Rocker Arm Lateral Movement

[mikedsilva]

I'm at the stage of putting the rocker arms back into this 964 motor. They have been re-faced locally and rebushed.
The motor was quiet running before disassembly but now I can see there appears to be a lot of side to side lateral movement with a noticable 'clack'... the feeler gauge says it is between 0.4mm (goes in) 0.45mm (does not go in).

The inside of the cam tower does not show any obvious wear marks.

Is this normal? Or should I be seeking out some sort of shim kit?

[Mark Henry]

It's not noise it's music.

So .04mm is .0015", you can't have it any tighter or it will bind.

[Eagledriver]

I think you’re correct in your assessment. I don’t think it’s something worth fixing though.

[Walt Fricke]

I wonder if this ability to move laterally a little, or at least this clearance between bushing and casting wall, isn't needed given how the rockers are oiled. A little movement maybe pumps the oil out a little, the clearance reduces resistance to its movement, and between the two you get fresh oil in there via the hole in the rocker?

[BURN-BROS]

Mike, That looks more like .43 than .043 in the video

[911pcars]

If the rocker arm bore is square (perpendicular) to the cam lobe, there should be minimal side loads causing the rocker to hit in the clearance space with the cam carrier. Thinking out loud: If the cam lobes are ground slightly off-axis, that would load the rocker in only one direction.

Are the others the same? If they are and this was the source, you'd have multiple tapping from multiple rockers (Check noise source, both banks).

What you're demonstrating is merely side clearance, yes? Not rocker bushing-to-shaft clearance.

I suppose one could tighten up the clearance with pre-selected shims prior to final assembly.

Any aftermarket machining that might tighten clearances enough for rotating parts to touch/nick something?

Sherwood

[mikedsilva]

Originally Posted by Mark Henry

It's not noise it's music.

So .04mm is .0015", you can't have it any tighter or it will bind.

sorry, I put the zero in there erroneously.

It is 0.4mm to 0.45mm!!

[mikedsilva]

Originally Posted by BURN-BROS

Mike, That looks more like .43 than .043 in the video

Yes, spot on!
It was def I put the 0 in the wrong spot!

So what do you think, do anything about it or just suck it and see?

[mikedsilva]

Originally Posted by 911pcars

If the rocker arm bore is square (perpendicular) to the cam lobe, there should be minimal side loads causing the rocker to hit in the clearance space with the cam carrier. Thinking out loud: If the cam lobes are ground slightly off-axis, that would load the rocker in only one direction.

Are the others the same? If they are and this was the source, you'd have multiple tapping from multiple rockers (Check noise source, both banks).

What you're demonstrating is merely side clearance, yes? Not rocker bushing-to-shaft clearance.

I suppose one could tighten up the clearance with pre-selected shims prior to final assembly.

Any aftermarket machining that might tighten clearances enough for rotating parts to touch/nick something?

Sherwood

Thanks for the reply Sherwood.
The cams and rockers are freshly resurfaced.. and the bushings are new with maybe 1 thou clearance. When I removed the rockers, some of the bushes had 5 and 6 thou clearance and a lot of slop.. but still, the engine was fairly quiet.. I did not take a note of the lateral clearance at that time..