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Thread: 4A084 inline motor rebuild

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    Member Bart's Avatar
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    Dec 2015
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    4A084 inline motor rebuild

    I am starting to wonder if I will ever get this in the boat, or it I will be just going from one project to another with it..
    over the summer I have found out some things that might be worthwhile, for anyone out there looking for parts and pieces. for the 084 motor
    I know last summer, fall and winter Saturn Surplus was trying to sell all of his inventory, and shut the door, I am still glad he is still answering his phone though..
    but there was a big frenzy in gathering up all, or any part that you thought you might need. in case of the dreaded rebuild.
    me I picked up a few items, but I was told the motor had just been rebuilt. so why should I worry????

    so after finally finishing the EFI and ignition. The motor would idle, okay, and I was stoked, there was a lot of time and energy in getting all the parts and pieces together. But there just was something always going on with the motor. I would look at the fuel table charts and things just were not where they were supposed to be. I kept thinking it was an air leak, bad injector, I had done a compression test, had great oil pressure. and it all looked good. my #2 & 4 cylinders were the big problem children, one or the other was always going down, or running way to hot...
    Finally I had enough and delved into it, to look for what was the bigger issue.
    I knew someone had been through this motor before, a few of the bolt had been replace with grade 8, and gone where the slotted ones..
    I did a leak down test, and the pressure really didn't hold on the one cylinder that I tested. a lot was going past the rings..
    all the pistons and rings looked okay, but then I measured the ID of the cylinders. max is 2.995, and in the middle of mine 3 were measuring 3.005
    at least at the moment I am thinking this might have been the problem, at least I hope so..
    now comes the fun part looking for replacement parts, and I found a few items along the way, but now I had wished I had known about the suppliers below earlier, it would have saved me a lot of time looking for rod bearings and the correct chrome rings...

    the Pistons and cylinders both have a stamp on them, A,B, C, & D. that designates the ID of the cylinder, & OD of the piston..
    NEVER use a "D" piston with a "A" cylinder, it will work for a little, but there is not enough expansion, sooner or later it will over heat and seize to the wall...

    this and other useful information I found when I started looking at the forums that dealt with the 274 mule or the 2A042 motor and the link that started it all
    https://forums.g503.com/viewtopic.php?f=148&t=262382
    I visited with Charles Witt, a couple of times, he has been rebuilding the 2A042 motor for the past 40 years. and had some great information, on what to look for. and will always need to be replaced, and depending on what rings you use with the piston. Cast Iron rings, will wear out the cylinder wall. Chrome rings, just put a light hone on the cylinder walls and new rings, you will be good to go.
    also replace the rod bearings,, the other problem that he has seen is the camshaft bearing will spin, his fix is to loctite the outer flange to the case.
    the beauty about the 2a042 motors, you have plenty of crankshafts, and camshafts out there, and they are cheap.. not so lucking for those using a 4A084 motor, I have yet to find a spare.
    so as I was looking at this forum, a name of John Emery, kept coming up, that carried an inventory of parts. so I got in touch with him and found out that he carries, matching piston to cylinder sets, rod bearings, stock and undersized, an double chrome ring sets. (he sends the piston and cylinder to a machine shop, where they are fitted as a matching set. and are sold as a set)
    when I found out the pricing, I was wishing I had found him a week earlier, before I purchase a bunch off Ebay, now I gots lots of stuff...

    one of the things that impressed me, when I got my shipment from John was the bearings and rings where still in the manufactures sealed pouches, the dates were over 50 years ago, and when I opened them up. they didn't look over a day old.
    the rod bearings looked tired, but when I measured the crank journals they were still in factory spec. so I didn't need to send the crank out to be reground, and that helped out a lot.. and I plasti gauged the new bearings, they all were close to .002 clearance.

    the one thing I did notice is when I picked up the motor, without the plugs I could turn the motor over by using the rope pulley. I could do it with 2 of the new kits in, but once all 4 cylinders with new rings, I had to use a strap wrench to rotate the crank...but the starter has no problem...
    also with this style of ring, you will need a ring compressor to install them to the cylinder,, the old ones I could do it with just my hands,,,

    true to my nature I had to spruce something up on this motor, with this rebuild. the exhaust nuts were driving me crazy, I needed 2 different wrenches, a 7/16 & a 5/16, so I picked up some 7/16 brass hex rod and turned out some custom exhaust nuts,

    also one other thing that I am attempting on this rebuild, I notched grooves on the connecting rod to squirt oil at the base of the piston. to see if I can get the heads to run a little cooler. from all that I have read, it can reduce the head temp from 50 to 100 degrees. I will find out if that is the case, for my motor also before too long. some of my friends are worried that it might stress crack the rods, where this motor should never see anything over 4000 rpms. I am thinking why not..
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