Thread: 400 sbc knock

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I recently tore motor down to check all internals all looked good replaced all bearings and put it all back together. I primed it up 40pounds to back of block but never got oil to rocker arms but was in valley. I crunk it this week for the first time and fired right up still have to adjust the valves a little. so I got it to idle so I could start adjusting everything but I heard a knock from the bottom end and I still wasn't getting oil to rocker arms. when it was running the first couple of times it sounded good nothing wrong besides a few rockers ticking where they needed to be adjusted. but last night it just started a knock sounded like from the bottom end and it only has been run 4 times no more than five minutes. i don't want to tear all the way apart just wondering if anyone had any ideas

Oilpan to pickup clearence checked?
The pickup may be too close to the pan to efectively draw oil. This will cause little to no oil flow.

Pickup fall off oil pump?
Causes no oil flow.

Did it vibrate or shake real bad?

Check the oil for metalic particles.
If there are particles, can you possibly post a pic?
I always had problems trying to put in pics bit never worked for me!
A pic woild be great, then we could see the condition of the oil.

no shavings in the oil and the pickup is fine we crunk it over the weekend and it didn't knock this time like it did before but it never did vibrate or shake real bad. could it be just a timing knock?

Look at the pistons real close see if you have a crack and check to see if wrist pin fit is too loose .....ted

Had a new motor broke in on a test stand, and put it in the car, developed a slight "tick" down low, I revved it up and she came apart badly, everything was good but the balanced rotating assembly I had purchased had too small wrist pins in it, they where slightly hitting the cylinder wall and ended up gouging the cylinder (cracked piston, bent valves, cracked block everything bad), never checked it since they where assembled and balanced together from a factory machine shop. Good news was they came from a very reputable company, I contacted them and they had knew about the problem and they picked up the bill for a whole new motor. Don't assume new parts are always perfect! Best of luck Matthyj

Originally Posted by brmadi

.....could it be just a timing knock?

IMO "Timing Knock" is a condition at WOT under heavy load, not in the idle range. Also called "spark knock", and is really detonation caused by too much advance for the fuel you're running. The knock you describe is not timing knock.

Maybe put an ear over by the fuel pump actuator rod, concerned about no oil at the top end, what's the oil pressure?

I always prime my motors until the oil reaches upper valve train no mater how long it takes. Sometimes I will do it three times before start up. Not much help I know but just my two cents.