Tomstang

I recently put a rebuilt 351w in my mustang. The heads were also rebuilt. From the initial start up the #4 cylinder has been tapping and the warmer the engine gets the worse it taps. I looked at the spark plugs and the first 3 are nice and clean the 4th is black with carbon. I took the head off and the #4 valve stem is also carboned up. I've heard a few different solutions to my problem. Could someone please narrow it down for me. Thanks. Tom.

wrenchturner75

from the carbon it sounds like your #4 cylinder isnt working, and from the tapping sounds its "possible" you wiped a lobe on the cam. pull the lifters from your #4 cylinder and check the bottom of em, if you see any scoring or gouge marks you wiped a cam. they can start out running fine but the more the motor runs itll start running rough and start ticking louder and louder and then missfiring and sometimes even backfiring. "if" this what happened you can count on pulling the motor and rebuilding it again, those metal shavings will have found their way to the bearings and possibly cylinder walls. a tell tale way to find out is cut your oil filter open and inspect the filter media if you see shavings and metal specs your in trouble. hopefully im wrong! good luck

Tomstang

I did take the lifters out this evening. I didn't see any scoring but there were some small chips around the edges of a few of them. I'm not sure what happened, but I took the engine out anyway. Cylinder walls look fine. I guess I'm gonna rebuild my rebuild. Any ideas about what happened? Thanks for your help.

wrenchturner75

its imperative that the lifters rotate in their bores, if they dont they will get ruined and destroy a cam, this can be checked when assembling the motor. install the cam and using just engine oil coat the lifter body and bottom of the lifter, install all lifters, now i use white out, put a small dab of white out on the top of the lifter so you can see it, i use a speed wrench and turn the cam with the cam bolt and watch each and every lifter, you should see the dab of white on the lifter rotating slowly. if one is not stop and inspect the lifter bore for any scratches or burs, try some very light sand paper soaked in oil and lightly rub them out, i use a brake wheel cylinder hone and it works very well. once you hone a lifter bore clean it before installing the lifter! try again till you get them all rotating. then break it down and clean everything again. good luck