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arjr111

12HP Briggs, 300421, cam timing

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arjr111
The rod was busted and crank journal badly chewed. Upon reinstallation, I tried to carefully match up the timing mark on the cam and the curved tooth directly in front, of the mark on the crankshaft throw, as per the manual. After reinstalling the flywheel and adjusting the armature timing, the points do not open until about five degrees past the marks on the flywheel and the mark on the armature. Should I assume that I missed the cam timing by a tooth, and begin tearing it back down? I'm thinking that I may have lined up with the bottom of the crank tooth (on the crank timing line) instead of the top, setting me back one tooth. Before I tore it down, I could feel the electric going through the plug wire when I turned the flywheel, now I do not. Would I still feel the current, if it was out of time by a tooth? Would that be a further indication of a missed timing mark, or possibly just a bad coil? ..thanks

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roma3112
arj When i redid my 300421 on my 3112h i rember destinctly having 1 heck of a time seeing that my marks were lined up. I too was off by just a tooth the first time i did it. i went so far as to dissamble the engine press out the vrank bering (if memory serves me right) and what i did was paint in some whitness marks so i knew i was on the money. I had a jar of this paint that junkyards use to mark old car parts with dates ect. What i did was mark the face of the tooth on the crank and mark the cam where the tooth engages, that seemed to help alot. Even after all that it was still a tight fit in there from what i rember. i am on my way to work now but when i come back i will review the notes i have from when i redid the motor back in june, and post further.

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mr.jeffro
Art, I recently rebuilt my 326400 series and yes when installing the crank assem. you can possibly get it off if you are not careful. I used "White-Out" to mark not only the proper gear (tip and sides) but the timing marks as well so I could see them clearly. As far as the points.. Your manual should say to us a multi-meter set to Ohms. This is the easiest way to see the points opening. if the points do open and your arrow on the flywheel is to premature or to far past the alignment marks on the coil assem, then yes, most likely you are a tooth off. One good thing is that you should be able to salvage the gaskets and you don't have to worry about any broken bolts. Have fun and good luck Jeff

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arjr111
Thanks guys, I did do the ohms test, and the marks are not aligned. Honestly, if it wasn't so much fun taking it apart, and putting it back together, I'd probably be upset. Now, even if it is one tooth off, shouldn't I still feel the current through the plug wire? I'm wondering if the coil is also bad.

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HubbardRA
If you are running a magneto and have the cam timing off, you now have the magnet on the flywheel in the wrong location when the points open. This will decrease the spark output.

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CleanBee
Art, I know this sounds elementary, but make sure your point gap is set perfect. If it is to small, the crank timing will show up early as you noted. It doesnt take much to be off only 5 degrees. This also will cause a weak spark while cranking by hand. I used an ohm meter and clean points when I did mine and had to adjust the coil a degree retarded to get it perfect. I wondered if the plunger rod might wear that little bit over time.

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arjr111
Rod and Dan, I was getting a fairly good current before the tear down, and did not touch the points during the work. Now sadly, I feel nothing, and figured there should be a little tingle. I did check the points,(as per the manual) before the amature reposition - they were a tight .20 - That plus, plunger wear may be the problem.....I'll recheck them, and try retarding them a bit, see if I get a shock...thanks

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HubbardRA
Art, Maybe you misunderstood my previous comment. The coil is charged as the magnet on the flywheel swings past it. Then the points open the circuit to produce the firing pulse. Magnet is controlled by crank position, points are controlled by cam position. If the cam is off one tooth, then the point opening is off relative to the magnet. You can't fix this by adjusting the points. You have to get the cam in time.

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arjr111
Well, I tore it down and it was one tooth off. I had referenced to the back of the curved tooth right on the line, instead of the front of the next curved tooth, that is also in line, as per the manual. Whole process to tear it down fix it and put it back took about 45 minutes. The ohms test is now right on. Hopefully, I will never make that mistake again...thanks for the help. BTW, for those that will someday face this project. What makes it kinda tricky is the curvature of the teeth, there are actually two curving teeth on the crank throw timing mark and it seems more natural to pick the one that actually starts out at the line, instead of the correct one that curves out in front of the line.

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CleanBee
Glad to hear everthing is back working for you. I hope no one took my "point gap checking" as a solution to cam timing being off. Both a small point gap and cam timing retarded one tooth will have the same symtoms as you originally described.

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