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DeltaBravo

Briggs 16hp 326431 cam crank ignition timing

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DeltaBravo

I have a 7016 with a 1977 B&S 326431 16hp, magneto ignition. Since I bought it a few years back it was at times hard to start and had a tendency to backfire when starting. It was hard on points, condensers and spark plugs. Needing it, and it would start eventually, I never took the time to figure it out.

So I finally dove into it, and found the timing is off. Alignment of the arrows and points opening is off. When the points open, linearally speaking, the flywheel arrow is 1 1/4" behind the coil bracket arrow, say 10-15 degrees to the left. The coil bracket is in the gas position and as far left as it will go.

(1) I'm thinking the ignition timing is advanced.

I suspected the engine had been opened at some point and the cam and crank marks are 1 tooth off. Pulling the oil pan revealed the hash mark on the crank counterweight and scribe mark on cam (not dimple) are in alignment. That is hash mark on crank, follow that to crank gear tooth, follow down along tooth, meets with valley of cam gear where scribe mark is.

(2) From what I have read, the cam alignment dimple is located on the case side of the cam gear. Could the factory have put a scribe mark on the counterweight side of the cam gear, or is the scribe mark from whoever had the engine apart?

(3) Despite that I found the marks in alignment with the oil pan off, the timing is still off, and once I pull the pto side cover, I'm most likely to find there is a cam dimple and it doesn't align with the crank hash mark. Am I on the right track?

(4) What did I miss?

(5) I hope to have the pto side open Sunday

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Simplicity7013H

The PTO side of the motor is where you should be looking. That's where the factory timing marks are. There is a dot on the cam and dot on the crank and should be very easy to see once you remove the front cover.

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Mike_H

I don't know if it matters for you, but your engine should be a 326431. You have written 426431...just wanted to make sure you knew.

Also, regarding timing, pull the shroud and head. Check piston TDC vs flywheel position. That will give us some clues too. I fought a similar timing issue, and it turns out my valve clearance was way off.

Might also be a sheared flywheel key.

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MrSteele

You will have to check the timing marks when both valves are closed. If you are looking at marks as far off as you are describing, it would likely not run at all.. The cam gear has a punch mark between teeth, the crank on a tooth. Your valves likely need adjustment, or the points are too far open or closed

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DeltaBravo

42, dang, where did that come from?

Thanks for the feedback. So, this is what I found. Valve clearance is set to the B&S manual specs, intake .009 (maximum) and exhaust .017 (minimum). The flywheel key is not sheared.

I found the cam gear dimple is in line with the crank gear tooth. With the oil pan off, I found the dimple with an angled pick. Verified several times and traced it back to the crank gear tooth back to the counter weight hash mark.

Soooo, I elongated the coil bracket holes since there was a little room that the bracket could move to the left. This moved the flywheel arrow about 1/4" closer to the coil bracket arrow. Not a perfect solution.

So I have a new magneto coil, and decided to measure it and the old. The old magneto coil measured 255K ohms! The new is 5K. The new coil should help.

This is a fine situation.

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DeltaBravo

Thanks. When I found the cam and crank marks were in line, I checked that both valves were closed by checking for a gap between the stem and lifter.

I reread the timing section in the Briggs manual, a few times, then it occurred to me that I was checking the arrows when the points started to close, not when they were opening after closing. Dooohhh! I was taking it easy on the Duff, maybe someone shopped in Shelbyville instead.

So arrows align, and with no plug installed, the spark tester gives a nice white spark when hand spinning the flywheel.

I'm thinking a very weak coil could barely fire the engine with new and very few hour points, condenser and plug. I was replacing the plug about every 20 hours. For about the last two years I have been using an Atom module, after replacing points was driving me nuts. Either way the machine should kick butt now. I hope to start it Wednesday.

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DeltaBravo

Success! It popped off on the first turn of the flywheel. Ran it for about 3 minutes with just the head pipe. Amazing after how it had run in the past. I will put the deck on and mow tomorrow.

Another simple tractors success. Thanks for the help and suggestions.

The original Nelson muffler clamp allow the connection to leak a little, from the end of the 180 degree head pipe. Both are at the end of their adjustment. Use super small U clamps or wide strap clamps or other ideas?

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Simplicity7013H

I would do what you can to salvage the Nelson muffler. I would personally use small "U" clamps. The original mufflers are super quite compared to the round type mufflers. I had one on my 7016H but bought an OEM muffler just because it was so loud.

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Mike_H

I second keeping the Nelson muffler. I measured my NOS muffler at 78 dB. The Salt shaker style mufflers don't have enough volume to keep the noise under control...get some exhuast sealant and a couple muffler clamps from the auto parts store.

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Hudco

we had one come to the shop that ran that way newer one that doesnt have pionts the problem was the polarity on the flywheel was backwards used a differant wheel and all was good

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DeltaBravo

I finished the muffler repair. I will post some pictures soon. Here is what I did, and sort of stumbled upon a way to eliminate the putt-putt hood echo and louder exhaust without having to modify the hood.

I bought a Nickson 1 1/2" ID to 1 3/8" OD exhaust reducer at Advance. Cross cut it in half, leaving a trumpet on the 1 3/8" cutoff peice.

Rip cut 1/4" out of the 1 1/2" peice with a body saw. This will act as a coupler around the stub pipe on the Nelson muffler. When the head pipe is inserted into the stub pipe, coupler placed around stub and U clamp put around coupler and tightened, the U clamp will squeeze the coupler to squeeze and seal the pipes together. The stub pipe was also kind of thin in places. We also cut some more reliefs in the stub pipe, to let it conform a little better.

After getting the muffler outlet lined up with the hole in the hood, I put the 1 3/8" cutoff onto the outlet, trumpet side out, and pushed it back to clear the hood. No more hood echo! Its quieter! No putt-putt sound! Awesome! No doubt there will be less heat under the hood as well.

Lining up the muffler outlet took numerous adjustments and washer shimming, but its pretty much spot on now. The trumpet exhaust outlet, ala 442, is kind of cool.

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