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Cam Issues again

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Stewart

Stewart

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From my previous thread Cam thread

I've run into this problem again. Not as bad as before but contact is taking place. Since everything is apart I'd like to make sure this stops. Like last time I still can not find any damage to the #3 rod which is currently on the kitchen table. When the engine is turned by hand there is no contact but obviously this is not the case when its running.
 
is this on a relatively good, tight engine, or an older worn, maybe re-rung unit with bores honed staright and relatively loose piston clearances?.
turning and engine over by hand or on the starter will put the reciprocating assembly in a different geometry than when it loaded while running. there so very little clearance there that an overly loose bore from a "quicky" re-ring might have enough bore clearance to let the piston rock over on the power stroke. the piston rocking over just a few thousanths would offset the wrist pin from it's corect path and would allow rod to make contact with the cam.

how's the oil pressure on that motor? loose cam bearings would show as low pressures, even if the rod and main bearing clearances have plastiguaged good.(lots of "quick and dirty" rebuilds don't have cam bearings replaced, very few guys have cam bearing tools and don't realize the importance of good cam bearing clearances in respect to oil pressure) a cam in loose bearings might be flexing that far in a loose motor, that, along with a slightly loose bore might be making the contact under load.
 
I'm curious to know the outcome myself. I'm in the middle of collecting parts for an engine build and have straight connecting rods. Other than block, crank, head and connecting rods, all else will be new. The block, crank and head have all be re-done and are awaiting more parts that need to be ordered before assembly can commence.
 
Low end of the engine was tight at was showing just above 75psi hot at cruise and measured inspec. #3 piston had major issues and was missing bits of pistons along with shot and missing rings. Crank had be cut 10 under so one rebuilt it but left the bores stock which most likely caused the problem I had as there wasn't much of a ridge at the top but you sure could feel it at the bottom.
 
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