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Thread: D4 7U pony motor knock.

  1. #1
    Join Date
    Sep 2016
    Location
    nebraska panhandle
    Posts
    70

    Default D4 7U pony motor knock.

    This pony is the elec start type. When I start the pony it has a bad knock that lasts for about 3-5 seconds then the knock stops and the engine runs good. The idle on the motor seems to run to fast on start up even though the throttle is pulled clear back.
    1. I changed the oil in the pony and refilled with 30W oil.
    2. The crankshaft seal has a leak.... not serious but will run out 2-3 oz. during a start up of the main engine.
    3. There is no play in the flywheel when trying to move it up or down.
    4. I put a new lock/keeper on the flywheel nut and drew it down with an impact wrench. I did not take the flywheel off of the crankshaft I just tightened the nut.

    Some one said that the key/keyway on the crankshaft could be worn and cause that knock. I know the proper starting procedure would be to have the motor idle and get oil to the bearings but as of now it does start at to high of an idle. When we get some warmer weather I see about getting the idle down.
    Any advise,suggestions would be appreciated.

    Thanks.

  2. #2
    Join Date
    Nov 2006
    Location
    Faunsdale, AL USA
    Posts
    3,967

    Default

    The pony is warning you!

    Two things I would check before the next startup. Both would be after taking the heads off the pony. Remember to drain the main engine cooling system before popping the heads off.

    I think it's most likely you have a wrist pin bushing or a piston that is failing. Should be able to see some marks on the top of the piston that's affected.

    It could also be the connecting rod bearing, but I doubt it would still be running if it was that. I do have an OLD small block Chevy that when it was new, used to knock about 3 times when first started in the morning. I think they came up with the oil filter anti-drainback valve and the new style filter cured it. Hasn't knocked since the mid '90s. I doubt a Caterpillar pony motor would live long with that kind of clearance.
    D2-5J's, D6-9U's, D318 and D333 power units, 12E-99E grader, 922B & 944A wheel loaders, D330C generator set, DW20 water tanker and a bunch of Jersey cows to take care of in my spare time

  3. #3
    Join Date
    Jan 2019
    Location
    North Texas
    Posts
    99

    Default

    I can't help with actually fixing it, but you might try cranking it 10 seconds with the ignition off to get the oil moving before it fires up.

  4. #4
    Join Date
    Jan 2009
    Location
    Colorado Springs and Waitsburg WA
    Posts
    945

    Default

    Check the throttle linkage. Probably set up incorrectly to not let the governor close the throttle.
    John Liebermann
    2 9U's, 5J, IHC544, Ford860, (All working farm tractors)
    cojhl2@gmail.com

  5. #5
    Join Date
    Nov 2006
    Location
    Plains of NW Kansas
    Posts
    438

    Default Piston my Bet

    I think CC is onto the correct cause. Any loud knock cannot be good news. Sounds more like a cracked piston that when it gets heated expands and doesn't rattle as much. The early small block V-8 Chevy engines were notorious for cracked piston skirts and rattled when cold but calmed down when warmed up. The lack of noise when warm is only covering up a more serious problem that can be very expensive to fix if not fixed now.

    Let us know what you find out.
    D4Jim
    D47U (1950), 3U 112 Grader (1949), Cat 40 Scraper ACMOC Member 19 years

  6. #6
    Join Date
    Nov 2006
    Location
    Pittsford NY
    Posts
    4,363

    Default

    For the idle, check that the tang on the throttle rod is behind the throttle arm boss. The rod pulls the throttle closed against the governor spring. If yours is not doing this, then you won't be able to idle it down. Starting it at idle is important for longevity because it enables the oil to circulate/splash to fill the clearances before you run at high speed.
    Losing 3oz per run is 10% of your total oil volume (pony takes 1qt/32oz). Make sure you fill up to the mark before every start. This will have the side effect of keeping your oil generally newer because you're leaking the "old" stuff out.
    Cheers,
    Neil.

  7. #7
    Join Date
    Sep 2016
    Location
    nebraska panhandle
    Posts
    70

    Default

    I did get out today and got the hood off of the 7U for a look down onto the carb. The throttle tab/tang is on the outside of the governor linkage. As you push the throttle in the tab moves and lets the governor arm move out away from the tractor. The governor rod is hooked to the carb butterfly. The shaft that holds the butterfly moves when you push on the governor arm. So with that said, next is to get the air breather off and look and see what is wrong. Screws out of butterfly or something broken. Probably end up pulling the carb off for repairs. If I remove the air breather and fuel tank can I get it off the engine? This is an outside project, no shop so just so much time during the day to work on it. Thanks.

  8. #8
    Join Date
    Sep 2016
    Location
    nebraska panhandle
    Posts
    70

    Default

    Forgot to say that I did start the pony yesterday. Charged the battery to make sure it was full charge the spun the engine over for 10-15 seconds(ignition off) to circulate/splash some oil around before starting. Did it help? Considering the pony hadn't been started in 3 months I would say it did some. The knock was there but of a shorter time. The motor was choked down and didn't run as fast so that's why.

  9. #9
    Join Date
    Jun 2007
    Location
    Colorado West
    Posts
    1,169

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    Quote Originally Posted by bplunk View Post
    So with that said, next is to get the air breather off and look and see what is wrong. Screws out of butterfly or something broken.
    Throttle butterfly screws make a horrible noise when they're bouncing around between a piston & a head...and it tends to be intermittent until they embed into the top of the piston.

  10. #10
    Join Date
    Nov 2006
    Location
    San Gregorio Mariposa, CA
    Posts
    579

    Default

    When I bought my HT4 the pony had a bad knock. I found the pony flywheel was loose. The nut was tight but the key way was wallowed so it could rock. A flywheel from a parts pony fixed it.

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