Pistons hanging out

[moparspares]

Put my pistons in my 408 build and I have a variation of .010" thou to .014" of pistons sticking out the top of the bores. These measurements are closest to the valley on both sides of engine. On the other side of the piston I have "003 - 004" sticking out. I asked my machinest not to deck the block but when I got it back it was decked. I never asked the guy about it figuring he measured everything and decked it to achieve zero deck height. How can there be this much variation and what should I do to fix it. Thicker gaskets or mill pistons?

 

[360duster]

It seems that the deck of the block is not perpendicular to the bore axis....i´d call the machinist what he did and why, at least he should know about his mistake.

I´d use a thicker head gasket to get the proper clearance. If your rotating assy is not balanced yet you can also mill the pistons.....your choice.

Michael

 

[mopar373]

Your not supposed to measure deck hight at the top and bottom of the piston, because of piston-rock within the cylinders. Always take your measurement by the wrist-pin. this is the only accepted way to check deck hight!

 

[vitamindart]

Your not supposed to measure deck hight at the top and bottom of the piston, because of piston-rock within the cylinders. Always take your measurement by the wrist-pin. this is the only accepted way to check deck hight!

yeah what he said , re check it at the pin. the adjust the gasket thickness to get your desired quench.

 

[67Dart273]

.................and when you check the block you need to use ONE piston / rod assy and check all 4 corners with this one set. Pistons may NOT be all that "flat" so you need to mark a spot in the middle and put your indicator on that same spot in all 4 positions.

 

[70aarcuda]

and all your rods may not be 6.123 center to center..and unless your crank has been index and stroke equalized ...it still may not be perfect....

did he square the block?

 

[autoxcuda]

and all your rods may not be 6.123 center to center..and unless your crank has been index and stroke equalized ...it still may not be perfect....

did he square the block?

I agree.

Block was probably not "square decked". That is an extra cost. Not that necessary on a common rebuild. The compression difference is not that big of a deal on a street motor. It's a bummer though when you are looking for a specific quench. But there is a desired quench range. So you probably can get in the quench range with the right head gasket choice.

I ran into the same deal. But I did get in the quench range with a Fel Pro Hi Po head gasket.

You can pay to get all the trick pro stock motor machining done for your street motor. But you will have very little added HP per dollar spent. Sometimes you gotta take a step back and look at the big picture.

 

[moper]

I agree.

You can pay to get all the trick pro stock motor machining done for your street motor. But you will have very little added HP per dollar spent. Sometimes you gotta take a step back and look at the big picture.

Normally I'm with you but I can't agree with this. The main difference between factory 40 yrs ago performance and a modern performance engine is the machining accuracy. Square decking is not "pro stock" machning. It should be part of any performance build and it is no more money if the shop you use has modern equipment. Iff they don't, find a better shop. IMO if you build for quench using a flat top it is critical to have the block square decked.

 

[OldmanRick]

Your not supposed to measure deck hight at the top and bottom of the piston, because of piston-rock within the cylinders. Always take your measurement by the wrist-pin. this is the only accepted way to check deck hight!

I think that may be the main malfunction here. Your decks may be more square the you think. If your just talking a variance from the valley side to the exhaust side, i don't see a real problem. Looking at your max number, just use a gasket in the .050 range and you'll probably be good. Different numbers from front to back would definetely raise a red flag though.

 

[autoxcuda]

Normally I'm with you but I can't agree with this. The main difference between factory 40 yrs ago performance and a modern performance engine is the machining accuracy. Square decking is not "pro stock" machning. It should be part of any performance build and it is no more money if the shop you use has modern equipment. Iff they don't, find a better shop. IMO if you build for quench using a flat top it is critical to have the block square decked.

What's the net affect of .004 difference quench? IF, it's within the range needed for quench.

I guess in hindsight it should have been square decked.

Should he go back and pay to have that done at this point? Is that cost effective?

 

[moparspares]

I will measure at the pin however wouldnt that be somewhere between the 14" and 4" measurements which I already have. No matter how I measure it they are still out of the bores.

How much piston rock would you normally have in the bores and how do you measure to account for the piston rock.

My other concern is that I already was going to use a 40 thou gasket which had my static compression on a zero deck of 10.6 to 1.

I called my machinest and he suggested I measure them all again note the measurements on the pistons, take them back and he would give them a skim.