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  1. #1
    PWCToday Guru
    Join Date
    Oct 2013
    Location
    Ohio
    Posts
    313

    770 Crank Bearing retaining pins

    I am seeking information from those of you who have had a lot of 770's apart.

    I have had 3 770's apart. Two of the engines have a small pin, about 2.4mm in each bearing. These pins rest in small notches that are cast into the intake side of the upper case half. When the bottom half of the case is installed, the pins are captured in those notches.

    I purchased a 3rd engine (non running condition) in my quest to collect parts to reassemble an engine which someone assembled with incorrect parts.

    This 3rd engine has larger, 4.9mm pins. The pins in this engine fit into holes in at the very top of the bearing location in the upper case half. (They would be on the bottom while the case is upside down during crank installation) Then when the crank is lowered into the case, these 4 pins must fit into corresponding holes in each bearing. I believe the engine I purchased failed because 2 of these pins, on the PTO end of the crank, were not in the bearings correctly. This held the cases apart, causing an air leak which melted the PTO piston. It also was not good for the case as it appears one of the bearings was able to spin in the case.

    The 1999 service manual states, "Be sure the alignment pin on each bearing is positioned in its respective alignment notch in the crankcase." The photo shows notches between the case halves as described above.

    My questions are;

    Have any of you with more experience see both types of bearing alignment pins on the 770's?

    When you purchase new bearings, do those alignment pins some with them or do I have to make new pins?

    Have any of you ever had these pins work their way out and damage your engine?

    Thanks,

    John
    2, 1998 TS 770 L, restored and running great. (Except for the one with engine that SBT put the WRONG crankshaft bearing into and is now sitting as I collect repair parts)

  2. #2
    PWCToday Newbie
    Join Date
    Jun 2010
    Location
    Roseville, MI
    Age
    30
    Posts
    7

    Re: 770 Crank Bearing retaining pins

    Hello John.

    I believe I have found the solution to your whole problem.

    I believe that the two similar 770 engines that you have taken apart have had SBT cranks put into them, whereas the 3rd has the original or a correctly rebuilt crank put into it.
    The 644 (650) and 640 engines used bearings with the pins built into them, that fit into notches in the cases, according to the parts fiche.
    The 770 engines used bearings with the 4.9mm separate pins, that fit into holes in the upper case half, according to the parts fiche.
    The 644 (650) and 640 engines used a 72mm OD bearing, whereas the 770 engines used a 75mm OD bearing.
    644 (650), 640, and 770 cases have the notches for the bearing pins machined into them, although the 770s don't use them.
    Your SBT engine seems to have been assembled with the wrong style, but correct size, of bearing, with the pins built in, and Arctic Cat/Suzuki deemed that setup incorrect for the 770, probably due to vibration working the pins out of the bearing, and causing your situation.

    Your 1999 service manual says that because Cat has always had a proofreading problem.

    The answers to your questions.
    1. I've never taken apart a 770 engine, but I've helped build countless Cat sled engines that use the 4.9mm pin setup.
    2. Purchase your crank bearings from a Koyo distributor, using the part numbers on your 4.9mm pin crank bearings. You can buy the pins from Cat, part number 3003-658.
    3. I've never seen, or heard, of the 4.9mm pins working their way out.

    Hope this helps.
    Kyle T

  3. #3
    PWCToday Guru
    Join Date
    Oct 2013
    Location
    Ohio
    Posts
    313

    Re: 770 Crank Bearing retaining pins

    Thanks for your input, I believe you are correct Kyle. It appears that there was a design change what was not updated in the service manual. It is interesting to also note that the the Artic Cat parts lists show those same 303-658 pins for both the 640 and 770 for several years prior to 1999.

    I did order the pins from Cat since I posted that message.

    Thanks,

    John
    2, 1998 TS 770 L, restored and running great. (Except for the one with engine that SBT put the WRONG crankshaft bearing into and is now sitting as I collect repair parts)

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