zero deck pistons?

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silvadful

silvadful

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hey guys. i have a 318 bored 20 over kb 399 pistons. block been bored, honed an it time to mock up an see where pistons sit. what is the method to do this an what tools u need? thanx for help in ++
 
I dont know what others use but I used the depth end of my calipers to measure this. Bring the piston up slowly might take you a few turns you will notice as it comes up there will be sort of a dead spot for just a bit then back down. Once you hit that dead spot you are at TDC.
 
these things dome tops +6cc so do you measure to centre of piston? or ring lands?? or at edge of bore above pin?
 
Best method of zero decking a block is to use the tallest 4 piston and rod assembly,one on each corner and then measure down to the piston from the deck at TDC,marking on the deck the measurement and do each corner.Once you have found the amount,you can tell the machine shop what needs to come off from each end.This is with the assumption that your piston/rod assembly not been blue printed.You need a depth mic and need to measure to the higest point of the pistons rocking the pistons to see if there is any change in the readings,on all 4 corners,MMT
 
A dial indicator is the best way to both measure your deck and to find true tdc. you cannot go off the balancer timing marks. Just 2 degrees can throw off you deck height measurement. If you don't have a dial indicator use a straight edge and feeler guage at the highest point of your piston. To find true tdc with a feeler gauge takes some patience. You have to rotate crank very slowly till you find the thinnest guage that will fit. Once you find tdc measure at the dome, measure at ring lands top and bottom there may be a difference between top and bottom ring lands. This is due to piston rock. Add the 2 measurements together and divide by 2. This is your true deck height
 
dial gauge is what was thinking. so you find tdc then put straight edge across bore and measure the gap? at the pin?.
any pics would be awesome or links to such. cheers for quick replys guys. not so flash at da maths thing.read this a few times get to sink
 
Mrmopartech said:
Best method of zero decking a block is to use the tallest 4 piston and rod assembly,one on each corner and then measure down to the piston from the deck at TDC,marking on the deck the measurement and do each corner.Once you have found the amount,you can tell the machine shop what needs to come off from each end.This is with the assumption that your piston/rod assembly not been blue printed.You need a depth mic and need to measure to the higest point of the pistons rocking the pistons to see if there is any change in the readings,on all 4 corners,MMT
Click to expand...

not sure what u mean by tallest.shouldnt they be the same ?
 
true. weighed the pistons and they varied within a gram so spose the same applys to the rods etc. so measure from top inside big to bottom small end and go from that?. to find the tallest
 
The crank throws can be off,rod length can be shorter or longer,piston pin to crown can be shorter or taller than others.Unless all the rotating assembly has been blue printed,you could have a short and long rod installed and screw up the deck clearance,as the 2 other rods MIGHT be taller and then you have +deck height.Connsistancy is the key to decking a block,and making every assembly the same,in length and weight.If you do not do this,you roll the dice on what happens.Mrmopartech
 
thanks for all the help wicked.!! am going to balance all weights but this the first i heard of dif heights for rods but when you think bout it it how it gonna be. now i know to find that point and work from there. love this site. cheers
 
They way I'd go is take all 8 and check the hieght in the #1 crank throw. Then take the longest and measure at #2, #7, na d#8. You only have to measure along the pin axis as that measurement will be the same as averaging the tall side and the short side. Be prepared if the block was not square decked. decking the block is not the same operation and chances are good that it was only decked you will have some variance.
 
u mean take the longest rod and use that one for all measures??. it a virgin block outa factory so figured wont be true.cheers
 
Yes. Find the longest rod by putting them all in the #1 hole on the #1 crank throw. Then use that one for the four corner measurements. Then the differences you record are either the deck height, or the stroke variation, rather than those two and the rod length.
 
hmmmmm.:newb::sign3: that take a bit to sink me think .get back to ya morro.thanx .lol
 
Mrmopartech said:
The crank throws can be off,rod length can be shorter or longer,piston pin to crown can be shorter or taller than others.Unless all the rotating assembly has been blue printed,you could have a short and long rod installed and screw up the deck clearance,as the 2 other rods MIGHT be taller and then you have +deck height.Connsistancy is the key to decking a block,and making every assembly the same,in length and weight.If you do not do this,you roll the dice on what happens.Mrmopartech
Click to expand...

This is so true...thanks for mentioning. I totally blew this off in my previous post.:coffee2:
 
Thank you all for replys. had cpl reads over this all and think got it sorted. some good info that you can only get from here. cheers.
 
hey guys back again. is it normal to get a different measure from front o piston to back. used mopars method to find longest rod and used that 1 for all measures. and all were positive on 1 side and negative the other?. from front o engine # 1


front o pist back o pist above pin.
# 1 /- 0.009 +0.006
# 2 /+ 0.008 -0.006

# 7 /- 0.009 0.000
# 8 /+ 0.003 -0.003

- being below deck + above. kb 399 dome tops 0.020 over minus 6.cc.
does this just mean the deck not square to crank or somthing else?
 
There are multiple factors at work here.

Rod lengths, piston heights, crank throws and deck height.
Each of these can have there own measurements. Deck height can vary front to rear, side to side. The crank can have a longer or shorter throw for each cyclinder it is in, etc for the rods and slugs.

This is where a good machinist comes In and takes care of it all.
 
hey rumble. yes will be talking to mchineist tomorrow. just want to get a good understanding of whole process .if he does it all i learn f all.lol
 
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