When we pulled the motor out of my sons Dart to locate the low oil pressure problem ( cracked pick up tube) we of course pulled everything apart to check for damage. It appears the crank is Ok and can be re-used without a re-grind, but I did find something else that I need some help on.

The exhaust valves on a couple cylinders have been making contact with the top edge of the block. This is my fault I know, because I never checked this clearance when it was put together. I had run the head on a .060 over engine without problems, but this is a .030 engine and I didn't even think to check it. The valves are 1.75" / 1.5"

My Questions are these:

1) Do any of the head gaskets have a larger bore diameter than the others?? My son would like to put forged pistons and overbore the engine to something larger while the engine is down. This will help with the valve problem but we still may need a bore notch? The current head Gasket (from PAW) is just large enough at ..030 over. If we go larger the head gasket will be over hanging the cylinder wall.

2) What do you do at the bore notch(if needed) when the head gasket would be hanging over the notch?? What is the max. depth we should be looking at on the bore notch?

3) If he orders forged Pistons and wants to go to say.100 over, what are the head gasket options then? O-rings and copper?? Or are there other options.

If we custom order pistons we will probably get them for use with 198 rods. I'd be interested in input on the size pistons you guys would recommend? We will probably be working towards somewhere around 10-10.5 on the C.R. I do have access to a U.T. gauge to check cylinder wall thickness before we order pistons.

Sorry this was so long, and aI appreciate your help,

Rick Covalt

When we put big valves in the head for the Valaint (1.72 , 1.50 sbc) we used the chamber radiusing information on Panics site. Its well thought out and reasonably easy to achieve. It provides clearance for flow arounf the valves. The head needs to be CCd after. The block can be notched to match. Obviously CCing the deck area should be done to ensure proper compression ratio. I would notch to the depth of the top of the centre of the piston (different from the side)

I dont know if there are gaskets for larger overbore.
I have notched gaskets with good results.
I have not notched gaskets on notched/over bored blocks and had them burn/melt.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Most of the SL6 gaskets are at 3.5 so you may want to check the head locating dowl pins to be sure they keep the gasket centered over the bores.
I usually have to adjust the dowl location on heads with large over bores and O/S valves.

If you do have to notch, try to find an OEM embossed steel head gasket, you can notch right thru those without any problem.
DD

Thanks All,

Do they make off set dowels for the block??


Rick

Yes, off set 1/4" dowel pins are available.
I have also made them up with a little braze and a lathe.
DD

After reflecting on Ricks problem (valves hitting block surface) it would seem to make some sense to mill the block deck for compression rather than the head. If the head was left unmilled it would leave the valves further from the block deck and less likely to hit the block. This would allow the block to remain un notched. It seems easier and more accurate to sweep the chamber for flow around the valves.

Comments?

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Yeah....Im the one who destroyed this rare, vintage automobile.....

I like your thinking here. Given the enormous negative deck height of a stock \6, there's certainly plenty of meat to mill the block. (Aluminum blocks might be a different story...)