I have been building an f23 motor, I finally put it all together timed it, everything went smoothly. it is an f23 block with a h23 pistons and a ported f23 head. when i went to set the valve lash, the motor locks up, i think the valves are hitting the pistons because the reliefs on the h23 pistons are incompatible with the valves in the f23. the timing is correct on the cam and the crank. has anyone tried this yet? i feel that i have just found the f/h piston combo that DOES NOT work lol....if so i really wasted a lot of money. does anyone have any suggestions?

 

The compression height of the H23 pistons will put the pistons into the head with stock F23 crank and rods.

F23: 1.181" CH
H23: 1.202" CH

Run a thicker head gasket. You can try to turn the crank over with the cam out of the head to see if the rotating assembly will even turn over. If pulling the cam doesn't aleviate the issue then it's definatley the pistons.

 

really? the pistons sit perfectly flush in the block. i guess it's time to get some 40 over f23 pistons , that really messed my plans up. can i mill the pistons .1" to make it work?

 

If the pistons are flush then it shouldn't be an issue. The F23 cams are not big enough to make the H23 piston's valve reliefs "too small" assming that everything's timed right.

Will the crank turn over with the cam out? If it does then count the teeth on the lower timing belt gear and the cam gear. There should be half the number of teeth as the cam gear.

What are your cam specs?

 

i didn't take out the cam, i removed the valvetrain and it still got stuck when i tried to turn it over, i think im going to have they pistons machined to have them match the compression height of the f23 pistons, i can't think of anything else. the head turns over fine off the block and the block turns over fine without the head. i had the cam/crank timing dead on. my cam is stock.

 

I used H22 pistons in my F23 shortblock and they look like this:



The H22 pistons are taller than the H23's but I had the same issue. I cut the combustion chamber out to clear the pistons. Another solution is to run a thicker head gasket.

Something you can try is to remove the headbolts and have the dowels align the head on the block. Turn the crank over slowly and let the pistons lift the head off the block and use a set of feeler gages to determine how much of a gap there is between the head and the block. This gives you an idea of how bad the interference is.

If you do cut the pistons to the 1.181" CH then it should fix your problem.

 

yea i thats exactly what my pistons looked like coming out of the block, i told my machine shop to cut it down .021...

 

lol i just did the math on it, and that's exactly the difference, i just used my feeler gauges and my fingers to feel when its flush...

 

Is that with the head gasket? You want at least .040" total clearance between the head and the pistons...

The reason it's an issue is that the combustion chamber is probably a smaller diameter than the bore. The pistons around the edge hit the head's gasket surface.

Glad you figured it out.

 

lol noooo not with the gasket....i just realized that with it cut .021 its gonna bump up the compression a little bit more....oh well.....