Knock under load when warm
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Joined: Apr 2003
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Knock under load when warm
I am looking at a truck and the salesman told me that it has been in the shop for them to try and track down a knock. Apparently, it does it when it is warmed up and under load. They held the truck with the brake and accelerated slightly to hear it. Is this common? They seem to think it is a camshaft. The truck is an '03 with 92K on it.
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Joined: Jul 2002
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From: Long Island USA
No camshaft will knock under load. Period. Nothing happens to the camshaft under a load vs. unloaded. There may be a slight difference in the crankshaft, endplay-wise, that can pull the timing chain one way or the other. But the chances? Infinitesimal.
Most of the time, a knock under-load is a rod bearing. Rarely, it's a main bearing (main bearings can knock when not under load, as in, rev it, and less off, and just as you let off, it knocks a bit). And somtimes, it's a wrist-pin, but you usually get the tinny/aluminum sound, not a full knock. And a wrist-pin doesn't do it just under load.
Sometimes, it's the torque converter coming loose from the flexplate, or a cracked flexplate.
I'd move on and look for another truck.
Most of the time, a knock under-load is a rod bearing. Rarely, it's a main bearing (main bearings can knock when not under load, as in, rev it, and less off, and just as you let off, it knocks a bit). And somtimes, it's a wrist-pin, but you usually get the tinny/aluminum sound, not a full knock. And a wrist-pin doesn't do it just under load.
Sometimes, it's the torque converter coming loose from the flexplate, or a cracked flexplate.
I'd move on and look for another truck.
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Thanks for the info. The dealer has not diagnosed it fully yet. They are willing to sell as is for $13500. The truck is a '03 F350 4x4 supercab with about 90K on it. I have checked on engine prices if it is the worst case scenario and Ford wants $4200 and Jasper is $3900. Both prices uninstalled.
