Cam gear position on B&S OHV 16.5HP

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  #1  
Old 04-12-07, 12:54 PM
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Cam gear position on B&S OHV 16.5HP

I made repairs on a B&S 16.5HP OHV lawnmower engine and am having trouble finding the correct lineup for the cam gear and cam drive gear to set the timing correctly. I lined up the circles stamped into these two gears, but the timimg is wrong. When I turn the engine over, some exhaust is pushed out the air intake. What have I overlooked? I set the valves at .004. This is what I get for working without a manual as I am ready to take the engine apart again and get it right the second time. Thanks for any help.
 
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  #2  
Old 04-12-07, 04:13 PM
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You may have the cam gear out of step with the crank. The crank turns twice for every turn of the cam so you may have to turn the crank a full 360 and line up the marks again.
 

Last edited by backyardwonder; 04-12-07 at 05:40 PM.
  #3  
Old 04-12-07, 05:52 PM
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You mentioned lining up the "circles". Timing marks are usually short, straight score lines; one centered on a tooth and the other centered on the valley between teeth on the opposite gear.
 
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Old 04-12-07, 07:38 PM
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Huh?? It doesn't matter how many times the crank turns etc... Just line up the marks and it's set right no matter what. If the marks are lined up, it can't be wrong.

The cam mark is a dot between two teeth. The crank mark is a dot on a tooth. Line these up and it's timed.
 
  #5  
Old 04-12-07, 08:16 PM
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Cam drive gear and cam gear dots

I lined both of the dots up as you describe. Well, it seems that's not the problem. If you put a paper towel in the intake and turn over the engine, pop, out it comes. I figured it had to be timing somehow. ?

Piston and rings are good, engine turns freely, about 90lbs compression. I cleaned the valves and seats. New head gasket.

Maybe something slipped when I put the case back together?
 
  #6  
Old 04-14-07, 03:45 PM
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Originally Posted by cheese View Post
Huh?? It doesn't matter how many times the crank turns etc... Just line up the marks and it's set right no matter what. If the marks are lined up, it can't be wrong.

The cam mark is a dot between two teeth. The crank mark is a dot on a tooth. Line these up and it's timed.
Absolutely right, of course. My apologies for the misinformation.

As to the problem, it would seem your intake valve is not seating as it should.
You could remove the valve cover and rotate the engine to monitor the valve operation and ensure there is adequate clearance to allow the valve to seat fully. I don't have the specs but the valve springs may also be a little different and were perhaps installed in the wrong order or are weak. It may help to lap the valves with grinding compound.
 
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