83 crank vers 84-88 cranks

[ditdit]

what is the differences between the 79-83 cranks and the 84-88 cranks  258 cu in I have been told the 84-88 crank is the one to put in a 4.0 to increase its cu in


thanks

[eaglefreek]

My guess is 12 counter weights vs 4 counter weights. 

[carnuck]

The crank length is different. You can use a 10mm spacer to make up the difference to push the 4.0L balancer all the way on. Early cranks are heavier ('72 till around '79. You DON'T want a '71 crank because the flange is oddball and won't take a newer flywheel) Then '79 till @'81 (last of the tin valvecover motors and the first plastic cover motors) were lightened a bit. Serpentine belt motors ('84-'90 4.2L also used in YJs) were the lightest with fewest balance weights.

Lighter crank makes for faster revving, more for racing than offroad where the heavier crank helps keep you from stalling when lugging over obstacles.

[eaglefreek]

I was thinking about it and had to search. The short snout didn't show up until 87.   All cranks from 81-90 were 4 cw.
http://www.jeepstrokers.com/forum/viewtopic.php?f=34&t=51

Year_____Crank Casting No._Part No.
1971_____3199738________4488665 For Borg Warner automatic, small pilot
1972-74__3214723________8120508 12 counterweights, 66lb, 64mm nose
1975-79__3214723________8125450 12 counterweights, 66lb, 64mm nose
1980_____3214723________8132619 12 counterweights, 66lb, 64mm nose
1981-86__3235477________3235444 4 counterweights, 46lb, 64mm nose
1987-90__3727___________53005535 4 counterweights, 46lb, 54mm nose

[captspillane]

There was a rumored difference between Jtruck 258s and passenger car 258s. By those casting numbers the 258 in my 1980 J10 is the same as my 1980 Eagle.

Did you see any reference to J-trucks being different in your research?

[eaglefreek]

There was a rumored difference between Jtruck 258s and passenger car 258s. By those casting numbers the 258 in my 1980 J10 is the same as my 1980 Eagle.

Did you see any reference to J-trucks being different in your research?

I didn't look for that and don't recall seeing anything.

[carnuck]

The crank in my '84 Eagle wagon with factory serpentine belt was the short one.  I discovered the difference when I went to put the Eagle motor in my Jeep J10 (full size). The blocks changed in '80 (added the casting for the axle hanger) and were lightened up (along with the head) @81 when they did away with the tin valvecover. My '83 wagon had a Mexican 282 in it from a CJ that I put into my '83 Cherokee full size. (had some fun with that but I didn't know it was the bigger motor at the time)

[amcfool1]

hi, btw, the controversy about earlier cranks being stronger than 81/up cranks may be put to rest. The earlier cranks were Heavier, not necessarily stronger. this made for a smooth motor at low rpms. I did that. In my first Eagle build, in 2000, I got an 80 Spirit block, btw, the ONLY block that will fit both 2wd/4wd  cars, and mated it to a 82 head, for my 82 Eagle. Not easy, had to enlarge the 7/16 head holes to 1/2 inch for the 80 block, then find workable headbolts (Ford BB) then do the SBC valve conversion. then...it ran without a hitch for 15 years. My new motor is all 84, meaning the "lighter" crank. I expect the same.long story short, don't worry about the differences in crank strength, these motors done right will probably outlast the cars they're in. good luck, gz