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  • Reforming a main bearing cap

    Well into the job of getting a 1960s Kelvin marine diesel back into service, we made a nasty discovery yesterday.
    The decision had been made to replace all the main bearing shells, as inspection of the two end bearings showed significant though not really bad wear to the shells, and there had been an issue with the oil filtration (ie there hadn't been any for some time!) in the past.
    This can be done in situ, through the crankcase doors, but it's not a five minute job and they can't all be done at once. The nuts have a tightening torque of 500 lbft, working through a little 'window' with a 90 degree spanner and at ankle height. Loads of fun!
    Anyway, nearly had them all done yesterday apart from final tightening when I found that the centre main had spun in its housing, and then discovered that the bearing cap was distorted, the sides had come in by about 15 thou. This was the one I least expected to be trouble, as it's the first in line for the oil feed.
    A problem like that would be dealt with in a vehicle sized engine with a complete strip down, then cutting down the bearing cap and reboring. That's simply not an option in this case, with a 3.5 ton engine in a restricted engine room and a lot of work already done. Anything I did had to be done with crankcase and crankshaft in place.
    The options seemed to be to machine the cap away from the engine and probably have awkward hand fitting to do to refit properly, or to 'straighten' it out. The second option seemed the better bet if it would work, so here's what I did:-

    The bearing housings have a nominal bore of 5.25". I took a piece of 6" CI bar, that's the nearest I had to hand, and turned it to 5.258" DIA. This was a guessed size, with some help from Sir John on the guesswork, as to how much oversize it needed to be:-



    Then the bearing cap was heated to about 500C



    I used an infrared thermometer to check that the heating was reasonably uniform.

    Then the idea was to press the CI former into the housing and let it cool.



    In fact, the heating expanded the cap sufficient that the former just dropped into place, the press wasn't really needed.

    Anyway, after allowing to cool and releasing the cap from the former, it was still about 6 or 7 thou undersize at the opening, so I repeated the process with a strip of 4 thou shim under the former. Result, the cap is now within a thou of an undamaged cap so should be OK.

    The real test comes tomorrow, when I'll try a test assembly with some plastigage strips to check clearances.

    Tim

  • #2
    Resourceful----------My bet's on you.

    --G

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    • #3
      It seems like the mating surfaces of the cap would be at a slight angle to each other after the fix. Have you checked that? Is it an issue?

      What kind of jaws are those on your lathe chuck? I've never seen any with so much grip area.
      Any products mentioned in my posts have been endorsed by their manufacturer.

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      • #4
        Originally posted by winchman
        It seems like the mating surfaces of the cap would be at a slight angle to each other after the fix. Have you checked that? Is it an issue?

        What kind of jaws are those on your lathe chuck? I've never seen any with so much grip area.
        The cap should be pretty much back where it started, the aim was to remove distortion and get it back as close as possible to its original shape. The faces might have been at a slight angle before doing the work, never thought to check.

        The jaws are a fairly standard form of soft jaw for serrated-jaw chucks, I picked up a bucket full of them, used but plenty of life still in them, at an auction. I took a chance, and they needed only very slight modification to fit my chuck. Really made for power chucks but very handy.

        See
        http://www.thame-eng.com/DiamondSerratedSoftJaws.pdf

        Tim

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        • #5
          If the main bearing shells spun in the bore you still have a problem. I have never seen what your doing work for very long. The problem is the clearances in the main bore are oversize and distorted after the shells spin and there may be metal buildup on the bearing bore in the block.

          Someone will end up pulling the engine and doing it right.

          If the faces your talking about are the surfaces that mate up to the block they are perfectly flat as is the block. The way to do a line bore is to machine off the surfaces that mate with the block and then set the boring bar up and machine the cap bore to match the block bore. You have to be very careful to not cut the block part of the bore.
          Last edited by Carld; 09-16-2010, 09:12 PM.
          It's only ink and paper

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          • #6
            I think its a pretty cool way of getting the engine back to power. I was trying to visualize how you do it. Ive only worked on car engines and I have yanked the crank out of the engine while it was still in the car, but never did open heart surgery like you are doing..

