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Hot!Briggs won't hold valve clearance

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Scott
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2019/05/15 14:54:56 (permalink)
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Briggs won't hold valve clearance

Ongoing problem:  B and S model 31000 series, 31C707-3346-G6, after setting valve clearances of Intake .003-.005", exhaust .005-.007" (cold), engine runs fine for a couple hours, then starts making a racket.  Opening the valve cover reveals the valve caps (p/n 691843) have fallen out, creating huge valve clearances.  It appears the ball pin adjusters are working loose, on their own.  How can I stop this from happening, or am I missing something?  Push rods are straight, renewed 3 years ago, thinking that was the problem.  It wasn't.  Any clues? 

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    AVB
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    Re: Briggs won't hold valve clearance 2019/05/15 20:00:36 (permalink)
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    Check the rocker arm studs. They may have broken loose and are backing out. If loose remove, clean of all oil, apply blue Loctite, reinstall, and torque to 150 in-lbs.
     
    The Rocker Ball Set Screw or Nut is torque to 45 in-lbs.
    Scott
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    Re: Briggs won't hold valve clearance 2019/05/16 14:46:49 (permalink)
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    Thanks for the response.  By the way, I'm performing the method of setting valve-lash by rotating the crankshaft CCW to TDC of compression stroke, inserting a rod in the plug hole, continuing CCW crank rotation until piston lowers apprx 1/4", then setting the valve lashes.  My ref for this is the B&S-published repair manual (online), and I'm defining CCW as viewed from looking down on the top of the engine.  Am I correct in these procedures?  
    AVB
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    Re: Briggs won't hold valve clearance 2019/05/16 17:37:08 (permalink)
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    Scott
    Thanks for the response.  By the way, I'm performing the method of setting valve-lash by rotating the crankshaft CCW to TDC of compression stroke, inserting a rod in the plug hole, continuing CCW crank rotation until piston lowers apprx 1/4", then setting the valve lashes.  My ref for this is the B&S-published repair manual (online), and I'm defining CCW as viewed from looking down on the top of the engine.  Am I correct in these procedures?  




    Hmmm I always did the CW rotation per Service bulletin ASPI 28. Into the power stroke and not into the compression stroke.
     
    https://drive.google.com/...pKUJnh7ek5rNEMzb2tHc2s
    Scott
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    Re: Briggs won't hold valve clearance 2019/05/16 18:23:57 (permalink)
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    Thanks!  This is enlightening, and quite possibly my problem...tho it doesn't answer why it did it in the first place...my ref for the CCW direction is 
    https://www.manualslib.com/manual/1207216/Briggs-And-Stratton-276781.html
    chapter 1, page 21.  The engine in question is a model 310000 series.  This ref is from 2009, but the service bulletin says 1996, I think.  Ennyway, I'll give the CW procedure a try, this weekend.  Thanks again!!
    AVB
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    Re: Briggs won't hold valve clearance 2019/05/16 22:01:18 (permalink)
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    As long as I been servicing these Briggs engines [10 years now] I didn't see the reference in the service manual until you pointed it out.
     
    I actually use a difference method anyway which is a very old method. What Briggs has is a newer method but prefer the old method as I am set in my ways being nearly 60 now.
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    Re: Briggs won't hold valve clearance 2019/05/17 00:36:42 (permalink)
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    Once again, thanks for the advice.  That leaves me wondering what the correct procedure is, and it'll help if I can try to envision what's happening inside the engine cycle with this compression release feature of the exhaust valve.  I don't think I'll hurt anything too badly if I try going CW versus CCW....feel like sharing your method?  By the way, I have two years+ on ya!!
       I'm editing/adding to this...I just watched some U-tube videos on how the B&S comp release works (pictures!!), and it makes sense to me now that the valve lash setting should occur CW, past TDC of compression stroke, with piston 1/4" into the firing stroke.  I have no answer why the instruction I referenced says something different.  By the way, is your method for setting valve clearances the one where the exhaust is fully compressed, then intake is adjusted...then repeated the other way around?  I've done that on some older motorcycle engines....  
    post edited by Scott - 2019/05/17 01:32:26
    AVB
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    Re: Briggs won't hold valve clearance 2019/05/17 04:50:47 (permalink)
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    Sorry for the late resonance I tend to fall off to sleep when I sit down and relax after putting in 10-12 hrs in the shop. I burn my dinner the other night that I had in the oven because I didn't wake up until 4 in the morning. At least I only had the oven at 250 but the chicken was still charcoal.
     
    Yes it is the setting of the valves by doing one valve at a time on these singles and twins. Takes longer but at least don't need to measure the piston position beside I got careless when learning to Briggs way and had to pull the head to retrieve the broken dowel once. When it came to V8s you can do half one time and then the other half but I don't see solid lifters anymore except on old engines and a few racing engines.
     
    As for the ACR [compression release] bump it occurs on the intake for the 793880 camshaft. As you look at the engine this is the lower valve with the aluminum push rod. Much less raw fuel is wasted as it gets reused and not just not discharge with exhaust. Either way the ACR bump only occurs at start up. There are guys that insist it is always the intake but it depends on which engine you are working on as it can be the exhaust on some models.
     
    With the ACR being fragile on these camshafts you do need make sure the bumping occurs. It shouldn't hurt it by turning CCW as it just swing the ACR arm out but it doesn't make sense to me to turn the engine backward of its normal running directions. Now I do see enough of these 310000 series engine where they have broken ACR causing hard starting that I stock a camshaft kit and crankcase gasket at all times.
     
    Must be an inherit thing for the 310000 as the 280000 and 330000 uses the same camshaft without problems so far on my end. Just like the head gasket design used on these engine tends to fail a lot too but this follows this design to other models using it. I have several engines destroyed because of this as they burn a lot oil without smoking.
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