The V8 Owners Forum -

I thought I'd make a new thread rather than continue this in the "big-end bearing wear" thread I made a while back.

I'm trying to figure out what is causing the tapping noise in my 4.6 engine that's in my P38. The noise is there all the time at idle, when accelerating, when decelerating and you can hear it inside the car whilst driving which is really annoying. The noise is there both whilst cold and warm. Pretty much every part is new recently such as lifters, cam, rockers, rocker shafts, pushrods, pistons, all bearings etc.

Yesterday I took the rocker covers off and all but one of the lifters were solid. The none solid one was replaced for a brand new one that I had extra which has possibly improved it slightly but it's still as bad. I've tried with the various different thickness shims for the preload but none of them make the noise any better.

Here's a video of the noise from today. It's hard to pinpoint where the noise is coming from; if I put a screwdriver on the rocker covers there's not any very loud noises that give me any clues.

Does anyone have an advice on what to check next as I'm out of ideas? I apologise for the constant questions

Thanks

Could be worn out rockers already by fitting the rockers shafts wrong side up.
You sure the rocker shafts are fitted correctly notch up front, right side up ??

Did you check lifter preload also which is important even with replacing the lifters with standard replacement items. Just a light skim of the heads can cause lifter preload issues or swap from tin to composite head gaskets can.

I think I did assemble the rockers the right way round as I remember spending ages trying to figure out if I had them oriented correctly.

I did check it when I assembled the engine - ended up putting in the medium thickness shims from the kit I had (like this).

I'll make sure I check the rocker shafts next time I take the rocker covers off when I get some more idea of what else to check whilst I'm in there. I'm thinking my V8 would rather be a diesel with the sound it likes to make.

I had a similar issue on my Small Block Chevy and yup ots was the preload on one rocker that was causing it.

Now sorted and runs nice and quiet, well as quiet as a SBC with a straight through exhaust can do

I tried all each of the different size shims I have (small, medium, large) and no shim under the rocker posts and none of them made any difference to the noise. It might have been louder with the largest size shim if anything.

Checked all the pushrods and they're all solid and can't be pushed down and there doesn't seem to be any slack. The pads look good and none of the pushrod seats move about noticeably. I'm going to put my old rocker shafts back together and try them on one side later.

Larger shims will reduce the pre-load and this could lead to a situation where one or more valves end up with no preload at which point they will rattle.

Personally I don't like shims but they are better than nothing I suppose, I prefer adjustable pushrods.

Exhaust blowing on one port?

Chris.

Fixed! I swapped back to the old rockers and rocker shaft and the noise went away.

Perhaps the new ones ended up being damaged when the valves hit the pistons? I couldn't see anything obvious and it didn't have a huge amount of play between the rockers and the shaft. It was assembled correctly too so it shouldn't have been wear due to an oil restriction.

Thank you for all your help