Small Engines (Lawn Mowers, etc.)/mower engine knocking


QUESTION: It is a craftsman push mower with rear wheel drive. Do not know the year because i bought it used. Does not appear to be old and appears in very good condition. Was mowing and all of a sudden engine started vibrating and making loud knocking sound. The blade did not strike a stump or rock. I took blade off and it not bent or out of balance. The engine will start on first pull but makes loud banging sound and vibrates. The bolts holding engine to the deck are tight. Could the push rod be snapped. Could the key on the flywheel be sheared allowing mower to run but vibrates because timing off. It is Briggs & Stratton 190 cc engine. Engine family BBSXS.1901VH. Engine serial 1106095892408.

ANSWER: Did you pull the blade adapter off and check to see if the key is broke?


---------- FOLLOW-UP ----------

QUESTION: Yes,  pulled the blade adapter off, key is good,, not broke.

If the blade, blade adapter are not broke, and tight, then we usually remove the top engine covers and look to see if anything around the flywheel is loose causing the knocking.  If there is nothing outside the engine causing the noise then it must be an internal problem.  It could be the rod, cam or even the valves.  The vibration is an interesting aspect of you problem along with the fact it still starts.  A rod, cam or valve issue usually prevents the engine from running.

I would check the flywheel area just to make sure nothing is loose.


Small Engines (Lawn Mowers, etc.)

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Eric A. Jones


Lawnmower Repair . Certified Master Service Technician from B&S. Have 23 years experience on B&S, Lawn Chief, Weed Eater, Echo, Peerless, Wheel Horse, Snapper, Atlas, MTD, McCulloch, Homelite and many other numerous brands. Specialize in electrical repair.


Born and raised in the midwest. Started tinkering with engines when I was about 14 on my Suzuki RM-80. I began lawn mower repair at a small hardware store. I knew absolutely nothing. I read lots of repair manuals and met an older fellow who taught me many lessons. I continued working on small engines through high school and paid my way through college working on mowers at the same hardware store. Decided to get away from the midwest and mower repair so I joined the Air Force. I repaired air traffic control electronic equipment and ended up in Hawaii where I got a part time job at Small Engine Clinic. I gained a lot of experience from the Small Engine Clinic and had a blast repairing small engines. I then took the Briggs and Stratton Master Service Technician test and earned my MST. I then traveled to Wisconsin where I attended the factory update training seminar and received formal training. Continued working on mowers part time as I completed 20 years of military. Retired from the military on a Friday and continued in the lawn and garden industry the next Monday.

MAS Aerospace Operations BA Mathematics AAS Electronic Communications AAS Electronic Technology

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