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Northstar Engines and System Technical Discussion Discussion, Main Bearing pics in Cadillac Engine Technical Discussion; After getting a new oil manifold I opted to go for the case 1/2 seals too. Here are some pics ...
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    Main Bearing pics

    After getting a new oil manifold I opted to go for the case 1/2 seals too. Here are some pics of the bearings, I don't think they look to bad for 137K, but the new ones are $50 a pr. and that is definitely outta the question at this point in time. The bearing surface is still completely smooth.
    I can't believe how sweet the timing chains and tensioners look, almost like brand new. I did a visual on the bores as much as I could and the crosshatch is still very visible.
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    Re: Main Bearing pics

    The bearings look fine. All you are seeing is some marking of the overplate on the bearing surface. It is only a few microns thick so it marks easily and typically will look like that just after breakin. Pretty good main bearing life to look like that this far along, eh...???

    The mains can be reused but the rod bearings CANNOT be reused. If you disturbed or dissassembled any of the rod bearings to look at them or inspect them you have to replace them or they will fail later. The crush used in the rod bearings make them a throwaway if they are torqued into the rods and the engine is run and thermocycled. Hopefully you did not take any rods apart.

    Put the LCC(lower crank case) back on with the new seals and the red, anearobic sealer along the sides of the joint outside of the LCC seals. The anearobic sealant is really redundant but does help make the joint totally dry. Use a dab of RTV at the rear main seal where it contacts the LCC side seals. One hint for an easier reassembly is to slide the rear main seal onto the crank, put the dabs of RTV at the side seal intersection and then install the LCC with the rear main seal already in place. Otherwise you will have to use the special installation tool to seat the rear main seal as it is a press fit.

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    Re: Main Bearing pics

    bbobnski, the crush on the rod bearings is why I always cringed at the idea of using Plastigage to measure bearing clearances. The multiple assembling always worried me. I would carefully measure journal diameters, the saddle or big end diameter, and measure the thickness of the bearing shell with a tubing wall thickness mike. The final check was how everything felt as the bolts were tightened. I never had a bearing failure in hundreds and hundreds of engine overhauls.

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    Re: Main Bearing pics

    DUDE!!! I just have to say that you give encouragement, enthusiasm, and peace of mind to all of us with high mileage Caddys.

    Mine has almost 168k and while it really runs good & seems to have been well maintained, I still worry about the future possibilities due to the high mileage. I've never owned a car with this kind of mileage before, and my past vehicles have tended to begin dying at around 130-140k.

    I do have a Montero Sport that I've owned from 65k up to the 134k currently with absolutely no problems, so I AM luckly on that one so far. I just hope it continues to last.

    Seeing the mains on your n* looking so good w/ 137k definitely eases my mind about mine. Please keep posting your progress. I've become eager for you to get your Caddy back on the road.

    Cheers,
    96 STS

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    Re: Main Bearing pics

    Bbob, Thanks for checking this post. Your opinion really gives me some piece of mind. I think the bearings look pretty good, I've added a couple callouts to give perspective. You can see a dog hair and a strand of cotton from a shop rag. I did follow the book when replacing the LLC. I didn't use the anerobic sealer, I did place the rear main on before bolting the case together but forgot to dab the RTV on the T joint (Stupid). I got as far as torqueing the main bolts down when I realized I hadn't picked up a new pick up tube o-ring. I stopped by the Chev dealer yesterday and got my new rings, but in the converstation the parts guy was telling me that he rememebered a TSB that said the pick up tube & baffle had to be replaced because of the new oil manifold. I have a subscription to alldata and checked all the TSB's listed there and didn't find one. The only difference in the old and new oil manifolds that I could see was the molded in seal around the pick up tube. I'm going to go by the Stealership this morning and double check. As long as I'm where I'm at I can pull it apart again and use the anerobic sealer. Is that something that I can only get @ the dealer?
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    Re: Main Bearing pics

    Quote Originally Posted by 96 STS
    DUDE!!! I just have to say that you give encouragement, enthusiasm, and peace of mind to all of us with high mileage Caddys.

