340 Block Deck Height

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Tom Oliver

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Hi Fellow Members,

I been studying Mopar literature of various sources and am getting conflicting 340 C.I., technical information. I want to know (1) what is the correct factory block deck height for a 1970, 340 c.i. motor, 9.94", 9.85", (2) piston deck height with the stock, factory cast piston? Also, (3) what is the compression height of the stock, factory cast, piston, 1.84", or something else?

I would appreciate your expertise,

Tom
 
deck height on LA engines are "around 9.59-9.60"...due to production variables ...unless the block has been Squared...the front to back number with be different ...and left to right bank will be different...

deck height on the piston...is going to vary due to issue above..plus production tolerances in the stroke of the crank..plus the actual center to center of the rods...a 70 should have a positive deck height around .008....NHRA blue print spec is +.045...

the early pistons had a compression height around 1.84...
 
so if you square the block...and have the crank shaft strokes indexed...and have the all 8 rods center to center corrected....

and in the process of doing this...you can set your deck height to what you want...and you can set your deck height on your pistons to what you want...

otherwise the production tolerances are going to put you all over the place....
 
deck height 9.599

piston to deck -.020

com height 1.800

they surley had to run a thinner head gasket to get the 10.-1 compression
i dont have the pistons any more but i think the compression height is close.
 
Deck height is definitely going to vary a bit on production tolerances. When I had my '71 318 square decked the right hand deck was taller than the left, and both had to come down to be trued up.

But unlike the 318's, or even the later 340's, the early 340 pistons put the piston over the deck. Spec was .018" proud of the deck. Surprisingly enough, on my '68 340 I found all of my pistons to be around .017-.018" above the deck.
 
In the book i have it is on page 27....1st paragraph on left column,,,,

but .001 is nothing...lol
 
I had the deck height on my '71 340 milled to 9.588" to zero deck the pistons so the stock deck height is just a little taller then that.
 
I had the deck height on my '71 340 milled to 9.588" to zero deck the pistons so the stock deck height is just a little taller then that.


I think that is would I had my 70 340 done also....
 
It's a little misleading. The "zero" in your reference means they are decking the block to theoretically get the piston top even with the deck... Or in at "zerp deck". However, unless all the blueprinting steps are taken, as noted earlier in the thread, they will be above or below in addition to even with the deck on an individual basis.
 
It's a little misleading. The "zero" in your reference means they are decking the block to theoretically get the piston top even with the deck... Or in at "zerp deck". However, unless all the blueprinting steps are taken, as noted earlier in the thread, they will be above or below in addition to even with the deck on an individual basis.
Thanks
 
Technically, no. Because the centerline of the crankshaft doesn't change when align boring or honing is done properly. But - sometimes either the job's done poorly, or the machinist has to make minor adjustments due to damage or wear. So it can be a variable.
 
As Krooser says... they came in a variety of flavours. Low deck, 48° and 59° blocks etc.
 
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