ARareBreed Posted December 21, 2017 Share Posted December 21, 2017 I have a 1991 4.0ho eliminator and plan on tackling an engine rebuild next month. I'm going to drop the pan, again...(I replaced the rear main seal last winter) and need a new head gasket anyway. While I'm in there I'd like to replace the rings as shes burning more oil than I'd like. Is there a "tool of the trade way" to determine what size rings to get? I'd obviously like to get them in advance but I head rumors that back in the early 90's Jeep wasn't the most consistent with their assembly process. I do not want to get the wrong ring size. Also, does anyone have any leads on a good brand to buy? Link to comment Share on other sites More sharing options...
cody4359 Posted December 21, 2017 Share Posted December 21, 2017 more than likely standard bore if it hasn't been touched. pull the head and put a inside mic down there to be sure. I just put mahle or whatever they are called in, no file to fitSent from my SM-G900V using Tapatalk Link to comment Share on other sites More sharing options...
sinkrun Posted December 21, 2017 Share Posted December 21, 2017 Might as well do Rod bearings there cheap and you will have them out also oil pump. You can ROLL new main bearings in also if you feel up to it theres some videos on you tube. Link to comment Share on other sites More sharing options...
Eagle Posted December 21, 2017 Share Posted December 21, 2017 There's an assembly code stamped on the side of the block, near the distributor. Next to the distributor there's a boss with a recessed, square drive plug in it. If there are any non-standard rings or bearings needed, there will be one or more letters stamped on that boss. The following are from the 1994 FSM, but I think they should be the same for 1991: P = One or more rod bearings 0.010 undersize M = All crank bearings 0.010 undersize PM = All crank bearings and one or more rod bearings 0.010 undersize B = All cylinder bores 0.010 oversize C = All camshaft bearings 0.010 oversize Link to comment Share on other sites More sharing options...
ARareBreed Posted December 22, 2017 Author Share Posted December 22, 2017 4 hours ago, sinkrun said: Might as well do Rod bearings there cheap and you will have them out also oil pump. You can ROLL new main bearings in also if you feel up to it theres some videos on you tube. Won't I need to machine the crank if I change the rod bearings? Link to comment Share on other sites More sharing options...
ARareBreed Posted December 22, 2017 Author Share Posted December 22, 2017 3 hours ago, Eagle said: There's an assembly code stamped on the side of the block, near the distributor. Next to the distributor there's a boss with a recessed, square drive plug in it. If there are any non-standard rings or bearings needed, there will be one or more letters stamped on that boss. The following are from the 1994 FSM, but I think they should be the same for 1991: P = One or more rod bearings 0.010 undersize M = All crank bearings 0.010 undersize PM = All crank bearings and one or more rod bearings 0.010 undersize B = All cylinder bores 0.010 oversize C = All camshaft bearings 0.010 oversize Man, you're a wealth of knowledge. I'll check that out. Thank you. Edit: Found it has 012MX14 The 1's literally look like the capital letter i, but I assume they're 1's. So it's safe to say my piston bore issss, what? Link to comment Share on other sites More sharing options...
sinkrun Posted December 22, 2017 Share Posted December 22, 2017 2 hours ago, ARareBreed said: Won't I need to machine the crank if I change the rod bearings? Not as long as its not knocking or rapping you will need to know the size for sure. There is a book on rebuilding a jeep 4.0 thats really nice that can be had for about $25.00 on ebay or elsewhere thats what I used on my first one well worth the money. Link to comment Share on other sites More sharing options...
Eagle Posted December 23, 2017 Share Posted December 23, 2017 22 hours ago, ARareBreed said: Won't I need to machine the crank if I change the rod bearings? Not if the crank journals aren't scored. Link to comment Share on other sites More sharing options...
Eagle Posted December 23, 2017 Share Posted December 23, 2017 22 hours ago, ARareBreed said: Man, you're a wealth of knowledge. I'll check that out. Thank you. Edit: Found it has 012MX14 The 1's literally look like the capital letter i, but I assume they're 1's. So it's safe to say my piston bore issss, what? That sounds like the build date code, not the bearing size code. The boss with the bearing info isn't big enough to hold all those characters. The date code is in a flat, machined rectangle on the surface of the block. The bearing codes (if any) are on a raised boss, behind the distributor, near the oil filter adapter, that has a recessed, square-drive plug in it. If the boss doesn't have any letter codes, all your bearings and rings are standard. And the codes are the same for 1990 as they are for 1994, so probably good for all years. Link to comment Share on other sites More sharing options...
Eagle Posted December 23, 2017 Share Posted December 23, 2017 From the 1990 FSM this time: Link to comment Share on other sites More sharing options...
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