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  1. #1
    Moderator OsideBill's Avatar
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    Smile Thrasher63 OSB 1390 motor assembly

    I recently did a motor assembly for a friend and decided to post some pics for another friend to help him out.

    I had the crank installed and cases sealed previously. I laid out all the items I needed to install the pistons and cylinders first, to make sure I was not missing anything.

    I then prepped the cylinders for installation, I cleaned all the threaded holes and gasket surfaces. Then I installed the studs for the #2 cylinder, this is one of the few places I will use red loctite. I hate it when you take the exhaust manifold off, and the studs back out from the cylinder instead of the nut coming off.
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  2. #2
    Moderator OsideBill's Avatar
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    I had painted the cylinders earlier with a two part epoxy i get from the auto paint supply, it is a primer and I have them color it black, the stuff is excellent for this application.

    I installed the PV caps and the aluminum plugs I get from Lowell, gives it a nice look.

    I installed the anodes, then was ready for the piston install.
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  3. #3
    Moderator OsideBill's Avatar
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    Note the paper towel wrapped around the rods, I do this to protect the mating surface on the case from damage when the rods move during handling.

    Now I prepare the base gasket and install it, I use just a light coat of marine grease for a sealing aid.
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  4. #4
    Moderator OsideBill's Avatar
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    Now it is time to prepare the bearing and piston.

    I put the bearing in two stroke oil to soak.

    I then check the size of the piston ring gap, spec was .004 min.

    I put the ring in the cylinder, I then use the piston to square it to the cylinder.

    Then I check the gap with a feeler gauge, this one was .024" no need for extra work
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  5. #5
    Moderator OsideBill's Avatar
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    I insert the wrist pin clip in the front side of the piston, I use a wrist pin and push from either side to insure that is in correctly.

    Then I lube the wrist pin and inside the piston with assembly lube.

    I put two stroke oil in the case oilers and rod bearing.

    I smear a light coat of two stroke oil in the cylinders and a coat on the pistons

    I install the rings, then I install the pistons onto the rod, be sure the arrow points toward the exhaust. I always use new wrist pin bearings, wrist pins and thrust washers. be sure the sharp edge of the thrust washer is facing towards the rod.

    Torque the cylinder bolts to spec per manual.
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  6. #6
    Moderator OsideBill's Avatar
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    Next up is to get the exhaust manifold installed, and the head installed.

    I use a light coat of marine grease on all the gaskets, all bolts were cleaned. I use blue loctite on the exhaust bolts torque to spec per manual. then align the head and torque to spec, I use antiseize on the head bolts as I will be re-torque them after first heat cycle and remove head a couple times during the tuning process.
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  7. #7
    Moderator OsideBill's Avatar
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    Next I will install the reeds pretty simple not much to cover here. VF-III reeds and my Reed stuffer plate were installed on this one. Gasket between the reed plate and case, gasket between the reed plate and stuffer plate. Put all bolts in and torque to spec (8.9 ft-lbs).

    After this I installed the pressure test block off plates, the tee'd together hoses I use to plug the pulse lines and the spark plugs.

    Then it is time to pump it up to 10 PSI and pressure test. This motor dropped 1.1lb in twenty minutes she will be fine.
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  8. #8
    Moderator OsideBill's Avatar
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    Next up is mount the flywheel, bendix and front cover. I lap every flywheel I install, this is easy but must be done properly. I use a little bit of lapping compound, then slide the flywheel on the snout and while applying pressure I rotate it side to side. This whole operation takes less then 10 minutes.

    I deburr the sides of the keyway I find this always seems to be needed.

    I clean all the parts well, then I use some red loctite on the snout and the bolt. then install and torque to spec.

    After this I lube and install the bendix. Note: there is a small thin thrust washer on the case side of the bendix and a spring with a washer on either side in the front cover. Be sure and lube the holes that the bendix slides into. Install the fron cover and torque to spec.
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  9. #9
    Moderator OsideBill's Avatar
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    Hopefully Thrasher63 will come in and finish this thread, and add some more pics. I have a duplicate of this motor that I am in the process of building over the next couple weeks. I will post up all the rest of the pics I missed in this one.

    I heard the thing fire tonight and it purred like a kitten. I have the OEM Carbs jetted to 120 lows, 145 highs, 2.0 N&S, black 80 gram spring, chokes removed, drilled return with 95 restrictor jet and dual fuel feed. It fired on the first try and revved effortlessly. I can't wait to see this get broken in. Compression checked out to 150 across the board the squish is at .050" Lowell Head work and cylinder touch up. Pistons were swaintech coated, balanced and chamfered. Crank was trued and welded by Crankworks, and has their HD Mag bearing installed.

  10. #10

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    Well you pretty much got it all covered. It sounded so sweet fired right up and purred like a kitten. Thanks so much for all your help. What a differance it makes when a motor is put together with detail to perfection. It used to shake so bad even at idle since I had it built by G.K. now the motor hardley moves when it's idling. Im so greatfull for this site and meeting such a great person as yourself. If it was not for you I would still be wasting my money sending stuff back and fourth to group K. I will post my new speeds when I get it broken in.

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