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Okay just want to check my stats and get some opinions.
Pulled apart the new engine block a bit and rough measured the cylinders with my calipers.
If I understand correctly the stock bore was 3.125 (I could not find the tolerance but I may be blind) The following are my numbers #1-4 front to back and side to side.
3.14 - 3.133
3.138 - 3.131
3.139 - 3.138
3.138 - 3.135
now for the opinions should I get it done to .015 over or 0.20 over? or can you only go 2 over? Also will I have to replace pistons or just rings?
As always tanks everyone

Are the pistons marked .010 that were in it? If so, and the pistons look good, I'd just lightly hone the cylinders and re-ring it. Or buy new 10 over pistons and hone it. The taper as I take your measurements is fine. Any discernable ridge at the top of the bores? bad pits or rust? John

TM 9-1804A Pages 121 & 124 cover the piston, rings and bore limits. You'll need to take a few more measurements starting with lower bore diameters.

The only marking on the pistons is front-> I have to clean things up a bit more and get a proper bore measuring tool. It was seized when I started but I have driven the pistons out without damaging anything.

As you can see here you need to get lower bore dimensions before making any decision on bore size. You are definately at least a .010 OS with the top measurements you have thus far provided. Rings and pistons are needed for OS.




I've seen OS pistons and rings as large as .080 OS. Have you measure piston wear yet?

I have not measured the pistons yet, there is a lot of build up over the rings that I need to take off to see the rings even. I will get them from at least one today though.

Have you taken the taper dimensions yet? If so post them. I always glass bead the pistons to clean them before dimension checks it does a better job on the ring lands and doesn't damage the piston. Do you have a copy of TM 9-1804A? If not download it free here on our downloads page.

Try to get your hands on a copy of the civvy jeep manual which gives much more detail on the L134 overhaul.

I have the pdf of the TM. I do not have the correct caliper to measure down in the bore at the moment. I have measured the #2 piston and I believe the engine was .010 over already.
Top of piston 3.122 X 3.120
Top of skirt 3.128 X 3.135
Bottom of skirt 3.130 X 3.135
so it needs replacing even if I was not going to rebore as they are more than 0.005 out of round.

That 0.005 out of round limits applies to the bore in the block not the piston.

If you look at page 123 in TM 9-1804A the piston diameter limits are taken only at 90 Deg's to the piston pin bore because the pistons were machined out of round new. Often referred to as cam ground. Your dimensions look like stock STD piston dimensions if you use page 123 wear limits.


Note the 0.005 piston to bore limit is the primary guide to when reboring and oversize pistons are needed.

You should be able to rent a dial bore indicator to check taper. I usually just haul my block and crank and pistons and cam to the engine machine shop and have them do the measurements with accurate tools.