340 Rod questions

Small Block Mopar Engine

  1. gzig5

    gzig5 FABO Gold Member FABO Gold Member

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    Were the rods and wrist pins on 68-71 340s press fit or floating from the factory? I thought they were pressed, but what I have are floating.

    I may need to install new rod bearings, have one with uneven wear that is into the copper. I only have 2 of 8 pulled so far. Can I just get new bearings, check clearance and install, or will they need to be reconditioned? If the other bearings are OK, I may just replace this rod because it is an oddball 3418645 rod from a later motor, not a 2899469 340 rod like the other seven. A friend suggested that the uneven wear could indicate a tweaked rod. I hope to have the rest pulled after work tonight.

    I'm trying to avoid a complete redo on the short block. It was running fine, the only reason I'm getting into it is the motor is out while car is in the body shop and I wanted to know what the motor condition was and what parts it had. Looks like the car needs to go to the frame shop so any budget I had for the the motor in the near term has evaporated. I'm going to have to get it back together with a minimum of parts invested so I have a running motor. May still be able to install the heads and cam I already have but will go with the old J-heads if I can't figure out the difference I have in piston height.
     
  2. Professor Fate

    Professor Fate Push the button, Max...

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    340s had floating pins from the factory.
     
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    • yellow rose

      yellow rose Overnight Sensation FABO Gold Member

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      AFAIK all the 340 rods were bushed, as were many 273 and 318 rods. I’m old enough to have taken apart more than my fair share of unmolested stuff and have seen it.

      You can change out the rod bearings if the crank isn’t gouged up. I’d for sure double check the clearance with a mic. And I’d measure the rod bores to see where they are. You can do it with a snap gauge and mic but it’s much easier and more accurate with a bore gauge.

      If the clearance is wrong, or the rods are tight (which means the clearance is probably wrong) or bell mouthed or over the high side of spec you’ll need to rebuild the rods.
       
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      • nm9stheham

        nm9stheham Well-Known Member

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        Yes, bushed for the 340s and the light rod 318's IIRC as well as the 273's.

        Is the rod bearing with the wear worn even across the face of the bearing or over on one side? How does the journal look for that bearing? Pix?

        If you have them all apart, I'd measure the rod center-to-center distances. With that one odd rod and the .010" variation in deck height, you could have some re-con rods in there. Ditto on the big end bores; not hard to check with the cap torqued back on, once they are all apart.
         
      • MoparMike1974

        MoparMike1974 Well-Known Member

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        x4 Agree. ALL 340 used floating pins. I think the early 318 did too but cant remember the cutoff date.
        As far as reconditioning I would visually inspect the bearings. If you see any odd wear you might take them and have them checked at a machine shop.
        For a driver or moderate HP street car its not that critical. I cant tell you how many times I just did a re-ring / bearing job and never had any problems.
        Dont sweat the rod with a different part number. Its not uncommon for engines to leave the factory with mismatched rods. If you ever pull an engine down and see some copper rods, they are factory reconditioned. Specs were off so they copper plated them and remachined.
         
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        • gzig5

          gzig5 FABO Gold Member FABO Gold Member

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          The one is only worn partly across the face. I took the "longest" and one of the "short" ones off, put them on the same wrist pin and so far don't see an obvious .010" difference but I'm not done measuring. The journal looks OK but I need to mic the diameters around the clock to make sure it isn't egg shaped and is even across. The worn one happens to be the one 645 rod in the mix but I think if it was balanced correctly it shouldn't matter. Hope to get the rest out tonight. It was too hot in the garage yesterday.

          IMG_3776.JPG

          IMG_3779.JPG
           
        • 66fs

          66fs FABO Gold Member FABO Gold Member

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          I'd polish the journal with 600 wet or dry sandpaper and some WD-40. Then clean it really good.
           
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          • gzig5

            gzig5 FABO Gold Member FABO Gold Member

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            I do plan on polishing it up.
            I got all the pistons out. The journals measure within spec across the face but there is a little taper on them. I apparently can't read because I actually have six 645 rods and two 489. The mirror tricked me or I was seeing what I wanted to see. Three bearings are into the copper like the one in the pic, not wore slap out but a bit uneven. So new bearings are in order before it goes back together.

            I also have a broken top ring on #4. Looks like it was cracked most of the way through for a while and let get when released from the bore. Not sure how I will deal with that yet.

