Decking M20 engine block??? 2.7 Seta

[Chuckcruzin1986]

I have read and read the forums but I do not feel comfortable with some of the ideas.

I have a 88 325 super eta engine and want to raise the compression from the stock 8.5 to 9.5.....part of my thinking is that by the time the valves are ground and sunk into the head and I smooth the pistons and combustion chamber I will end up at 8.25 (guess).

So I was thinking of milling the top of the block .050" AND turn the outside face of the piston .050" back so the pistons will not hit the head.

I will run a 272 cam and will mill valve clearance in the top of the pistons.

I understand the cam will have to be retimed.

Ideas???? I am ready to roll unless I hear that I am missing something

Thanks, Chuck

[jlevie]

That should work. It would be a good idea to use modeling clay to measure valve clearance just to be sure that you have enough. Though if you cut the valve relief in the pistons 0.050' deep everything should be okay.

A good way to correct the cam timing is to install an bushing in the cam sprocket with an offset hole for the index pin.

[Imagine_M]

why not just get custom pistons and save the block and your time...

[Chuckcruzin1986]

on a budget...??

why not just get custom pistons and save the block and your time...

The cost adds up. I figure if I have to bore (all of the new pistons that I found were oversized) the engine at a cost of around $100 plus. I might as well go 1mm over to get the cubic inches up a little to 2.8. those pistons and rings plus the boring adds up to around $1350. I simply could not justify the cost. Yes, it is true, this is taking some time....always a balance between time, money and results

[jlevie]

Before doing any work, you need to gage the cylinder bores and see if they are worn beyond the wear limit. In a like manner you need to check for wear in ring grooves. The block may have to be bored and/or new pistons fitted just because of wear.

[Chuckcruzin1986]

Thanks for the input.

Before doing any work, you need to gage the cylinder bores and see if they are worn beyond the wear limit. In a like manner you need to check for wear in ring grooves. The block may have to be bored and/or new pistons fitted just because of wear.

The cylinders still have faint crosshatch

BUT, I will double check with a bore gage.

Thanks