Quote:
Originally Posted by DanB
Look not trying to sound like an Richard but here are the facts!!!!!!
This is wrong!!!! Just to state the obvious here when you removed your heads and had bronze guides installed the machine shop also did a valve job to insure that the valve sealed after the new guides, when they tore in to the heads the also milled the bottom ( also known as the deck surface) in order to make it smooth enough for a MLS gasket to reseal when you mill a head you are making more cylinder pressured because the combustion part of the head is closer to the piston thus means less square area in turn adds more pressure to the piston thus stabilizing the piston to one side or the other (it Dampens to noise). The noise is actually still there it is just that you cant hear it due to added pressure. On a cobra it gets real bad because of the cylinder pressure they have due to the supercharger that is why it is more prone when idle and not under high boost. there is already enormous pressure on top of the piston so the clearance on a forced induction would have to be enormous for you to hear when the car is pullied and under pressure. That is why you hear it loudly when at idle due to less pressure
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This thread makes my head hurt. The tick was/is caused by excessive stem to guide clearance, end of story. The guides had too much clearence right from the start. This allowed the valves to hammer back and forth in the same plane as the followers. The guides would wear into a oval shape. This movement scrubs the valve on the seat and the valves soon lose the ability to seal. Low compression is the result.
Most all of the new replacement heads sold over the counter had the same problem. Ford specification was .002 max stem to guide cl. the brand new heads were .004-.005+
Also..Piston slap gets worse as the pressure goes up. When the thrust transfers from one side of the skirt to the opposite side of tdc that is where the rattle comes from. This gets really ugly with the big piston to wall clearence some builders seem to like. We tore down a 4V this week and had a suprise.
The owner stated the oil fumes were making him sick. This thing had a few thousand miles on the rebuild. The engine had .020 over pistons in a .030 over bore.
Some pistons have pin bores offset to help reduce the slap on cold starts. Many new engine designs have the cylinder bores offset in relation to the crank centerline.