            Are the tri-metal bearings going to bring anything significant to the party over the bi-metal for a stock-ish build? King or Sealed Power? I'm reconsidering doing the head and cam swap, so these rods won't see a lot of abuse. I'm looking to put the motor back together so I can have the car running while I work on the body. Then it comes out for a full Monty rebuild. It was running pretty well before so should be same with new bearings.
             
          • nm9stheham

            nm9stheham Well-Known Member

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            You can buy single ring sets. You could try to scratch the cylinder with 240 wet or dri.. since the motor is coming back out.

            Any ridge in the cylinders?

            My thought on the bearings is that I would probably put in the cheapest new set I could find for now, since the motor is coming back out. Or even just re-use what you have, depending how much you plan to drive the car 'til the rebuild......? BTW, Kings are mostly AL and so are usually harder.
             
          • gzig5

            gzig5 FABO Gold Member FABO Gold Member

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            There is a couple thousandths wear but the "ridge" is very gentle. Good thought on the wet/dry. I just want to scuff it a bit to give it a chance to seat. Even if it doesn't and it smokes a bit, I'll just be happy to have the car mobile.

            Summit has a Hastings cast iron single set for $16, which won't break the bank. I'll make sure the others are OK before ordering.
            Hastings Piston Ring Sets 694S

            I'm tempted to just run the bearings as they are with 20W-50 VR1. I hate doing stuff half-assed, but I doubt I'll put more than 1500 easy miles on it before it comes back out. If I'm going to order bearings I think I need to verify the diameter on the big end first? But for $25-50 it doesn't make much sense not to change them. I'm going to have a couple hundred in gaskets to get it back together so may be foolish not to do the rod bearings too. Just talking out loud, going crazy....
             
          • gzig5

            gzig5 FABO Gold Member FABO Gold Member

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            Is there any benefit to leaving the current second and oil rings in there and just replace that top ring, or is it an all or nothing? Appreciate the input. I'm pretty familiar with the right way to do these things, but a bit ignorant on what you can get away with without wrecking stuff.
             
          • nm9stheham

            nm9stheham Well-Known Member

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            The oil rings' function is obvious. The 2nd ring is as much for oil control as anything. So, yes, you could put in just the top ring to run around.... I have seen and heard of lots worse LOL. But you can only buy the rings as sets.

            The comment on the ridge was if you put in a 'thicker' rod bearing, it will push the rings up a tad higher in the bore.... I am sure that folks have gotten away with it, but it also has been known to break a top ring. You just don't want to break the new top ring and score the cylinder before you get it back apart. Sounds like experiment time! Be brave!
             
          • gzig5

            gzig5 FABO Gold Member FABO Gold Member

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            Gotcha. There is no real step at the top of the cylinder. I cleaned the carbon rings at the top as well. Still a little remnant of the cross hatch at the top of the bore.
            upload_2020-6-4_13-25-8.png
            Thus far I have restrained myself from posting a Wanted for used standard OEM rings.....:realcrazy:

            You're right. I don't have enough excitement with this thing yet. :drama:
            Feeling better already. But I'm not pulling the crank out unless I absolutely have to. Will have to be careful to keep it clean as I do the prep.
             
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            • pishta

              pishta I know I'm right....

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              This can't be accurate as a thicker bearing will still center the rod on the journal as its equally "thick" the entire way around the journal. The ring pack wont move on an undersized bearing.
               
            • Wyrmrider

              Wyrmrider FABO Gold Member FABO Gold Member

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              20 50 0il in 2020?
              20 50 oil in WI???
              check against a clearance vs viscosity chart
               
            • gzig5

              gzig5 FABO Gold Member FABO Gold Member

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              it was 95 degrees Tuesday. I don't tend to drive this car when it is snowing. My BMW runs 10w-60 synthetic. Personally, I think any good quality oil from 10w-30 to 20w-50 should work. Lots of guys running 15w-40 for the zinc. Running a heavier oil with worn bearings or large bearing gaps is fairly common, whether it is right or wrong, I know my older motors are quieter with a heavier oil. Lets not turn this into an oil discussion just yet though.
               
              Last edited: Jun 4, 2020
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              • nm9stheham

                nm9stheham Well-Known Member

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                You're right pishta....if the oil wedge stays constant all the time, all around. But it doesn't.... and I think that is the reason. Probably worth some more thought...at least on my end. Tnx
                 
              • pishta

                pishta I know I'm right....

