Engine Balance

[Bent]

Really? I was under the impression that the 71-86 AMC 258 i6 / 4.2l all had the same 64mm snout. From what I can tell, since they are stroking 4.0s which have the short snout, they use a spacer to take up the extra 10mm. For me the issue is the difference between a AMC 258 i6 / 4.2l with a long snout vs a short snout. Are the cranks interchangeable between the two?

I'm thinking the old AMC 258 i6 / 4.2l cranks and the newer AMC 258 i6 / 4.2l and 4.0 cranks were short and mid 80s AMC motors with the serpentine set-up had the long snout. So the spacer would be for using a long snout crank with the V belt pulleys or the 4.0 serpentine belt. I may be wrong. I never looked into it in as much depth as you need to.
Please post your findings.

 

[mtnwhlr]

Really? I was under the impression that the 71-86 AMC 258 i6 / 4.2l all had the same 64mm snout. From what I can tell, since they are stroking 4.0s which have the short snout, they use a spacer to take up the extra 10mm. For me the issue is the difference between a AMC 258 i6 / 4.2l with a long snout vs a short snout. Are the cranks interchangeable between the two?

If the difference is only 10mm I would think a machine shop could mill 10mm off the front of a crank.

 

[Tophipe]

If the difference is only 10mm I would think a machine shop could mill 10mm off the front of a crank.

Since the stock one has 64mm and the new one is 54mm it wont be 10mm too long but 10 too short. About the radius of a penny too short. I'm not sure how the pulley/balancer setup is different on the years of the cjs so I'm not sure where that extra space fits into the equation.

 

[Bent]

Since the stock one has 64mm and the new one is 54mm it wont be 10mm too long but 10 too short. About the radius of a penny too short. I'm not sure how the pulley/balancer setup is different on the years of the cjs so I'm not sure where that extra space fits into the equation.

I was thinking you had a short nose crank. So your jeep has a serpentine belt? If it is maybe look into a 4.0 crank pulley and dampener to use on a short nose crank. If you have v belts maybe look into an older set.

 

[Tophipe]

I was thinking you had a short nose crank. So your jeep has a serpentine belt? If it is maybe look into a 4.0 crank pulley and dampener to use on a short nose crank. If you have v belts maybe look into an older set.

I have the serpentine belt but only because it's a california CJ7 . All other states at the time had the vbelts. So maybe I do have the short nose crank. I was under the impression that they didn't even start manufacturing the short nose crank until 1987 though, or am I mistaken?

 

[Bent]

More likely I'm mistaken. I don't think AMC would make two different cranks for the same year. Maybe they did switch when Chrysler took over. I look forward to finding out.