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Discussion Starter · #1 ·
Well, this is my second post here. I am not unfamiliar with OPE, as I have been an active member over on SBF for sometime. But this machine is giving me fits..... It is a friends machine, that has handed off to me to resurrect.

The details:
  • Briggs series 12000 (12S912-0121-B1)
  • Attached to a Troybilt pressure washer, but I have seen, and worked on lawn mowers with this series of engine.
  • What has been done, Oil change-due to fuel in oil, Carb- ultrasonic cleaning, due to fuel in oil, added filter and fuel shut off, valves adjusted

What I found when it arrived:

  • the machine would only backfire, thankfully after find gas in the oil.
  • no fuel shut off- resolved
  • sheared flywheel key- resolved

After getting things back together:
  • would not fire with out dripping in some gas into the intake
  • Backfired, and sheared the flywheel key, again.

Other observations:
  • it appears to have reasonable compression (pull test approximation)
  • valves were not not far out of adjustment.
  • as far as timing, the only other thing that I have not checked, is that the camshaft is synced with the crank, I have not done so to preserve the gasket. But I guess this may be my next step.

Am I headed in the right direction? I'm more knowledgable with the old "L" heads, these OHV's seem to be more finicky.
 

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Discussion Starter · #3 ·
I used the specs off the briggs link to the owners manual. I found TDC, and adjusted them to .004 in./ .10mm.

I've done a little more digging, and come up with this video, which might explain somethings. Your are correct in saying that cracking the case is not what I want to do, but I have to rule out the timing gear on the crank. Interestingly, the replacement is no longer a nylon gear, it appears to be a cast replacement.

 

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Briggs has been using those plastic cams for ages; they seem to be actually pretty durable, but they do fail more than the cast iron ones do. Sounds like you've got the right specs on the valves for sure.
 

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I had a briggs engine that had been run overheated and melted the camshaft gear so you may be onto something like what was found in that video.
 

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Discussion Starter · #6 ·
Thanks guys, but I've been know to be completely wrong, just ask my wife.....

I'll let you know what I find. For now, I need to re-drain the crankcase, and unbolt the engine. I can't say for certain that this engine was overheated, but being a pressure washer, it's quite possible. As you start it and walk away while it's running, and pay attention to the piece that you are trying to clean.
 

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Discussion Starter · #7 ·
Well, I cracked the case open. Nothing dramatic to report, the witness marks on the camshaft and the crank, match up.

Both gears are plastic/nylon. I'm thinking that the camshaft is nylon, it is a pale yellow/white. Whereas the ring gear on the crank was black, and not as rigid.

Upon a closer look, the ring gear seemed to have some rotational play, and orbital play. I thought, that this may be because of the output shaft not being anchored.

At this point, I am not sure that the replacement part, being different and metal, will honestly resolve the issue. In the old "L" heads, the lock up between these two gears, was much tighter, and positive.

Thoughts?
 

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You said you found top dead center and adjusted valves, did you turn it past TDC 1/4 inch before you adjusted ?
If you didn't you adjusted at compression release and it won't be right.
 

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Discussion Starter · #11 ·
Well, you live and you learn. Thanks for the heads up.

I created a video, hopefully this demonstrate three things. One, my lack of camera skills, two, my lack of knowledge, and three, maybe what is my concern.

 

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I think what you describe as lateral play will be eliminated once the sump cover is put back on. You can see the cam shaft move from side to side and the cover in place will remove that. The crank shaft gear, I'm not familiar with how much play is acceptable. It MIGHT be normal??
 

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Discussion Starter · #13 ·
I agree on the camshaft, and I do not have a way to anchor it, without the bottom half of the case attached.

And the timing gear, in part, that is not what I am familiar with the plastic/nylon setup. More over, I'm not sure if it is, or enough, to cause the backfire issue.
 

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Discussion Starter · #14 ·
Update: well, things have been busy around here, so I have not forgotten about the engine on the bench, just had other priorities.

I did get a few minutes to go out and play a bit. And thankfully I have taken your advice on the valve adjustment and 1/4 clock of the flywheel. Interestingly, with the flywheel key pointed to 90 deg of the head, seems to be TDC(+/-5 deg.) This makes find 1/4 past TDC, all that easier.

Not sure if that information helps anyone, or if it was already common knowledge, but I'd thought that I'd pass on what I have found.
 

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Discussion Starter · #15 ·
Got some time today, and buttoned things back up, and mounted to the washer stand without the pump. And filled the crankcase, and put a splash of gas in the tank, and a dribble down the carb.

On the third pull, it sputtered to life and ran for a good 20-30 seconds, then died out. I attempted a restart, doing the same as above. On the second pull, it backfired and no life after that. I pulled the starter and shroud, pulled the flywheel nut, and the flywheel key sheared again.

I am truly back to square one on this. At this point, I will rule out the valve adjustment, but I am still at a loss as to why it is happening. I checked the valve seat and valve engagement, using the "dark room and flashlight against the valve and chambers" method. It's not a precise method, but effective enough for me in times past. Now, I'm at a loss. Shy of the play in the crankshaft timing ring, what else could it be?
 

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make a steel key and see what happens. otherwise the key slot in the flywheel may be damaged and either cracked or too wide. i have made keys before out of bar stock steel and usually just make them on a bench grinder
 

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Discussion Starter · #17 ·
If this were an older engine, with thick cast block, I might. But these newer block designs, just don't seem as able to withstand the "fudge-ability" that the older ones could. I suppose if push comes to shove, that's what I may have to do.


For the life of me, I can not narrow down what is causing this. I know what typically causes a backfire, and how it happens, but I thought that I have eliminated those...... Ah well, back to the bench. It's got to be something simple that I am overlooking.
 

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For what it's worth...I had similar backfires and key sheer...One was because it was aluminum flywheel and needed rotating weight on crankshaft [ie Blade].....Second [larger BS eng] was my mistake of not tapping the fltwheel key down into its grove far enough before tightening the nut...[was hard to imagine, but flywheel will then be actually loose and sheer the key]...sometimes helps to add a concave washer under the flywheel nut..
 

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Discussion Starter · #19 ·
I could understand the lack of mass in a lawnmower situation, but this being a pressure washer, I'm not sure that there would be as much rotational mass. Resistance will be present , but the additional torque of what is essentially a secondary flywheel would be absent in this application.

Insofar as the key, it is seated as low in the way, that I can get it, and the nut is tightened to specs.

I appreciate everyone's input, and I am not trying to appear negative to any suggestions, rather to verify a process of eliminating the possible faults. I know that I am not as known over here as I am on the SBF, so I do not mean to wear out my welcome.
 

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you want a honda gcv160 to go on there instead? depending on your location i can sell you one off a husky power washer with a bad pump, needs a carb cleaning and it will be fine, right now it runs and surges. pm me if you want it, ill let it go cheap
 
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