    Please keep posting your progress. I've become eager for you to get your Caddy back on the road.
    Dude..I really have to thank you....your the one of the people who's been giving me encouragement to keep going deeper into this, Thanks
    My last caddy, 91 Brougham had 184K on it when I sold it. It had the 305 chev in it and I wouldn't have hesitated to drive it clear to Calif from Tenn, it really held up well. I was really surpised to find this engine in this good of shape when I took it apart and I can see where it's feasible to get another 100K out of it.
    It's been over 10 yrs since I've worked as a mechanic and I thought I'd forgotten how to do this kind of work. After I had installed the powertrain the first time and it was still leaking I was so ready to throw in the towel, but opted to just bite the bullet and do it again. The second time as a lot easier and I got done in 6hrs what took me 3 days to do the first time. I just want to thank all you guys for giving me the determination and and encouragement to get this project done, and done right.
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    Re: Main Bearing pics

    Quote Originally Posted by bbob
    The mains can be reused but the rod bearings CANNOT be reused. If you disturbed or dissassembled any of the rod bearings to look at them or inspect them you have to replace them or they will fail later. The crush used in the rod bearings make them a throwaway if they are torqued into the rods and the engine is run and thermocycled.
    What are you talking about? Are you trying to say that the Northstar rods and/or bearings are somehow different from everything else? I hate to be the one to break this to you but the mains have "crush" holding them in place as well. I have taken literally hundreds of motors apart for service and NEVER have I seen a used rod bearing fail after reassembly, if the rod bearing was servicable to start with. Unless there is something radicaly different about the Northstar rods, you guys are passing around a bunch of Urban Myth and Mountain Medicine.

    BTW If what you are saying were true the Plasti-gage people would have been long sued out of existance. What is vital is that the crank and bearings be spotlessly clean and that the bore and the backs of the bearings be clean and dry. The bearings in the pictures show lots of signs of "trash" in the oil. The light scoring evident is from contact between crank and bearing when the oil "wedge" is lost or not yet established, such as cold starts. It is quite problematic to attempt a diagnosis from such pictures, but I would probably consider replacing the mains as long as I had them out. Bearings that have always been run with clean oil and never suffered a loss of oil pressure will usually only show a small polished area. Such a wide "wipe" of the bearing material usually indicates inferquent oil changes.

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    Re: Main Bearing pics

    duecentoi, my experience is with aircraft engines that run for long periods of time at high power settings and thus high stresses. I did engine teardown and failure analysis for the FAA and NTSB for years. The rod failure mechanism is as follows: The rod bearing is held in place by crush. The tang only serves to position the bearing at assembly. A used rod and bearing are reassembled. The crush has been relieved slightly by the process. The bearing doesn't spin but moves ever so slightly in the bore. The movement produces metal fret and eventually pinpoint areas of galling in the rod bore. At this pinpoint of galling the fatigue crack starts. Once the crack starts the rod fails in short order. High powered, geared Lycoming engines are particularly prone to this type of failure. I have seen this type of failure in connecting rods that were not assembled with used parts but did have enough oil on the back side of the bearings that was trapped at assembly and resulted in excessive crush and looseness when the oil seeped out. Ask someone in the aircraft engine overhaul business if you can look at their Lycoming Service Bulletins and Instructions. I am sure that you will have your eyes opened. This type of failure is seldom seen in the automotive field because car engines loaf along at part throttle and only produce at maximum for short bursts. In one instance involving a twin engine Aerocommander, shortly after one engine failed in this manner the second also failed while putting out full power to compensate for the first. It appears that your experience is far too parochial for you to be criticizing others and making broad generalizations about their judgement and experience. I agree that the same problem exists with the mains and I have actually seen more main bearings come loose and chew up the saddles than rod failures although this usually results in a lot of warning from metal in the oil rather than a catastrophic failure like a broken rod.

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    Re: Main Bearing pics

    Quote Originally Posted by duecentoi
    The bearings in the pictures show lots of signs of "trash" in the oil. The light scoring evident is from contact between crank and bearing when the oil "wedge" is lost or not yet established, such as cold starts. It is quite problematic to attempt a diagnosis from such pictures, but I would probably consider replacing the mains as long as I had them out. Bearings that have always been run with clean oil and never suffered a loss of oil pressure will usually only show a small polished area. Such a wide "wipe" of the bearing material usually indicates inferquent oil changes.
    I know the pictures really a hard gauge but I'm not really trying to diagnose anything. I thought y'all would like to see what these would look like @ the milage of this engine. The previous owners oil changes possibly may have been infrequent, but at the rate at which this thing leaked oil (and there is NO sign of oil starvation anywhere) coupled with the fact that there is no dirt, grime, sludge or any other contaminates in the engine indicates to me that there has been clean oil all along. The bearing surfaces look scored in the photos, but you can't feel anything but smooth, even with your fingernail. The cams, timing components and every other surface on the interior of this engine exhibit only a slight varnish discoloration.

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    Re: Main Bearing pics

    The pictures you show are textbook examples of good servicable used automotive type main bearing. There is no distress indicated.

