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Thread: 4 Stroke Top end knock?

  1. #1
    MPDano's Avatar
    MPDano is offline At The Back Of The Pack Arm chair racerAt the back of the pack
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    4 Stroke Top end knock?

    Just restored my Fat Cat. I didn't have this noise before the build. I never opened the engine besides replacing a leaking clutch cover. I did put 10/40 instead of 10/30 4 stroke motorcycle oil in it. I was also thinking I could have put the brass exhaust gasket in crooked? Valves adjusting?

    Disregard the high idle, I rebuilt the carb and used the needle in the kit and I noticed it was a little different in diameter.

    Oil pump not getting oil to the top? Any thoughts on this noise?

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    MPDano's Avatar
    MPDano is offline At The Back Of The Pack Arm chair racerAt the back of the pack
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    I also didn't drain the fuel as it was sounding fine prior to the rebuild last month. Old fuel detonating? Gonna drain it regardless.

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    Drained gas and added a little slosh old stuff out. Tank reinstalled and filled with 91 octane. Replaced carb needle, same noise and the idle is smooth but upon throttle up, I get the high idle and slow coming back down. Seems like I got an air leak.

    Noise is still there and will verify valve adjustments. Oil is new 10/40 and oil level is good.

    Weird how this noise wasn't there before. Ughhhhhhh.

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    Doink's Avatar
    Doink is offline At The Back Of The Pack Arm chair racerFirst time rider
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    MPDano,
    If you're hearing a noise, it is not likely the fuel.
    Start by checking the spark plug (detonation oil/gas fouling), re-tighten all mounting bolts (rattles), and drain and examine the oil and the oil filter (burning or shavings). If all that checks out, then I would recommend having a pro listen to it for better advice.
    "If it were easy, everyone would be doing it."
    1987 Yamaha BW350 (dealer find, never oiled or gassed)
    1990 Suzuki DR350 Fat Cat/ Big Wheel conversion
    2011 Suzuki KingQuad

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    Quote Originally Posted by Doink View Post
    MPDano,
    If you're hearing a noise, it is not likely the fuel.
    Start by checking the spark plug (detonation oil/gas fouling), re-tighten all mounting bolts (rattles), and drain and examine the oil and the oil filter (burning or shavings). If all that checks out, then I would recommend having a pro listen to it for better advice.
    Fuel change is because I didn't know the age of the gas, hence possible detonation due to old gas. Spark plug looked perfect when I checked this morning. Gave it a blast of air to make sure nothing was in there as well. Going to check the valve adjustments after work and then verify compression. She runs strong regardless. That idle speed up could also be a sign of an air leak and leaning. Either way, we can all figure this out together, no need for paid (pro) help, lol.

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    Check the gap on the valves and the slack in the timing chain, not the chain on the rear of the bike. lol.
    It sounds like a consistant rotating mechanical issue from what I can tell from the video, so those would be my first stop. It could be the exhaust leaking, but unlikely. The cam would be the next thing to check out while adjusting the valves.

    It should be something is those areas. Good luck.


    Sent from my SAMSUNG-SM-N900A using Tapatalk

  7. #7
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    Did you possibly double up the soft copper exhaust ring? I know sometimes its hard to tell when there smushed flat they look like part of engine. I had the opposite with a slow rising idle, it was either carb top related (fixed) or not using a new orings in the intake. (Fixed).
    If you smoke hold one near the exhaust flange see if theres any flow (leak)(carefully)......
    Ok the smoke may not be a good idea but you know what i mean.
    Nice bike by the way.

    Shep

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    Quote Originally Posted by wrightracing View Post
    Check the gap on the valves and the slack in the timing chain, not the chain on the rear of the bike. lol.
    It sounds like a consistant rotating mechanical issue from what I can tell from the video, so those would be my first stop. It could be the exhaust leaking, but unlikely. The cam would be the next thing to check out while adjusting the valves.

    It should be something is those areas. Good luck.


    Sent from my SAMSUNG-SM-N900A using Tapatalk
    Will be checking the valves after work. Is the timing chain adjustable or does it slack from getting old and stretching? I do know this engine has a tensioner on it.

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    Quote Originally Posted by Shep1970 View Post
    Did you possibly double up the soft copper exhaust ring? I know sometimes its hard to tell when there smushed flat they look like part of engine. I had the opposite with a slow rising idle, it was either carb top related (fixed) or not using a new orings in the intake. (Fixed).
    If you smoke hold one near the exhaust flange see if theres any flow (leak)(carefully)......
    Ok the smoke may not be a good idea but you know what i mean.
    Nice bike by the way.

    Shep
    I had used a screwdriver to make sure the surface was clean before installing the copper o-ring. Lol, yes I do smoke but was going to try the torch gas trick after work as well. Torch unlit of course.

  10. #10
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    Timing chains stretch over time, i dont think i've ever read on here about a tensioner failing but if you find yours is junk dont buy one- i have extras i'd just send it to you. Did u use synthetic oil?
    Just put the old oil back in maybe the noise will go away. (Just kiddin)

    Shep

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    Quote Originally Posted by Shep1970 View Post
    Timing chains stretch over time, i dont think i've ever read on here about a tensioner failing but if you find yours is junk dont buy one- i have extras i'd just send it to you. Did u use synthetic oil?
    Just put the old oil back in maybe the noise will go away. (Just kiddin)

    Shep
    Ha ha, I just use Yamalube dino oil. Even on my KTM 250SXF I only use Semi-Syn. That Synthetic stuff is pricey

  12. #12
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    If you feel the need (probably should) you can check for oil pressure. Its the small rusty one in my pics, if you look u can see where the oil travels up and past that bolt then drips/pours i have no idea how much on to the cam where the orings are. If you take it right out you'll know pretty quick if its getting oil up there.
    I suppose u could run it for no more than 10 seconds or kick it over a few times w/switch off. Just dont forget to put the bolt back in!!!

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    Shep
    Did u use rtv or a new side cover gasket when u replaced it?
    Last edited by Shep1970; 06-13-2017 at 11:46 PM.

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    Quote Originally Posted by Shep1970 View Post
    If you feel the need (probably should) you can check for oil pressure. Its the small rusty one in my pics, if you look u can see where the oil travels up and past that bolt then drips/pours i have no idea how much on to the cam where the orings are. If you take it right out you'll know pretty quick if its getting oil up there.
    I suppose u could run it for no more than 10 seconds or kick it over a few times w/switch off. Just dont forget to put the bolt back in!!!

    Click image for larger version. 

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    Shep
    Did u use rtv or a new side cover gasket when u replaced it?
    Nice tip to check the oil pump operation. Clutch cover is just gasket, no RTV. Sealed perfectly.

  14. #14
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    Put it TDC per manual. Marked original settings. Adjusted per procedure and they were almost spot on, not much change. Also verfied the exhaust copper gasket was in correctly. Starting this think the prevous owner put heavier oil to hide an issue. Also broke the cap right below the valve adjusters. Ughhhhh, another Honda order and delay.

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  15. #15
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    i was thinking decomp cable but i dont think there is on on the fat cat right? On the 86/87 200x (its close to the same topend) if the cable is to tight it'll click like crazy up there. But prob not your issue. I see the lever now in your middle pic does it move freely(spring back) it only moves 1/4 inch anyway.

    Shep
    Last edited by Shep1970; 06-15-2017 at 06:19 AM.

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