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Small Engines (Lawn Mowers, etc.)/17.5 HS Briggs shears flywheel key


few months ago I asked you about issue

Riding mower Troy Bild 13AD609G063 with Briggs Stratton 311777 type 148-E1 engine 17.5 HP
I assembled the engine  verifying a good timing (camshaft to valves aligned, etc) and at the start, with engine cranking, it pop and shared the flywheel key. It happened twice., I got the keys from online supplier, original B&S (I think) but looks like soft metal.
What would be the reason for that?

Do i need a "better" key or is there other issue like compression release not working.

I would really appreciate your help on this (before I take this engine apart yet again).

Thank you.


ANSWER: What are the valve clearances?


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

They were as per spec - 004 (intake) and .006 exhaust valve.; I do have a pdf manual and I checked that before couple of times.

ANSWER: Did the manual describe how to check the compression release and did it discuss how to properly time the crankshaft and camshaft?

One trick that I have used over the years it to lap the flywheel and crankshaft taper.  Do you have some fine grit lapping compound?

Is there a washer on top of the flywheel retainer cup?


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

QUESTION: I'll have a look at re-lapping as I haven't done that, of course.
There is a washer but I think I didn't torque the bolt enough.

When i assembled the engine I didn't paid attention to compression release, hence my question if that could be the issue.
I made (double ) sure that camshaft/crankshaft gears are aligned as per manual (very good picture) so that is 100% good.

Basically, plan is to open the engine and have a look at compression release mechanisms and make sure flywheel is properly torqued with new key.
does this sound reasonable? what else should I look for?

Thank you.

It wouldn't hurt to very/check the compression release on the cam.

Make sure to look at the parts diagram and make sure the flywheel washers and bolt are assembled in the correct order.  I forgot to put the washer on once and the engine kept shearing keys.


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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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