            How do you get the top shell in, and out? Do you remove all the caps then lower the crank to the pan? Also, with the cap sprung so much were the bolts very tight when removing them? Or do you use studs. Seems if the cap was bent in a lil the bolts would be hard to line up in the bolt holes. Unless the cap bolt holes are large enough.

            Anyway, I think the engine will be fine. Certainly a whole lot better off than she was. JR
            My old yahoo group. Bridgeport Mill Group

            https://groups.yahoo.com/neo/groups/...port_mill/info

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            • #7
              Originally posted by JRouche
              I think its a pretty cool way of getting the engine back to power. I was trying to visualize how you do it. Ive only worked on car engines and I have yanked the crank out of the engine while it was still in the car, but never did open heart surgery like you are doing..

              How do you get the top shell in, and out? Do you remove all the caps then lower the crank to the pan? Also, with the cap sprung so much were the bolts very tight when removing them? Or do you use studs. Seems if the cap was bent in a lil the bolts would be hard to line up in the bolt holes. Unless the cap bolt holes are large enough.

              Anyway, I think the engine will be fine. Certainly a whole lot better off than she was. JR
              The top shell is removed by barring the crank around, with a suitably folded split pin or similar in the crank oil hole. Reverse to replace, though finger pressure is just about enough to help the new shell in following the rotating crank.

              The bearing caps are on studs, in fact the studs go right the way through from cylinder head to crankshaft. They're threaded into the crankcase, and also have nuts to hold the cylinder blocks in place. They're 1 1/8" BSF. They are 'necked' below the threads where they pass through the bearing caps, but yes this cap was a little tighter than the others to remove.

              Tim

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              • #8
                Originally posted by Carld
                If the main bearing shells spun in the bore you still have a problem. I have never seen what your doing work for very long. The problem is the clearances in the main bore are oversize and distorted after the shells spin and there may be metal buildup on the bearing bore in the block.

                Someone will end up pulling the engine and doing it right.

                If the faces your talking about are the surfaces that mate up to the block they are perfectly flat as is the block. The way to do a line bore is to machine off the surfaces that mate with the block and then set the boring bar up and machine the cap bore to match the block bore. You have to be very careful to not cut the block part of the bore.
                That isn't an option, certainly not at present. Priority is to get it up & running.
                If it comes to pulling the engine and that scale of work is needed, at that stage it'll make more sense to have another engine ready to fit as replacement. I'm well aware of your last part about the line boring, I did mention it in my original post. It's never going to happen with this engine, too big & too expensive.

                EDIT to add :-

                Wear to the inside of the cap appears to be no more than a slight polishing. As said, I'll be checking clearances with Plastigage strips before final assembly.

                Re the soft jaws, I had them set up for this job, for a different engine:-



                They're ideal for this sort of thing, actually a water pump drive gear. A new pump was being fitted, but it has a 25mm shaft while the original had a 1" shaft.. Bore out, sleeve, bore again, broach keyway. Sleeve held with Loctite retainer plus three M5 screw dowels at 120 degrees along the interface, also loctited. Pic shows reaming to size with adjustable floating reamer.

                The outer recess in the jaws was then easily adaptable to hold the piece of 6" CI bar,which had very little spare length.

                Tim
                Last edited by Timleech; 09-17-2010, 05:47 AM.

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                • #9
                  If it spun enough to damage the main cap it damaged the upper part of the main bore.

                  Good luck.

                  I probably still have the short bolts I ground the heads down on to roll main shells out and in doing in the chassis overhauls laying under the truck with the old black oil dripping all over the fender cover I layed on me from my neck to below my waist. That's one job I always hated.
                  Last edited by Carld; 09-17-2010, 09:58 AM.
                  It's only ink and paper

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                  • #10
                    I'm with you on this one Carld, unless he has a big bag of horseshoes .......
                    I can really appreciate what/why OP is trying this and have seen similar things done over the years but generally with less than great outcomes. While this may 'last' for a while it won't have the longevity of a proper repair. The fact that this one (of the five?) failed in the first place tells me there is something else going on that needs to be scienced out. The spun bearing is a symptom not the 'problem'.
                    Of course I could be wrong, so here's hopin it works out for you and I like your method(s) and creative thinking to problem solve!
                    I spent most of my money on women and booze, the rest I just wasted.

