How close is too close.

Im doing a rdbuild on a motor & was doing the plastercine sqwish test to confirm clearences, everything is fine except that intake valve is real close. The valve dips into the relief by 0.060, but the edge of ghe fave face only misses the valve pocket side wall by 0.045. Wohld you consider that too close? Maybe I should advance the cam half a degree? Whats your call?

I ran an engine like that one time and didn't cause an issue until piston rock came into play. I think mine was closer than that though because it lightly scuffed the valve relief area exactly like yours is showing, but never hurt anything. Ran it for a couple years till we pulled it down I found it.

You could use some off set head dowels and increase the clearance.

I just had to cut mine. The general rule was .050" clearance.
Doug

I would just chamfer (bevel) the top edge of the valve relief to give insurance against piston rocking.

I ruined a very nice block running .045 valve clearance. Probably the stupidest thing I have ever done.

It survived seven dyno pulls and a few runs down the track until it dropped an intake valve.

I would recommend much more.

This would be my fix also.

I would just chamfer (bevel) the top edge of the valve relief to give insurance against piston rocking.

What's your quench ?? Thicker head gasket would work.

Quench is 0.039, right on the money i'm thinking. I dont think piston rock would take up the 0.045 side clearance I have. I think the fact that the block is Aluminium, the gap should increase as the heat expands everything. maybe?

Wouldn't you need to retard the cam to gain intake valve clearance?

Knowing nothing else I wouldn't be concerned but also inclined to use lighter weight/smaller diameter parts and higher spring pressures. My opinion may change with heavy parts, marginal pressures and aggressive ramps.

Mock it up again with the clay and use a screw driver or some other narrow tool to push the piston top back and forth to rock it through the spark plug hole and see how much clearances you have after that

I'd be fearful of running an engine with .045" clearance, especially if it were the exhaust valve which gets hotter an expands more. I've gone by the basic rule of .080" on the intake and .100" on the exhaust, but on occasion have run them slightly tighter than that. When it comes to advancing or retarding the camshaft, it depends on which valve you're having insufficient clearance on. In most problematic cases the the piston is chasing the opened intake valve and hits it before it can fully shut or hits it as the valve "bounces shut". To help reduce the risk of this situation you can retard the camshaft some and it will provide additional intake valve clearance as well as reduce your dynamic compression slightly. If your exhaust valve is the concern, retarding will only make that situation worse, and you'd want to advance the camshaft a few degrees to pick up some extra clearance on the exhaust valve. So you really need to know how much clearance you have on both valves before knowing if you have the room to advance or retard the cam -it's not always an option as it's a bit of a balancing act.

Different head gaskets vs optimal quench have been discussed here already.

You can also choose a camshaft that has a different intake closing or exhaust opening point to help improve your situation.

-Dan

The 0.045 clearance is side clearance, not end on & it is the intake so it's closest when opening, so the piston is rapidly going away from the opening valve. I retarded the cam centerline 0.5* & retested it with new plasticine. The side clearance may have gained 0.010 but the depression barely went 0.030 deep. I think I can live with that, it just means the cam centerline is limited to 103*. with these pistons as they are. I had run this cam at 105* before & found clearance more than adequate, 102.5* is just a bit close for Peace of Mind

Radial clearance should only be addressed by material removal. I would radius the top edge of the pocket. Its probably worth a few cfm also.

.045 radial clearances should be fine

X2!