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                oil wedge is but .0024x thick (bearing clearance) yikes, if that moves a ring pack into an existing groove (that had the same bearing clearance, or more because its worn) My guess is if it were to move it any it would be <.0012 inches at that. (bearing clearance divided by 2 as in full circumference oil wedge), and that is within the .001~.005 compression ring clearance anyway. . Maybe someone that does shop work doing a rod bearing R&R on the same main bearings could measure deck height of a before and after rod bearing change.
                 
                Last edited: Jun 4, 2020
              • gzig5

                gzig5 FABO Gold Member FABO Gold Member

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                I might just have that data in a few weeks. I've mapped the worst case piston height above deck (in another thread) and since I'm probably going to put new bearings in the same rods, I will have apples and apples to compare. I probably should do the bearings first before ordering the head gasket, because if anything, I expect the piston to be higher with fresh bearings.
                 
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                • nm9stheham

                  nm9stheham Well-Known Member

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                  Deck height would be static so of no use. You can find a lot of info on this matter.... here is one ilustration, but IIRC the best info comes from the bearing manufacturers.
                  https://www.machinerylubrication.com/Read/30741/lubrication-regimes
                  Just some food for thought....
                   
                • pishta

                  pishta I know I'm right....

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                  Oops, piston height compared to deck height, that would be the control, correct.
                   
                • gm1236

                  gm1236 Well-Known Member

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                  If your going to replace any of the rings you’ll need to run a brush hone though it or you’ll have problems. Once you pull old pistons and rings out, they never seal right again. If it’s standard bore, brush hone and use the hasting rings. You should pull the crank, make sure the block is super clean before you reassemble it. It’s not going to cost much more to do it right, like you said your already into the gaskets etc.
                   
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                  • gzig5

                    gzig5 FABO Gold Member FABO Gold Member

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                    So what is the mechanism for the ring not working if removed and reinstalled? I'm not calling BS but I don't understand. The parts all move relative to each other to begin with so I don't see what would change?
                     
                  • yellow rose

                    yellow rose Overnight Sensation FABO Gold Member

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                    Taking a ring out of a bore has ZERO affect on its sealing ability. That’s rediculous. I was going to let it go, but you asked what I figured many guys would ask.

                    First of all, the moly filled ring was developed so when an issue came up about ring seal in the field, you could slap a moly faced ring in the hole, WITHOUT honing and it would seal. And they do.

                    Second, ring seal is about bore geometry, surface finish, honing technique and some other things. BUT, the function, the physical sealing function of the ring is done by compression pressure on the compression stroke, and combustion pressure on the power stroke, and NOT by the racial tension of the ring, the fruit jar affect (yep...had an assclown in 1995 try to tell me that once a ring comes out of a bore, it breaks the seal like opening a jar of home canned fruit????????? WTF????? And this idiot was the resident expert) or anything else.

                    The vast majority of top rings have an orientation marker on them that says what side goes up. If it doesn’t, it’s either a cheap assed ring set, or more likely it has a bevel on the ID and this side always goes up.

                    That bevel is what allows compression and combustion pressure to go down the side of the piston, where it hits the top of the ring, and then that pressure moves across the top of the ring, around the bevel and that pressure gets behind the ring and forces the ring into the bore and THAT is what causes the ring to seal.

                    When you get to performance rings and high horsepower engines (which is now happening to what I consider very low performance street/strip junk such a my own garbage) you have the option of thin rings (IMHO anything thicker than an .043 ring is too thick...so IMHO a 1/16 ring pack is a low performance ring pack) and vertical or lateral gas ports in the pistons.

                    These are simple holes drilled in the deck of the piston that break through to the back of the ring groove (these are verticals gas ports) which makes ring response to pressure much quicker AND you can use thinner rings, with less racial tension which saves power by way of less drag.

                    Horizontal gas ports do the same thing, except these are slots milled in the top of the top ring groove. They do the same thing, and these are less prone to carbon fouling, but if your tune up is decent it shouldn’t be an issue with either form of gas porting.

                    The newest “gas porting” system is made by Total Seal and this system is a series of grooves in the top of the ring itself. There are said to be several benefits to this system, and I’m going to pull my junk down and and get my top rings machined for this.

                    At any rate, ring seal has nothing to do with taking rings out of a bore.
                     
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                    • Wyrmrider

                      Wyrmrider FABO Gold Member FABO Gold Member

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                      racial tenson
                      wat about the new total seal rings with the horizontal gas ports built in
                      anyone try them or is yr our guinea pig
                      whoever said it's all been done already is just not with it
                      I have a 360 on the stand with KB's for stock heads
                      have to decide if going aftermarket heads will help 1500- 5000
                       
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