chevy 400

why do they say u cant use 5.565 rods on a crank that is for 5.7 rods or 6.0 rods

can someone help

You need to explain your question better....like who says this?

For a small block Chevy, the deck height is 10.400 inches; that is, the distance from the crank centerline to the top of the block surface where the heads bolt. This distance is equal to the sum of 1/2 of the stroke plus the rod length plus the piston height (from the piston pin to the top of the piston) plus how far the piston top is below the deck surface (a minor amount). A piston therefore is designed to fit the above equation. Also, on a piston, there is the skirt that is below the piston pin. The skirt is designed to clear the crankshaft counterweights....if a piston designed for a long rod is put on a short rod, the skirt would probably hit the crankshaft and the piston height would be so short that the piston would not go to the top of the bore..... and have low compression. Therefore, the pistons must match the rod length that the piston was designed for. Is this what you are asking about?

i got a 400 small block and i want to use my crank that i bought for my 383 i got the spacer for the mains so the crank will work in the 400. the thing is that i wanted to know will the 400 rods work with this crank. my friend said that i have to have 5.7 rods or 6.0 rod. i bought piston for the 400 rods will the crank work with this. the 383 stroke is a 3.75 and so is the 400 right.he said something about the counterweights. but it should work right

Pistons dictate whether or not you use the original 400 rods. If your rods out of the 383 are 5.7, buy the pistons accordingly. Same with 6.0 rods. The difference is in the pin height built into the piston to accomodate the length of the rods you hsve.

so i can use the 383 crank with the 400 rods and piston

It sounds as if you already have the block, bearing spacers, crank, rods, and pistons. If the pistons are for the 400 rod length, the block is a 400, then the only unknown is if the piston skirts will interfere with the crank counterweights. This should be easy enough to assemble one piston/rod and install it on the crank and rotate it to check (don't even need the rings to check).

i took it all to the machined shop and bought everything new.new piston,spacers rod bolts and even had work done to the block

first the deck hight is only 9" on avg.. i would run a 5.7 rod if your going to run a power adder later.. the 6" rod is pushing the top ring to close to the top. the crank will work and the 5.7 rods will work just buy the pistons for a 400 with 5.7 rods like nitro said.. ROBOT were did you get the info for deck hight.small blocks 9" a big block is 9.8..

Caddy, you are right, a small block is 9.025 deck

so the 5.565 rods going to work fine the piston are speed-pro h400cp for the 5.565 rods.

so the 5.565 rods and the seed-pro piston h400cp is going to work fine. thats what u all are saying. thanks

Dont know about the other guys, but I wouldnt say that it is OK....I say that it is super easy to check...why not be sure by checking it before you do the final assembly of the engine? A little work on the front end would potentially save a headache later.....I personally dont like to pull the pan after the engine is installed in the car!!

Speed Pro designed that piston for your set up. 1970-1980 400 engine with 5.565 rod. Will leave you at .025 in the hole and skirts should not be an interference problem.

thanks alot

If the crank you are using is a stock 400 gm crank that has just had the mains turned down, then your set up with the 400 rods will work fine.Eagle cranks as an example say 5.7 or longer because their counterweights are a little taller and will hit the skirt at BDC .a 400 piston has the same comp height as a 350 they just use the shorter rod to make up the diff in the increased stroke.we used to call these the poorboy 383. gm400 crank with the mains turned down, 400 rods and 350 pistons. these work ok but the 5.7 has a better rod ratio.less side thrust on the piston, less friction, more power,last longer.:toocool: Jeff

thanks motorman and all of u

the crank is scat by summit it ask for 5.7 rods

Crank doesn't set the rod length, that's up to the builder. Pistons adjust pin heighth to accomodate what ever rod you can run.....put the thing together. Just double check everything as you assemble it. We all can't keep saying the same thing, you have to get it done.

ok thanks u all