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    Re: Main Bearing pics

    I agree. I have reviewed 100's of engine teardowns with high miles and hard usage. Your main bearings look fine and do not indicate any sort of trash or debris in the oil nor do they indicate any sort of problem. They look perfectly normal especially for the miles you have on them. The wear or contact area looks perfect. Notice that there is no contact at the split line of the bearing. That is as designed. The split line is where the oil film is established. Oil can enter between the bearing surface and the crank at that point and the rotation of the crank creates the bearing film as the crank rotates under load. The width of the contact area looks fine as well as the length of the contact around the perimeter of the bearing shell. Funny thing is that I bet that when you look at them in another 100K they will look the same....!!!


    duecentoi...what I am talking about is that the Northstar rod bearings have more crush than the "normal" engine you may have taken apart over the past century. The crush in the bearing (the OD of the bearing shells is slightly greater than the ID of the bearing bore in the rod) is what holds it in place....it is the only thing holding it in place from moving and spinning. The tang is simply an assembly aid and alignment feature...it does absolutely nothing in maintaining bearing position. During engine development we often use bearings with no tang and/or file off the tang to change bearing alignment or orientation with absolutely no consequences. Typically, rod bearings in the past ran about .0002-.0003 crush on the diameter. During Northstar engine development it was notices that the rod bearings were moving slightly in the bores...not enough that the bearings actually moved position but enough that areas of micro-fretting developed on the backside of the rod bearing shells....material transfer from the rod to the steel back of the bearing indicating microscopic movement of the bearing as it "squirmed" in the bearing bore under load. 100's of hours on the dyno at 6500 RPM and 300 HP continuously will show you things like this. These engines are validated on a test that runs at 6000 for 400 hours at full throttle continuously....they have to endure FAR FAR more than a 15 second dyno "pull" on the speedshop's water brake dyno. The microscopic movement of the bearing indicated that more clamp load or crush was needed in the bearing. The crush was increased to the .0003-.0004 range. This solved the microfretting problem on the backside of the bearing. Microfretting like this can commonly be seen on high performance race engines as it appears as a black area on the back of the bearing shell and if left alone long enough it will actually transfer tiny chunks of material. Eventually this microfretting on the backside of the bearing will casue the rod to fail as the microscopic pits caused by the material welding or transfer causes a stress riser that a crack propogates from. Seen it happen many times.....no LOL.

    The down side to the extra crush is that the bearing is put into such a high compression when assembled that it actually takes a slight "set" if the engine is run and the bearing subjected to high loads and high temperatures. It happens, trust me. Every time I have ever seen a Northstar dyno engine taken apart and the rod bearings reused the engine would eventually fail a rod bearing. This did not have to happen too many times to teach us that you do not reuse the high crush rod bearings over again if the rod is taken apart. I saw this with my own eyes, have measured the bearings and know that it happens.

    One could probably take an engine from a street driven Northstar, dissassemble and reassemble the rod bearings and maybe get away with it 75% of the time as the engine will never be run as hard on the street....but....why risk it. It is a known failure mode in a high stress situation. Some mechanic will say that he has done this, I am sure, and no problems were seen but the next time he may not be so lucky if the driver runs the engine to redline like it is designed for...... Personally, I would NEVER reuse a rod bearing on any engine especially a Northstar. I have seen the results or reassembling Northstar rods with used bearings. Not in my engine so that is the reason I recommend what I do.

    The main bearings for the Northstar, if you look carefully, are somewhat unique. They have a very very thick (4mm) steel backing or shell. This is done because of the all aluminum construction of the block and lower crankcase. The main bearing bore is all aluminum. Aluminum expands a great deal more than cast iron or steel as the temperature changes. Correspondingly, the main bearing clearance on the crank would change significantly with temperature if there were no design changes made to prevent it. What was done was to make the main bearing shells with very thick steel backing (4 mm vs. 1 or 1.5 mm on conventional mains) so that they can handle a tremendous amount of crush without distorting. So...the main bearing clearance is set up for a hot engine and as the engine cools toward a minus 40 cold start in Kapuskasing the bearing can handle the extreme load the shrinking aluminum exerts on it without collapsing and causing the bearing clearance to shrink to zero. That is why the thrust bearing on the Northstar crank is three pieces instead of the normal thrust main bearing that has the sides/thrust face simply folded over. The 4mm backing is too thick to fold over for the thrust face sides so the thrust faces are separate "fences" staked into place.

    So...even though the mains in the Northstar are set up with a large amount of crush they can be safely reused due to the 4mm thick steel backing. The thick backing resists any permanent distortion from the crush. It is perfectly fine to reuse the mains.

    The rod bearing shells should never ever be reused. They do NOT have the same thick steel backing and do take a set with use and will not have the adequate crush if dissassembled and reused. If reused, it will likely lead to a rod failure due to stress risers forming in the rod bearing bore due to microfretting of the bearing against the bearing bore.

    The recommendation is based on fact, observation and sound engineering. It is not a bunch of Urban Myths nor Mountain Medicine. There really is something radicaly different about the Northstar rods......



