I finally finished assembling and installing my 351w to replace the 302 that was in my 1990 Bronco. I had a 1991 Bronco that the engine, wiring harness and computer came from. The only problem is its making a knock/slap sound from the passenger side and it sounds like a sewing machine.

I had the crank ground .010 under stock, cylinders bored .030 over, new pistons, .010 under stock bearings, Edelbrock Performer Heads 1.900 intake and 1.600 exhaust, Crane 444232 with new cam bearings, roller tip lifters, BBK twin 56mm throttle body, new oil pump, etc. I installed it at my uncle's house because he has a welder for welding exhaust pipe and he had a engine hoist. I was away for almost a week and wasn't around to see the job finished(radiator, accessories and exhaust needed installed when I left). He drove 25-35 miles before I got back home and said it seemed to run fine. He said he broke in the camshaft but I have a slight suspicion he didn't. I drove it today and it felt a little under powered from what I was expecting and the gas pedal feels like your pushing on a brick which I assumed must be the new throttle body having a stiff spring or needing broken in. I drove it a little over 50 miles today at varying speeds and rpms before it started making a slap/knock noise on the passenger side and it sounds like a sewing machine from 1500 rpms on up and is louder when its going up a hill. In addition the knock is more frequent when under a load than it is when the engine is just revved up in neutral. It started doing this about a mile from my house after which I immediately drove it home. The knock increases with the rpms but doesn't seem frequent enough to be a piston. The oil pressure is fine and I don't think it has anything to do with it.

I'm at a loss as to what it could be. I really am hoping I don't have to tear it out of there to fix it. Any help would really be appreciated.

 

Can you get a stethoscope and try to isolate the noise? Pull the valve covers and look for rocker/pushrod issues next. (they clunk every other crank rotation)

After that, you are pretty much looking at a tear down. You will just destroy more parts the longer it runs.

 

double check your exhaust manifold to make sure it hasnt come loose from the head. you can use a broom handle as a stethoscope as well to isolate the noise. What oil and what oil filter are you using? what is your timing set at with spout connector removed?

 

I'm using Super-Tech 10w30 from Wal-Mart and a Napa ProSelect oil filter. The exhaust manifold is still on there tight. The timing should be set at 10*btdc but I'll check it again tomorrow just to make sure.

 

I hope not.. that cam is not a roller cam.

 

Sorry, I meant roller rocker arms.

 

You need to pull the valve covers off and examine the pushrods, you have aftermarket heads and if you didn't measure for pushrod length the stock ones may be too short.. one or more may have slipped out of a lifter and got bent.

A fresh rebuild motor may take 1000kms or so to fully breakin, it will continue to loosen up over this time, be patient and follow recommended breakin procedures.