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Unread 02-27-2010, 06:12 PM   #1
flashfludjr
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To rebuild or not to rebuild?

I am in the middle of doing a 4.0 swap into mt 81 cj5. I have the 4.0 on a motor stand and had plans of rebuilding it. I have it all tore down and was looking in the cylinders. I can still see the factory cross hatching on the cylinder walls. all the rod bearing dont have any play in them. should I rebuild it anyway just to be safe? the donor cherokee had 160,000 miles and ran fine. I dont want to do the stroker yet im just getting the 4.0 in and ready to go for the summer. Maybe take my time and build a stroker while I can still run the jeep. any thoughts? advice?

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Unread 02-27-2010, 06:19 PM   #2
CjAl
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just roll in a new set of rod and main bearings and put some new rings in it. You can check the cylenders to see if they are ovaled out, if they are not an are withing spec then it doesn't need to be bored just run a hone through it.
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Unread 02-27-2010, 06:35 PM   #3
flashfludjr
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yeah thats what I had planned. I have a set of bearings and rings on the way. only cost me $40. so it seems worth it. any idea what the specs for the cylinders are?
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Unread 02-27-2010, 06:47 PM   #4
CjAl
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I don't know them for that motor but any repair manual should have them. You may want to consider a slightly warmer cam too while your at it
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Unread 02-27-2010, 06:49 PM   #5
Cutlass327
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I'd think that if you can still see the crosshatch, the cylinders would have very minimal wear at all. A bottlebrush hone, new rings, and new bearings would be just fine.
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Unread 02-27-2010, 07:33 PM   #6
CjAl
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the cross hatch is why I said just rings and bearings too. I just said the rest to C.M.A lol

that's pretty good to have cross hatches with 160k miles. makes me wonder if the motor has been redone. is there a .30 or .40 or anything ,stamped in the top of the pistons?
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Unread 02-27-2010, 07:49 PM   #7
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When I had my AMC 360 rebuilt the pistons had .020 stamped on the top. Also.. the back of the bearings are date stamped. If I were you I'd take it to a machine shop while you have it out of the vehicle and have them hot tank it and check it over. That way if it is in great shape you'll know for sure and if something needs to be done they can do it.
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Unread 02-27-2010, 07:52 PM   #8
flashfludjr
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no they just say FRT with an arrow then 50 meaning that side of the piston goes forward but what is the 50? im gonna try and load some pictures so you can see
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Unread 02-27-2010, 08:00 PM   #9
flashfludjr
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I would send it to a shop but I am on a very limited budget. anyone know how to post pictures? let me know and Ill put some up of the cross hatching and the top of the pistons
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Unread 02-27-2010, 08:11 PM   #10
CjAl
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upload them to phtobucket the copy the direct address link. come here and click on the little mountain post card looking thing on the toolbar of the message box and paste the address into the box that pops up
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Unread 02-27-2010, 08:14 PM   #11
CjAl
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it could be the block has already been bored out .050" inch. that's kind of an odd oversize but they could do it.

you need to know the size of the bore to be able to get the right size rings. You also need to know if the bearings are oversize. if they are they will be stamped .010 or .020 etc.
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Unread 02-27-2010, 08:26 PM   #12
flashfludjr
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Unread 02-27-2010, 08:29 PM   #13
flashfludjr
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well i just figure that if this motor has been gone through already I'll just leave it. clean everything up paint it and run it. its only a summer rig and doesnt get ran that often. just my toy.
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Unread 02-27-2010, 10:05 PM   #14
only in a jeep cj
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Yep, thats a recent rebuild of 50 over. I'd clean it and make sure everything goes back just as it was. Paint it and go. You should be good.
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Unread 02-27-2010, 10:06 PM   #15
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That cross hatching looks pretty deep.. maybe done by hand with one of those power drill dealies.

If you don't want to dump a ton of cash in it.. just do a "poor man's rebuild" by replacing all the gaskets. Did you take a look at the back of the bearings to see if the year matches the year of the vehicle?

I still vote for a machine shop drop off just for a hot tanking and inspection... It would suck to get everything back in the vehicle after all that work (and a spendy gasket kit) for it to crap out after a few thousand miles. Tell them this is a mega budget motor and they will only do the things that ABSOLUTELY need to be done.. if anything.

If it was recently machined then at least you'll know that it's still in spec. I mean we are only talking maybe $100 for the hot tank + inspection.
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