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                    • #11
                      One does what one has to do to get the problem down the road/river to the next mechanic.
                      It's only ink and paper

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                      • #12
                        I do not see why the intended repair should not give satisfaction...

                        The lower shell is locked to the cap (?) and that is what stops the upper shell from rotating. If the bearing shell has removed material such that the upper shell has excess clearance I am sure there are all sorts of filler materiald that could be used.

                        What is the likely cause of failure of repairs like this is that the oil feed has become blocked and the new shell gets starved of oil leading to the predicted premature failure. A good dose of compressed air in the oil gallery may avoid this.

                        Just my opinion.

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                        • #13
                          I am convinced that no significant material has been lost from the cap, it's simply a distortion issue. The new top shell slid into place with exactly the same level of ease/difficulty as all the others. I've measured the crank journal as best I can, good old fashioned firm joint calipers were the only option given the limited access and it's within a thou or so of original (and it is 42 years old). The maker's specs allow for a bearing clearance of up to 14 thou before work is needed, from a new clearance of 4.5 to 7 thou. I did need to polish a small amount of bearing material off it, that was before measuring. There is one simple score line on the crank, it's otherwise looking good.
                          I've discussed this with my local friendly engine reconditioner, in case he had tried anything similar or had any better ideas. He hadn't, but has seen the cap and has approved of my methods. Incidentally he has a big V8 Cummins generator engine in the shop at the moment for line boring after exactly the same problem. It's a well established and respected outfit.
                          Don't forget this is not some highly-stressed vehicle engine but one essentially designed for long hours (and dare I say poor maintenance!) in a fishing boat, so relatively 'over engineered' by modern standards, and with a max speed of 1000 rpm and expected many tens of thousands of hours between major overhauls.
                          I know it's not going to be like new, but wouldn't be putting the work in if I wasn't confident of a useful result.
                          As to the cause, there is evidence that there's been water in the oil and as already remarked the filtration had been inadvertently disabled. How long for, we'll never know, but I suspect quite a long time.

                          Tim

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                          • #14
                            Hey Tim, when you get 'er back together and take 'er out on a test run; cruise on over t'other side of the pond. When you see the east coast, ignore it and and swing down south around Florida and back up the Gulf and into the mighty Mississippi. Head north but watch out for sandbars; she's a bit low this time of year. When you go under the old bridges and see a Pyramid on your right, that'll be Memphis. (TN, not Egypt)

                            Gimme a shout on the dog n' bone and I'll meet you at the Rendezvous (less than a mile from the riverbank.) I'll buy you all the Memphis BBQ ribs & beer you can scarf down.

                            I have faith in yer engine repair so when we're finished eatin' ribs, I'll hop on board and you can show me how good she runs on the way back home. She ought'a be good & broke in by then. By the time we get there, I'll be hungry again (I'm always hungry.) Harry Ramsden's'll do I reckon.
                            Milton

                            "Accuracy is the sum total of your compensating mistakes."

                            "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

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                            • #15
                              Originally posted by DICKEYBIRD
                              Hey Tim, when you get 'er back together and take 'er out on a test run; cruise on over t'other side of the pond. When you see the east coast, ignore it and and swing down south around Florida and back up the Gulf and into the mighty Mississippi. Head north but watch out for sandbars; she's a bit low this time of year. When you go under the old bridges and see a Pyramid on your right, that'll be Memphis. (TN, not Egypt)

                              Gimme a shout on the dog n' bone and I'll meet you at the Rendezvous (less than a mile from the riverbank.) I'll buy you all the Memphis BBQ ribs & beer you can scarf down.

                              I have faith in yer engine repair so when we're finished eatin' ribs, I'll hop on board and you can show me how good she runs on the way back home. She ought'a be good & broke in by then. By the time we get there, I'll be hungry again (I'm always hungry.) Harry Ramsden's'll do I reckon.

                              Thanks for the tempting offer, Dickey
                              Sadly it's not my boat, anyway it's a little dry cargo barge with some coasting capability but the Big Pond might be a bit much for it.

                              Incidentally this is the engine:-

                              http://www.sky-net.org.uk/kelvin/die.../t6/index.html

                              Cheers
                              Tim

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