a new 
engine. That should be the same at the top and bottom of the bore. When 
I pulled my engine down it had just enough wear near the top to catch a 
fingernail. With the rings off the piston I could easily slip a 0.018" 
feeler gauge beside the piston near the bottom. That was a FLAT feeler 
gauge, so it had close to 0.030" wear near the bottom. I wouldn't think 
much about that on an engine with well over 100K on it, but it seems 
excessive for a 60K engine. When stroking the 4.0L with a 258 crank and 
rods the piston skirt comes out of the bore a good bit on the bottom, 
the bottom of the bore is just a bit lower than the wrist pin. IIRC the 
bottom edge of the wrist pin is just about even with the bottom of the 
bore. This probably causes a bit more wear than the shorter stroke 4.0L 
crank. There is 0.44" stroke difference between a 258 and 4.0L crank, so 
the piston moves 0.22" lower in the bore than the 4.0L piston does. This 
makes me suspect that the bore in the 258 block is a bit lower than the 
4.0L block. The longer stroke obviously causes a bit more side to side 
wear. This isn't a big problem for a hobby engine, but for a driver that 
is going to get a lot of miles it may be. The 4.0L rod is a bit longer 
than the 258 rod and would probably work better, not bringing the piston 
quite as close to the bottom of the bore. Of course shorter pin height 
pistons are needed, but those are now available. Not cheap, but readily 
available. For longevity that's probably the way to go. My engine had 
been run hot four times since it was built in late 1999 due to electric 
fan issues. I tore it down thinking I could just re-ring it at ~60K 
miles. I might be off by as much as 10K miles (70K total), but even then 
there is still more wear than I expected by a factor of two.

--
Frank Swygert
Publisher, "American Motors Cars"
Magazine (AMC)
For all AMC enthusiasts
http://www.amc-mag.com
(free download available!)

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