258 to 4.0 flywheel question - JeepForum.com
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post #1 of 3 Old 09-16-2013, 07:18 PM Thread Starter
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1984 CJ7 
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Cj 258 to 4.0 flywheel question

First time posting but been reading the forum for a while. I am getting ready to swapping in a 4.0 that I rebuilt to replace my worn out 258 in my 84 CJ7. I will be using the
Hesco CPS kit so the tone ring will not be needed. The question I have is that I have a fresh resurfaced 258 flywheel that was given to me but has a worn ring gear, I also have the 4.0 starter that I would like to use. Has anybody installed a 4.0 ring gear on a 258 flywheel? Or will there be a spacing issue with the 4.0 starter on the flywheel.

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post #2 of 3 Old 10-19-2013, 09:38 PM
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1986 CJ7 
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Either set up can be used but the spacing is different. The flywheel must match the starter and vise-verse. The cost of putting a new ring gear on the 258 flywheel vs resurfacing the 4.0 flywheel is kinda a wash. Do one of the two. How you wire the 4.0 should also play into the decision. If using the 4.0 distribution power block and relays would be easier with the 4.0 starter and flywheel.

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post #3 of 3 Old 11-05-2013, 06:40 AM
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I haven't done that swap on my jeep but I have swapped ring gears on several Harley Evo Motors, They come stock with about 110 teeth or 102 teeth on the ring gear 'Don't remember' The starter gear is about ten or eleven teeth. If you build 9.5-1 compression or higher teeth brake off. So I have used parts 'ring gears & starter gears' from older Shovel Heads Much fewer teeth per inch - larger teeth in the same space.
I went with this theory, If the OD of the ring gear is the same on the two ring gears 'and it was' and the OD on the starter gear teeth was the same in each case, 'and it was' it would work, And it does. I have done this conversion on some very fast machines and have had perfect success in doing so.
In your case the starter must fit check the travel or throw of the gear Is it the same? Then the ring gear must match ID and OD to the pressure plate exactly. The gear pitch is already established just consider diameters and distances to be critical.
Good Luck
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