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Old 12-27-2014, 11:58 AM
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Fabrokoner's Avatar
Join Date: Apr 2013
Location: Plymouth, CT
Posts: 384
4.2 Engine replacement

Hello all. I have a 1990 wrangler with the 4.2 motor and the tf999 automatic transmission. My motor is on its last leg. I found a good 4.2 close by but it has a BA10 transmission attached.

Will this motor bolt up to my TF999 or will need to replace the flexplate or something?

Thanks in advancefor any info!

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Old 01-17-2015, 09:00 AM   #2
harleydragon's Avatar
Join Date: Jul 2012
Location: south georgia
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should bolt up fine

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Old 01-19-2015, 07:50 AM
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Join Date: Apr 2013
Location: Plymouth, CT
Posts: 384
Sorry I forgot to update this thread. Also had meant to put it in the YJ section but oh well. It pertains to CJs with the 258 as well.

For anyone who finds this thread in the future. Yes it did bolt up fine but I had to move a few things.

The BA-10 is a manual transmission which requires a clutch and flywheel assembly. The TF-999 is an automatic which has a flexplate and torque converter.

You will need to move the flexplate from the old motor over to the new one. You should also inspect the flexplate for stress cracks around the four bolt holes that mount it to the torque converter as well as the teeth around the edge where the starter engages.

Mine had cracks when I got it out and I already knew the starter teeth were chewed up. I had a new one waiting to go in, cost about $60 on amazon. I wish I had replaced my torque converter too while I was in there.

Also make sure you keep the shorter bolts with the flexplate and the longer bolts with the flywheel.

The one major surprise was, I forgot to account for was the fact that my new motor came with a MC2100 carb but has no provisions for a kickdown cable. I'm in the process of monkeying with some of the brackets that were on my previous Weber setup to get my kick down going.
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