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G’Day experts.
I have a tricky one. Completed a top end rebuild on my 450, piston and valves, setup valves to spec all bolts torqued to spec ect ect.
Now, starts, runs sweet for about 10 sec then starts knocking/rattling like a valve is hitting piston then engine dies!
Rechecked cam timing and tensioner-all g. Pulled head and checked for any valve piston contact-nill. Rechecked valve clearances-spec. Vac tested valves-good
I’ve rebuilt a few of these engines before and never had this problem. Could it be timing slipping causing ping then stall?? Flywheel nut still tight and woodruff key in place. Anyone have any ideas? TIA
Jay
 

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Ha :LOL: he says experts!!
Poor fellow is desperate😂
Seriously. Sorry for your troubles. If you are certain you have no mechanical interference I might suspect a faulty ignition module was advancing your ignition timing and causing your stalling as you describe. You didn't mention a history of previous troubles prior to your top end work. I would expect mechanical interference would show witness marks on piston top from interference but would expect it would not start easily. I wonder if a TPS error or other sensor has advanced timing on you or defective module is advancing timing to ping and stall. Just a thought. You may find timing light can help you here. Did she run good prior to your engine work?
 

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I have had a few rebuilt (car) engines come through to me with similar symptoms. On two of them recently, turned out to be rags left in intakes. Worth a consideration (?)
 
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