Warning MN47 clearance

[caen fred]

Just to let you all know that an F54 with flat top pistons and a felpro head-gasket may sound funny. Kinda funny when the piston gently hit the flat part of the head, it make a tic tic tic very entertaining. I had to take the head out and put a thicker head-gasket. No more noise, only music.

It's less than a .10 mm problem, yet it doesn't fit in mine.

[1 fast z]

Many of us have run this setup perfectly. You should ALWAYS check piston to valve clearence (PTV). .022" is perfect. How far above the deck were your pistons above the deck? The block could of been surfaced before.

[ozconnection]

In my experience, it's the valve that hits the piston, not the piston hitting the head unless........

 

You need to provide us with more information on your bottom end, head and cam and how you set it all up so we can work out who or what to blame for your "tic tic tic".

[caen fred]

Please, do believe that I have check, double check and check again the pistons to valve clearance

I am taking here about the domed part of the piston hitting the flat part of the chamber just above the spark plug.

I am sure it's that because I took the head out, and I have a small mark on the piston and on the head, nothing on the valves.

The bottom end is rebuild by me, all was still in original spec, just renew all the seals, cleaned and rebuild.

The head is unknown. I cleaned-it, gave it a pass on a late (close to nothing just to have a nice part), ported the Ex and Int, made grooves for sienZe sake and put it on with a Felpro.

So maybe it's that the head have been milled in a previous life, + the Felpro is 1 mm resulting in a 0,15 mm issue.

I just hope that the pounding didn't harm the cap bearing, time will tell!

[attworth]

So the pistons are domed? or flat?

 

I just can't see how they'd hit the head before hitting the valves.

[caen fred]

So called OEM "Flat piston" aren't really flat, they have a small raised surface, not much but enough to contact the head with the Fel-pro on mine anyway. You could really see the metal where the contact was, all the rest was already spray with carbon dust. I had marks on the pistons AND on the head, the valves cannot hurt the head me think?

 

After thinking it doesn't have anything to do with a previous milling because this part of the head is flat to start with, and for the piston sake, all that's above the chamber doesn't count, right?

The car is running great now with the other head gasket, I will collect data on the PC to fine tune my FI MAP before going to the rolling stand.

[yo2001]

Sounds like he's talking about the euro spec pistons. I heard they are slight raise as he mention. I've not checked mine but I got a similar set up those pistons in a N42 block/head combo.

[BRAAP]

The domestic AND Euro spec OE L-28 Flat top pistons do protrude above the deck surface of the stock block approx .012"-.022". 1 fast z and my self have covered this topic before. Depending on the clamped head gasket thickness, rod/piston stretch, and piston rock over TDC while operating, the pistons could "kiss" the quench pad of the head. It is NOT uncommon for the over size stamp on the top of the pistons to be imprinted/stained onto the quench pad of the head, i.e. the piston was within mere thoudandths-ten-thousandth of an inch from the head while operating. That scenario is perfectly fine and is about as close to a perfect quench as you can get. Now if the piston rocks enough, and or gasket is crushed enough, or as 1 fast z brought up, the block deck has been surfaced, the piston could be smacking the head, which is not good, requiring a thicker head gasket as the original poster did.