So I started driving around my freshly built 350 and it was fine then it started getting a valve tap so I readjusted the valve lash on the one rocker arm that was tapping but it seems to be about 2 threads tighter than the rest of the other rocker arm nuts. This concerned me but it got rid of the valve tapping. After doing this the car now seems to misfire, as it hesitate and shakes back and forth as I accelerate...

I'm not really sure what to do here, I tightened the nut by backing it off until it started tapping and then tightened it down 3/4 of a turn as I've always done. Is there something else that could be wrong? Thanks.

 

a bad lifter could do that.

 

All new lifters.

 

1 shorter pushrod

 

just because they are new ,doesent mean that they are good. are they cheap? Chinese? and as has been mentioned ,are all the push rods of equal length? any bent ones? how about the cam, is it a flat tappet? did you add ZDDP to the oil when you rebuilt it? if not you might have wiped a lobe off of it. I would pull the intake and inspect these items.

 

They are melling lifters with a new melling flat tappet cam. When I installed the push rods they were all the same length, im going to check it its bent and redo the valve lash on all the rockers today but I feel as though something else has happened. The lifters are hydraulic but I guess I don't see how they would just fail like that.
And yes I used ZDDP with Rotella T 10w-40 motor oil for break in.
What's odd to me is that it ran fine for about 50 miles of which i was very nice to it and then that tapping started.

 

even melling lifters go bad

 

So how do I tell its bad aside from these symptoms?
I also redid the valve lash, that rocker arm had an extra thread then the rest and still taps and still seems to misfire or hesitate but not nearly as bad.
Thanks

 

drop one new lifter in , and re adjust it. while you have the old one out. rotate the engine and inspect the cam lobe for damage.

 

Took out the lifter, its all beat up, i fear the cam lobe is whiped...

 

Check the lifter bore in the block too.

 

The lifter bore is all scratched up

 

You must use a break-oil not an additive. The additive is only fine after the break-in process. The reason is that it is not mixed in the oil so the first 10-20 seconds or so there is no ZDDP in the oil and the lifters go south.

I have used comp cams break-in oil and have had zero cam failures in the last 3 flat tappet cam installs. I have heard good things about brad penn break-in oils as well.

 

Well I primed the motor for like 20 minutes before running it so that should have mixed the Zinc pretty well but you do make a good point.

 

you can have the lifter bore re sleeved.and if your block is new enough .and it has the roller provisions. that is the way to go.