55 plymouth 230 engine block

[Bob S.]

Hi , All

I am rebuilding this engine for my old Plymouth. The head gasket was leaking between cylinders 3 and 4. It must have sat with coolant in these two cylinders for a long time. The deck surface is sunk in around the valve area about .035''. This caused the area where the head gasket seals to be narrow

and probably won't seal. Do you think I can get away with resurfacing the block .035-.040'' Or should I find another block. I know the valve seats would have to be lowered also. The pistons would stick out about .020''. The head gasket is .070''  thick used.

  Thanks, Bob S.

[Don Coatney]

You should be good to go. You can use a dial indicator to measure your valve lift to insure you have ample valve to head clearance. You could also use a wad of silly putty placed on top of the valve. With the head resting on the block not bolted down spin the engine by hand a couple of rounds. Remove the head and measure the silly putty after it is squished. 

 

[Lumpy]

If you wind up with .050" piston to head clearance, (.070" head gasket minus .020" pop-up, or positive deck height) that's about ideal as far as getting good squish, and insuring that there won't be contact when the engine is hot and the rods and pistons "grow" a bit. One can go as tight as .030" if your measurements are absolutely accurate and correct. Otherwise .050" is the general rule and more safe.

 

As mentioned you should be okay on valve to head clearence...but easy to check. Airflow around the valves is best with generous clearence between valve and head, but thats' a minor detail...not hitting the head is more important...obviously. !!!

 

Good luck.

 

Edit: I forgot to mention, anything larger than .050" between the piston and head at TDC will increase the engine's tendency to "ping" or detonate quite dramatically, as that gap enlarges beyond .050". Or...the larger that gap, the lower the compression will need to be, and the less timing advance that can be used. I hope that made sense. !!!

 

ken.

Edited February 21, 2014 by Lumpy

[james curl]

I had my head milled .090 and they surfaced the top of my block .010.  I had to tighten the radius on the intake and exhaust side of the head to clear the outside edges of the valves.  If I remember I used a 3/8" round bur in my high speed die grinder to tighten up the radius enough to clear the valves without a head gasket installed.  I used modeling clay from, the children's dept at Wal Mart.  I rolled it into a 1/4" rope and rolled it around the outer edge of the valves.  After turning the engine through several rotations with the head snugged down I was able to measure the clearance at each valve.  Go slowly with the die grinder, you do not want to go into the water passages in the head.

[Lumpy]

Don's engine even looks good just laying on the bench.

 

k.

[Bob S.]

Thanks for the replies. Time to get the machining done.