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Small Engines (Lawn Mowers, etc.)/6.5 Intek simply will not matter what


QUESTION: Hi Eric.  I have a Scotts mower with the 6.5 BS Intek OHV engine.  The engine died while mowing and never started again. Fuel and spark were fine.  I even tried a little starting fluid directly into the intake and would get an occasional backfire through the carb...very occasional.  I then checked valve clearance...near perfect.  In my little brain, with the back fire i thought there must be a valve problem so i removed the head...everything is just fine and the valve seats look great.  I'm scratching my head on this one...could the timing have jumped or slipped?  I haven't torn down that far and I'm not sure what the mechanism is anyway or what i would be looking for.  Is that even a possibility, because I am at a loss.

ANSWER: How is the flywheel key and the blade adapter?

The best way to check the timing is to check for valve overlap at top-dead-center.  This can be difficult to do on OHV engines but it can be done.

The head must be on to check for overlap.  I use a drinking straw inserted in the spark plug hole to follow the piston and down.  As the piston reaches one of it's top-dead-center you should be able to feel some valve overlap where both valves are just slightly open...aka, the push rods will have tension on them as the valves are just slightly open.

I'd recommend checking You Tube for videos on valve overlap as the video will clarify how to check it.


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

QUESTION: Are you saying that there SHOULD be overlap at TDC?  Wouldn't that negate the compression stroke?
When I was checking my valve clearance the was NO overlap at TDC.  Both rods had some play at TDC.

Valve overlap will negate the compression stroke, a little.  

Did you check Wikipedia for 4 cycle engine valve overlap?

There is some good information on the subject.

If there is no overlap then the mechanical timing is off.  In the older L-head engines it was easy to feel both valves just barely open, you could rotate them by hand as they were not fully seated.

OHVs are much more difficult to tell.  You may have to check 1/4 inch, approximately 6 mm, before and after TDC to feel it.


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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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