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O/T - Briggs motor on power washer starts now

Discussion in 'Off Topic Threads' started by joe kuhn, Jul 5, 2012.

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  1. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    This little Briggs motor is on a power washer from Craftsman/Sears. A neighbor of mine gave it to me because it wouldn't start. He didn't know what was wrong with it and since I like the challenge I dragged it home.

    The intake manifold was broken on the end that goes into the carb. Replaced that but the thing still wouldn't start. Noticed fuel spray coming out of the carb when the air cleaner was off.

    Took it apart again and noticed that there was no compression. I could turn the flywheel by hand with no trouble. Expected it to turn harder as the piston came to the top but that didn't happen.

    So I'm now reseating the valves, particularly the intake valve. There are no visible holes in either valve. My theory is the guy who had it ran it without water running through it and over heated the motor thereby heating the intake manifold, which is plastic, causing it to crack and crumble. When I put my hand over the piston hole and turn the flywheel there seems to be plenty of suction. I'm betting the rings are ok.

    I wonder if the valves are warped as in the cup at the top is cupped more. Should I replace them or just reseat what I've got? I've got some grit, but have to get that little tool for turning the valve to seat it. Turned the valve by hand some in order to try to seat it. That showed the adjoining surface is 'wavy'. Head gasket is not blown. As you can see, the unit is nearly brand new. Spark plug was seated fine. It gives plenty of spark.


    [​IMG]
     
  2. scooterbum

    scooterbum Active Member

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    You probably had a piece of the intake manifold lodged under the intake valve, holding it open.
     
  3. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    Will look in the exhaust system for that. Didn't see anything, but good possibility.
     
  4. Johnny

    Johnny Well-Known Member

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    Joe, the older Briggs engines are just junk and that is what they do. I have an 8hp Briggs go-cart engine blowing gas out the carb. Very little compression. Same problem, valves are leaking. Change the rings and valves while you have it apart.
     
  5. W.P.T.

    W.P.T. TS Member

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    You got it for the right price, thats for sure ... WPT ... (YAC) ...
     
  6. Tralfaz

    Tralfaz TS Member

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    You might want to pull the flywheel and check the key that holds it in alignment. It controls the timing and it doesn't take much to through it off. You will still have spark, just not at the right time. It's on a tapered shaft so a puller is required.
    Dave
     
  7. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    You guys tell me if the timing seems right. Captions are always on top of pic.

    Spark per fly wheel - both valves closed:


    [​IMG]


    End of power stroke - both valves still closed:


    [​IMG]


    Top of exhaust stroke - exhaust value on bottom is fully open:


    [​IMG]


    Intake stroke, but intake valve remains closed:


    [​IMG]


    Compression stroke on the way to spark, but intake valve is open:


    [​IMG]


    It seems wrong to me. The intake valve begins to open when the piston is at the bottom and on the way back up to the spark - the compression stroke! I always thought the intake valve should be opening on the down stroke to pull the air in. Looks like I'll be taking more of it apart.

    I got the valves seated.
     
  8. halfmile

    halfmile Well-Known Member

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    looks like the intake valve is out of time. It should close at or a little after BDC. the "after" is because the incoming charge has inertia and can pull a little more mixture into the chamber. A little overlap at the end of the exhaust stroke is pemisible because the exiting gases can help pull the new charge in.

    Check for timeing marks on the cam gears. If it's all on one gear you have a problem, lol.

    HM
     
  9. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    Hey halfmile. Looks like it's time to split the cases.
     
  10. G550

    G550 TS Member

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    Does it have a compression release system? If so, below idle, the cylinder will leak through either the exhaust or intake valve. Not sure how to troubleshoot the system though.

    RCH
     
  11. Brian in Oregon

    Brian in Oregon Well-Known Member

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    Sure you're not turning the crank in the opposite direction?
     
  12. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    Hah! Good question. Yes, I made sure I was turning it the way the string would pull it. And I made sure I got the pictures in the right order. I checked them with the motor after posting here.

    I don't see a compression release system anywhere. It's clear that the intake valve is opening on the compression stroke. Will take the cases apart and see what's inside.

    More later.
     
  13. Caribou woodland

    Caribou woodland Member

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    Look at the timing mark on cam-shaft and on crank-shaft.Might look like * or 2 '
    Salutation Pierre
     
  14. motordoctor

    motordoctor Shoji Tabuchi in Branson

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    One other thing that you might have missed is something called valve recession. On some of the engines without hardened valve seats the valves tend to sink deeper into the seat. You have to grind the end of the valve stem to have clearance between the end of the valve stem and the lifter. Just like a car with solid lifters. I think the spec is about .010" but not sure about that spec. The ones that I fixed we just put some clearance in and the valve would seat. This usually is the problem that the valve will not close all the way ans might NOT be YOUR problem but make sure to check it. motordoc
     
  15. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    I was able to seat the valve nicely with some grit and a lapping tool. Will check the gap and see where it's at to be thorough. Thanks.
     
  16. G550

    G550 TS Member

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    The 10.5 hp Briggs on my mower relieves pressure through the intake valve during start. Pull starter. If I take off the air cleaner I can hear it when I crank the motor. The system is automatic and invisible to the operator. Don't know what engines they are incorporated into. Makes it easier to pull start higher hp engines.

    RCH
     
  17. grntitan

    grntitan Well-Known Member

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    Joe,

    Remind me again why you would split the cases? If the connecting rod is still attached to the crank and pushing the piston up/down, then your problem is likely not in the lower end.

    That engine looks awful clean and newer to be having many serious issues. I know B&S had timing issues with some of their engines several years ago. If I'm not mistaken, the 6.75hp was one of the problem engines. I think halfmile and Pierre have the answer. Find the timing marks and see where they are in referrerence to each other. Also the post about having a piece of broken manifild holding the valve open sounds very plausable too. Make sure it didn't bend the valve.
     
  18. scooterbum

    scooterbum Active Member

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    As Brian in Oregon has indicated, you need to revisit the crankshaft direction of rotation. Try rotating it in the other direction, and see if the valve sequencing is not indeed, correct.
     
  19. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    Motor is a smaller 6.75HP Briggs.

    The timing marks are inside the engine. The cases have to be split to get at them.

    The engine turns in a clockwise direction (from above) based on the pull cord. Nothing makes sense going the other direction.

    I'm going in.
     
  20. Jim101

    Jim101 Active Member

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    Split the case, I bet you will find a plastic camshaft gear that has slipped on the shaft. Have seen that several times.



    Jim
     
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