Couple of questions about a small engine

Last sunday i visited a tool/flea market and bought this lawn mower engine. You can read the label, is a Italian copy of 3,5 hp tecumseh engine, i've changed the oil, checked it has strong spark, new spark plug fresh gasoline, and then i tryed and start it, it kicks back, also i heard couple of loud pops from the exhaust, the flywheel is aluminium and it doesn't have blade, i've heard on some engine blade acts like a flywheel is this the case here and can i turn this engine and use it i vertical configuration without taking it apart ?

 

On most vertical shaft motors used for lawnmowers the blade does act as a flywheel, the actual flywheel is very light. Those vertical engines used for other purposes like pressure washers will have a heavy flywheel like a horizontal shaft engine. The lubrication for vertical engines will not work when the engine is turned horizontal.

<slightly off topic>

Back in the dark ages my Dad ran a small engine shop. Some of the the old horizontal Clinton brand engines had a very heavy cast iron flywheel. We put one of those very heavy flywheels on a vertical shaft mower that also had a large heavy steel disk blade with replaceable tips. That was one of the smoothest running mowers but it would take forever to coast down to a stop when you shut it down, it took so long that we considered it dangerous!

 

Years ago I had a Jacobsen 22" "Turbo Cut" mower with 4 sickle type blade ends attached to a large "suction lift disc". I think the blade/flywheel assembly weighed around 15 lbs. The blades were designed to turn to the center if you struck a hard object. I did hit something hard a couple times. When a blade turned to the center the flywheel was so out of balance you had no choice but to shut down the machine. Fortunately the blade end could be rotated back to the proper position and all was well. It was a beast to start with the heavy blade assembly and would take a couple minutes to wind down when it was shut off.

https://www.magazine-advertisements.com/uploads/2/1/8/4/21844100/jacobsen-rotary-mower-1.jpg

It was a tough old mower, but it was very tiring to mow 1/2 an acre.

 

An issue that I ran into recently was a loose valve seat. Aluminum block engines have steel or cast iron valve seats and they have a tendency to work out when running an overheated engine. This would cause a backfire through the intake or exhaust depending in which seat came loose. This is a fairly common problem. A compression test will be low to none.

 

Backfire and popping could be caused by a stuck valve

 

Briggs & Stratton and Tecumseh used aluminum keys to hold the flywheel in the proper position for timing the spark. They were meant to shear if you hit something. Often times the key would just get deformed and cause the flywheel to be out of time with the coil pack. Popping and backfiring would be common but the engine wouldn’t start

 

I have NEVER seen an offset key except in racing engines in my 50-plus years of repairing small engines.

 

Post deleted

 

I originally answered this post in response to fixit's last post. I thought he was referring to my mention of a deformed key. For some reason posts 8 through 10 would not appear until I refreshed the screen several times. That's when I realized he was referring to an actual offset key mentioned in post #9.

Tecumseh did use offset keys in some of their smaller solid state ignition engines. "Offset key used on engines with solid state ignition models TVX, TNT, ECV, H30-70, AH600, HSK600, HXL840, SHK845 and SHK850"

I believe Tecumseh made them in both a 4* and an 8* offset.

 

I have NEVER seen an offset key except in racing engines in my 50-plus years of repairing small engines.

WELL!!!! I guess I was wrong. I have been corrected. I just have never seen it.

 

They will sometimes deform like that from a rock strike on a mower. Hard to diagnose since the timing is only a little bit off.

Definitely used them on racing Briggs flatheads.

John