Call from California...

[mrcaptainbob]

This laptop has a need to close out windows. Usually the popup is for a crash report to be sent to Mozilla, but several times a popup displayed claiming to send a crash report to Microsoft. And, of coarse, in each or them they say they may contact the user. So today I got a phone call from California, claiming it was from Microsoft and that there were reports of computer malfunction on my unit, and to speak with a rep just press '1'. Well, I did not.
So, was this a legit call?

[HayZee518]

I wouldn't trust it. How did mickey-soft get your phone number? Why would it single out ONE computer.
Hey! You do lawnmower repairs, right? Well I got a Yardman by MTD with a Briggs engine. I tore it down because it was making an awful sound, thinking something let go in the crankcase.
Well everything was intact inside so I put it back together will new gaskets etc.
There's a keyed ring gear on the crankshaft which mates with the valve timing gear. Two punch marks line up. Next comes valve settings. Been there done that, now it backfires through the carb. How close or how far am I in getting it to work properly? Valves are moving.

[mrcaptainbob]

If the gear marks were lined up during assembly and the valves adjusted to their correct lash, then it could be points. Usually point gap is around .020, but can vary. Timing is affected by how soon, or how late, points open/close. Try opening the points up a bit from what they presently are. That will allow the engine to turn a bit more before the spark is made.

[HayZee518]

there are NO points in this machine. underneath the flywheel [magneto] there is a series wound alternator with magnets along the rim of the underside of the magneto.
these wires terminate in a bridge rectifier [like what I suggested on your mower] then feed the battery and lights.
all I have to work with is a valve adjustment and something called a compression release when the piston reaches TDC.

[mrcaptainbob]

The compression release slightly opens the exhaust valve, I believe. Once the engine goes to higher revs the spring load is not enough to do that and the valve opens/closes normal. How did the flywheel key look? All four sides nice and flat? Could be a sticky intake valve. When you had it apart, did you notice the condition of the valves and seats? If all else is good, HayZee, I'd recheck the valve lash to verify they're opening/closing correctly....

[mrcaptainbob]

Any results? Disturbing about that "awful sound". Must've been bad to warrant a tear down. What kind of sound was it? Grinding? Knocking?

[HayZee518]

the noise could only be described as a "CLUNG" - CLUNG and rpms would drop, then pick back up, CLUNG then drop and pick back up. Now, after tearing it down and putting it back together I think it is the double engine pulley somehow got bent. See, I rapped a birch tree stump slightly above the second to last height setting.
I released the mower deck and the sound was still there.
I checked the end of the crankshaft and it wasn't bent. I used two dial indicators on either side of the shaft.
So that left me with the pulley. [which I didn't check] I just ordered a new one and threw out the old one.
I got the engine running in top notch rpm-s. The compression release slightly opens the exhaust valve just before top dead center or when the magnet whiz by the coil poles. Then it's counterweight retracts and the engine speeds up and goes!

[mrcaptainbob]

Glad it was a cheap and (relatively) easy fix, HayZee. But why was there carburetor backfire? Since that engine pulley got compromised from that birch stump, what condition are the blades/spindles? I'm surprised that pulley got mangled. Come to think of it, a neighbor has an MTD and that same pulley came apart for him. It was a clean break, though, and I was able to weld it back on. That lower pulley center was manufactured as a bell shape instead the more stable flat. Too much flex on that center web and the original welds and metal cracked. Poor initial design.

[HayZee518]

Two years ago I bought two new spindles because the old ones were making a grinding noise. They're sealed bearings pressed into a bracket and the spindle is a shrink fit inside the bearing race(s).
Anyway there's no place anywhere to lubricate them. I wish there was!
The belt is the original one from day one. So that makes it almost 18 years old come 2016.
About the carb backfire - I didn't have the valves where they should have been. during the compression stroke the intake was slightly open when the magneto let loose its charge and that is why it backfired thru the carb.
I made a mark on the flywheel and fan housing so I could tell where the magnets were as I rotated the flywheel and watched the valves opening and closing, and whether it was the intake or compression stroke. when the intake closed, the exhaust was already closed so I felt I was at the compression stroke. when the magnets went past tdc, the exhaust started to open. So I just backed off to where the exhaust closed again and took the feeler gauge reading and locked the rocker. did the same with the intake and tried it. still made a slight pop so I fine tuned both valves and tried it and it fired right up.