cut pistons or not?

B

blackdieselram

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Dec 1, 2009
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I'm about to get new pistons for my 05. The block was decked and I run a Hamilton 188/220 cam. The machine shop said the finished deck height is 12.715. How do I know if I need to cut my pistons to clear? Will I have to put it together to measure? Everything cleared before the motor was pulled. I still drive my truck on the street so I want to keep the compression as close to stock as I can.
Thanks.
 
What was the deck height before machining. You are referring to the block-height since you are listing a 12.715" measurement, Deck height pertains to your piston crown and the deck of the block itself at TDC. Also look at your cam compared to the stock cam or whatever you had prior.
 
Lower compression doesn't hurt on the street as much as you may think.
If it were me, I'd cut them .020-.050 anyway to make SURE you don't have issues and up the reliability a bit..

With proper tuning you wil be Very happy with spool on a decompressed motor..
 
That is why there are different sizes of head gaskets. :poke:

How much did they take off the block? If you had a std. gasket on before, use a thicker one now. It will end up being the same clearances.
 
I had thought about changing gasket but from what I've heard they won't hold as good as a stock mls gasket. I didn't want to use any rings because I have heard a lot of people have problems with them on daily drivers. I guess ill talk to the shop about it again tomorrow.
 
use a stock thickness headgasket. put a piston in the hole and if it's .030 out of the hole oor lower run it. if not.....deck the pistons accordingly. adding thicker headgaskets kills performance way worse than decking a piston.
 
blackdieselram said:
I had thought about changing gasket but from what I've heard they won't hold as good as a stock mls gasket. I didn't want to use any rings because I have heard a lot of people have problems with them on daily drivers. I guess ill talk to the shop about it again tomorrow.
Click to expand...

The stock mls gaskets come in 2 different thicknesses. Grade A (0.95 mm) for piston protrusions less than 0.30 mm and Grade B (1.25 mm) for protrusions over 0.30 mm. They hold the same.

lenahan05 said:
use a stock thickness headgasket. put a piston in the hole and if it's .030 out of the hole oor lower run it. if not.....deck the pistons accordingly. adding thicker headgaskets kills performance way worse than decking a piston.
Click to expand...

Huh?

If a stock (Grade A) gasket was used originally and then 0.30 mm was taken off the block deck, using a Grade B gasket will put everything back exactly the way it was. That would be MUCH BETTER than decking the pistons which changes the depth of the combustion bowl.:what:
 
I would assemble and clay the pistons before you cut anything but know how much was machined off your cylinder block deck too which is what is needed to make a good decision.
 
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