Alexander Posted April 2, 2017 Report Share Posted April 2, 2017 Hi Folks! While changing out the rear main seal, I noticed some scoring on the rear main bearing. Crank seems ok for the most part and should clean up with 2000 paper. Measuring the rear main bearing with plastigage shows .003 clearance. Checking the shop manual seems to suggests I am still in spec? Would you agree? I am not ready to do a full rebuild at this time but would like to possibly refresh the bottom end by replacing all the bearings. Is that ok to do? If so how do you determine the current size bearings without measuring the crank? The current bearing is marked x10. (see attached pictures). Does that mean standard? My oil presure has always been poor (10 at hot idle). I am seeking the boards advise and possible direction. Thanks! Alexander Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted April 2, 2017 Report Share Posted April 2, 2017 actually...the main consideration is check the journal for out of round by mic'ing ever 30 degrees or so and see if there is any egg in the mix. Ma Mopar in the day made these replacement bearing inserts in undersize for just such type of refreshing. I would have to search it out but my memory tends to think they were available in .001, .002 and .003 undersize. 1 Quote Link to comment Share on other sites More sharing options...
Alexander Posted April 2, 2017 Author Report Share Posted April 2, 2017 This project can quickly snow ball :-( I Don't want to take out the crank to mic anything out. Short of put it all back together and calling it a day, what off the shelf shortcut can I take to give this old girl a quick refresher? Thanks, Alex Quote Link to comment Share on other sites More sharing options...
55 Fargo Posted April 2, 2017 Report Share Posted April 2, 2017 Why not do a bearing freshen up. Might get you a lot of use before a full rebuild. Some will tell you it's best to do the rebuild now and most likely that is the best. You and your pocket book can decide. How about the top end rings and valves? Whichever way you proceed please post your progress along the way. That will be a point of reference and info for others. Quote Link to comment Share on other sites More sharing options...
Mike36 Posted April 2, 2017 Report Share Posted April 2, 2017 If you are not going to remove the crank to mic it, carefully check it with plastigage, then give crank a 1/4 turn and check it again. This will give you an idea if the crank is out of round. If it is out of round, I would not run this engine until a total rebuild is possible. You are in danger of destroying the block if you do. It might run a year, or it might run one more day. Do you feel lucky? If not out of round, check shop manual for clearance recommdations and go for it. Use assembly grease, and clean out pickup for oil pump. What weight oil are you using? Pressure may come up with new bearings, if not go to a heavier weight oil and stay away from higher RPM. If you do not have a shop manual, that is your first step! Get one! Good luck and keep us posted. 1 Quote Link to comment Share on other sites More sharing options...
dpollo Posted April 2, 2017 Report Share Posted April 2, 2017 It is a good bet that the bearing shown is .010 undersize and I would say it has significant wear. I would be inclined to install two new rear main shells and check the clearance with plastigage. 002 would be ideal. It is an old trick to put 001 or 002 shim stock behind the lower shell to take up clearance BUT if you do only the rear main, you will be creating a misalignment problem which will work itself out by pounding the bearing harder than it may be able to survive. If you do not want to spend any money on this engine just put it back together. The bearing shell you show is worn but shows no signs of impending failure. I would also check #2 and #3 mains as they can take a beating. #1 is lightly loaded and is more difficult to access because of the arch that forms the front pan rail. When plastigaging a crankshaft in the car, you must support its weight or you will get a false reading. 2 Quote Link to comment Share on other sites More sharing options...
ptwothree Posted April 3, 2017 Report Share Posted April 3, 2017 You could also use a dial indicator to determine run out and rotate the crank by hand..pull the spark plugs to make things easier. 1 Quote Link to comment Share on other sites More sharing options...
Alexander Posted April 3, 2017 Author Report Share Posted April 3, 2017 Thanks gentlemen! All great feedback. The more I read about this the more I realize, the time has come for a total rebuild. However its just not the right time right now. I have a few scheduled car events coming up that I cant miss. Perhaps I should just put it all back together and do a full rebuild over the Fall season. I need the car to do another 300-400 miles this year before can commit to a total rebuild. I hope she can do it? Ill keep you posted as this develops. Thanks! Quote Link to comment Share on other sites More sharing options...
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