Question about Decked Block

[TheBoz]

Galant GSX, with Wiesco 9:1 pistons.

1. Can the machine shop take too much off the top?
2. My Pistons come up out of the top of the block about .01 of an Inch.
3. Do I need to scrap my block and get a new one?

You can check out my profile, how ever I did not take any pics of the piston poking up a little bit.

I am just wondering if that is something kinda normal on a block that has been decked.

Thanks.

 

[Defiant]

You need to find out what your machine shop screwed up, how, why, and what they plan on doing for you to correct the situation.

Did you get aftermarket pistons without telling them about them?

 

[Big Woo]

Yes too much can be cut from the deck surface. However there are many things that determine piston height.
For example
1: align honing or boring the main bearing journals will move the crankshaft centerline closer to the deck surface.
2: Decking the head surface of the block lowers it relitive to the piston.
3: Connecting rod reconditioning can result in a slight change in connecting rod center to center length. If the rod becomes slightly longer it will cause the pistons TDC posistion to be that much higher.
4: Pistons have a set pin height if the new pistons have a differnt pin height than the old pistons then the piston top could move closer or further away from the deck surface depending on wether the pin height has moved up or down.
5: Some shops will correct a crankshaft for stroke length during the regrinding process, or standard regrinding of the crank can result in slight changes to the actual half stroke length.

Basicly you have a set deck height measured from the centerline of the crankshaft to the deck surface. Your stroke half length, connecting rod center to center length, and piston pin height add up to how far above or below the deck surface the piston will be.

Your block is not junk, but you will need to find out exactly how far the pistons protrude. You should also check all of them, because if the deck surface and the centerline of the crankshaft are not parallel then there will be a difference in piston height from end to end.
There are several things you can do to correct this if the amount is small a thicker head gasket may be all that is needed. Cometic for example manufacturers several differnt thicknesses of head gaskets for the Mitsu 4G63. Pistons could also be changed be a differnt pin height, although this would most likely be a custom set of pistons.

Joe