Lapping question!

[sylquebec]

Hi, i<m in the process of lapping the deck of my 7mgte. I read while searching that i need to do it in a "8" pattern. I just realise that its not a good idea to do it with a 8inx8in lapping plate because the center of the deck get lap 2 times while the corner end only get lap 1 times. I made a drawing to explain it to you. So the question is : How should i lap my deck with a 8x8 plate? I want a perfectly flat surface.
thanks

 

[IJ.]

Lapping is a finishing process only, you need to start with a milled true surface so shouldn't be removing enough material tol make a difference.

 

[sylquebec]

Ok, but why the "8" pattern instead of "up and down" ?

 

[IJ.]

So you don't drag lines into the finish.

 

[suprarich]

No lapping is needed anyway if a proper milling job has been done. We are not trying to lap only are we and skipping the milling process?

 

[sylquebec]

No lapping is needed anyway if a proper milling job has been done. We are not trying to lap only are we and skipping the milling process?

Yes i am skipping the milling process. (I dont have any other choice right now) Deck is completely straight (never overheat and only 40k miles). The surface is in great shape, no corrosion pitting, i'm only trying to remove the mark leave by the gasket around the cylinder wall.
Head have been to the machine shop and i think i will lap her too since machining is not was i was expecting. (look like a 50-60RA with a RA Comparator)

 

[IJ.]

Due to human physiology using an 8" plate I seriously doubt you'll ever get a true surface, mine is 12"x12" with handles at the centrepoint and I wouldn't try what you're doing.

 

[CyFi6]

If it is hardly removing any material though wouldn't it just show any high/low spots if there were any by where it polished and where it didn't? Is a lapping plate with compound enough to take a flat block out of true? I guess my question is, cant he just begin lapping and if there are any high/low spots get it machined, but if it is flat like he says why is it a problem? Thanks I have never lapped anything personally, would like to know since I have heard of people actually lapping a block in car too.