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OT/Briggs&Stratton compression release?

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  • OT/Briggs&Stratton compression release?

    My 18 HP single cylinder B&S Intek engine swallowed a screw that came loose inside the carburetor which ruined the piston and severely damaged the head I repaired the head and replaced the piston and the engine runs fine, AFTER I finialy can get it started! It seems that most of the time it will simply spin a few degrees then the starter can not turn it any farther but if I turn the engine backward manually so that it is coming up on the exhaust stroke when the starter is engaged it will spin up to speed and start just fine. I tried 2 different starters including a new one and even a new fully charged battery but the darn thing simply acts as if it has too much compression for the starter to spin the engine unless it comes up on the exhaust stroke first. Now when researching the valve rocker arm clearance on the net I saw reference to "make sure the engine is at the right crankshaft position so the compression release will not cause an error".


    Compression release?
    Is there a mechanical compression release in this engine? Is it possible I have something I did wrong while it was torn down and if there is such a device can it be accessed without tearing down the engine again?

  • #2
    Don't know all your problems but a compression release is very easy to install.

    http://www.hotbikeweb.com/tech/0306h...ses/index.html

    My Harley has one in each head. It's a 103" engine but has the old 88" starter so these are pretty nice on hot days.

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    • #3
      It would seem that if you had the head off (obviously you did) that a compression release would have been VERY obvious, if it were there,so for whatever reason yours doesnt have it. A good many of the newer S&S motors come with electric compression releases now,screw into a threaded hole in top of head.Maybe something of that nature would do the trick? That would eliminate have to push the release button every time you started the unit.Best of luck with this,let us know how it turns out.

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      • #4
        On a Briggs twin, I have an 18 hp also, and it is hard to spin over. If it is a mechanical centrifugal controlled comp release, it may have a weight with a spring that pushes a pin that open the exhaust valve during cranking rpm. This is a common design. If it is the Briggs "Easy-spin" starting compression release, then that is the intake lobe having a very slight rise that opens the intake valve a slight amount during the compression stroke. There is no centrifugal weight, it always functions to open the intake valve slightly at ALL rpms. You would think reversion would be a problem, but they do run. It is sort of a variant of the Miller-cycle, like the Otto-cycle, but intake timing bleeds pressure during compression by timing. Anyhow, if the valve lash has increased any amount, this additional lift from the easy spin intake cam is taken up in the lash, and does not lift the valve. It will run ok, actually better, but starting compression is a bear. Also, did you have the other head off? Carbon buildup will cause increased compression. Come on guys, it is a Briggs, not a Harley.
        --Doozer
        DZER

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        • #5
          any chance the crash buggered up the flywheel key?
          gvasale

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          • #6
            No the flywheel key was replaced, I felt it a good idea since the flywheel was off anyway and it was only 40 cents. This is the Intek single cylinder 18 HP engine and inside the crankcase there are some counter-balancing weights, springs, etc so I guess some of these parts might have something to do with a compression release. I have one of those service manuals on CD that while seemingly quite complete in coverage can be a PITA to find any specific info and try as I might I can not find any reference to a compression release. Since if it might be an internal centrifugal device that opens one of the valves slightly then maybe the valve lash being too loose might be the problem?

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            • #7
              Here is an excerpt from another website relating to the same problem.

              I have a Cub Cadet ZRT42 mower with an Intek 17hp Briggs motor and had the same problem of hard starting.
              I read alot of threads trying to find the answer and read severalposts that recommended valve adjusting but I thought my mower ran just fine when I was able to get it started (using an elec drill with a socket on the top flywheel bolt to assist the poor starter)so I blew off adjusting the valves.
              Bought a brand new starter and stuck it on. SAME PROBLEM! AARRGGHH!!! More searching the internet for the answer. Thought I had a bad compression release mechanism for sure.
              I saw how easily I could access the valves and decided to go ahead and check them. They needed adjusted alright. I turned both nuts in about a half turn each to get them to .004-.006. I thought, "No way is this the problem", but I reassembled it and hit the key and don't ya know that sucker started up like a new one! I tried it two more times and each time it fired right up.
              Wish I would have tried the valve adjust before I dropped $84 on a new starter. I have the original starter on now and it's fine.
              Just F.Y.I. fivestring
              Here is a link to the complete page.
              Home, down in the valley behind the Red Angus
              Bad Decisions Make Good Stories​

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              • #8
                Originally posted by Willy
                Here is an excerpt from another website relating to the same problem.



                Here is a link to the complete page.


                Hey man, THANKS that is exactly what my engine is doing! I will get out there and re-adjust those valves and see what happens.

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                • #9
                  Report back! I have a similar problem but mine is not keeping the motor from strating... yet.

                  Separately, I also had a rodent issue and the cutout wire for the "safety switch" on the seat was grounding to the frame causing a backfire on every left turn. That was a pain to hunt down.

                  rock~
                  Civil engineers build targets, Mechanical engineers build weapons.

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                  • #10
                    I will have to wait for this monsoon to move through here before I can get to it, it is really coming down out there right now.

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                    • #11
                      Briggs has had "compression relief" built into their cams for many years. You shouldn't have to add one. Things to check is the valve adjustment as mentioned. They could be too loose. Also a bent crankshaft and a spun or sheared flywheel key. I have both the 18 and 22 hp Briggs. A charged battery will spin them like crazy.

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                      • #12
                        If memory serves me correct, adjust the intake .003-.005 exaust .007-.009

                        If you tighten the exaust it will cause the compression release to work better. A common problem for the briggs is for the adjuster to loosen up. This defeats the purpose of the compression release. The compression release is on the camshaft. It works with centrifigual force. Put some blue locktite on the adjusting screw and it'll be good for quite awhile.

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                        • #13
                          I just got back in from working on that thing and no luck, it still does it but the curious thing is that it is not nearly as bad and will start now sometimes, before adjusting the valves it would never start unless I backed it up to the exhaust stroke. I temporarily adjusted both valves down to .003 just to see if it would make a difference but it didn't, they certainly were loose because when I checked them they were intake .008 and exhaust .007. I set both valves at .005 and the problem got some better but going tighter does not create any further change. I think it is time to tear into it again and find out what the problem is, probably something simple once I find out what it is.

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                          • #14
                            Originally posted by ahidley
                            The compression release is on the camshaft. It works with centrifigual force.
                            I believe you're thinking of the governor. That works by centrifugal force off the cam. The compression release is designed into the cam lobe(s). (Intake, as I recall.) It holds the valve open longer. At cranking speed, it lowers compression but at running speed it's immaterial.


                            Rad - Did the engine stop suddenly when the screw came loose?

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                            • #15
                              Originally posted by CCWKen
                              Rad - Did the engine stop suddenly when the screw came loose?

                              No it just started rattling and miss-firing, when I shut it down it would not restart because the compression was so low. I took the head off and found the screw embedded in the piston and a valve stuck open slightly because it was bent. I replaced the valve, both push rods and the piston (the cylinder walls were not harmed and the valve seats and moves freely) and the thing runs fine now except for this starting problem. The pieces that came out of the carburetor were from the throttle butterfly, one of the screws holding it to the shaft and a tiny bushing that the shaft sits in.

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