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Whats the difference between 3817 and 3817t connecting rods for a Mercruiser 181???

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  • Whats the difference between 3817 and 3817t connecting rods for a Mercruiser 181???

    I am rebuilding my engine and apparently the connecting rods I have and need to replace are thicker than the typical ones. Does anyone have specs on them. Did the thinner rods just use wider bearings or was the crank and block different all together? I have read a few places that they are all the same rod but I am finding out this is not the case. Thanks

  • #2
    its a GM 3.0 industrial motor (same ones powered fork lifts, gensets, trash pumps, etc.

    save your money and buy rods for a 3.0 GM industrial motor vs buying from mercruiser.

    Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

    1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

    Past Boats
    1970 Wooster Hellion - Merc 9.8
    2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
    1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

    What’s behind you doesn’t matter.Enzo Ferrari

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    • #3
      Thank you, I will look into this. Any idea on part numbers to look for?

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      • #4
        Don't know the specific answer to your question, but there were small and large journal 181 rods. Been 10 years since I rebuilt my 181, and not sure if there was a difference in the rod width, but the diameters are different. (I have the large journal engine, 1973 181CI 140HP....) Far as I know, the main bearings are the same, just different sized rods and rod journals.

        Are the rods so messed up that they can't be resized?

        I bought a engine rebuild kit from Green Bay Parts World, but other internal engine parts like rockers, water pump pulley, etc, from an automotive engine 68 ChevyII 153CI. Some of the parts even had the GM P/N stamped on them. External engine parts (pumps, electrical, ignition, fuel) have to be marine, no auto parts can be used.

        FWIW, one of my cam bearings was oversized, from the factory by the looks of it, rear cam bearing. I had to run to the machine shop to have them cross it to something that would fit...
        2001 Crestliner SuperHawk 1800, Mercruiser 140HP
        2007 Tracker 1436 jon boat, 7.5HP Force

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        • #5
          Originally posted by fishrdan View Post
          Don't know the specific answer to your question, but there were small and large journal 181 rods. Been 10 years since I rebuilt my 181, and not sure if there was a difference in the rod width, but the diameters are different. (I have the large journal engine, 1973 181CI 140HP....) Far as I know, the main bearings are the same, just different sized rods and rod journals.

          Are the rods so messed up that they can't be resized?

          I bought a engine rebuild kit from Green Bay Parts World, but other internal engine parts like rockers, water pump pulley, etc, from an automotive engine 68 ChevyII 153CI. Some of the parts even had the GM P/N stamped on them. External engine parts (pumps, electrical, ignition, fuel) have to be marine, no auto parts can be used.

          FWIW, one of my cam bearings was oversized, from the factory by the looks of it, rear cam bearing. I had to run to the machine shop to have them cross it to something that would fit...
          I'm still trying to figure this out myself honestly. The machinist mentioned wider and I found a few places the mentioned 1.30" width vs .9xx" width so I assumed that's what is was. The rods could be reworked but if I can get new old stock ones for a reasonable price it would be my preferred choice. He was able to find 2 at a warehouse for 50.00 each, assuming they are that cheap because they only have two. the old ones would cost at least that to rework.

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          • #6
            I've been doing a little more digging into this, I believe a big part of my original problem is misidentification of the engine itself. The serial number plate showed this as being a 1986 +/- but based on the size for the crank and rods it appears to be quite a bit newer. From what I can tell, They used 5 different cranks, 1987-1998 (87 was as far as I went back).

            87-89 #0423-3816

            90+ #0423- 810842
            #0423-810842T (1.037 - 1.043 wide rod journal) (I'm pretty sure this is the crank I have however the part number on the crank is a completely different number, N383778, that last 8 is a guess because its not very clear.
            #0423-804957 (0.952 - 0.958 wide rod journal)
            #0423-804957T01

            I am wondering if the 42 and 57 and the end of the part numbers signifies the width of the rod journal or maybe just a fluke. I don't have any dimensional data on the other cranks to verify this but if anyone can help fill in the gaps it could be helpful. I am also curious is the "T" designates thicker or thinner diameter rod journals. I know mine is 2.100"dia which is also bigger than normal.

            I am assuming at this point the short block was replaced and possibly with a industrial version because the part number on the crank is foreign to Mercruiser or general GM parts list I can find.


            Honestly I can say, this is becoming quite the puzzle and now I am being pulled deeper and deeper into it. I know these parts are used elsewhere but there doesn't seem to be any cross reference.

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            • #7
              with the 3.0, there is 1990 and older, and 1991 and newer.

              the crank and rods changed for 1991 production year to go to the 1-piece RMS.

              however if you keep looking at Mercruiser stuff, you will get confused as mercruiser used plenty of 1990 motors well into the early 1990s to use up stock

              use the block casting or simply look at the crank - 1-piece RMS or 2-piece RMS

              all marine 3.0 motors come from GM powertrain industrial engine division. everything in the longblock is GM.

              it wouldnt mater if they replaced the longblock from a forktruck...... because it is identical down to the fasteners, pistons, cam, etc. the 3.0 motor is the same, starting in the same parts bin in Tonawanda NY, and coming down the same assembly line

              the manifold, rotating electrics, mounts, coupling and flywheel housing are specific to the marinizer (OMG, VP, Mercruiser)

              so for internal parts...... source from GM

              however that begs another question. since 3.0 motors are literally under $300 for a running motor (once you get the free boat, and pay to scrap the rotten hull). why would you rebuild one?
              Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

              1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

              Past Boats
              1970 Wooster Hellion - Merc 9.8
              2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
              1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

              What’s behind you doesn’t matter.Enzo Ferrari

              Comment


              • #8
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                $200 for a set of rods? I'd be looking for a rebuildable core engine before spending $200 on rods. Plus, rods don't need to be replaced unless messed up (bent, cracked, bearing spun too bad to resize, etc) and $50+- would most likely have the entire set magnafluxed and resized.

                The rods from my 73' 181 were in spec, had them magnafluxed at the shop while they were pressing on the pistons, but I didn't have them resized. Other engine builds, I've had the rods resized....
                2001 Crestliner SuperHawk 1800, Mercruiser 140HP
                2007 Tracker 1436 jon boat, 7.5HP Force

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