    Personally, I have little faith in plastigage...it is of some general use I suppose but it is really not that accurate. I don't mind the dry assembly and dissassembly of the rod/rod bearing for clearance checks as long as the bearing is not put under load against the crank and subjected to any heat. It will not take a set under those conditions of temporary assembly for clearance checks.


    If you look at the pictures of the bearing shells in the post above you can make out the thick steel backing I mentioned.

    The "marks" that look like scoring are just marks in the tin overplate that is put on the bearings for breakin. The fact is that the bearings look so good that the breakin overplate is not even completely worn away...it is just removed in streaks that look like scoring. The bearings are fine.

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    Re: Main Bearing pics

    Remember when you reassemble the engine that you need to pull the damper on with a puller and that the large bolt that holds the damper on needs to be VERY tight. It takes about 250-300 ftlb to get the bolt to the torque-angle spec required. Otherwise the oil pump drive sleeve can slip and cause the engine to loose oil pressure.


    Don't those sprockets look great after all those miles....LOL Just the way we planned it.

    The chain guides should have a "mark" where the side plates of the chains ride. That is normal. That happens almost immediately when the engine is first run and stays that way forever.

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    Re: Main Bearing pics

    Those bearings look great!

    So the bearing material is aluminum with a steel backing as compared to babbit or something of the sort?

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    Re: Main Bearing pics

    Bbob, once again you show why you are so appreciated here. Not only because of your knowledge but your patience as well.
    Urban legends. Mountain medicine. It was not directed to me, and even so, I got mad...
    Kudos to you.

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    Re: Main Bearing pics

    Quote Originally Posted by Pjs
    Bbob, Thanks for checking this post. Your opinion really gives me some piece of mind. I think the bearings look pretty good, I've added a couple callouts to give perspective. You can see a dog hair and a strand of cotton from a shop rag. I did follow the book when replacing the LLC. I didn't use the anerobic sealer, I did place the rear main on before bolting the case together but forgot to dab the RTV on the T joint (Stupid). I got as far as torqueing the main bolts down when I realized I hadn't picked up a new pick up tube o-ring. I stopped by the Chev dealer yesterday and got my new rings, but in the converstation the parts guy was telling me that he rememebered a TSB that said the pick up tube & baffle had to be replaced because of the new oil manifold. I have a subscription to alldata and checked all the TSB's listed there and didn't find one. The only difference in the old and new oil manifolds that I could see was the molded in seal around the pick up tube. I'm going to go by the Stealership this morning and double check. As long as I'm where I'm at I can pull it apart again and use the anerobic sealer. Is that something that I can only get @ the dealer?

    Something bothers me about what you are saying....

    If you look at the old oil manifold plate you should see an oval shaped steel washer with two holes in it at each of the main bolt holes. The steel washer is cast directly into the aluminum of the plate itself. The new plate should be the same way if it is the correct one..... If the plate you got does NOT have the steel washers cast into it it is not the correct plate. The plate design and the assembly sequence was changed on the engine in 1996.

    The 93/94/95 Northstar had an oil manifold plate with the 10 steel washers at the main bolt holes. The main bolts bolted down the plate and the LCC. All the mains were stud headed bolts so that the windage tray attached to the stud headed bolts with 10 nuts. That is the way your engine should have been. The steel washers were imbedded in the aluminum oil manifold plate to act as the load bearing member of the plate to distribute the load of the main bolts.

    Starting with 1996 the 10 steel reinforcing washers were eliminated. The plate still looks the same with the raised area for the washers but the raised area is aluminum, not an imbedded steel washer. With the 1996 engine the windage tray changed shape slightly and the windage tray is placed directly onto the oil distribution plate and the main bolts then go thru the windage tray, the oil plate and then the LCC into the block. There is only one stud headed main bolt for 1996 as the windage tray mounts under the mains as described and not onto stud headed bolts as the 39/94/95 did.

    Here's the punch line. The 96 and later plate had the oil pickup seal molded in place....so...if yours has the molded in seal I would not expect to see the steel washers imbedded in the oil manifold plate. Without the steel washers you cannot simply put the main bolts directly against the aluminum plate. It will crack and fail as the bolts exert too much load to bear directly against the aluminum plate. In the 96 engines the windage tray acts as the load bearing surface for the main bolts that replaces the steel imbedded washers. If you have a plate without the imbedded washers it is the wrong one and the only way to use it is to get the 96 windage tray and install it under the main bolts to act as the load bearing surface.

    Unless...possibly someone later on released a "service" oil manifold plate that has the imbedded washers and also the later versoin of the molded in oil pickup seal....I don't remember this happening..but my memory is not perfect at all. You really should check this out... If the plate you have does not have the imbedded steel washers then don't just plop the main bolts directly against it the way the engine was assembled originally.

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