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Old 10-12-2011, 09:06 PM   #46
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Joined: Jul 2008
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This is quite a gear heads brain teaser. Nothing really seems to add up. Im going to throw something out. I am not an expert on these 650 twins, but have worked on alot of similar engines. The camshaft drive sprocket is usually a press fit onto the crankshaft, nothing else holds it on except the press fit. Sometimes manufactures will use a key or pin of some type to locate the sprocket and to aid in preventing the sprocket from rotating on the crankshaft, but still the primary retension is a press fit. Some manufactures will use a "D" shaped crank OD and a matching gear "D" shaped ID, but again retension is by a press fit. Some manufactures use nothing but a round crankshaft and a round bore on the sprocket, again retained by a press fit.

I have seen engines (round bore, round shaft type) where the press fit was not to spec and the sprocket has turned and guess what the cam timing is off. This often happens during a backfire when the piston reverses travel and the inertia of the valve train keeps it moving forward.

I know you said you confirmed piston TDC with the marks. Did you confirm that while the piston was at TDC compression stroke that the cam sprockets were aligned correctly and the base circles were on the buckets (valves closed)? In the scenario of the cam drive sprocket "slipping on the crankshaft" the timing marks on crank position sensor would still be correctly timed with the piston, but the cams would not be.

Again this is just a shot in the dark, because I have no idea what method Kawasaki uses to retain the sprocket.

ktmklx screwed with this post 10-12-2011 at 09:23 PM
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